Hella Boumaiza

Mbolantenaina Aurélien Renard

Rakotomalala Robinson

Gwendal Kervern

Loïc Vidal

Christian Ruby

Latifa Bergaoui

Romain Coustel

A multi-technique approach for studying Na triclinic and hexagonal birnessites

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Among the various manganese oxides, birnessite was found to be the most common occurring form in soils and sediments [START_REF] Bargar | Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ[END_REF]. The crystal system of birnessite was shown to be either hexagonal or triclinic [START_REF] Lanson | Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell[END_REF][START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF][START_REF] Post | Rietveld refinement of a triclinic structure for synthetic Na-birnessite using synchrotron powder diffraction data[END_REF]. The triclinic form was initially reported as monoclinic but this symmetry was repealed by the study of Post et al. [START_REF] Post | Rietveld refinement of a triclinic structure for synthetic Na-birnessite using synchrotron powder diffraction data[END_REF]. Hexagonal and triclinic forms are both lamellar with negatively charged layers which consist of edge-shared MnO 6 octahedra with interlayer spaces containing hydrated cations (e.g. Na + , K + , Mn 2+ …). It is noteworthy that discrepancies appear in the nomenclature of layer type Mn oxide. In here, birnessite varieties are distinguished by the unit cell symmetry according to the recommendation of Villalobos et al [START_REF] Villalobos | Characterization of the manganese oxide produced by Pseudomonas putida strain MnB1[END_REF].

The triclinic and hexagonal forms are essentially differentiated from each other by the origin of the charge deficit, the nature of interlayer cation and by the oxidation state of the manganese in the layers and/or interlayer. In the triclinic form (Fig. 1a), the layers have been described as an alternation of two Mn IV O 6 rows and a Mn III O 6 one along the b axis [START_REF] Lanson | Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell[END_REF][START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF]. This structure, is actually the result of a partial substitution of Mn(IV) by Mn(III) in the MnO 6 octahedra [START_REF] Post | Rietveld refinement of a triclinic structure for synthetic Na-birnessite using synchrotron powder diffraction data[END_REF][START_REF] Post | Crystal structure determinations of synthetic sodium, magnesium, and potassium birnessite using TEM and the Rietveld method[END_REF]. The charge deficit thus created in the layers is compensated by the presence of a hydrated cation in the interlayer space (typically Na + ). In the hexagonal form (Fig. 1b), MnO 6 octahedra contains mainly manganese in the oxidation state +IV and the negatively charged layers are the result of the presence of vacancies [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF]. This charge deficit is compensated by the presence of interlayer H + and manganese in the oxidation state +II and/or +III. The interlayer manganese ions are located above and below the vacancies [START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Drits | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: I. Results from X-ray diffraction and selected-area electron diffraction[END_REF].

Consequently, the relative proportions of Mn II , Mn III and Mn IV are different in the two forms of birnessite.

Both forms of birnessite have been reported to participate in a large variety of reactions: ion exchange and sorption reaction [START_REF] Golden | Ion exchange, thermal transformations, and oxidizing properties of birnessite[END_REF][START_REF] Jiang | Sorption and desorption of tetracycline on layered manganese dioxide birnessite[END_REF][START_REF] Goff | Synthesis, ion exchange and electrochemical properties of lamellar phyllomanganates of the birnessite group[END_REF][START_REF] Peacock | Sorption of Ni by birnessite: Equilibrium controls on Ni in seawater[END_REF], as well as redox reaction with heavy metals, organic or inorganic molecules [START_REF] Rao | Oxidative transformation of aqueous phenolic mixtures by birnessite-mediated catalysis[END_REF][START_REF] Remucal | A critical review of the reactivity of manganese oxides with organic contaminants[END_REF][START_REF] Renuka | Investigation on layered birnessite type manganese oxides for battery applications[END_REF][START_REF] Scott | Reactions at oxide surfaces. 2. Oxidation of Se(IV) by synthetic birnessite[END_REF]. Considering that the birnessite reactivity depends on the manganese valence state, the evaluation of the relative fractions of Mn II , Mn III and Mn IV is of great importance. Even more, it is important to quantify these fractions at the solid surface where the reactions actually take place. Fig. 1: Scheme of Na-Triclinic (a) and Hexagonal (b) birnessite layers (Mn IV rich rows: dark grey, Mn III rich rows: light grey, vacancy: empty triangle). In the triclinic form (a), the interlayer cation Na + is located close to O atom that can either be coordinated to three Mn IV (environment A), to two Mn IV and one Mn III (environment B) or to one Mn IV and two Mn III (environment C)

In previous studies, the manganese Average Oxidation State (AOS) in the birnessite was measured either by chemical titrations [START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Lingane | New Method for Determination of Manganese[END_REF][START_REF] Vetter | Potentialausbildung an der Mangandioxid-Elektrode als oxidelektrode mit nichtstöchiometrischem oxid[END_REF] or by solid characterization via Mn K-and Ledge XANES analysis [START_REF] Chalmin | A pre-edge analysis of Mn K-edge XANES spectra to help determine the speciation of manganese in minerals and glasses[END_REF][START_REF] Manceau | Structural chemistry of Mn, Fe, Co, and Ni in manganese hydrous oxides: Part II. Information from EXAFS spectroscopy and electron and X-ray diffraction[END_REF]. Despite the fact that these methods provide very useful information, they are bulk techniques that do not give any information about the near-surface chemistry of the oxide where the reactions actually take place.

To this purpose, X-ray Photoelectron Spectroscopy (XPS) appears to be a preferred technique for the determination of the valence state of manganese located near the surface. There are only a few reports on the determination of Mn II , Mn III and Mn IV relative proportions in birnessite at the surface. The earliest study used the fitting procedure of the Mn2p 3/2 XPS feature [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF]. The same approach has been used by other authors [START_REF] Boumaiza | Conditions for the formation of pure birnessite during the oxidation of Mn(II) cations in aqueous alkaline medium[END_REF][START_REF] Mckendry | Decoration of the layered manganese oxide birnessite with Mn(II/III) gives a new water oxidation catalyst with fifty-fold turnover number enhancement[END_REF][START_REF] Yin | Characterization of Ni-rich hexagonal birnessite and its geochemical effects on aqueous Pb 2+ /Zn 2+ and As(III)[END_REF] and the obtained surface-Mn AOS values were systematically lower than the bulk ones. More recently, Ilton et al. [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF] discussed the Mn AOS determination through Mn2p 3/2 , Mn3s and Mn3p lines analysis.

This study raised some doubts about the use of Mn3s multiplet splitting. The Mn2p 3/2 peak shape was also suspected to be too sensitive to Mn bonding environment. Then, the authors recommended a method based on Mn3p line decomposition.

When submitted to an acidic treatment, the triclinic birnessite undergoes a symmetry conversion to hexagonal [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF][START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Drits | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: I. Results from X-ray diffraction and selected-area electron diffraction[END_REF]. Several solid characterization techniques were recently reported in order to understand both birnessite structures: Fourier Infrared Spectroscopy (FTIR) [START_REF] Johnson | Water in the interlayer region of birnessite: Importance in cation exchange and structural stability[END_REF][START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF], Raman scattering [START_REF] Hsu | Reversible phase transformation of MnO 2 nanosheets in an electrochemical capacitor investigated by in situ Raman spectroscopy[END_REF], Mn K and L-edge extended X-ray absorption fine structure (EXAFS) [START_REF] Zhao | Redox reactions between Mn(II) and hexagonal birnessite change its layer symmetry[END_REF], 23 Na Magic Angle spinning Nuclear Magnetic Resonance (MAS NMR) [START_REF] Aldi | Investigation of cation ordering in triclinic sodium birnessite via 23 Na MAS NMR spectroscopy[END_REF] or XPS [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF]. However, as far as we know, conversion from triclinic to hexagonal form was not yet investigated by a multi-technique approach.

The main goals of this study are thus (i) to probe the changes of triclinic birnessite placed at pH 3.5 by monitoring both the liquid and, especially, solid properties by a comprehensive set of physical chemistry methods: Transmission electron microscopy (TEM), Scanning Electron microscopy (SEM), powder X-ray diffraction (PXRD), FTIR, Raman scattering, 23 Na and 1 H MAS NMR and XPS, (ii) to discuss the XPS use for the Mn AOS assessment at the nearsurface of different studied solids.

Materials and methods

Chemicals

All chemicals were purchased from Sigma-Aldrich. Manganese (II) chloride tetrahydrate ACS reagent, ≥99.0%) were used to measure the Mn AOS in birnessite. Hexaamminecobalt(III) chloride ([Co(NH 3 ) 6 ]Cl 3 , 99%) was used for the determination of the Cation Exchange Capacity (CEC) of the birnessite. Hydroxylamine hydrochloride (NH 3 OHCl, ACS reagent, ≥ 96 %) was used for the complete digestion of birnessite before ICP-AES analysis.

(MnCl 2 •4H

Synthesis of birnessite

The triclinic birnessite was obtained following the alkaline method of synthesis proposed by Boumaiza et al. [START_REF] Boumaiza | Conditions for the formation of pure birnessite during the oxidation of Mn(II) cations in aqueous alkaline medium[END_REF] in which 125 mL of NaOH (8.8 mol L -1 ) is added dropwise during 2 hours to a mixture of 250 mL of NaMnO 4 (0.1 mol L -1 ) and 125 mL of MnCl 2 (0.6 mol L -1 ).

The mixture is then kept under stirring during an additional 30 minutes, aged at 60 °C during The hexagonal birnessite was obtained from the transformation of triclinic Na-birnessite in acid solution: Na-birnessite suspension (6 g L -1 ) was maintained at pH 3.5±0.1 throughout the experiment using a computer-controlled titrator (736 GP Titrino, Metrohm) by adding hydrochloric acid solution (0.2 mol L-1, for a total HCl amount of about 4 mmol). Aliquots were collected at different contact times and filtered through 0.22 µm syringe filter. After 24 h of contact time, the remaining birnessite was collected for solid state characterizations. In sake of comparison, a similar experiment without pH stabilization was also performed (pH = 10).

Characterization techniques

In order to establish the chemical formula of the Na-birnessite, the Na and Mn contents were measured by Inductive Coupled Atomic Emission Spectroscopy ICP-AES (JobinYvon-Horiba, Ultima) after complete digestion of about 5 mg of solid in NH 3 OHCl (0.7 mol L -1 , pH = 1.9). The water content was determined by thermogravimetric analysis (LABSYS Evo Setaram Instrument) under dry inert gas flow. The sample was heated from room temperature to 800 °C (heating rate: 10 °C min -1 ). The interlayer water was evaluated based on the endothermic curve between 70 and 250 °C.

The CEC was determined using a Cobalt-hexaamine method [START_REF] Afnor Nf | Détermination de la capacité d'échange cationique (CEC) et des cations extractibles[END_REF] by putting 150 mg of birnessite in 20 mL of Co(NH 3 ) 6 Cl 3 (16.67 mol L -1 ). The mixture was then shaken for 2 hours, without temperature regulation, and microfiltered. The measurement of the cobalt-hexaamine concentrations before and after reaction time was performed by UV-visible analysis at 472 nm using an Agilent Cary 60 spectrophotometer.

The Mn AOS in birnessite samples was measured by a potentiometric titration using Mohr salt, potassium permanganate and sodium pyrophosphate dibasic. This method is based on the work of Lingane and Karplus [START_REF] Lingane | New Method for Determination of Manganese[END_REF] and Vetter and Jaeger [START_REF] Vetter | Potentialausbildung an der Mangandioxid-Elektrode als oxidelektrode mit nichtstöchiometrischem oxid[END_REF][START_REF] Gaillot | Caractérisation structurale de la birnessite[END_REF].

After acidic treatment of Na-birnessite, Mn content in the supernatant was also measured by ICP-AES (JobinYvon-Horiba, Ultima).

TEM images were obtained by using a Philips CM 200 (accelerating voltage 200 kV). SEM images were obtained using a JEOL JCM-6000 microscope (accelerating voltage 15 kV).

PXRD was performed at room temperature by using a Panalytical X'Pert Pro diffractometer and an X′Celerator as a detector. Data collection were carried out using 0.02 rad Soller slits, programmable divergence and antiscatter slits, the irradiated area was fixed to 10x10 mm.

The PXRD patterns were recorded using CuK α1 radiation (λ=0.15406 nm). Data collection was carried out in the scattering angle range 5-70° with a 0.0167° step over 2 hours.

FTIR analysis was performed using a Bruker Vertex 70v equipped with a DLaTGS detector in transmission mode using KBr pellets containing 2-5 mg of sample. For each sample, 100 scans were collected in the 4000 -220 cm -1 range with 4 cm -1 resolution. The KBr spectrum was also recorded at the same conditions and was subtracted from the sample spectra.

Raman scattering measurements were performed on a Renishaw inVia Qontor spectrometer equipped with a Leica confocal microscope and using a Nd:YAG laser source emitting at 532 nm. The laser was focused on the sample by a ×100 objective. The laser power was kept at 0.05 mW to avoid any heating effect. Each scan consists of 50 accumulations of 10 seconds.

X-ray photoelectron spectra were recorded on a KRATOS Axis Ultra X-ray photoelectron KRATOS Axis Ultra DLD spectrometer equipped with a monochromated Al Kα source (hυ = 1486.6 eV, spot size 0.7 mm×0.3 mm). The samples were pressed onto a Cu tape fixed on a sample holder and introduced into the spectrometer. The detector is a hemispherical analyzer at an electron emission angle of 90° and pass energy of 160 eV (survey spectra) or 20 eV (high resolution spectra). For the high-resolution spectra, the overall energy resolution, resulting from monochromator and electron analyzer bandwidths, was better than 800 meV.

Charge correction was carried out using the C1s core line, setting adventitious carbon signal to 284.6 eV. Na1s and O1s spectra were decomposed using Gaussian peaks after using Shirley method of background subtraction.

All 1 H (reference adamantane 1.8 ppm) and 23 Na (reference NaCl 0 ppm) NMR spectra were realized on a 7.05 T Bruker AVANCE III spectrometer equipped with a 4 mm CPMAS probe, under 12.5 kHz MAS, direct acquisition and no proton decoupling. The 23 Na spectra were acquired after a 1 second delay and 1 µs hard pulse, the proton spectra were acquired after a 10 ms delay and 1 µs hard pulse. The proton spectra were acquired with a presaturation prior to acquisition, as well as a rotor synchronized echo in order to get rid of the slow relaxing signals (probe background signal, free water).

Results

Birnessite solubility in acidic medium

When submitted to an acidic treatment at pH = 3.5 during 24 h, triclinic Na-birnessite undergoes a change of symmetry to hexagonal accompanied by Mn release in the solution that has been monitored during time (Fig. 2). This soluble Mn is assumed to be Mn 2+ since Mn III and Mn IV are essentially stable in solid-phase. In fact, the Mn IV complexes, even in coordinated state, are hydrolyzed to form MnO 2 and, in the absence of complexing agents, Mn III disproportionates to form Mn II and Mn IV [START_REF] Langston | [END_REF][START_REF] Davies | Some aspects of the chemistry of manganese(III) in aqueous solution[END_REF]. The evolution of the Mn 2+ concentration over time (Fig. 2) is characterized by two stages. The first step is an increase of the Mn 2+ to a maximum of 1.6 mmol L -1 after 30 minutes. The second step is the slow decrease in concentration up to 1.3 mmol L -1 at 180 minutes and stabilization around this value for up to 24 hours of reaction. At this pH, the amount of Mn 2+ released in the solution represents 3% of the total Mn while at pH 10, no Mn 2+ was detected in the supernatant.

Solid analysis

The TEM images of as prepared Na-birnessite and after acidic treatment (Fig. 3a and3.b) highlights a rectangular shaped particles morphology similar to what has been previously

observed [START_REF] Villalobos | Characterization of the manganese oxide produced by Pseudomonas putida strain MnB1[END_REF][START_REF] Ma | Layered MnO 2 nanobelts: Hydrothermal synthesis and electrochemical measurements[END_REF][START_REF] Zhang | Synthesis and characterization of one-dimensional K 0[END_REF]. Moreover, both samples present a lamellar structure with an appearance of well aligned layers having an interlayer spacing of ca. 0.6 -0.7 nm for hexagonal birnessite and ca. 0.5 -0.6 nm for triclinic birnessite. These values, less important than the ones measured by XRD analysis (ca. 0.7 nm), are probably the result of a loss in water molecules from the interlayer space when sample is under vacuum (5.10 -5 Pa) during the TEM analysis [START_REF] Zhu | Birnessite-type MnO 2 nanowalls and their magnetic properties[END_REF]. SEM images (Fig. 3) show that both samples consist of aggregates of layered particles in the range size of few µm. The morphology of birnessite seems to be not significantly affected by acidic treatment. After acidic treatment, basal reflections shifted slightly toward lower 2θ values which correspond henceforth to the distances 7.24 and 3.62 Å. For 2θ range from 30 to 70°, the initial reflections of the triclinic form collapsed and the product maintained at pH 3.5 during 24 h revealed other reflection peaks corresponding to hexagonal birnessite [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF][START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF]. The measurements of lattice parameters using the Le Bail method gave a = 2.844(2) Å and c = 7.238(3) Å (uncertainty was taken to be 3 times the standard deviation derived from Le Bail extraction, see Fig. S1).

• FTIR and Raman scattering characterizations

The solids were further characterized by FTIR analysis (Fig. 5A) and the obtained band positions are compared with reported existing studies on Table 1. Both triclinic Na-birnessite and hexagonal birnessite show strong absorption bands in the 220 -700 cm -1 range. These bands are assigned to Mn-O lattice vibration in good agreement with the reported spectra of triclinic [START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF][START_REF] Cui | Birnessites with different average manganese oxidation states synthesized, characterized, and transformed to todorokite at atmospheric pressure[END_REF][START_REF] Feng | Pathways of birnessite formation in alkali medium[END_REF][START_REF] Potter | Mineralogy of manganese dendrites and coatings[END_REF] and hexagonal birnessite [START_REF] Johnson | Water in the interlayer region of birnessite: Importance in cation exchange and structural stability[END_REF][START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF].

Triclinic Na-birnessite is characterized by the presence of bands located at 245, 360, 417, 478, 513 and 636 cm -1 and by a shoulder at 550 cm -1 . As expected from its higher degree of symmetry, the FTIR spectrum of hexagonal birnessite presents a reduced number of absorption bands located at 341, 426, 496 and 658 cm -1 . These band positions are in fair agreement with previous experimental results [START_REF] Johnson | Water in the interlayer region of birnessite: Importance in cation exchange and structural stability[END_REF][START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF] in the 400 -700 cm -1 range (see Table 1). On the basis of DFT calculations where birnessite was modeled with a cluster approach, these authors indicated that clear band assignment remained delicate due to strong overlap of Mn-O vibration modes below 700 cm -1 .

Interestingly, measurement in the far infrared range allow the identification of additional absorption band at 245 and 360 cm -1 for triclinic Na-birnessite and 341 cm -1 for hexagonal birnessite. DFT calculations predicted absorption band below 400 cm -1 for hexagonal birnessite but no absorption band was predicted for triclinic birnessite in this range [START_REF] Johnson | Water in the interlayer region of birnessite: Importance in cation exchange and structural stability[END_REF][START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF].

Actually, these calculations were based on Mn x O y H z clusters without considering Na + species in the interlayer region. Then, one may suggest that these extra bands could be associated to cation vibrations.

Additional vibration modes appear at higher wavenumber. Interlayer water gives rise to absorption band in the regions of ~1400 -1650 cm -1 and 3000 -3600 cm -1 corresponding to bending and stretching modes. In both regions, triclinic Na-birnessite presents narrower bands than what is observed for hexagonal form. This could be attributed to higher degree of order of the water molecules in the interlayer region and/or to higher degree of crystallinity of the whole material. The latter point is supported by PXRD results where the triclinic form presents sharper diffraction pattern. Lastly, no feature is observed in the range of 950 -1200 cm -1 , which is generally associated with the Mn-O-H bending mode [START_REF] Bayoudh | Hydrothermal synthesis, characterization and electrochemical properties of γ-MnOOH nanobelts[END_REF][START_REF] Ocaña | Uniform particles of manganese compounds obtained by forced hydrolysis of manganese(II) acetate[END_REF]. Then, significant amount of MnOOH as well as Mn-OH moieties in birnessite samples can be ruled out.

The Raman scattering spectra of triclinic Na-birnessite and hexagonal birnessite shown in Figure 5B are compared to reported existing studies on Table 1. The position as well as the relative intensities of the Raman bands are in good agreement with the reported spectra of birnessites [START_REF] Julien | Raman spectra of birnessite manganese dioxides[END_REF][START_REF] Yang | Investigations into the origin of pseudocapacitive behavior of Mn 3 O 4 electrodes using in operando Raman spectroscopy[END_REF].

Indeed, both spectra display characteristic manganese oxide Raman fingerprints in the range from 400 to 700 cm -1 showing: 1) a strong band between 635 and 650 cm -1 that can be attributed to the Mn-O symmetric stretching vibration ν 2 (Mn-O) of MnO 6 group, 2) a band around 575 and 587 cm -1 corresponding to the Mn-O stretching vibration ν 3 (Mn-O) in the basal plane of [MnO 6 ] sheets [START_REF] Julien | Raman spectra of birnessite manganese dioxides[END_REF], 3) additional bands with weaker intensities displayed at 509, 485 and 405 cm -1 for the triclinic symmetry, and around 500 and 387 cm -1 for the hexagonal form that are attributed to Mn-O-Mn bending vibration. Due to its higher symmetry, the hexagonal form presents less characteristic bands than the triclinic form [START_REF] Julien | Spectroscopic studies of the local structure in positive electrodes for lithium batteries[END_REF].

An additional band is observed in the Raman spectrum of the triclinic Na-birnessite located at 279 cm -1 . This band has been previously attributed to the weak bond of the intercalated Na + between MnO 6 layers [START_REF] Yang | Investigations into the origin of pseudocapacitive behavior of Mn 3 O 4 electrodes using in operando Raman spectroscopy[END_REF]. Finally, an unassigned additional band located at 610 cm -1 appears in the hexagonal birnessite spectrum. Previous studies have shown that the appearance of this

Raman band is strongly dependent on the synthesis parameters [START_REF] Morgan Chan | Electrochemical trapping of metastable Mn 3+ ions for activation of MnO 2 oxygen evolution catalysts[END_REF].

14

Then, in complete agreement with PXRD results, FTIR and Raman scattering spectra confirm that, triclinic Na-birnessite is converted into hexagonal birnessite when maintained at pH = 3.5 during 24 h, as it has been previously observed [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF][START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Drits | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: I. Results from X-ray diffraction and selected-area electron diffraction[END_REF]. • 23 Na and 1

H NMR analysis

The 23 Na MAS NMR spectra of triclinic and hexagonal birnessite are presented in figure 6-A.

The spectrum of triclinic Na-birnessite seems quite similar to those shown in a previous study [START_REF] Aldi | Investigation of cation ordering in triclinic sodium birnessite via 23 Na MAS NMR spectroscopy[END_REF]. The spectrum displays 3 signals corresponding to different chemical environments within the triclinic birnessite with isotropic shifts of 435, 376 and 329 ppm respectively (crystalline NaCl has been used to set the 0 ppm signal). The other observed peaks in the spectrum correspond to the spinning side bands due to a strong chemical shift anisotropy (CSA) due to hyperfine interaction with the unpaired electrons in Mn III and Mn IV as well as first order quadrupolar coupling. Those signals are broadened by magnetic field distribution due to field inhomogeneity as well as second order quadrupolar interaction. According to Lanson et al. [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF] Na-birnessite layer is formed of one row of Mn III O 6 octahedra separated by two rows of Mn IV O 6 octahedra. Each Na + ion is bonded to the oxygen layer, then coordinated to three Mn III/IV ions via the bonded oxygen. Aldi et al. [START_REF] Aldi | Investigation of cation ordering in triclinic sodium birnessite via 23 Na MAS NMR spectroscopy[END_REF] attributed the three 23 Na peaks to different chemical environments where Na + ion was coordinated to i) three Mn IV (environment A, see fig. 1), ii) two Mn IV and one Mn III (environment B) or iii) one Mn IV and two Mn III (environment C). Following Aldi et al's work [START_REF] Aldi | Investigation of cation ordering in triclinic sodium birnessite via 23 Na MAS NMR spectroscopy[END_REF], we assume that these environments correspond to the peaks at i) 435, ii) 376 and iii) 329 ppm respectively. This assignment is validated despite the slight differences in isotropic shifts between our observations and those made in Aldi et al's work [START_REF] Aldi | Investigation of cation ordering in triclinic sodium birnessite via 23 Na MAS NMR spectroscopy[END_REF]. Indeed, since the shifts that are presented in this paper are strongly field-dependent, a simple extrapolation shows that the assignment proposed in here falls close to the one observed in Aldi et al's work. In consequence, it appears that Na + ions occupied A, B and C sites thus suggesting that the synthesis method used in this study provides birnessite with cation disorder in the interlayer space.

Lastly, there is an additional, relatively narrow and weak signal at -11 ppm that corresponds to an unidentified impurity that does not undergo the effects of hyperfine interaction and may thus not be inside the material. Given its limited NMR shift, this signal is compatible with traces of sodium salt. There should be a counter anion associated with that Na + . As XPS did not show the presence of Cl -, SO 4

, NO 3 -(see hereafter), one can assume this sodium salt to be NaOH. Moreover, since hydrated NaOH is expected to be not crystalized, this assumption is also consistent with PXRD result.

All 23 Na signals disappear completely in the hexagonal birnessite, thus confirming the total sodium removal when the triclinic Na-birnessite turns to a hexagonal one.

The 1 H MAS NMR spectra of triclinic and hexagonal birnessite are presented in figure 6-B.

Both spectra show two signals. The first one has an isotropic shift close to 0 ppm. It presents very little CSA and has the same intensity in both spectra. This signal could be assigned to water molecule physisorbed at the surface [START_REF] Nosaka | Photoinduced Changes of Adsorbed Water on a TiO 2 Photocatalytic Film As Studied by 1 H NMR Spectroscopy[END_REF] or to a background signal that remains from the presaturation. The second signal, also present in both spectra but with different intensity this time, presents a very strong CSA. This signal is weaker with a shift of 13 ppm for the hexagonal birnessite with respect to the triclinic one. The very large observed CSA is due to the hyperfine coupling with the manganese unpaired electrons. This indicates the close proximity of those protons to the metallic center. These protons probably belong to hydration water located in the interlayer space. Since the triclinic birnessite contains more water than the hexagonal one [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF], the intensity of the related signal is larger for the triclinic form. Furthermore, the PXRD study concluded that the thickness of the interlayer space is smaller for the triclinic Na-birnessite which suggests that the water molecules are closer to the Mn oxide layers for the triclinic birnessite when compared to hexagonal variety. This observation may explain the difference in the CSA and the 13 ppm shift between the two signals. The shift can also be explained by the chemical environment of the nuclear probe; H 2 O … Na + for Nabirnessite vs H 2 O … H + for the hexagonal form.

• XPS analysis

Surface properties of Na-birnessite and hexagonal birnessite were examined by XPS.

Overview XPS spectra (Fig. 7.a and 7.b) show core-level photoelectron peaks at ~50 eV (Mn3p), ~285 eV (C1s), ~530 eV (O1s), ~642 eV (Mn2p 3/2 ), ~654 eV (Mn2p 1/2 ), ~770 eV (Mn2s) and ~1071 eV (Na1s). The C1s peak should be attributed to atmospheric hydrocarbon contamination of the birnessite surface before introduction into the XPS chamber.

The Na1s spectrum of Na-birnessite presents one peak located at 1070.7 eV (FWHM = 1.5

eV) corresponding to one chemical environment of Na atom at the surface. Na1s peak is no more observed for the hexagonal form. This disappearance indicates a complete release of Na ions observed at the surface from the solid at pH = 3.5. This is in line with the triclinic to hexagonal conversion observed by FTIR, Raman, PXRD as well as NMR analyses. On the contrary to XPS, various Na environments in Na-triclinic birnessite can be distinguished by NMR measurements. This should be mainly attributed to the fact that the position of XPS feature essentially depends on the oxidation state of the atom while NMR displacement also depends on the local chemical environment (packing, hyperfine interactions).

The O1s spectra of both samples present a maximum at 529.6 eV and a broad shoulder at higher binding energy. The low binding energy peak corresponds to lattice oxygen (O 2-). The medium binding energy peaks (531 eV) are assigned to O -and OH groups. The higher binding energy peak (533 eV) is attributed to adsorbed water [START_REF] Santos | The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds[END_REF][START_REF] Wang | Preparation, characterization and adsorption performance of cetyltrimethylammonium modified birnessite[END_REF]. For both samples O -and OH contributions represent more than 20 % of O1s spectrum. This result is in line with a high amount of surface defect.

Particular attention was paid to Mn2p 3/2 and Mn3p peaks from which it has been claimed that the valence state of Mn can be extracted [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF][START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF]. Following these studies, the Mn2p 3/2 and Mn3p peaks were then decomposed and the results were compared to each other and to the bulk analysis in order to determine the accuracy of each method. The corresponding results are given in Figure 7 and Table 2 while the fitting parameters are given in supplementary materials (see Table S1).

The Mn2p 3/2 spectrum of Na-birnessite (Fig. 7.c) is centered at 642 eV with shoulders at 641 eV and 643 eV, as expected for Mn III -Mn IV birnessite [START_REF] Boumaiza | Conditions for the formation of pure birnessite during the oxidation of Mn(II) cations in aqueous alkaline medium[END_REF]. Similar but widened feature is observed for hexagonal birnessite (Fig. 7.d) with additional contribution at 639 eV. This low binding energy component is attributed to Mn II contribution [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF][START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF].

Based on the earlier work of Gupta and Ken [START_REF] Gupta | Calculation of multiplet structure of core p-vacancy levels. II[END_REF], Nesbitt and Banerjee [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF] have proposed a method to isolate the Mn II , Mn III and Mn IV contributions of Mn2p 3/2 peak in birnessite.

According to calculations of multiplet structure core p-vacancy levels, each valence state contribution was modeled as a multiplet whose parameters were derived from ab-initio calculations. Mn2p 3/2 spectra of triclinic Na-birnessite and hexagonal birnessite were fitted following the recommendations of Nesbitt and Banerjee [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF]. This analysis confirms that Nabirnessite presents only Mn III and Mn IV while hexagonal birnessite presents an additional Mn II component representing a relative area of 7±2 %. It also appears that Mn III content decreases while Mn IV content increases after acidic treatment, in line with the mechanism proposed in previous studies [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF][START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Drits | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: I. Results from X-ray diffraction and selected-area electron diffraction[END_REF].

Recently, Ilton et al. [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF] claimed that a more reliable evaluation of Mn II , Mn III and Mn IV distribution on the surface can be obtained from the Mn3p signal. Actually, the Mn3p peaks for triclinic Na-birnessite and hexagonal birnessite are located at 50 eV with a shoulder at 48 eV. These authors proposed an empirical approach where each valence state contribution was described as a multiplet whose shape is experimentally determined from XPS measurement on monovalent Mn oxide (MnO, MnOOH and MnO 2 ). Following the same Mn3p fitting procedure, the obtained results indicates that Mn II appears after acid treatment while Mn III and Mn IV content decreases and increases respectively, as observed when using Mn2p 3/2 spectra.

The Mn II , Mn III and Mn IV distribution on the surface obtained from the Mn2p 3/2 and Mn3p peaks fitting along with the Mn AOS of the bulk given by potentiometric titration are summarized in Table 2. Our results show that, regardless of the fitted Mn peak, surface analysis by XPS give the same value of Mn AOS, unlike what has been previously observed in Ilton et al. work [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF]. Indeed, the Mn AOS of triclinic form is found equal to 3.43±0.05 and 3.47±0.05 according to Mn2p 3/2 and Mn3p fittings respectively while it was equal to 3.60±0.08 and 3.56±0.06 according to Mn2p 3/2 and Mn3p fittings respectively for the hexagonal form. These values derived from surface analysis are significantly lower than the bulk values of 3.65±0.02 and 4.00±0.02 obtained for the triclinic and hexagonal forms respectively. Actually XPS is a surface sensitive technique that only probes the first few nanometers of birnessite particles whose size are in the range of µm (determined from SEM measurements). These results support Mn AOS gradient between surface and bulk.

It should be noted that PXRD did not evidence any Mn II salt along with hexagonal birnessite.

Accordingly, XPS measurements did not evidence any counter-ion (e.g. no chloride) likely to form Mn II salt. Then, it comes that Mn II content is intimately associated to hexagonal birnessite phase.

In brief, following the approaches of Nesbitt et al. [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF] and Ilton et al. [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF], we showed that Na-triclinic birnessite conversion to hexagonal one leads to (i) Mn II formation at the solid surface as well as (ii) %Mn III decrease and %Mn IV increase. Moreover, unlike what has been claimed in the study of Ilton et al., [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF] (iii) Mn average oxidation state at the surface given by these two methods are essentially similar.

Discussion

As evidenced by PXRD, FTIR and Raman scattering results, when dispersed during 24 h in an acidic aqueous solution (pH = 3.5), triclinic Na-birnessite changes its symmetry to hexagonal.

This structural transformation is accompanied by complete Na removal form the solid, as confirmed by XPS and NMR measurements. This is in line with earlier works in which the symmetry conversion was studied by different techniques [START_REF] Lanson | Structure of H-exchanged hexagonal birnessite and its mechanism of formation from Na-rich monoclinic buserite at low pH[END_REF][START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Drits | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: I. Results from X-ray diffraction and selected-area electron diffraction[END_REF].

At pH 3.5, the amount of Mn 2+ released in the solution is characterized by two phases: an increase within the initial 30 minutes up to 1.6 mmol L -1 and then a decrease to stabilize at 1.3 mmol L -1 at 24 h (Fig. 2). This result can be brought into connection with the previous observation showing that the reaction of triclinic birnessite placed in an acidic medium could be explained by a two steps reaction. The first step corresponds to the partial disproportionation of Mn III contained in the layers into Mn II and Mn IV . Mn II is then dissolved in acidic medium leading to vacancies formation in the layers following reaction: 2Mn 3+ (layer) → Mn 4+ (layer) + Mn 2+ (layer) → Mn 4+ (layer) + vacancy + Mn 2+ (aq) [START_REF] Bargar | Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ[END_REF] In a second step, a part of the dissolved Mn 2+ re-adsorbs on the surface, above and below vacancies, resulting in the diminution of the amount of aqueous Mn 2+ [START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF][START_REF] Drits | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: I. Results from X-ray diffraction and selected-area electron diffraction[END_REF]. According to this mechanism, if final Mn 2+ (aq) represents reduced fraction of total Mn, the AOS of the solid would scarcely evolve but these authors did not evidence any AOS change (~3.6). At this point, it should be highlighted that Silvester et al. [START_REF] Silvester | Structure of synthetic monoclinic Na-rich birnessite and hexagonal birnessite: II. Results from chemical studies and EXAFS spectroscopy[END_REF] preserve the reactive medium from further oxidation with Ar bubbling.

In here, while birnessite's conversion was performed without any protection against oxygen, a significant increase of the Mn AOS was evidenced both in the bulk (from 3.65 to 4.00) and at the surface (from 3.4 to 3.6). It is interesting to note that soluble Mn 2+ release ([Mn 2+ ] = 1.3 mmol L -1 , after 24 h) represents only 3 % of the total Mn. Actually, the disproportionation of Mn III according to reaction (1) should lead to the Mn 2+ release in the solution and an increase in the corresponding Mn IV content in the solid. From the observed Mn 2+ release and the Mn AOS of the as prepared Na-birnessite equal to 3.65, the Mn AOS in the solid is expected to increase up to 3.68, while Mn AOS was measured equal to 4.00 for hexagonal birnessite. It should be noted that several reports mention also hexagonal birnessite with high Mn AOS up to 3.99 [START_REF] Villalobos | Characterization of the manganese oxide produced by Pseudomonas putida strain MnB1[END_REF][START_REF] Zhao | Redox reactions between Mn(II) and hexagonal birnessite change its layer symmetry[END_REF][START_REF] Feng | Pathways of birnessite formation in alkali medium[END_REF][START_REF] Feng | Adsorption and redox reactions of heavy metals on synthesized Mn oxide minerals[END_REF][START_REF] Gao | Interaction mechanisms and kinetics of ferrous ion and hexagonal birnessite in aqueous systems[END_REF][START_REF] Wang | Sorption behavior of heavy metals on birnessite: Relationship with its Mn average oxidation state and implications for types of sorption sites[END_REF][START_REF] Ye | A comparative investigation on catalytic oxidation of CO, benzene, and toluene over birnessites derived from different routes[END_REF]. Then additional oxidative step should be considered.

Let us consider the reaction where Mn 2+ undergoes oxidation to form additional Mn oxide (noted a-MnO 2 ):

Mn 2+ (aq) + ½ O 2(aq) + H 2 O (lq) = a-MnO 2(s) + 2 H + (aq) (2)
Considering that activities of dissolved or ionic species are equal to their respective concentrations, activity of a-MnO 2 equal to 1 and taking the Henry's law constant for O 2 dissolution in water to be 7.92 10 4 kPa kg mol -1 [START_REF] Moelwyn-Hughes | Physical Chemistry[END_REF], the chemical equilibrium constant of reaction (2) can be determined (with equation S1) and hence the corresponding standard Gibbs energy of reaction can be derived. Finally, from tabulated thermodynamics data of aqueous Mn 2+ , dissolved O 2 , liquid H 2 O and ionic H + (see Table 3), the standard Gibbs free energy of formation of the obtained Mn oxide can be calculated (with equation S3). The obtained value of ∆ f G°(a-MnO 2 ) is equal to -443.4 kJ mol -1 .

Interestingly, this value is lower to the one given for birnessite (δ-MnO 2 ) obtained by hausmannite oxidation in acidic medium ∆ f G°(δ-MnO 2 ) = -452.8 kJ mol -1 [START_REF] Bricker | Some stability relations in the system Mn-O 2 -H 2 O at 25° and one atmosphere total pressure[END_REF] and also lower the one tabulated for most stable β-MnO 2 ∆ f G°(β-MnO 2 ) = -465.2 kJ mol -1 [START_REF] Lange | Handbook of Chemistry[END_REF]. It is valuable to calculate the Mn 2+ concentration at equilibrium when assuming δ-MnO 2 and β-MnO 2 formation, respectively. At pH = 3.5 and under atmospheric condition (298 K), the law of mass action gives a Mn 2+ concentration equal to 30 µmol L -1 and to 0.2 µmol L -1 , respectively. It is necessary to point out that experimental analysis of the solution has given a much higher concentration of Mn 2+ equal to 1.3 mmol L -1 .

After 24 h at pH = 3.5 in aerated conditions, triclinic Na-birnessite turns into a Na free hexagonal birnessite with Mn AOS equal to 4.00. Such birnessite is obtained from suspension with higher Mn 2+ concentration than the one expected for β-MnO 2 particles suspension at the same pH. Considering that β-MnO 2 is the most stable MnO 2 phase, it appears that, in our case, birnessite was obtained from a solution presenting Mn 2+ excess with respect to thermodynamic equilibrium. Therefore, reduced form of Mn can be anticipated at the near surface despite the high Mn AOS of bulk birnessite. This supposition is evidenced by XPS measurements where Mn II and Mn III were present. After acid treatment, the Mn AOS of the hexagonal birnessite at the surface was equal to ~ 3.6 (see Table 2) according to two different methods that correspond to the state of the art concerning Mn2p and Mn3p lines interpretation [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF][START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF]. Similarly for triclinic Na-birnessite, the Mn AOS of the surface located in a range from 3.4 to 3.5 is lower than the Mn AOS of the bulk (3.65). The discrepancy between XPS and titration measurements may originate from the fact that XPS only probes the first few nm of the particles that are in the range of µm as determined from SEM measurements. One may argue that manganese at the near-surface of birnessite is significantly more reduced than in the bulk. It should be noted that the O1s core-level spectra of birnessite evidenced appreciable amount of defects at the surface (O -and OH moieties), which supports specific surface composition. Low Mn AOS at the surface can be attributed to the strong oxidative properties of Mn IV as supposed in previous studies [START_REF] Nesbitt | Interpretation of XPS Mn(2p) spectra of Mn oxyhydroxides and constraints on the mechanism of MnO 2 precipitation[END_REF][START_REF] Boumaiza | Conditions for the formation of pure birnessite during the oxidation of Mn(II) cations in aqueous alkaline medium[END_REF][START_REF] Mckendry | Decoration of the layered manganese oxide birnessite with Mn(II/III) gives a new water oxidation catalyst with fifty-fold turnover number enhancement[END_REF][START_REF] Yin | Characterization of Ni-rich hexagonal birnessite and its geochemical effects on aqueous Pb 2+ /Zn 2+ and As(III)[END_REF][START_REF] Ye | A comparative investigation on catalytic oxidation of CO, benzene, and toluene over birnessites derived from different routes[END_REF]. In contrast, Ilton et al. [START_REF] Ilton | XPS determination of Mn oxidation states in Mn (hydr)oxides[END_REF] performed angle resolve XPS measurements, from which they did not evidence any significant reduction of the top surface. However it may be argued that this discrepancy arises from the difficulty to carry out angle resolve XPS measurements on powder where particles are poorly oriented.

Conclusion

The conversion of the triclinic birnessite into hexagonal one was monitored measuring the Mn amount in the liquid phase and a comprehensive set of solid characterization techniques. ICP, FTIR, Raman scattering and PXRD characterizations provide a consistent description of both solids. These investigations evidence the full transformation of single-phase triclinic Nabirnessite into hexagonal birnessite in acidic solution. Measurements in the far infrared range allow the identification absorption bands at 245 and 360 cm -1 for triclinic Na-birnessite and 341 cm -1 for hexagonal birnessite. It is worth noticing that the DFT cluster approach reported in previous works [START_REF] Johnson | Water in the interlayer region of birnessite: Importance in cation exchange and structural stability[END_REF][START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF] predicted absorption bands at low wavenumber for hexagonal birnessite but no one was predicted for triclinic birnessite spectrum. To get a further insight into this band assignment, additional investigations by DFT should be performed with periodic boundary conditions allowing explicit description of the interlayer region and in particular of the Na + ion. To the best our knowledge, the first 1 H NMR signature of triclinic and hexagonal birnessites is provided. 23 Na NMR measurements discriminated various chemical environments of sodium in triclinic birnessite, in particular NMR discriminate sodium close to Mn in the interlayer from sodium outside of the birnessite structure. This latter component was not detected by others techniques and clearly illustrated the relevance of a multi-technique approach in material study. The determination of the Mn II , Mn III and Mn IV distribution on the surface based on the XPS Mn2p 3/2 and Mn3p features analyses gave similar results on both Na triclinic and hexagonal birnessites. In each case, surface AOS derived from XPS results were systematically lower than the AOS derived from bulk analysis.

This leads us to recommend the determination of the surface AOS when birnessite reactivity is investigated.

Fig. 2 .

 2 Fig. 2. Evolution of soluble Mn concentration in triclinic birnessite suspension as function of time at pH 3.5 and 10 ([Na-bir] = 6 g L -1 , T = 25 °C).

Fig. 3 .

 3 Fig. 3. TEM (lower panel) and SEM (upper panel) images of a) as-prepared triclinic Nabirnessite and b) after acidic treatment (pH = 3.5, [Na-birnessite] = 6 g L -1 , T = 25 °C, reaction time = 24 h).• PXRD characterizationsFigure 4 presents the PXRD pattern of the prepared Na-birnessite before (Fig. 4.a) and after

Fig. 4 .

 4 Fig. 4. PXRD patterns of a) as-prepared triclinic Na-birnessite and b) after conversion into hexagonal birnessite by acidic treatment (pH = 3.5, [Na-birnessite] = 6 g L -1 , T = 25 °C, reaction time = 24 h).

Fig. 5 .

 5 Fig. 5. FTIR (A) and Raman scattering (B) spectra of a) as-prepared triclinic Na-birnessite and b) after conversion into hexagonal birnessite by acidic treatment (pH = 3.5, [Na-bir] = 6 g L -1 , T = 25 °C, reaction time = 24 h).

Fig. 6 .

 6 Fig. 6. (A) 23 Na solid-state MAS NMR of as-prepared triclinic Na-birnessite, the center bands on the spectra are identified by the arrows above them and the corresponding isotropic shifts. All the other peaks are spinning sidebands. (B) 1 H solid-state MAS NMR spectra of a) asprepared triclinic Na-birnessite and b) after conversion into hexagonal birnessite by acidic treatment (pH = 3.5, [Na-bir] = 6 g L -1 , T = 25 °C, reaction time = 24 h).

Fig. 7 .

 7 Fig.7. Survey, Mn2p 3/2 , Mn3p, O1s and Na1s XPS spectra of the triclinic Na-birnessite (a, c, e, g and i) and the hexagonal birnessite (b, d, f, h and j) (pH = 3.5, [Na-bir] = 6 g L -1 , T = 25 °C, reaction time = 24 h).

  [START_REF] Lanson | Structure of synthetic Na-birnessite: Evidence for a triclinic one-layer unit cell[END_REF]

  O, ACS reagent, ≥98%), sodium permanganate monohydrate (NaMnO 4 •H 2 O, ACS reagent ≥97%) and sodium hydroxide (NaOH, BioXtra, ≥98% pellets anhydrous) were used for birnessite's synthesis. Hydrochloric acid (ACS reagent, 37%) was used to convert Na triclinic birnessite into hexagonal one in acidic medium. Mohr salt ((NH 4 ) 2 Fe(SO 4 ) 2 •6H 2 O, ACS reagent, 99%), sodium pyrophosphate dibasic (Na 2 H 2 P 2 O 7 , practical grade) and potassium permanganate (KMnO 4

  14 h, washed until the supernatant pH is 9 -10 and dried at 60 °C for 16 hours. The obtained

	product	consisted	on	triclinic	Na-birnessite	with	a	general	formula
	[Mn III 0.35 Mn IV 0.65 O 2 ][Na +	0.35, 0.7 H 2 O]. For this triclinic birnessite, the Mn AOS is equal to
	3.65 and the CEC is equal to 2.3 meq g -1 .

Table 1 :

 1 FTIR and Raman band location (cm -1 ) and attribution for triclinic Na-birnessite and hexagonal birnessite in comparison to previous studies (the reported FTIR bands are based on ref.[START_REF] Johnson | Water in the interlayer region of birnessite: Importance in cation exchange and structural stability[END_REF][START_REF] Ling | Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites[END_REF] while the reported Raman bands are based on ref.[START_REF] Julien | Raman spectra of birnessite manganese dioxides[END_REF][START_REF] Yang | Investigations into the origin of pseudocapacitive behavior of Mn 3 O 4 electrodes using in operando Raman spectroscopy[END_REF])

		FTIR band position (cm -1 )	Raman band position (cm -1 )
		This	Previous		This	Previous
		study	studies		study	studies
	Triclinic Na-birnessite	245 360 417 478 513 636	418 478 511 639	interlayer Na + vibrations Mn-O lattice vibrations	200 279 405 485 509 587 635	195 281 408 480 509 584 637	interlayer Na + vibrations Mn-O-Mn bend. ν 3 : Mn-O stretch. in the basal plane of [MnO 6 ] sheets ν 2 : Mn-O symm. stretch. of MnO 6
		341				296	*
					387
	Hexagonal birnessite	426 496 658	440 494 659	Mn-O lattice vibrations	500 575 610 650	506 575 646	Mn-O-Mn bend. ν 3 : Mn-O stretch. in the basal plane of [MnO 6 ] sheets * ν 2 : Mn-O symm. stretch. of MnO 6
						730	*
	*Unassigned

Table 2 :

 2 Mn II , Mn III and Mn IV distribution on the surface derived from XPS measurements compared to AOS of the bulk.

		Triclinic Na-birnessite	Hexagonal birnessite
		Mn2p 3/2	Mn3p	Mn2p 3/2	Mn3p
		fitting	fitting	fitting	fitting
	Mn II (%)	-	-	7±2	2±1
	Mn III (%)	57±6	53±5	26±4	40±4
	Mn IV (%)	43±5	47±5	67±6	58±5
	AOS surface 3.43±0.05 3.47±0.05 3.60±0.08 3.56±0.06
	AOS bulk	3.65±0.02	4.00±0.02

Table 3 :

 3 Standard Gibbs free energies of formation of different species involved in studied reactions from[START_REF] Bricker | Some stability relations in the system Mn-O 2 -H 2 O at 25° and one atmosphere total pressure[END_REF][START_REF] Lange | Handbook of Chemistry[END_REF].

	Compound	Mn 2+	(aq)	β-MnO 2(s)	δ-MnO 2(s)	H 2 O (lq)	O 2(aq)
	∆ f G° (kJ mol -1 )	-227.8	-465.2	-452.8	-237	16.3

Acknowledgements

We would like to acknowledge Pierrick Durand (Institut Jean Barriol, CRM2) for the PXRD characterizations, Claire Genois for the ICP-AES measurements (LCPME, Université de Lorraine, Villers les Nancy). We also thank Marc Hébrant for fruitful discussion and comments. We would like to thank the Tunisian Ministry of Higher Education and Scientific Research for the mobility grant accorded to Hella Boumaiza.


Amine El

Mahdi Safhi

Mahfoud Benzerzour

Nor- Patrice Edine Rivard

Edine Abriak

Amine El Mahdi Safhi
email: amine.el.mahdi.safhi@usherbrooke.ca

Feasibility of using marine sediments in SCC pastes as supplementary cementitious materials

Keywords: Sediments, Mix design, Rheology, Recycling, Cohesiveness, SCC pastes

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

In a vision of sustainability, and to limit the depletion of natural resources, reduce CO 2 emissions, and strengthen biodiversity, the adoption of the circular economy as a model of consumption has become a major necessity. Dredged sediments could be an alternative additive in concrete, as well as a new source of construction materials. Sediments have been considered as waste materials for a long time [START_REF] Dang | Design of new blended cement based on marine dredged sediment[END_REF]. However, when subjected to particular treatment, they have been demonstrated to have pozzolanic properties that may allow them to be used with Portland cement as a reactive or a simple mineral additive in the production of concrete [START_REF] Amar | Study of the pozzolanic activity of a dredged sediment from Dunkirk harbour[END_REF][START_REF] Amar | Durability of a cementitious matrix based on treated sediments[END_REF]. Dredged sediments can be regarded as a suitable alternative for greener concrete structures.

The type of cement, the presence of additives, the water-to-cement ratio, the different types of admixtures, the dosages, the type and the size of aggregates are some of the factors that determine the final quality of concrete. However, a suitable mix design is not enough to achieve the expected properties. Fresh concrete must have rheological properties allowing it to properly fill the space in the workform between the rebars with the lowest segregation. High workability and good rheological stability are required for concrete. That is why concrete must meet very strict performance requirements to ensure the expected service life of any structure, especially for reinforced concrete elements, where the use of self-compacting concrete (SCC) is increasing.

SCC is a very fluid material, homogeneous and stable, that perfectly fits the shapes of the most complex forms. It was designed by Okamura in Japan for the purpose of facilitating casting in pieces of complex geometry, or located in inaccessible areas set up under their own weight without vibration. Different approaches to mix design have been proposed in previous studies [START_REF] Shi | A review on mixture design methods for self-compacting concrete[END_REF] such as:

The empirical design method: Okamura proposed an empirical method based on laboratory tests by fixing different ranges for each component in the SCC concrete [START_REF] Okamura | Self-compacting high-performance concrete[END_REF]. Khaleel and Abdul Razak proposed an empirical method for SCC based on metakaolin and coarse aggregates with different properties. Using this method, they found that metakaolin enhances the SCC properties [START_REF] Khaleel | Mix design method for self compacting metakaolin concrete with different properties of coarse aggregate[END_REF].

The compressive strength method: Kheder and Al Jadiri proposed a method based on targeting a range of compressive strength by varying the water-to-cement ratio [START_REF] Kheder | New Method for Proportioning Self-Consolidating Concrete Based on Compressive Strength Requirements[END_REF]. Dinakar et al. proposed a method started by fixing the total powder content; based on the required strength, the other parameters like W/C and fresh properties were then evaluated to meet the self-compactibility criteria [START_REF] Dinakar | Design of self-compacting concrete with ground granulated blast furnace slag[END_REF].

The close aggregate packing method: Kanadasan and Razak proposed to use the particles packing concept to secure the fresh and the hardened properties of SCC [START_REF] Kanadasan | Mix design for self-compacting palm oil clinker concrete based on particle packing[END_REF]. This method helped to promote sustainability by incorporating palm oil clinker aggregate. Sebaibi et al. proposed a method based on optimizing the SCC concrete using RENE LCPC software [START_REF] Sebaibi | Composition of self compacting concrete (SCC) using the compressible packing model, the Chinese method and the European standard[END_REF].

The mixture design method based on the statistical factorial method: Bouziani developed a simplex-lattice mixture design with different factors and levels [START_REF] Bouziani | Assessment of fresh properties and compressive strength of self-compacting concrete made with different sand types by mixture design modelling approach[END_REF]. This study confirms that this approach is valid for a wide range of mixture proportions. Ozbay et al. used Taguchi's experiment design by using different factors [START_REF] Ozbay | Investigating mix proportions of high strength self compacting concrete by using Taguchi method[END_REF]. This study analyzed the mixture proportion parameters of a high-strength SCC and it shows that the laboratory tests can be reproduced in a full-scale production.

The mixture design method based on the rheology of the paste model: Ferrara et al.

proposed a method for formulating a steel fibre-reinforced SCC based on developing a rheological model for pastes [START_REF] Ferrara | A method for mix-design of fiber-reinforced self-compacting concrete[END_REF]. The model proved to be an efficient tool for the optimization of the SCC mixture.

Recently, studies have been focusing on the rheological understanding of this material and it has been reported that the control of the rheological properties is fundamental to optimize the SCC [START_REF] Tregger | Correlating dynamic segregation of self-consolidating concrete to the slump-flow test[END_REF][START_REF] Wallevik | Rheology as a tool in concrete science: The use of rheographs and workability boxes[END_REF][START_REF] Wu | Development of a mix design method for SCC based on the rheological characteristics of paste[END_REF]. The rheological properties depend on many factors such as: the packing density, the specific surface area, water content, and film thicknesses [START_REF] Li | Concrete mix design based on water film thickness and paste film thickness[END_REF][START_REF] Zhang | New approach to calculate water film thickness and the correlation to the rheology of mortar and concrete containing reactive MgO[END_REF][START_REF] Xie | Maximum paste coating thickness without voids clogging of pervious concrete and its relationship to the rheological properties of cement paste[END_REF][START_REF] Ng | Packing and film thickness theories for the mix design of highperformance concrete[END_REF][START_REF] Kabagire | Experimental assessment of the effect of particle characteristics on rheological properties of model mortar[END_REF]. Other studies show that the main factors influencing the rheology are the water-to-powder ratio and the superplasticizer dosage [START_REF] Li | Effect of water-powder ratio on shear thickening response of SCC[END_REF][START_REF] Grünewald | Characteristics and influence of paste on the behaviour of selfcompacting concrete in the fresh[END_REF]. Despite previous studies investigate if those parameters influence individually or jointly the rheology of cementitious paste, it is still difficult to tell [START_REF] Chen | Effects of CSF on strength, rheology and cohesiveness of cement paste[END_REF].

Rheological models are mathematical tools used to characterize the behaviour of a material during flowing. The choice of a model is determined by the type of material, as well as the rate of deformation the material is subjected to. Many rheological models have been proposed for the cementitious matrix since the beginning of the rheology study [START_REF] Atzeni | Comparison between rheological models for portland cement pastes[END_REF][START_REF] Nehdi | Estimating rheological properties of cement pastes using various rheological models for different test geometry, gap and surface friction[END_REF], especially for the cementitious matrix [START_REF] Bui | Rheological Model for Self-Consolidating Concrete[END_REF][START_REF] Papo | Rheological models for cement pastes[END_REF].

The rheology of SCC can be described with the Bingham or Herschel-Bulkley model [START_REF] Li | Effect of water-powder ratio on shear thickening response of SCC[END_REF]. In this paper, the Bingham model is considered to be the most appropriate. It includes three intrinsic parameters (τ 0 , k, η) that describe the steady-state flow of the material in a homogeneous condition (no particle segregation). The shear stress τ (Pa) is then related to the shear rate γ̇ (s -1 ) using Eq. 1:

Eq. 1 = + .
where τ 0 is the shear threshold of the material and η is the viscosity (Pa.s). Although some studies on SCC used the rheological Herschel-Bulkley model, some others demonstrated that the rheological model of Bingham is the most adaptable for use in the field of cementitious matrix [START_REF] Huang | The rheological properties of self-compacting concrete containing superplasticizer and air-entraining agent[END_REF][START_REF] Singh | Rheological behaviour of different grades of self-compacting concrete containing recycled aggregates[END_REF][START_REF] Girish | Influence of powder and paste on flow properties of SCC[END_REF]. The volume of the paste in SCC is much higher than in ordinary concrete, which leads to the use of more additives and admixtures. The composition of the paste is the main parameter affecting the self-compactibility properties [START_REF] Mebrouki | A Self-Compacting Cement Paste Formulation using Mixture Design[END_REF].

The purpose of this work is to incorporate treated sediments as a replacement for Portland cement, and to evaluate their influence on the rheological behaviour of the mixture, which will have good environmental and economic benefits. This study is a part of a wider project on recycling sediments in SCC. This experimental study indicated that the volumetric amount of sediments in the mixtures can reach up to 14%, in other words, up to a sediments-to-cement-ratio of 0.29 in mass.

Materials and methods

Test equipment

The morphology of the treated sediments was analyzed using a Scanning Electron Microscope (SEM) Hitachi S-4700. The thermogravimetric analysis (TGA) was carried out with an apparatus NETZSCH STA 449 using nitrogen gas in a controlled environment with argon flow (75 ml/min) at variable temperatures (105 °C to 1100 °C, ramp rate = 2 °C/min).

A mini-slump test developed by Kantro [START_REF] Kantro | Influence of Water-Reducing Admixtures on Properties of Cement Paste-A Miniature Slump Test[END_REF], with the proportional dimensions of the standard slump test cone was used to determine the workability. Strong correlations between this test and the apparent viscosity [START_REF] Cyr | Contribution à la caractérisation des fines minérales et à la compréhension de leur rôle joué dans le comportement rhéologique des matrices cimentaires[END_REF][START_REF] Wallevik | Relationship between the Bingham parameters and slump[END_REF], and, in certain cases, with the yield stress have been reported previously [START_REF] Ferraris | The influence of mineral admixtures on the rheology of cement paste and concrete[END_REF][START_REF] Roussel | From mini-cone test to Abrams cone test: measurement of cementbased materials yield stress using slump tests[END_REF]. The fluidity and the consistency were determined with a 10-mm orifice Marsh cone. The outflow time through the cone was measured to fill 1000 ml.

A Vicat apparatus was used to determine the water demand of the sediments. It is equipped with a consistency probe of 10 mm in diameter, as described in NF EN 196-3 standard [START_REF] Afnor | NF EN 196-3 : Méthodes d'essai des ciments -Partie 3 : détermination du temps de prise et de la stabilité[END_REF].

For the rheological analysis, a robust Anton Paar Modular Compact Rheometer MCR 102 (Fig. 1) was used with a plane geometry. The shear rate varied from 1 to 100 s -1 .

Fig. 1. Anton Paar Modular Compact Rheometer MCR 102

Material properties

The cement used in this study is an Ordinary Portland Cement (OPC) CEM I 52.5 N (standard NF EN 197-1 [START_REF] Afnor | NF EN 197-1 : Ciment -Partie 1 : composition, spécifications et critères de conformité des ciments courants[END_REF]). This cement is communally used in studies about recycling sub-products because it contains no admixtures, in order to measure the real effect of the sediments. The sediments were dredged from Grand Port Maritime de Dunkerque (GPMD), located in the North of France. The raw sediments were heated at 850°C for 1 hour, after having been crushed and sieved through 120 µm sieves [START_REF] Amar | Durability of a cementitious matrix based on treated sediments[END_REF] (Fig. 2). This technique was very efficient to eliminate the high-water content and organic matter, and to modify the mineralogy and the composition of the raw sediments. The physical properties of the powders are shown in Fig. 2. Process of treatment (from left to right: sediment after drying, after grinding, after thermal treatment) Table 1. The distribution of particles is given in Fig. 3. X-ray fluorescence (XRF) analysis was performed on the cement, and on the raw and treated sediments. The results are provided in Table 2. One can note that the concentration of most of the oxides increased in the sediments after the treatment. Fig. 4 shows the mineralogical composition of the raw and treated sediments obtained from X-ray diffraction (XRD). Quartz (SiO 2 ) and calcite (CaCO 3 ) were found as the main phases for the raw sediments. The analysis also indicated some minor phases such as gypsum (CaSO 4 , 2H 2 O), haematite (Fe 2 O 3 ), natrosilite (Na 2 Si 2 O 5 ) and halite (NaCl). After treatment, quartz (SiO 2 ), gehlenite (several forms), and anhydrite (CaSO 4 ) were found as the main phases. The analysis also indicated some minor phases such as haematite (Fe 2 O 3 ), augite, gypsum, and microcline (KAlSi 3 O 8 ).

The morphology of treated sediments is shown in Fig. 5Fig. 5, it was observed that it consist of fine angular particles. According to Fig. 6, EDX analysis confirms the XRD analysis and it

shows that the mineralogical nature of treated sediments is mainly siliceous.

The demand of superplasticizer (S P ) was measured using two types. The S P Chryso Fluid

Optima 206 appears to be the most suitable and the saturation assay starts from 1.5 % of the S P dry extract to the cement mass.

The TGA analysis was conducted on the raw sediments. The results are presented in Fig. 7 and it shows that:

Between 30 and 120 °C: the free water and some of the adsorbed water escape from the material. Unbound water is completely removed at 120°C

Between 130 and 170 °C: a double endothermic reaction can take place associated with the decomposition of gypsum (CaSO 4 .2H 2 O)

Between 180 and about 300°C: the first stage of dehydration. The heat breaks the particles and pulls the inter-granular water molecules At about 250 and 370 °C: small endothermic peaks may be produced indicating decomposition and oxidation effects of metallic elements (haematite)

Between 450 and 550 °C: decomposition of the organic matter and organic pollutants Around 570 °C: there is a structural transformation from quartz α to quartz β

Between 600 and 700 °C: this is the second step in the decarbonation of calcite.

Between 700 and 900 °C: a highly endothermic reaction due to the decomposition of limestone (CaCO 3 ) that releases carbon dioxide (CO 2 ) and calcium oxide (CaO)

Above 1000 -1400 °C: the material goes to the mud state

The analysis confirms the choice of the calcination temperature, which is above the optimum of 750°C.

Fig. 2. Process of treatment (from left to right: sediment after drying, after grinding, after thermal treatment)

Table 1. Physical properties of cement and sediments

Experimental protocols

Packing density and water demand

Water demand consists in determining the mass of water M w required to make the cementitious paste go from the state of pellets to a state of homogeneous paste. Tests were carried out on 350 g of cement using a standard kneader (described in standard NF EN 196-1 [START_REF] Afnor | NF EN 196-1 : Methods of testing cement -Part 1: Determination of strength[END_REF]) and the Vicat apparatus. The optimisation of water demand was performed by using the Réne-LCPC, a developed software by Sedran and Larrard [START_REF] Sedran | Détermination de la compacité des ciments et additions minérales à la sonde de Vicat[END_REF], which is based on a mathematical model in order to secure a maximum packing density of the skeleton. This model makes it possible to calculate the theoretical compactness of any granular mixture, and the viscosity of any suspension at a given concentration of this mixture, based on various material characteristics. Physically speaking, a higher compactness refers to a minimum percentage of voids between solid grains.

Penetration measurements were performed for different water contents. The mass of water M w required to obtain a height h = 6 mm can be determined by successive tests. In order to limit the number of tests, it is possible to interpolate M w from two points (A & B) framing the normal consistency. However, in order to minimize the error, points A and B must fulfill the following conditions (Eq. 2):

Eq. 2 ≥ 2 0.25 ≤ / ≤ 0.4 - ≤ 5
The compactness ∅ of the powder is then determined by Eq. 3:

Eq. 3 ∅ = ! " !
where ρ C is the density of the cement, M w and M C are the total mass of water and cement, respectively. The theoretical compactness (∅) was calculated using the commercial software Réne-LCPC as it shown in Fig. 8. It represents that the amount of sediments up to 70% improve the density of the mixture which can be explained by the finesse of the marine sediments and their ability to fill into voids between the cement grains. The water demand for treated sediments was 0.4.

Fig. 8. Theoretical packing density of the mixtures using René-LCPC software

Experimental design

The design of experiments (DoE) approach is based on a statistical method that can be used to optimize experimental tests. It is a well-known approach commonly used for the optimization of cementitious mixtures [START_REF] Fatemi | Optimization of the water-based road-marking paint by experimental design, mixture method[END_REF][START_REF] Imanzadeh | Formulating and optimizing the compressive strength of a raw earth concrete by mixture design[END_REF][START_REF] Matos | Design of self-compacting high-performance concrete: Study of mortar phase[END_REF][START_REF] Mirabedini | Application of mixture experimental design to optimize formulation and performance of thermoplastic road markings[END_REF]. It allows the measurement of multiple responses without extra experiments. In our case, DoE allows us to quantify the influence of each mix parameter on the fresh properties of the mixtures. Furthermore, the responses depend only on the proportions of the compositions in the mixture and not on the mass or the volume.

The main characteristic of a random mixture is that the sum of all the components must be equal to 1. The experimental plan was based on four factors: cement (C), sediments (S), water (W), and superplasticizer (S P ) taken in volumetric proportion. With a total volume equal to unity, the mix design implies that there is an interaction and dependence between the parameters. The experimental field was constrained by Eq. 4:

Eq. 4 ∑ $ % %&' %& = + ( + + () = 1
However, another important parameter was taken into consideration, namely the solid volumetric concentration (Г). This is the ratio of the volume of solids to the total volume, which comprises the solid particles coming from cement, sediments, and superplasticizer in dry extract.

This parameter is known to correlate with the yielded value [START_REF] Ghosh | Advances in Cement Technology: Chemistry, Manufacture and Testing[END_REF]. It also correlates with the viscosity [START_REF] Justnes | Viscosity of cement slurries as a function of solids content[END_REF], which increases with the increase of the volume fraction of solids. This fact is valid only at a low shear rate and shear stress and for a Г max = 0.62 [START_REF] Nzihou | A rheological, thermal and mechanical study of bone cement-from a suspension to a solid biomaterial[END_REF]. This limitation was confirmed elsewhere [START_REF] Kurdowski | Cement and Concrete Chemistry[END_REF]. It was recommended to keep the volume ratio below 0.60 to avoid resistance against shear stress increase with the shear rate.

The mathematical model for this mix design converges toward a 2 nd degree polynomial (Eq. 5), which can be written in a matrix form (Eq. 7) as the following:

Eq. 5 + = , -% $ . / %&.
+ ∑ ∑ -%. $ % $ . + 0 . %1.

Eq. 6 2+3 = 243. 2-3 + 203

where Y is the response, x i and x j correspond to the volumetric proportions of the mix factors, and β i and β ij are the regression coefficients. This model is known as the Scheffé canonical polynomials, widely used in mixture experiment applications [START_REF] Scheffé | Experiments With Mixtures[END_REF][START_REF] Ghafari | Statistical mixture design approach for eco-efficient UHPC[END_REF]. This equation can be expanded to (Eq. where [X] is the experimental matrix, [β] is the vector of the model coefficients, and [ε] is the vector of the experimental error. After some preliminary tests in the laboratory, the range of variation of each component was as follows (Eq. 8):

Eq. 8 9 0 % ≤ ( ≤ 30% 0 % ≤ ( < ≤ 2% 0.25 ≤ / ≤ 0.4 0.57 ≤ Г ≤ 0.59

Table 3 represents the range of variation of the different components.

Table 3. Implicit constraints

The field of study was a space of four dimensions, since there were four factors. The experimental matrix generated a hyper polyhedral. Numeric analysis was performed using a commercial software (Design Expert) dedicated for experimental mixture plans. The volume proportion of each component was calculated based on the given criteria.

Parametric study

The optimal experimental matrix was defined to achieve reliable and effective results. The dedicated software gives the mix proportions of a total of 20 points for modelling. Table 4 presents the determined arrangements of the 20 runs and their corresponding responses. Six mixtures were removed from the model design because they did not meet the criteria of self-compactibility (having a low workability and fluidity).

The water demand of the sediments was not considered in this arrangement. It was added separately for each mixture depending on the mass of sediments. The significance of the model (linear, quadratic, cubic, two-factor interaction, etc.), was investigated using robust software (Design-Expert and SPSS) and using the statistical model ANOVA (analysis of variances).

Table 4. Mix proportions and fresh properties of the mixtures

Preparation of specimens and Test methods

Mixture preparation was made according to NF EN 196-1 [START_REF] Afnor | NF EN 196-1 : Methods of testing cement -Part 1: Determination of strength[END_REF] procedure. Tests were conducted on fresh paste first. Using the mini slump flow diameter, the spreading out diameter (D flow ) was measured on a horizontal glass plate after 1 and 5 min to determine the workability. The fluidity and the consistency were determined using the Marsh cone. The outflow time (T flow ) was taken for 500 ml according to EN 445 standard [START_REF] Afnor | NF EN 445 : Coulis pour câble de précontrainte -Méthodes d'essai[END_REF]. The rheological analysis was performed between 5 and 7 min after starting the mixing operation.

The fresh pastes were poured in three 50-mm steel cubes, according to ASTM C 139 [START_REF] Astm | Standard Specification for Concrete Masonry Units for Construction of Catch Basins and Manholes[END_REF], and allowed to fill under its own weight. The specimens were removed from the moulds one day after casting, and were placed in curing water at a temperature of 20 ±2 °C. At 28 days, the compressive strength was measured in accordance with standard ASTM C109 [START_REF]ASTM C109 / C109M : Standard Test Method for Compressive Strength of Hydraulic Cement Mortars (Using 2-in[END_REF].

Up to now there is no standard test method for evaluating the cohesiveness for a cementitious paste. However, Kwan has developed a protocol to measure this parameter using a mini version of the sieve segregation test [START_REF] Chen | Effects of CSF on strength, rheology and cohesiveness of cement paste[END_REF][START_REF] Kwan | Effects of superplasticiser on rheology and cohesiveness of CSF cement paste[END_REF]. The standard test consists in evaluating the sieve segregation index (SSI) by quantifying the portion of fresh SCC sample (4.8 ±0.2 kg) passing through a 5 mm sieve, from a height of 50 ±5 cm. Kwan suggested instead, to pour about 400 g of paste onto a 0.3 mm sieve from a height of 300 mm. In this study this protocol was used to measure the cohesiveness of the different pastes.

Results and discussion

The results of all the tests are presented in Table 5.

Table 5. Results of all the conducted tests

Workability

The results of the ANOVA analysis on the D flow are provided in Table 6. This model is characterized by a R 2 of 0.923 and a predicted R 2 (0.844) in this case is in fair agreement with the adjusted R 2 (0.900). The Model F-value suggests that the model is significant. There is only a 0.01% chance that such F-value could occur due to noise. A p-value below 0.05 indicates that the model terms are significant. Values greater than 0.1 indicate that the model terms are not significant. The "Lack of Fit F-value" of 12.95 implies that the Lack of Fit is significant. There is only a 0.69% chance that such "Lack of Fit F-value" could occur due to noise.

Fig. 9 shows the slump flow responses in a ternary graph while fixing the cement proportion.

For the same proportion of sediments (e.g. 0.112), the spread flow changes quickly from 140 to 185 mm, which means that the sediments have no effect on this parameter. The spread flow was not affected by the water content either; 180 mm could be obtained for a water range of variation between 0.41 and 0.43. The orientation of hatching confirms this fact. Again, the S P content appears to be the dominant parameter in this ternary combination. According to Gomes [START_REF] Gomes | Optimization and characterization of high-strength self-compacting concrete[END_REF] the value considered satisfactory for the flowing is 180 ±10 mm.

Table 6. ANOVA analyses of results for the D flow

Flowability

The linear model was a match for the flowability. The results of the ANOVA analysis on the T flow are presented in Table 7. This model is characterized by a R 2 of 0.888 and a predicted R 2 (0.734) in this case is in fair agreement with the adjusted R 2 (0.854). The Model F-value suggests that the model is significant. There is only a 0.01 % chance that such F-value could occur due to noise. A p-value below 0.05 indicates that the model terms are significant. The "Lack of Fit Fvalue" of 4.72 implies a 5.69 % chance that a "Lack of Fit F-value" could occur due to noise, which is very low.

Fig. 10 shows the Marsh flow responses in a ternary graph while fixing the cement proportion (four components generate a cubic form that is hard to analyze). While all three variables affect the fluidity, the S P content appears to be the dominant parameter in a ternary combination.

According to previous studies that used mini-slump and Marsh cones [START_REF] Nunes | Rheological characterization of SCC mortars and pastes with changes induced by cement delivery[END_REF][START_REF] Soltanzadeh | Steel fiber reinforced self-compacting concrete: from material to mechanical behavior table of contents[END_REF][START_REF] Basheerudeen | Particle Packing Approach for Designing the Mortar Phase of Self Compacting Concrete[END_REF][START_REF] Calmon | Effects of BOF steel slag and other cementitious materials on the rheological properties of self-compacting cement pastes[END_REF], good paste properties correspond to a D flow ≥ 165 mm and a T flow ≤ 40s, depending on the ratios of the concentration of solids to the total volume V S /V T , and of the volume of water to the total volume V W /V T .

Table 7. ANOVA analyses of results for the T flow Fig. 10. The counter plots for Marsh flow [s]: 2D and 3D plot

Rheological properties

The paste rheology was characterized using a rheometer and a plane geometry with variation of the shear rate (γ) from 1 to 100 s -1 . The following properties were determined: yield stress (τ 0 ), shear stress (τ), and viscosity (η). The temperature was kept constant at 20±0.1 °C. The results fitted perfectly the Bingham model (Table 5) with a coefficient of determination R 2 ≥ 0.95 as depicted in Fig. 11. This mixture can be characterized by a yield stress of 2.990 Pa and a viscosity of 1.163 Pa.s.

A correlation analysis was performed using the commercial software SPSS 24. Spearman's correlation coefficient (ρ Spearman ) was used to investigate the correlation between variables. The Spearman correlation is a non-parametric test that does not involve any assumptions about the distribution of the data.

Fig. 12 shows a moderate correlation between the V W /V C ratio and both viscosity and shear stress at a constant shear rate of 100 s -1 . The shear rate decreases with the increase of V W /V C ratio (ρ Spearman = -0.908), and the viscosity decreases with the increase of V W /V C ratio (ρ Spearman = -0.904).

A correlation analysis between both Marsh flow and yield point with the mini-slump flow is shown in Fig. 13. There is a strong relationship between both properties T flow and D flow (ρ Spearman = -0.913), a low flowability generates a high workability and vice-versa. There is also a strong correlation between D flow and the yield point (ρ Spearman = -0.911).

Fig. 14 presents a correlation between both D flow and T flow with the V W /V C ratio. There is a strong relationship between the V W /V C ratio and the fresh properties. D flow increases along with the V W /V C ratio (ρ Spearman = 0.915), and the T flow decreases while increasing the V W /V C ratio (ρ Spearman = -0.943). It is found that the good results (low T flow & high D flow ) are associated with a V W /V C ratio greater than 1.

Cohesiveness

The sieve segregation index (SSI) for all the mixtures is presented in Table 5. A low SSI refers to a high cohesiveness and vice-versa. SSI were lower than 10 % as recommended [START_REF] Kwan | Effects of superplasticiser on rheology and cohesiveness of CSF cement paste[END_REF],

which ensure that the SCC pastes have a good stability as a coherent mass.

Paste strength

Results of the compressive strength tests conducted on the pastes specimens are shown in Table 5 and Fig. 15. The strength values are the average of three test specimens at the age of 28 days. As it is seen, the compressive strength varies from 78 to 101 MPa and by fixing cement percentage to 0.442%, strength varies from 83 to 87 MPa. Treated sediments generated a low reduction in compressive strength. However, from the orientation of hatching, the S P content appears to be the dominant parameter in this ternary combination. The compressive strength increases with the increase of S P content. Compared to the reference paste, a compressive strength of 85 MPa is required.

Mixture optimization and validation of the model

The multi-criteria technique in Design-Expert allows us to set an optimization based on the overlay plots. The objective of this study is to maximize the mass of incorporated sediments while maintaining a good property of the pastes performances. Derringer and Suich [START_REF] Derringer | Simultaneous Optimization of Several Response Variables[END_REF] developed a global desirability function, represented in Eq. 9.

Eq. 9

@ = (B C D × B 5 C F × B 6 C G × ⋯ × B ' C I ) D ∑ K L
The combination of the different criteria is optimum for a D value close to 1. In Eq. 9, r i is the relative importance assigned to the response i. It is a comparative scale of weighing each of the resulting d i varying from 1 to 5. Goals can be assigned to the variables as to the responses and can be one of the following: maximize, minimize, target, or in the range. Table 8 provides the characterisation of the optimization function.

Fig. 16 shows the zone of desirability according to the overlay plot method. It suggests that the volumetric amount of sediments in the mixture can reach up to 14 %. Table 9 represents the optimal paste proportions according to both functions.

To assess the representability, repeatability, reproducibility, rapidity, and sensitivity of the model, a series of experiments were conducted with the optimal mixture proportions provided in Table 9. Table 10 shows the results with their absolute relative deviation (ARD) [START_REF] Fatemi | Optimization of the water-based road-marking paint by experimental design, mixture method[END_REF][START_REF] Ghafari | Statistical mixture design approach for eco-efficient UHPC[END_REF]. ARD is a parameter expressed in %, as in Eq. 10. It measures the predictability of the model and should not exceed 10%.

Eq. 10 MN@ (%) = OPQRC%SR'TUV W XYZRV OPQRC%SR'TUV × 100

According to Table 10, the results of the ARD are in the desirable range (less than 10 %). The model is validated by the small difference between the theoretical and the experimental values. This experimental study indicated that the volumetric amount of sediments in the mixtures can reach up to 14 %, in other words, sediments can replaces cement up to 0.29 as a sediments-to-cement-ratio, 0.30 as a water-to-cement-ratio, and 1.5 % of S P dosage in the extract sec of cement mass.

Conclusion

The production of cement is a major concern to the industrial and scientific community. The process of producing 1 ton of cement releases around 0.6 to 1.4 tons of CO 2 depending on the process in each country [START_REF] Licht | Co-production of cement and carbon nanotubes with a carbon negative footprint[END_REF][START_REF] Vizcaíno-Andrés | Industrial trial to produce a low clinker, low carbon cement[END_REF][START_REF] Shen | Cement industry of China: Driving force, environment impact and sustainable development[END_REF][START_REF] Wei | Clinkering-free cementation by fly ash carbonation[END_REF][START_REF] Xu | On the future of Chinese cement industry[END_REF]. The replacement of a part of the cement by treated sediments has a major economic and environmental impact. Treated sediments can play a relevant role in sustainability.

This paper focuses on the study of the effect of treated sediments on the rheological, fresh, and hardened properties of SCC pastes. The results demonstrated that sediments can be used as a supplementary cementitious material, with a volumetric amount up to 14 % (S/C = 0.29). At the economical level, this result is very encouraging especially that the used sediments are naturally available in large quantities and require less energy in the treatment comparing to the cement.

A mix design method based on the statistical mixture design approach was used in order to evaluate the influence of each component of the mix. A numerical optimization efficiently accomplished made it possible to design an SCC paste based on treated sediments. The statistical analysis of the results highlighted the real relevance of the measured effects on the various factors, as well as their interactions on the responses. The effects of the factors and their interactions were more significant than the uncertainties.

The treated sediments improve the packing density of the cementitious materials. The empirical tests on fresh properties performed on the pastes correlate perfectly with the rheological parameters of the SCC pastes, namely the shear stress and the viscosity. The rheological tests performed less than 7 min after the start of mixing confirmed that the rheological behaviour of the pastes evolves from young ages.

The developed mini version of sieve segregation test is very promoting protocol that can be used as a foundation for a standardized test. Further research in this direction is suggested.

The use of different superplasticizers and viscosity agents may affect the repeatability of the results.

An extensive research is going on at our laboratories in order to evaluate the effect of entrained air and viscosity agent on a SCC mixture incorporating treated sediments.

Fig. 3 .Fig. 4 .Fig. 5 .Fig. 6 .Fig. 7 .

 34567 Fig. 3. Particle size distribution of cement, raw and treated sediments

  7): Eq. 7 + = -. + -5 . ( + -6 . + -7 . (8 + -5 . . ( + -6 . . + -56 . (. + -7 . . (8 + -57 . . () + -67 . . ()

Fig. 9 .

 9 Fig. 9. The counter plots for slump flow (mm): 2D and 3D plot

Fig. 11 .Fig. 12 .

 1112 Fig. 11. The data from the 2 nd mix fitted perfectly the Bingham model

Fig. 15 .

 15 Fig. 15. The counter plots for compressive strength (MPa): 2D and 3D plot

Fig. 1 . 2 Fig. 2 .Fig. 3 .Fig. 4 . 6 Fig. 6 .Fig. 8 .Fig. 9 .Fig. 10 . 32 Fig. 11 .Fig. 12 .Fig. 13 . 40 R² 41 Fig. 14 . 43 R²Fig. 15 .Fig. 16 .

 1223466891032111213404114431516 Fig. 1. Anton Paar Modular Compact Rheometer MCR 102

Table 8 .

 8 Characterization of the desirability functionFig. 16 . Overlay plot optimization following the proposed criteria

Table 9 .

 9 Composition of the optimal pastes

Table 10 .

 10 Absolute relative deviation of the predicted responses

48 1 Table 1 .

 11 Physical properties of cement and sediments

	1
	components	Density (kg/m³)	Specific area BET (m²/kg)	Average diameter D 50 (µm)
	Cement	3176	914	15.9
	Raw sediments	2520	3652	5.90
	Treated sediments	2851	2335	9.80
	2
		2

Table 2 .

 2 Oxide composition of cement, raw and treated sediments using XRF (%)

	Oxides composition	Raw sediments	Treated sediments	CEM I 52.5 N
	SiO 2	38.8	36.4	17.3
	Al 2 O 3	11.0	10.1	5.41
	MgO	2.69	2.62	1.23
	Fe 2 O 3	13.3	12.7	4.09
	CaO	23.3	26.0	62.8
	Na 2 O	2.08	2.31	0.71
	K 2 O	2.08	1.65	0.76
	P 2 O 5	0.51	0.47	0.49
	SO 3	4.37	5.43	4.49
	TiO 2	0.54	0.51	0.35
	MnO	0.17	0.18	Traces
	ZnO	0.20	0.17	0.13

Table 3 .

 3 Implicit constraints

	Component volume	S	S P	E	C
	Coded	A	B	C	D
	Lower constraints	0.009	0.000	0.410	0.412
	Higher constraints	0.148	0.020	0.430	0.541

Table 5 .

 5 Results of all the conducted tests

	12

Acknowledgements

This work was funded by the research funds of the IMT Lille Douai and grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and from the "Fonds de Recherche Nature et Technologies du Québec" (FRQNT).