N Kanari

E Allain

N Menad

I Gaballah

First Version

Chlorination behaviors of two chalcopyrite concentrates and their pure constituents in Cl 2 +N 2 were investigated by thermogravimetric analysis in non isothermal conditions up to 1000 °C. The effect of temperature on the reaction of chlorine with both concentrates was studied between 170 °C and 300 °C under isothermal conditions. The effects of gas flow rate, chlorine content of the gas mixture and reaction time on the reaction rate were also investigated. The reaction products were analyzed by SEM and X-ray diffraction.

Results showed that the chlorination of the chalcopyrite concentrates generating chlorides of Cu, Pb, Zn, Fe and S was rapid at temperatures approaching 300 °C. The iron and sulfur chlorides were volatilized leading to a residue containing valuable metal chlorides. A process for the selective chlorination of sulfides' concentrates at low temperatures was suggested.

I. INTRODUCTION AND LITERATURE REVIEW

Sulfide ores and concentrates are still the major source of the primary production of metals such as Cu, Pb, Zn, etc. The extractive metallurgy of these metals from sulfides based on dry method is one of the responsibles for the environmental pollution due to the SO x generation.

Although the technological progress, the SO x emissions remain a serious problem from the ecological point of view. The conversion of SO 2 to H 2 SO 4 is marginal because of the transportation cost and the state of the sulfuric acid market. Different methods had been proposed to avoid sulfur dioxide formation during the extraction of valuable metals from sulfides. Gaballah et al. [START_REF] Gaballah | Thermal treatment of complex sulfide ores in N 2 and H 2 atmospheres : A new approach for the extraction of their valuable elements[END_REF] suggested the thermal treatment of complex sulfides' ores under controlled atmosphere (N 2 , H 2 ) at temperatures lower or equal to 1000 °C. The proposed flow-sheet permits the recovery of sulfur, galena, trace element's compounds, zinc and a residue rich in copper. Habashi [START_REF] Habashi | The future of copper metallurgy[END_REF] suggested that the hydrometallurgical route offers the possibility of obtaining sulfur at moderate temperature and pressure thus solving the sulfur problem of sulfides' treatment.

Several researches were devoted to the chlorination process as an efficient alternative to recover the copper from its sulfides at relatively low temperatures. Donaldson and Kershner [START_REF] Donaldson | Chloridization of certain mineral sulfides[END_REF] studied the chlorination of CuFeS 2 by chlorine between 25 °C and 300 °C in a horizontal experimental set. They observed that the intensive chlorination of CuFeS 2 , generating the copper and iron chlorides, started at 150 °C and almost full chlorination was achieved near to 250 °C. Landsberg et al. [START_REF] Landsberg | Chlorination kinetics of selected metal sulfides[END_REF] employed thermogravimetric analysis 'TGA' to investigate the chlorination of CuFeS 2 by Cl 2 +Ar from 25 °C to 300 °C. A value of apparent activation energy 'E a ' of about 35.6 kJ/mol was pointed out by these authors between 25 °C and 100 °C. They mentioned the formation of a product layer at about 200 °C and that the slowest step is the diffusion towards this layer.

Finally, they concluded that the chlorination reaction became exothermic at 300 °C and the sulfur, the iron and the copper were easily chlorinated, but the chlorination rate depended on the rate of volatilization of the reaction products.

Olsen et al. [START_REF] Olsen | Chlorination process for the recovery of copper from chalcopyrite[END_REF] developed a process for the chlorination of a pelletized chalcopyrite concentrate in a vertical reactor in the temperature range from 550 °C to 650 °C. They suggested, that in the absence of excess chlorine, the main products of CuFeS 2 chlorination were CuCl 2 , FeCl 2 and S°. About 99 pct of sulfur was distilled from the top of reactor. Iron and copper chlorides were treated with O 2 between 800 °C and 900 °C. Over 80 pct of the iron chlorides were converted to oxides while the copper chlorides remained unaffected. The authors recovered the copper in powder form by electrowining of chloride solution using a diaphragm cell.

Habashi [START_REF] Habashi | Zur behandlung von Chalkopyrit[END_REF] carried out the chlorination of CuFeS 2 concentrate by chlorine in a horizontal reactor between 100 °C and 500 °C. He recovered three main products that they were identified as S 2 Cl 2 , FeCl 3 and CuCl 2 . The author concluded that at 300 °C, practically all the sulfur was collected in the sulfur chloride liquid fraction, all the iron in the ferric chloride solid fraction, and all the copper remained in the reactor in a water-soluble form. The author mentioned also the exothermic character of the chlorination reactions.

Yee et al. [START_REF] Yee | Chlorination of chalcopyrite[END_REF] investigated the chlorination of a pelletized CuFeS 2 concentrate by Cl 2 +N 2 between 550 °C and 750 °C in a vertical reactor. They indicated that more than 96 pct of CuFeS 2 were converted to copper-iron chlorides and elemental sulfur. After filtration, elemental sulfur of greater than 99 pct purity was obtained. According to these authors, the valence state of copper and iron in the metal chlorides' product depended on the reaction temperature and chlorine flow rate used.

Kumar et al. [START_REF] Kumar | Gas -phase chlorination of chalcopyrite[END_REF] performed the chlorination by Cl 2 of a CuFeS 2 concentrate in powder and pellet form between 400 °C and 550 °C using TGA. According to these authors, the reaction products were condensed cuprous and ferrous chlorides as well as gaseous elemental sulfur. The ferrous chloride was transformed into gaseous ferric chloride. The last could intereact with chalcopyrite giving the same reaction products as in the case of CuFeS 2 with Cl 2 . The authors suggested a flow-sheet for extraction of copper, iron and other by-products from chalcopyrite. The proposed process was estimated to have an energy requirement of approximately 1780 kWh/tone of cathode copper, about half the energy consumption for conventional hydrometallurgical processes.

In another article, Kumar et al. [START_REF] Kumar | Kinetics and modeling of the gas -phase chlorination of chalcopyrite -I. Reactions with powder[END_REF] studied the kinetics of chlorination of CuFeS 2 powder in the same temperature range mentioned above. They developed a mathematical model to gain some insight into the reaction mechanism. The value of E a for the chlorination of CuFeS 2 by Cl 2 was about 2.1 kJ/mol while that of the reaction of FeCl 2 with Cl 2 to give FeCl 3 was about 10.5 kJ/mol. The authors concluded that the low values of E a could be due to highly exothermic nature of the reaction. Consequently, the increase of the reaction temperature affected not only the rate of the reaction, but also the physical structure of products. Finally, it has been mentioned by these investigators that the adsorption of chlorine on chalcopyrite could be the most possible reaction mechanism. Some aspects of the chlorination kinetics of chalcopyrite by chlorine were also given by Jena and Brocchi [START_REF] Jena | Extraction of copper from dry Salobo (Brazil) chalcopyrite concentrate and aqueous slurries thereof by chlorination with Cl 2 gas[END_REF] . They carried out the chlorination experiments between 350 °C and 450 °C.

The calculated value of E a was about 25.5 kJ/mol, while the chlorination rate of copper at 400 °C was almost independent of chlorine partial pressure ' P Cl 2 ' for the value of P Cl 2 higher than 0.4 atm.

It has been suggested that the chlorination of CuFeS 2 was controlled by an adsorption mechanism.

This paper is a part of a research program concerning the use of chlorine for the extraction of valuable metals from wastes such as spent catalysts [START_REF] Gaballah | Recovery of Co, Ni, Mo and V from unroasted spent hydrorefining catalysts by selective chlorination[END_REF] , tin slag [START_REF] Gaballah | Extraction of tantalum and niobium compounds from tin slags by chlorination and carbochlorination of pure oxides and concentrates[END_REF] and from raw materials such as chromite. [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF] It deals with the kinetics study of the chlorination of two chalcopyrite concentrates in order to achieve a selective separation of the valuable metal (Cu, Pb, Zn) compounds.

II. MATERIALS AND EXPERIMENTAL PROCEDURES

A. Materials

Two chalcopyrite concentrates were used for this study. The physico-chemical characterization of the samples was realized by different analysis such as : scanning electron microscopy 'SEM', X-ray diffraction 'XRD', inductively coupled plasma-atomic emission spectrometry 'ICP-AES', size and specific surface measurements, etc.

Figure 1 gives the SEM spectrum of two concentrates used in this study. The major elements detected in the first sample 'S 1 ' (Figure 1 of the quartz and clinochlore. The HGC was rich in chalcopyrite (81.7 pct). Moreover, it contained some amounts of lead and zinc compounds, while its gangue content was feeble.

The concentrates were obtained by the enrichment of their ores using the flotation technique. The size measurements indicated that d 50 is about 85 and 35 µm for the LGC and HGC, respectively. The average specific surface of two samples was 0.63 ± 0.01 m 2 /g.

The chlorination behaviors of two concentrates were compared with that of their simple constituents such as CuFeS 2 , ZnS, PbS, FeS 2 as well as S°. The used minerals were of natural origin. The SEM and XRD analyses were used to check theirs composition.

B. Experimental Procedures

Thermogravimetric analysis chlorination tests were realized with 50 mg of sample, using an experimental set schematized previously [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF] . Its main unit is a CAHN 1000 microbalance having a sensitivity of 10 µg. The chlorination gas mixture composed of Cl 2 +N 2 was purified through H 2 SO 4 and CaCl 2 columns before reaching the reactor. The sample was uniformly distributed in a quartz crucible. This crucible was hooked to the balance using quartz rods. For a TGA test under non isothermal conditions, the sample was directly heated in the chlorinating atmosphere. For TGA isothermal runs, the sample was first heated in nitrogen atmosphere to a given temperature before the chlorination atmosphere is introduced. The exhaust gases were purified by a NaOH solution before their release to the atmosphere.

III. THERMODYNAMIC CONSIDERATIONS

The thermodynamic calculations were used to forecast the possible reactions of CuFeS 2 , ZnS, PbS and FeS 2 with chlorine. These calculations were performed using the data listed in References 14 and 15 and the results were given in Figure 3 as evolution of the standard free energy changes (∆G°) between 25 °C and 1000 °C for the envisaged reactions. Equations [1] through [3] and [7] through [15] were suggested to describe the chlorination of these sulfides. The results indicated that the chlorination of all sulfides is thermodynamically favorable for the considered reactions. The reaction of CuCl with Cl 2 (Eq. 4) was also favorable up to 400 °C. The formation of ferric chloride and sulfur dichloride from ferrous chloride and sulfur monochloride (Eqs. 5 and 6, respectively) were also possible from the thermodynamic point of view. The phase stability diagrams of (Cu, Pb, Zn, Fe)-S-Cl systems at 300 °C showed that CuCl 2 , PbCl 2 , ZnCl 2 and FeCl 3

were the predominant phases of metal-S-Cl system at high partial pressure of chlorine. [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF] The chlorides generated from the chlorination of sulfides are characterized by a widely difference in their vapor pressure at a given temperature. Figure 4 shows the evolution of vapor pressure of several chlorides as a function of the temperature. [START_REF] Lide | Handbook of Chemistry and Physics[END_REF] The ferric and sulfur chlorides possess a high vapor pressure at temperature lower or equal to 300 °C. Thus, if the chlorination of sulfides could be achieved at this temperature, these chlorides can volatilize leading to a residue containing the valuable metals. It seems that this is the important factor to separate selectively the valuable metals. For this reason, the effects of some parameters on the concentrate's chlorination were studied at 300 °C.

IV. RESULTS AND DISCUSSION

A. TGA of non isothermal treatment

The thermogravimetric analysis of the two concentrates (LGC and HGC) under Cl 2 +N 2 (Cl 2 /N 2 = 1) were carried out between 25 °C and 1000 °C. The heating rate of furnace was about 25 °C/minute. The major constituent of these concentrates (CuFeS 2 , ZnS, PbS, FeS 2 ) as well as S°w ere also treated in the same conditions. Figure 5 traces the percent weight loss (pct WL) of the used samples as a function of temperature.

The chlorination of chalcopyrite started from room temperature. A weight loss observed at about 150 °C could be attributed to the volatilization of the sulfur chlorides. The weight gains observed up to 300 °C is due to the intensive chlorination of the chalcopyrite sample according to

Eqs. [1] through [3]. Then, the volatilization of ferric chloride could be the responsible of the pct WL observed up to about 475 °C. The slow down of the weight loss between 550 °C and 700 °C may explain by the partial volatilization of CuCl 2 and its decomposition into CuCl (Eq. 4) followed by the volatilization of cuprous chloride at higher temperatures (Figure 4).

Galena and sphalerite started to react with chlorine at temperature higher than 200 °C and the weight gains recorded at low temperatures were due to the formation of lead and zinc chlorides (Eqs. 7 to 12). The pct WL at temperatures higher than 600 °C and 700 °C for the ZnS and PbS, respectively were due to the volatilization of zinc and lead chloride (Figure 4).

The substitute of sulfur by chlorine (Eqs. 13 to 15) justified the weight gain detected when the pyrite sample was contacted with chlorine. While the losses of sample at temperatures higher than 250 °C were attributed to the volatilization of the gaseous ferric chloride. About 80 pct of sulfur were volatilized at temperature lower than 400 °C. It is probably that the curve of pct WL of sulfur could be the overlapping of the volatilization curves of sulfur and its chlorides. [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF] The curve of the LGC chlorination gathered the characteristics of the CuFeS 2 and FeS 2 chlorination curves (Figure 5). This is in good agreement with the composition of this concentrate containing 31.2 pct CuFeS 2 and 23.8 pct FeS 2 . About 75 pct of the sample was chlorinated and volatilized at 1000 °C. The final residue was essentially composed of Si, Al and Mg oxides.

The chlorination behavior of the HGC was close to that of the chalcopyrite. The high contents of chalcopyrite (81.7 pct) in this concentrate explain this similarity. More than 95 pct of this concentrate were chlorinated and volatilized at about 850 °C. This was due to low content of the inert compounds in HGC.

B. Kinetics of chlorination of concentrates

Effect of gas flow rate

To minimize the impact of external mass transfer on the chlorination kinetics of the copper concentrates, the effect of the flow rate of a gas mixture of Cl 2 +N 2 (Cl 2 /N 2 = 1) was studied at 300 °C between 8 and 80 L/h. Several of the isothermal chlorination tests of LGC using different flow rates are represented in Figure 6 as the pct WL versus chlorination time. The reaction started by a weight increase due to the chlorides' formation. This step was followed by a weight loss of the sample caused by the volatilization of sulfur and iron chlorides. Figure 7 gives the data obtained during the chlorination of HGC in the same conditions as LGC.

Figures 8 (a) and (b) trace, respectively, the evolution of the initial reaction rate of the

LGC and HGC as function the gas flow rate. It has been observed that the chlorination of LGC was almost independent of gas flow rates higher than 30 L/h. While the flow rates higher than 50 L/h were required for the chlorination of HGC. To be assured that the mass transfer phenomena will not affect the kinetics of chlorination of the chalcopyrite concentrates, the gas flow rate used for the kinetic study of the chlorination of LGC and HGC were chosen 60 L/h (gas velocity 'V g ' = 0.83 cm/s) and 72 L/h (V g = 0.99 cm/s), respectively.

Effect of partial pressure of chlorine

It has been studied during the isothermal treatment at 300 °C for both concentrates using a gas mixture of Cl 2 +N 2 varying the molar chlorine content in the gas mixture from 10 to 100 pct. In order to define the apparent reaction orders with respect to chlorine for the chlorination of LGC and HGC, the data were represented in Figure 12 as evolution of the initial reaction rate versus partial pressure of chlorine on natural logarithm scale. The apparent reaction orders deduced from this figure were about 1.19 and 1.28 for LGC and HGC, respectively. Such values indicate a complex chlorination mechanism consisting probably of intermediate steps.

Effect of temperature

This effect on the chlorination of LGC was studied by isothermal treatments in a temperature range from 180 °C to 300 °C. Figure 13 shows the evolution of the pct WL during the

LGC chlorination with a Cl 2 +N 2 gas mixture, having a Cl 2 /N 2 molar ratio of 1. The selective chlorination limit (L 1 ) was reached at temperatures higher than 250 °C and for a reaction time of 30 minutes. It seems that the volatilization rate of FeCl 3 is feeble at temperatures lower than 250 °C.

Ferric chloride remained in the chlorination residue and can stop the progress of the reaction.

The effect of the temperature on the chlorination of HGC was studied between 170 °C and 300 °C. Typical isotherms were traced in Figure 14 as the pct WL versus time. The chlorination curves for the temperatures lower or equal to 200 °C were characterized by a weight increase of the sample for the first three minutes of the treatment. Since then, the weight increase was very slowly.

This could be attributed to the presence of chlorides which prevent further chlorination. At temperatures higher than 220 °C, the weight increases of the sample was followed by the loss of the sample due to the volatilization of sulfur and iron chlorides. The final weight losses obtained at temperatures higher than 250 °C were closed to the calculation limit for the selective chlorination of HGC.

The evolution of weight loss as function of temperature and reaction time were compared in Figures 15 (a) and (b) for the LGC and HGC, respectively. These figures clearly show that for the temperatures higher than 280 °C and the reaction time higher than 20 minutes are necessary for the selective chlorination of both concentrates. It has been observed that the residues of HGC chlorination were systematically agglomerated while that of LGC did not undergo this phenomenon. This is probably due to the presence in LGC of inert materials towards chlorine such as quartz and clinochlore that prevent the sample particles' agglomeration.

Attempts were made to evaluate the effect of temperature on the initial reaction rate of chlorination of two concentrates. Figures 16 (a identified because of its hygroscopic and amorphous character. In presence of cuprous and ferric chlorides, it is possible to form eutectics having a melting point lower than individual chlorides as indicated by Figure 18. [START_REF] Levin | Phase diagrams for Ceramists[END_REF] One of these eutectics formed at about 260 °C containing more than 80 pct FeCl 3 . It is probable that this eutectic was responsible for the anomaly observed between 240 and 255 °C. The apparent activation energy for the chlorination of LGC between 255 °C and 300

°C was about 94 kJ/mol indicating that the chemical reaction could be the lowest step of the overall chlorination process.

The chlorination of HGC processed with the value of E a (Figure 16 The curves of these TGA tests are traced in Figure 19. The pct weight loss of the HGC chlorination residue and heated in nitrogen were situated between those of ferric chloride and sulfur heated in the same conditions. This suggests that the sulfur and probably its chlorides as well as ferric chloride were present in the chlorination residue of HGC.

The XRD result of the HGC chlorination residue at 200 °C for 10 minutes and leached at pH ≈ 2 is given in Figure 20. The sulfur was detected in the residue besides the CuFeS 2 non reacted. These results suggest that the sulfur and/or its chlorides as well as iron chlorides remained in the chlorination residue. Consequently, these compounds can act as a barrier for the diffusion of chlorine towards the sulfides.

The value of the E a of about 50 kJ/mol between 210 °C and 240 °C indicates that the chlorination of HGC is still little affected by the temperature. An apparent activation energy of about 54 kJ/mol (Figure 16 b) was obtained for the sulfur chlorination by Cl 2 +N 2 in the same temperature range. These values suggest that the liquid sulfur and/or its chlorides generated during the chlorination could remain in the residues thus preventing the progress of the reaction. Although the sulfur chlorides were in gaseous state at this temperature range (Figure 4), in presence of sulfur they can coexist in liquid state. Ingraham and Parsons [START_REF] Ingraham | Kinetics of the chlorination of Cu 2 S with Cl 2 gas[END_REF] mentioned that the sulfur monochloride is a good solvent for sulfur. The presence of dissolved sulfur decreased the activity of sulfur monochloride very noticeable. Substantial amounts of both materials may be present in a liquid phase even at 250 °C, according to these authors.

The apparent activation energy of the HGC chlorination between 240 °C and 280 °C was found to be about 2 kJ/mol. As mentioned before, Kumar et al. [START_REF] Kumar | Kinetics and modeling of the gas -phase chlorination of chalcopyrite -I. Reactions with powder[END_REF] revealed a value of E a 2.1 kJ/mol for the chlorination of CuFeS 2 by Cl 2 between 400 °C and 550 °C and they mentioned that this low value could be due to highly exothermic nature of the reaction.

The chlorination reactions of sulfides by chlorine are exothermic. [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF][START_REF] Roine | Outokumpu HSC Chemistry for Windows, Version 2.0[END_REF] For instance, the standard enthalpy (∆H°) of the chlorination of chalcopyrite at 300 °C according to Eq. 3 is equal to -453.7 kJ/mol of CuFeS 2 . In order to estimate the increase of sample temperature provoked by the heat evolved from the exothermic reactions a series of experiments was performed at 300 °C in a horizontal experimental set described previously. [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF][START_REF] Kanari | Low temperature chlorination of chalcopyrite concentrates[END_REF] About two grams of LGC and HGC samples were chlorinated by Cl 2 +N 2 containing 15 to 100 pct Cl 2 . Figure 21 traces the increases of the sample temperature as function of the reaction time for the HGC chlorination. As could be expected, the increase of temperature was higher in case of higher chlorine content in the gas mixture. On the other hand, the temperature increase was observed at the beginning of the treatment. Although, the temperature was measured at the sample surface, an increase of about 30 °C was observed when the chlorination of HGC was carried out using chlorine alone. The same observations were available for the LGC chlorination, but the temperature increase was somewhat lower. This agrees with the lower sulfides content of this concentrate.

The boat experiments using several grams of samples were performed to follow the chlorination rates of copper and iron contained in both concentrates. The chlorination tests using Cl 2 +N 2 (Cl 2 /N 2 = 1) were conduced from room temperature to 750 °C and the chlorination residues were subjected to the chemical analysis. [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF][START_REF] Kanari | Low temperature chlorination of chalcopyrite concentrates[END_REF] It has been observed that almost full extraction of iron and sulfur chlorinated compounds were achieved at about 300 °C for a reaction time of one to two hours. The calculated limits for the selective chlorination of two concentrates (L 1 and L 2 , respectively) agreed well with the pct weight loss obtained at 300 °C. More than 95 pct of copper was concentrated in treatment residue as CuCl 2 at this temperature. In the case of HGC, the majority of lead and zinc was found in chlorination residues as metal chlorides. However, small amounts of valuable metal chlorides (Cu, Pb, Zn) were detected in the condensates. As the vapor pressures of these chlorides were negligible at this temperature (Figure 4), their presence in the condensates was probably caused by the formation of gaseous complex metal chlorides between these chlorides and ferric chloride. It is well known that FeCl 3 (Fe 2 Cl 6 ) enhances the apparent vapor pressure of the metal chlorides thanks to the synthesis of these binary chlorides. [START_REF] Gaballah | A survey of binary chloride compounds M x N y Cl z (M = R[END_REF] Results reported early [START_REF] Kanari | Extraction des métaux de valeur des concentrés de chalcopyrite et de chromite par chloruration[END_REF][START_REF] Kanari | Low temperature chlorination of chalcopyrite concentrates[END_REF] concerning the use of chlorine technique for the selective extraction of valuable metals from copper concentrate and those described above suggested a simplify flow-sheet represented in Figure 22. According to this flow-sheet, the chalcopyrite concentrate is chlorinated at about 300 °C in a fixed bed for a reaction time 1 to 2 hours. The presence of the liquid phase in the sulfide-chlorine system suggested that the fluidized bed will not be suitable for the chlorination of sulfides. The reaction time depends on the concentrate composition. The gas-phase of the chlorination is composed essentially of iron and sulfur chlorides.

Ferric chloride is recovered by cooling the gas phase at room temperature. The obtained ferric chloride can be treated in oxygen [START_REF] Henderson | Dechlorination of ferric chloride with oxygen[END_REF][START_REF] Paige | Recovery of chlorine and iron oxide from ferric chloride[END_REF] to give hematite and chlorine. The last will be used in the chalcopyrite chlorination unit. In addition, ferric chloride can be used as chlorinating agent. [START_REF] Von Hahn Hardwin | Chlorination of copper, lead, zinc, iron, silver and gold[END_REF] The sulfur chloride, after its condensation, will be subjected to hydrolysis in order to obtain elementary sulfur. [START_REF] Allain | Recovery of Elemental Sulfur from Sulfur Chlorides[END_REF] However, as mentioned in the literature [START_REF] Landsberg | Chlorination kinetics of selected metal sulfides[END_REF][START_REF] Smith | Action of sulfur monochloride upon minerals[END_REF][START_REF] Titi-Manyaka | Chlorination behaviors of complex iron, copper and nickel sulfides[END_REF] , sulfur monochloride reacted with several sulfides producing metal chlorides and elementary sulfur.

The chlorination residue will leach with acidified water at a needed temperature in order to dissolve the chloride of Cu, Zn, Pb. Others hydrometallurgical treatments will required to recover selectively these metals.

Although the chlorination process was conduced at lower temperature compared with conventional pyrometallurgical ones, the problems related to the equipments' corrosion, the difficulties to proceed in a continuos system, etc. have to be taken into account.

V. CONCLUSIONS

The chlorination of copper, lead, zinc and iron sulfides is thermodynamically favorable up to 1000 °C. The selective separation of valuable metal chlorides from iron and sulfur chlorides at temperatures approaching 300 °C was possible thanks to difference in the vapor pressure of these two groups of chlorides.

During non isothermal treatment, the complete chlorination of the selected sulfides and volatilization of the reaction products can be classified by following descending order : S > FeS 2 > CuFeS 2 > ZnS > PbS. The overall chlorination behavior of low grade concentrate up to at least 500 °C was intermediate between that of FeS 2 and CuFeS 2 agreeing with the chemical composition of this concentrate. The behavior of HGC appeared to be closed to that of CuFeS 2 .

The initial chlorination rate of two concentrates was affected by the partial pressure of chlorine. The apparent reaction orders with respect to chlorine at 300 °C were 1.19 and 1.28 for

LGC and HGC, respectively. However, the chlorine content of about 40 pct during the chlorination for time higher than 10 minutes was sufficient to achieve almost selective chlorination of both concentrates.

Excepted for the chlorination of LGC between 255 °C et 300 °C for which the apparent activation energy was about 94 kJ/mol, the effect of temperature on the initial rate of chlorination of both concentrates was feeble. The presence of liquid and solid products' layer as well as the exothermic nature of the chlorination reactions seem to be responsible of low value of the apparent activation energy.

The selective separation of iron and sulfur chlorides from those of valuable metals was possible during the chlorination of the chalcopyrite concentrates at 300 °C for a reaction time less two hours. More than 95 pct of copper was concentrated in treatment residue free from iron and sulfur.

The obtained results confirmed that chlorination will be seen as an attractive technique for the treatment of sulfides at low temperatures without SO x emissions.

N. KANARI, E. ALLAIN * , N. MENAD ** and I. GABALLAH Figure 3 : Evolution of the standard free energy changes (∆G°) as a function of temperature for the chlorination of the compounds contained in the chalcopyrite concentrates. [START_REF] Roine | Outokumpu HSC Chemistry for Windows, Version 2.0[END_REF][START_REF] Barin | Thermochemical data of pure substances[END_REF] Figure 4 : Evolution of vapor pressure of several chlorides. [START_REF] Lide | Handbook of Chemistry and Physics[END_REF] Figure 5 : TG analysis of sulfides and two concentrates in Cl 2 +N 2 .

Figure 6 : Isotherms of chlorination of LGC with Cl 2 +N 2 using various gas flow rates. Figure 18 : Phases' diagram of CuCl-FeCl 3 system [START_REF] Levin | Phase diagrams for Ceramists[END_REF] . Fig. 4 : Evolution of vapor pressure of several chlorides [START_REF] Lide | Handbook of Chemistry and Physics[END_REF] . Fig. 3 : Evolution of the standard free energy changes (∆G°) as a function of temperature for the chlorination of the compounds contained in the chalcopyrite concentrates [START_REF] Roine | Outokumpu HSC Chemistry for Windows, Version 2.0[END_REF][START_REF] Barin | Thermochemical data of pure substances[END_REF] .

Q Cp Cp Q Q Cp Cp Q Q Cp Q Cp Q Q Py Cp :

Temperature, °C

Figures 9

 9 Figures 9 and 10 group the evolution of the pct WL as a function of the reaction time for the different chlorine content in the Cl 2 +N 2 in the case of LGC and HGC, respectively. These figures contain the calculated limits (expressed as pct WL) for the selective chlorination of each concentrates and they were designed as L 1 and L 2 for LGC and HGC, respectively. They were defined supposing a full chlorination of sulfides and volatilization of iron and sulfur compounds.

  ) traces the Arrhenius plots for the chlorination of LGC between 200 °C and 300 °C. The Arrhenius diagram for the chlorination of HGC from 170 °C to 300 °C is illustrated in Figure 16 (b). This figure contains also the effect of temperature on the chlorination of sulfur between 170 and 240 °C. The chlorination of LGC was characterized by a value of E a of about 21 kJ/mol between 200 °C and 240 °C. Then, an anomaly was observed in the temperature range from 240 °C to 255 °C where the chlorination rate decreased with the rise of temperature. To explain this phenomenon, a chalcopyrite sample was chlorinated at 260 °C for a reaction time lower than 20 seconds. The chlorination residue was analyzed by XRD and the obtained result is given in Figure 17. As shown by this figure, CuCl and FeCl 2 were detected in the chlorination residue. The ferric chloride was not

Figure 1 :

 1 Figure 1 : Results of SEM of two chalcopyrite concentrates.

Figure 2 :

 2 Figure 2 : Results of X-ray diffraction of two chalcopyrite concentrates.

Figure 7 :

 7 Figure 7 : Isotherms of chlorination of HGC with Cl 2 +N 2 using various gas flow rates.

Figure 8 :

 8 Figure 8 : Chlorination of (a) LGC and (b) HGC as a function of flow rate of Cl 2 +N 2 .

Figure 9 :

 9 Figure 9 : Isotherms of chlorination of LGC using different chlorine contents in the Cl 2 +N 2 gas mixture.

Figure 10 :

 10 Figure 10 : Isotherms of chlorination of HGC using different chlorine contents in the Cl 2 +N 2 gas mixture.

Figure 11 :

 11 Figure 11 : Effects of the chlorine content in the gas mixture and reaction time on the chlorination of (a) LGC and (b) HGC.

Figure 12 :

 12 Figure 12 : Apparent reaction orders with respect to chlorine for the chlorination of LGC and HGC.

Figure 13 :

 13 Figure 13 : Isotherms of chlorination with Cl 2 +N 2 of LGC between 200 °C and 300 °C.

Figure 14 :

 14 Figure 14 : Isotherms of chlorination with Cl 2 +N 2 of HGC between 170 °C and 300 °C.

Figure 15 :

 15 Figure 15 : Effects of temperature and reaction time on the chlorination with Cl 2 +N 2 of (a) LGC and (b) HGC.

Figure 16 :

 16 Figure 16 : Arrhenius plots for the chlorination of (a) LGC and (b) HGC with Cl 2 +N 2 .

Figure 17 :

 17 Figure 17 : XRD result of the chlorination residue of chalcopyrite at 260 °C, t ≤ 20 seconds.

Figure 19 :

 19 Figure 19 : Behavior of chlorination residue of HGC, of sulfur and FeCl 3 at 200 °C in N 2 .

Figure 20 :

 20 Figure 20 : XRD result of the residue obtained during the HGC chlorination at 200 °C for 10 minutes (leached at pH ≈ 2).

Figure 21 :

 21 Figure 21 : Increase of temperature during the chlorination of HGC in a horizontal experimental set using different chlorine contents in Cl 2 +N 2 gas mixture.

Figure 22 :Fig. 1 :Fig. 2 :

 2212 Figure 22 : Suggested flow-sheet for the extraction of valuable metal chlorides by chlorination.

Fig. 6 :

 6 Fig.6: Isotherms of chlorination of LGC with Cl 2 +N 2 using various gas flow rates.

Fig. 5 :Fig. 7 :Fig. 8 :Fig. 10 :

 57810 Fig. 5 : TG analysis of sulfides and two concentrates in Cl 2 +N 2 .

Fig. 9 :T

 9 Fig. 9 : Isotherms of chlorination of LGC using different chlorine contents in the Cl 2 +N 2 gas mixture.

Fig. 12 :

 12 Fig.12: Apparent reaction orders with respect to chlorine for the chlorination of LGC and HGC.

Fig. 11 : 2 Fig. 13 :

 11213 Fig. 11 : Effects of the chlorine content in the gas mixture and reaction time on the chlorination of (a) LGC and (b) HGC.

Fig. 14 :

 14 Fig.14: Isotherms of chlorination with Cl 2 +N 2 of HGC between 170 °C and 300 °C.

L 1 :

 1 full chlorination of sulfides and volatilization of iron and sulfur chlorinated compounds for LGC. L 2 : full chlorination of sulfides and volatilization of iron and sulfur chlorinated compounds for HGC.

Fig. 16 :Fig. 15 :

 1615 Fig. 16 : Arrhenius plots for the chlorination of (a) LGC and (b) HGC with Cl 2 +N 2 .

Fig. 20 :

 20 Fig. 18 : Phases' diagram ofCuCl-FeCl 3 system.[START_REF] Levin | Phase diagrams for Ceramists[END_REF]

Fig. 21 :Fig. 22 :

 2122 Fig. 21 : Increase of temperature during the chlorination of HGC in a horizontal experimental set using different chlorine contents in Cl 2 +N 2 gas mixture.

Table I :

 I Chemical and Mineralogical Composition of the Chalcopyrite Concentrates (Wt pct).

	Element	S 1 (LGC)	S 2 (HGC)	Phases	S 1 (LGC)	S 2 (HGC)
	Cu	10.8	28.3	CuFeS 2	31.2	81.7
	Fe	29.7	26.3	FeS 2	23.8	3.0
	S	24.0	32.1	ZnS	1.2	6.4
	Zn	0.8	4.3	CaCO 3	3.2	-
	Pb	-	3.9	PbSO 4	-	5.7
	Ca	1.3	-	MgO	1.9	-
	Si	6.7	0.3	SiO 2	14.4	0.7
	Al	2.1	-	FeO	11.8	-
	Mg	1.2	-	Al 2 O 3	4.0	-
	O	14.5	1.6	Clinochlore *	ND	-
	Total	91.1	96.8		91.5	97.5
	Clinochlore : (Mg, Fe) 6 (Si, Al) 4 O 10 (OH) 8 .

  b) of about 1, 50 and 2 kJ/mol in the temperature ranges of 170 °C to 210 °C, 210 °C to 240 °C and 240 °C to 280 °C, respectively.The low value of the apparent activation energy between 170 °C and 210 °C for the chlorination of HGC suggests that the overall reaction rate could be controlled by the diffusion through the liquid layers. To confirm that, a series of TGA tests was performed as follow :1. the HGC was chlorinated for 100 minutes by Cl 2 +N 2 at 200 °C in order to evaluate the evolution of its pct WL during the chlorination, 2. the same sample was chlorinated by Cl 2 +N 2 at 200 °C for 10 minutes. Then, the chlorination residue was heated at 200 °C in N 2 to obtain information about the presence of volatile products in the chlorination residue at this temperature. Another HGC sample chlorinated in Cl 2 +N 2 at 200 °C for 10 minutes was analyzed by XRD,

3. samples of ferric chloride and sulfur were also heated separately in N 2 at 200 °C for 90 minutes to estimate their volatilization rate.

Initial reaction rate) E a ≈ 94 kJ/mol ≈ 21 kJ/mol

	1 2 3 4 Ln (170 °C 200 230 260 290 LGC	1 2 3 4	E
	1.7 0	1.8	1.9	2.0	2.1	2.2	2.3	1.7 0	1.8	1.9	2.0	2.1	2.2	2.3
										1000/T [K -1 ]

a ≈ 2 kJ/mol ≈ 50 kJ/mol ≈ 1 kJ/mol

  Fig. 19 : Behavior of chlorination residue of HGC, of sulfur and FeCl 3 at 200 °C in N 2 . Fig. 17 : XRD result of the chlorination residue of chalcopyrite at 260 °C, t ≤ 20 seconds.

	CuFeS 2			CuFeS 2
	CuFeS 2	4H 2 O	CuFeS 2	CuCl
	CuCl	2 . FeCl		FeCl 2 .	CuCl 2 . 2H 2 O FeCl 2 . 4H 2 O
					290	260	230	200	170 °C
						HGC
					Ln (Initial reaction rate)	≈ 54 kJ/mol Sulfur	≈ 28 kJ/mol
		(a)				(b)

ACKNOWLEDGMENTS

This work was performed in the frame of contract N° BRE2-CT92-0173 thanks to the financial support of the European Union (DG-XII). The authors thank Dr. H. L. Schmidt for discussion, suggestion and help. They also would like to thank Dr. J. C. Mugica (INASMET, San Sebastian, Spain) and Dr. M. Coelho (INETI, Lisbon, Portugal) for providing samples and technical discussions. Authors are indebted to A. Bonazébi, M. Djona, S. Ivanaj and N. Mirghaffari for discussions and help on different subjects and to Mrs. C. Tanchel for technical and administrative support.


Frederic Audo

Sonia Boscolo

Julien Fatome

Bertrand Kibler

Christophe Finot
email: christophe.finot@u-bourgogne.fr

Nonlinear spectrum broadening cancellation by sinusoidal phase modulation

Keywords:

We propose and experimentally demonstrate a new approach to dramatically reduce the spectral broadening induced by self-phase modulation occurring in a Kerr medium. By using a temporal sinusoidal phase modulation, we efficiently cancel to a large extend the chirp induced by the nonlinear effect. Experimental validation carried out in a passive or amplifying fiber confirm the interest of the technic for the mitigation of spectral expansion of long pulses.

Whenever an optical signal experiences a temporal modulation of its phase, its spectrum is changed [1]. Such a phase modulation can be externally applied to a signal by an electro-optic modulator for example. But it can also be the result of nonlinear optical effects like the self-phase modulation (SPM) of the signal pulse arising from propagation in a Kerr medium such as an optical fiber [2,[START_REF]Nonlinear Fiber Optics[END_REF]. SPM usually causes spectral broadening of a short and intense optical pulse that is accompanied by an oscillatory structure covering the entire frequency range. This may highly impair the suitability of the resulting signal for applications requiring a high spectral resolution or chirp-free pulses. The level of SPM is therefore a limiting factor in fiber amplification, which has to be controlled carefully [START_REF] Richardson | [END_REF]. Various strategies can be deployed to this end. The most basic one consist in spectrally filtering the broadened spectrum. However, this approach is power inefficient and may induce large distortions of the pulse temporal profile. By stretching the pulses in time before amplification, chirped pulse amplification (CPA) has been extremely successful in mitigating undesirable SPM [5]. By subsequent cancellation of the linearly time varying part of the SPM-induced chirp, the pulse may also be temporally recompressed [6]. However, while the temporal intensity profile can be shortened to approach the Fourier transform limit, no narrowing of the expanded spectrum is attained with this method. Recent approaches to improve the performance of short-pulse fiber amplifiers include the exploitation of the peculiar dynamics of parabolic self-similar pulses [7], the use of pre-shaped input pulses [8], and the compensation of nonlinear phase shifts with thirdorder dispersion [9]. However, all of these techniques do not preserve the pulse temporal duration.

In this contribution we introduce a new method to mitigate nonlinear impairments of optical pulses propagating through fiberoptic systems. The proposed approach is based on the simple observation that the chirp induced by SPM on a pulse with a standard temporal intensity profile, such as a Gaussian or sech 2 shape, features a close-to-sinusoidal variation in the central pulse region. Hence, by applying to the pulse a sinusoidal modulation of the temporal phase with appropriate amplitude and frequency, we are able to reduce the nonlinear spectrum broadening to a large degree, and to significantly enhance the spectral quality of the pulse while its temporal duration remains unaffected.

In order to illustrate our idea and provide some simple analytical design rules, we consider an initial chirp-free pulse with a Gaussian temporal intensity profile: G(t) = exp(-t 2 /T0 2 ), where T0 is the 1/e intensity half-duration, propagating in a purely nonlinear fiber of length L0. As a result of SPM, the pulse acquires a nonlinear phase shift NL(t), hence, an instantaneous frequency shift NL(t) that is proportional to the opposite of the temporal gradient of the intensity profile NL(t) = -dNL /dt = -2 B t G(t) / T0 2 . Here, B =  P0 L is the maximum phase shift that occurs at the pulse center located at t = 0 and is widely known as the B-integral [6], P0 is the peak pulse power,  is the Kerr-nonlinearity coefficient of the fiber, L=(1 -exp(-L0))/ is the effective propagated length, and  >0 (<0) is the fiber loss (gain) coefficient [START_REF]Nonlinear Fiber Optics[END_REF]. Figure 1 shows the pulse characterizations at the fiber output for a B-integral accumulated in the fiber of B = 5 rad. The induced chirp NL has a non-monotonic temporal variation across the pulse with two extrema around the pulse center (panel (a), red curve). The time separation between these extrema and the corresponding frequency excursion can be computed by = 2 T0 and  = B 2 exp(-1/2)/ T0, respectively [START_REF]Nonlinear Fiber Optics[END_REF]. The pulse spectrum has been significantly broadened over its initial width by the SPM-generated frequency components and has developed a multi-peak structure (panel (b)).

The observed time dependence of NL(t) suggests that this chirp can be offset by applying to the pulse a corrective sinusoidal temporal phase modulation, C(t) = A cos(C t+0), producing the chirp c = AC sin(C t+0). Inspired by a previous numerical work relating to the optimization of the SPM-driven spectral compression process [10], we choose the angular frequency, phase shift and amplitude of the modulation as C = /= /( 2 T0), 0 = and A = /C = 2B exp(-1/2)/respectively. With this parameter choice, the external phase modulation indeed compensates the nonlinear phase accumulated by the Gaussian pulse to a large degree: the total chirp, c + NL, is now cancelled almost completely over the central region of the pulse (Fig. 1(a), blue curve). This entails a significantly narrower spectrum that is now close to its original width (Fig. 1(b1)). Small pedestals are still present in the spectrum, but their intensity level is below 20 dB. A measure of how close a pulse is to its Fourier transform limit is provided by the spectral Strehl ratio, defined as the ratio of the maximum spectral brilliance of the actual pulse to the brilliance obtained assuming a transform-limited pulse. While after nonlinear propagation in the fiber, the maximum relative brilliance of the pulse spectrum has dropped to 0.25, the application of the external phase modulation re-establishes a Strehl ratio of 0.7. We have also assessed the ability of our approach to counteract larger amounts of SPM. The results are summarized in Fig. 2, highlighting the excellent mitigation of SPM provided by the corrective phase modulation for values of the accumulated Bintegral as high as 10 rad: the full-width at half maximum (fwhm) of the spectrum remains constant and no spectral ripple develops.

Further, the corrective approach enables a reduction of the rootmean-square (rms) spectrum broadening by a factor close to 4 relative to the case when no phase correction is used, and the Strehl ratio of the pulse remains well above 0.5. For our proof-of-concept, we used the all-fibered experimental setup depicted in Fig. 3, which relies exclusively on commercially available components from the telecom industry. An external cavity laser at 1550 nm delivers a continuous wave that is intensity modulated by a lithium-niobate modulator with a bandwidth of 20 GHz. The electrical signal that drives the modulator is produced by electrical filtering with a 5.4 -GHz low-pass filter of an on-off keyed signal from a 10-GHz pattern generator. A 100-bit sequence with 1 one followed by 99 zeros is chosen to reduce the pulse repetition rate to 100 MHz. In our approach in which we assume a purely nonlinear propagation not liable to dispersion-induced distortions, the disposition of the nonlinear element and the external phase modulator does not impact the overall nonlinearitymitigation process. Therefore, the sinusoidal phase modulation can be imparted as a pre-propagation compensation rather than a postpropagation correction. It is noteworthy that in this configuration, the process can be reinterpreted as spectral focusing with the nonlinear phase accumulated by the pulse in propagation compensating an initial and opposite phase modulation [11,12]. Besides, placing the phase modulator before the fiber has the practical advantages of reducing the threshold of the deleterious Brillouin backscattering and avoiding damages to the optoelectronic component due to excessive optical power. Our The resulting signal is amplified by an erbium-doped fiber amplifier and propagated through a 500-m long section of HNLF with the nonlinear coefficient = 10 W -1 .km -1 and linear attenuation  = 0.7 dB/km. The group-velocity dispersion (GVD) of the fiber is normal (D = -1 ps/km/nm) to inhibit any signal degradation that may be caused by modulation instability. Two wavelength multiplexers and a 1455-nm quasi-continuous laser with a Wattlevel power can turn the passive fiber into a Raman amplifier. We favoured a counter-propagating pump configuration to avoid the emergence of extreme fluctuations [13]. The optical signal is characterized in the time and frequency domains with a 40-GHz electrical sampling oscilloscope and a high-resolution (100 MHz) optical spectrum analyzer (APEX 2443B). The value of the accumulated B-integral is varied by control of the peak pulse power at the fiber input with an optical variable attenuator. We note that the finite extinction ratio of the intensity modulator (23 dB) may cause a small residual coherent background. For clarity of the figures, we have numerically removed its signature, i.e. a coherent spectral line at 1550 nm, from the spectral measurements.

The experimental results obtained for B = 5 rad are plotted in Fig. 4. The initial pulses are Gaussian-like in shape and have fwhm duration of 120 ps. The temporal gradient of the pulse intensity numerically extracted from the experimental data (panel (a2)) shows that the SPM-induced chirp variation can be well approximated by a sinusoidal function (green curve) albeit featuring a small asymmetry. The pulse intensity profile at the fiber output is fully identical to the input, confirming our assumption that with the fiber and temporal pulse durations being used, the propagation regime is purely nonlinear and is not affected by chromatic dispersion. The initial spectrum of the pulse has significantly broadened after propagation in the HNLF, with a spectral width that has more than doubled (see Fig. 4(b1)). Note that the asymmetry in the intensity temporal gradient has been recast into a marked asymmetry of the output spectrum. When the external sinusoidal phase modulation with the appropriate frequency, amplitude and phase is switched on, the spectrum is mostly unperturbed by nonlinear propagation. Some small degradation is visible in the output spectrum when plotted on a logarithmic scale (Fig. 4(b2)). It stems from imperfect phase compensation due to the asymmetry of the input pulse profile and its deviation from the Gaussian shape used in the theoretical model.

Figure 5 summarizes the results obtained with and without phase pre-compensation for different pulse powers injected into the fiber up to B = 5 rad. While in the absence of phase correction we observe progressive expansion of the output spectrum from the fiber with increasing values of the accumulated B-integral, accompanied by the development of ripple and asymmetry, the use of a corrective phase modulation maintains an output spectrum that is only marginally affected. The benefits afforded by the phase correction method are also apparent in Figs. 5(b)-(c) when comparing the evolution of the rms spectral width and the maximum spectral brilliance of the pulse with the accumulated Bintegral between the two configurations. Lastly, we have assessed the effectiveness of the proposed approach in the context of Raman amplification. The results obtained with on/off gain of 9 dB, leading to a B-integral of 4.5 rad, are shown in Fig. 6. Once again, the external phase modulation enables preservation of the spectral intensity profile to a large extent, and yet the small side lobes present in the output spectrum can be ascribed to the input temporal intensity profile. In conclusion, we have proposed and experimentally demonstrated a new, effective method to mitigate the impact of SPM on optical pulses of several tens of picoseconds duration propagating through a nonlinear medium. Imparting a sinusoidal phase modulation to the pulse in the time domain enables us to counteract the deleterious effects of SPM to a large degree. Proof-of-principle experiments have confirmed the success of the proposed scheme in cancelling high levels of distortion of the pulse spectrum. From the experimental standpoint, we were only constrained by the maximum amplitude of phase modulation that could be imparted by the modulator being used (A = 2.25 rad). But much stronger modulations are currently feasible [1,14].

We believe that the method demonstrated here will prove useful for applications in the field of high-power pulse amplification, particularly with pulses of around a hundred picoseconds duration for which methods such as CPA are not practical due to the difficulty of adequately stretching them through a dispersive element. Temporal phase correction can, in this case, be accomplished prior to amplification. Our scheme can handle high pulse repetition rates. For pulse durations shorter than tens of picoseconds, it will be possible to combine the CPA method with our proposed technique into a hybrid scheme. In the absence of CPA, the interplay between GVD and SPM upon pulse propagation in a normally dispersive fiber may lead to more complex pulse dynamics resulting from the development of a close-to-linear frequency chirp [15][16][17]. In this case, the guidelines given in the present paper should be adjusted and the efficiency of the proposed approach will diminish, but noticeable correction of nonlinear impairments will be still possible. Ultimate performance of our phase-only pre-shaping method may be reached with an electrical arbitrary waveform generator combined with a feedback loop and learning or genetic algorithms.

Fig. 1 .

 1 Fig. 1. Numerically computed impact of phase correction on a Gaussian pulse after undergoing SPM: (a) temporal intensity and chirp profiles, and (b) spectral intensity profile on linear and logarithmic scales at the entrance (black) and the exit of the fiber before (red) and after (blue) phase compensation. The B-integral accumulated by the pulse is B = 5 rad. The corrective chirp δνc is plotted with a green dotted line.

Fig. 2 .

 2 Fig. 2. (a) Numerically computed evolution of the spectrum (logarithmic scale, 17 dB dynamics) of an initial Gaussian pulse after undergoing SPM with the accumulated B-integral, before (subplot 1) and after (subplot 2) phase correction. (b)-(c) Evolutions of the rms broadening factor and the Strehl ratio of the pulse at the exit of the fiber. The results obtained without and with phase correction are plotted with red and blue lines, respectively. The vertical dotted line indicates the B-integral value used in Fig. 1.

  phase modulator is driven by a C = 4 GHz electrical clock synchronized with the first electrical signal, and imprints a sinusoidal phase with the appropriate phase offset 0 and amplitude A on the optical wave.

Fig. 3 .

 3 Fig. 3. Experimental setup. CW : continuous wave ; IM : intensity modulator ; PM : phase modulator ; EDFA : erbium doped fiber amplifier ; OVA : optical variable attenuator; HNLF : highly nonlinear fiber ; OSA : optical spectrum analyzer ; ESO : electrical sampling oscilloscope ; WDM : wavelength multiplexer

Fig. 4 .

 4 Fig. 4. Experimentally measured temporal (subplot (a1)) and spectral (subplot (b)) intensity profiles of the input pulse (black), without (red) and with (blue) phase modulation. Subplot (a2) shows the opposite of the temporal intensity gradient of the input pulse (black) compared with a sinusoidal fit (green). The accumulated B-integral is B = 5 rad.

Fig. 5 .

 5 Fig. 5. (a) Experimentally measured evolution of the frequency spectrum (logarithmic scale, 17 dB dynamics) with the accumulated Bintegral, without (subplot 1) and with (subplot 2) phase pre-correction. (b)-(c) Evolutions of the rms broadening factor and the brilliance increase of the pulse. The results obtained without and with phase correction are plotted with red and blue lines, respectively.

Fig. 6 .

 6 Fig.6. Experimentally measured spectral intensity profiles at the entrance (black) and the exit of a Raman amplifier without (red) and with (blue) phase pre-compensation. Also shown are the results that can be numerically inferred assuming a close-to-Fourier-transform input waveform (dashed). The accumulated B-integral is B = 4.5 rad.

Funding.

  Région Bourgogne (Pari Photcom) ; Agence Nationale de la Recherche (Labex Action ANR-11-LABX-01-01) ; Program FEDER-FSE Bourgogne 2014-2020.

Acknowledgment. The article has benefited from the PICASSO experimental platform of the University of Burgundy.