J A Stegemann

N R Buenfeld

DISCUSSION WI TH END-USERS REGARDING CEMENT/WASTE SYS TEMS DATABASE AND PRE DICTIVE MODELS

Introduction of impurities into cernent is inherent to recycling of industrial by-products in building mate rials, and to treatment of industrial wastes by solidifi cation prior to disposai. These impurities can cause problems with materials handling and durability. ln

-Will information such as that from the project increase the amount of waste that can be utilised in construction?

-ln what ways can end-users help the project?

The discussion centred around 8 main tapies, which are discussed below.

THE DIFFERENCE BETWEEN A «WASTE» AND A «PRODUCT»

Several workshop attendees raised the issue of the impor tance of terminology, because there are negative associations with the term «waste», which can have serious economic implications. ln fact, the NNAPICS project is trying hard to avoid label ling materials in ways that have negative or positive conno tations. There are materials which are mixed with water, and perhaps with each other, to create new materials. The former are called «mix items» in the CWS Database, and the latter are called «products». «mix items» include materials which are commonly called «cements» or «binders», and also materials which may be classified as different categories of «wastes» (depending on the jurisdiction), but they are not identified as such in the database, although <<Wastes» may have a number associated with them if they can be found in the OECD or European waste catalogues. The philosophical basis for this approach is that material properties form a continuum; some materials may be inert (this could mean that they are not cementitious, or that they do not contain envi-ronmentally hazardous components), some may be reacti ve (again, in several ways), some are in between. lt is the objective of the project to catalogue and examine relation ships between the properties of the various materials, not to make judgements about whether the properties or mate rials are good or bad, or where the line between «non wastes» and «wastes» should be drawn. lt is hoped that one of the uses for information from the project will be to make it easier for the appropriate authorities to make these dis tinctions in a sensible way, in order that more «waste» materials will be utilized, conserving natural resources and minimizing landfill while protecting the environment.

WH AT KIND OF DATA IS BEING COLLECTED?

The relationships of initial interest for the project are those between cement/waste product composition, and setting, The project is collecting information about cernent pro ducts made with ail materials, including manufactured cements, which may contain no other additives, commercial accelerators and retarders, and/or industrial by-products of varying environmental concern at a variety of different addi tion ratios. lndustrial by-products may be added as cemen ting materials, inert filler, or aggregate. As much detail as possible regarding the characteristics of the materials, inclu ding particle size and pre-processing, is being collected. However, only those parameters for which a lot of infor mation is available will be useful for predictive modelling.

The project has been limited to cementitious systems, becau se it is expected that there will be trends in their physical and chemical effects. Immobilisation mechanisms in other systems (e.g. sulphur, organic polymers) would likely be entirely different, and other materials have therefore been excluded.

COMPLEXI TY OF MATERIA LS AND TE ST METHODS

The materials which go into a cement/waste product are DÉCHETS -SCIENCES ET TECHNIQUES -N" 16 -4c""' trimestre 1999 -Reproduction interdite highly complex and there were questions as to whether the database will be able to take this complexity into account. Also, there are many different test methods, with different parameters, many of which have changed substantially over the past 20 years.

The project has tried to deal with this issue by including a large number of parameters for the raw materials, the cement/waste products, and also the test methods in the CWS Database format. Not all of the parameters targe ted for collection are reported in the literature, but ini tial analysis of the data has shown that even when little information is available about composition, some valuable analysis of the data is possible.

The more information that is available, the more sophisticated and sensitive the analysis can be.

For the test methods, collecting detailed information regarding the test parameters allows results from different tests to be analysed together. For instance, in a leaching test, the contaminant concentration will be dependent on the liquid-to-solid ratio, contact time, and leachant characteristics, as well as upon the composition of the sample being tested.

CEMENT/WASTE PRODUCT PROPERTIES

The end-users felt that properties related to handling, leachability and durability are all important. Leachability in regulatory tests is important for convincing regulatory authorities, and durability is particularly important for materials which will be utilised.

WASTE TYPES OF INTEREST

Waste types of particular interest are:

-wastes containing heavy metals, -wastes containing very fine particles, and -high volume waste materials.

Demolition wastes, dredge spoil, contaminated soils, and industrial ashes and sludges of many different kinds are of particular concern.

USES OF THE NNAPICS PROJECT DELIVERABLES

The panel members ail mentioned that the database and predictive models must be highly user-friendly in order to find wide application. If possible, the predictive models should be transparent, e.g., it should be possible to inter rogate the database for similar cases/references, in order to try to ascertain the background to a particular pre diction by the models.

The end-users seemed to agree that one of the most basic functions of the CWS Database and the predictive models should be to answer the question of whether or not it is feasible to treat a particular waste type with cernent. For common, well-characterised wastes, it may even be possible to eliminate treatability testing, although some level of laboratory testing will likely remain. The DÉCHETS -SCIENCES ET TECHNIQUES -N° 16 -4"""' trimestre 1999 -Reproduction interdite

Ciment/Déchets representatives from the cernent industry present at the meeting were agreed that more information about the limitations of cement-based solidification is equally as valuable as information about successful applications.

Beyond answering this basic question, the CWS Database and predictive models could also be used to:

choose the most effective binder (or develop pre-mixed multipurpose binders)

avoid ineffective binders determine the highest proportion of waste that can be in the product determine optimal proportions of all mix components, taking into account both technical and economic factors

One of the most important applications of the NNAPICS database and predictive models will be in gaining public and regulatory acceptance of cement/waste products, either for utilisation or disposai. lt was pointed out that ensu ring the environmental acceptability of cement/waste pro ducts, and creating a positive image, is important for long term commercial success.

CONFIDENTIALITY CONCERNS

A number of those present thought that commercial orga nisations will not provide data to the project because of concerns about confidentiality. The issue of data confi dentiality appeared to centre around 2 aspects:

special formulations/special additives, and business information.

With regard to (a), it is the position of the NNAPICS consortium that most successful solidification is performed using generic processes. Although there may be some cases where special additives are used for problem wastes, the majority of data is likely to concern simple formula tions, e.g., portland cernent or fly ash without any special additives. This data may be of limited usefulness to the organisation that has generated it, but it may complement the other data in the CWS Database to yield new and use fui conclusions in the analysis. lt is also worth noting that data for formulations which are not particularly success ful are still interesting information for the database and for the analysis. Furthermore, it is even possible for commercial organi sations to provide only the final properties of their cement/waste products, without identifying the additives.

If their formulations are particularly effective, the results will stand out to their advantage from the others in the database. Such data can be used to advertise the capabi lities of the donor, or data can also be provided anony mously.

With regard to (b), it is not the purpose of NNAPICS to collect business information. Commercial data sets with all sensitive business information removed will still be useful.

Finally, the NNAPICS consortium can enter into confi dentiality agreements under which donated data would not be made available to the public, but would be kept as a confidential subset of the overall CWS Database.

Commercial organisations with suitable data should weigh whether their data can tell them everything they need to know on its own, or whether they will actually learn more by combining it with data from other sources.

LONG-TERM FATE OF THE CWS DATABASE AND PREDICTIVE MODELS

Development of a CWS Database and predictive models is an ambitious undertaking. While NNAPICS will give this undertaking a headstart, it is not a static enterprise, and consideration should be given to how the work will be continued at the end of the current 3-year project.

The current work is being funded as Brïte Euram Ill basic research, which recognises that additional work will be necessary beyond the end of the current project for full commercialisation. Continued development and mainte nance of the CWS Database and predictive models is depen dent on demonstrating their usefulness to the end-users and thereby obtaining financial support.

Future Interaction between the NNAPICS Consortium and the End-Users

Offers to provide data to the project were made by 10 end users at the workshop , as well as 5 others at the conference.

ln addition, the help of end-users will be sought for beta-tes ting the CWS Database and the predictive models, in the final year of the project.

lt is expected that a second end-user workshop will be held before the end of the project.

INTRODUCTIONA

  workshop was arranged to inform potential end-users about a 3-year project funded under the European Commission's Brite-Euram Ill programme, on Neural Network Analysis for Prediction of Interactions in Cement/Waste Systems (NNAPICS). Introduction of impurities into cernent is inherent to recy cling of industrial by-products in building materials, and to treatment of industrial wastes by solidification prior to dis posai. These impurities can cause problems with materials handling and durability. This project applies neural networks to predict the physical and environmental properties of cement/waste systems. Existing data concerning solidified DÉCHETS -SCIENCES ET TECHNIQUES -N° 16 -4.._ trimestre 1999 -Reproduction interdite L'introduction d'impuretés dans les ciments est inhé rente au recyclage des sous-produits industriels en matériaux de construction ainsi qu'au traitement de déchets industriels par solidification avant mise en décharge. Ces impuretés peuvent engendrer des pro blèmes liés à la manipulation et à la pérennité des matériaux. Pour étudier et prévenir ces problèmes, le Programme Brite-Euram Ill de la Commission Européenne, finance un projet en 3 ans sur !'Analyse par Réseau Neuronal pour la Prévision des Interactions au sein des Systèmes Ciment/Déchet (NNAPICS). Ce projet utilise les réseaux neuronaux afin de pré voir les propriétés physiques et environnementales des systèmes Ciment/Déchet. Des données déjà exis tantes sur les déchets solidifiés et les matériaux de construction contenant des sous-produits industriels sont collectées afin de constituer une base de don nées ; elles sont ensuite analysées en utilisant les réseaux neuronaux et complétées par les résultats d'une étude en laboratoire. Ainsi, les principales pro ductions de ce projet seront : ( 1) une base de données contenant des informations sur les systèmes Ciment/Déchet (Cement/ Waste Systems «CWS Database») et (2) des modèles de prévision construits à partir des informations de la base de données. wastes and building materials containing industrial by-pro ducts are being collected into a database and analysed using neural networks, and supplementary data are being generated in a laboratory study. Thus, the main deliverables from the project will be: ( 1) a database containing information about cement/waste systems (the «CWS Database»), and (2) pre dictive models constructed using the information in the database. End-users of these deliverables are expected to include waste generators, waste treatment facilities, suppliers of construction materials, users of construction materials, regu lators, and consultants to these sectors. The NNAPICS consortium is seeking participation from potential end-users to provide input and feedback regarding the project. ln particular, large data sets regarding the composition, engi neering properties, durability and/or leachability of cernent systems containing wastes or other impurities are needed. Assistance from the end-users is also needed to review the deliverables from the NNAPICS project and to plan a conti nued strategy for their use and exploitation. The NNAPICS End-User Group has about 200 members, 24 of whom attended the workshop. The workshop started with presentations by members of the NNAPICS consortium (Imperia! College, UK; British Nuclear Fuels, Ltd., UK; University of Surrey, UK; Universidad de Cantabria, Spain; Euroresiduos, Spain; T rinity College Dublin, lreland; GESE NU, ltaly; and Universita di Roma «La Sapienza», ltaly). These are summarized in the conference proceedings for the conference on Waste Stabilization and Environment. The presentations by the NNAPICS consortium were fol lowed by presentations by 4 members of an industry panel (K. Bradshaw, Blue Circle Cernent; J. Frenay, ENCI; Marie Claire Magnie, lntertec; and R. Vogels, lntron), who led a dis cussion regarding the following questions: -What do end-users want the CWS Database to do? -How will the CWS Database be used? -Can the CWS Database improve the business of endusers? How? -What cement/waste product properties are of greatest interest? -Which waste types are most important? -What cement/waste product properties are useful to predict?

  strength, pH and acid neutralisation capacity. Composition may be expressed simply as the formulation, or in more detail, as the elemental, oxide, or phase analysis. pH and contaminant concentrations are being collected for diffe rent types of single batch extractions; acid neutralisation capacity is being collected for continuous, incremental and batch titrations. These properties are being collected for the raw materials, as well as the final products.An example of the CWS Database (in Access) can be down loaded from the project web pages (http://concrete www.cv.ic.ac.uk/iscowaa/nnapics/intro.html ). The example contains the full literature list, and data for 10 sample refe rences. However, the field headings and pull-down menus show most of the parameters being collected. lt should be noted that additional refinement of the database is on-going, and the final product will be considerably more user-friend ly, but the current version serves to show the type of infor mation that the project is collecting.

  Format 16•21 -1 64 pages -1 999 -1 80 F TTC franco de port (170,62 F HT -TVA 5,5 % : 9,38 F) Société Alpine de Publications (SAP) 7, chemin de Gordes -381 OO Grenoble Tél. : 04 76 43 28 64 -Fax: 04 76 56 94 09 DÉCHETS -SCIENCES ET TECHNIQUES -N° 16-4''-trimestre 1999 -REPRODUCTION INTERDITE

  The tentative date is to coïn cide with WASCON 2000, which will be held from May

						Gérard Bertolini,
						économiste. directeur de recherche au CNRS,
						Pierre Melquiot,
						Docteur ingénieur en génie industriel et environnement,
						responsable de projets au Cetih (Centre technique des
						industries de l'habillement),
						Informer et éclairer le consom mateur ainsi que les industriels concernés; sensibiliser à l'écolo gique ; verdir les productions et les achats (promouvoir à la fois l'offre et la demande), faire de l'écologie un argument de vente ...
	31-June	2,	2000	in	Harrogate/Leeds,	UK
	(http://www .efm.leeds.ac.uk/wascon2000).

J.A. Stegemann and N.R. Buenfeld Imperia! College of Science, Technology and Medicine -London SW7 2BU UK -Telephone: +44 (0) 20 7594 5956 -E-mail: j.stegemann@ic.ac.uk JO A LA RECHERCHE DU VETEMENT ÉCOLOGIQUE

this respect, 3-year project is funded under the European Commission's Brite-Euram


Behrooz Abbasi
email: abbasi@unr.edu

Vahid Nasiri

Babak Azarfar

Kyle Riemenschnitter

Ce

Pr

Pm

Sm

Tb

Ho

Tm

Ac

Pu

Am

Cm

Bk

BIOMINING THRIVING ON LIFE-MINERAL COEVOLUTION

Keywords: Life-mineral coevolution, microorganisms, bioextraction, low-grade minerals BIOMINING: LIFE-MINERAL COEVOLUTION

The history of biomining is very broad and rich, starting from the evolution of stars and planets to the coevolution of terrestrial life and minerals. In this paper, we briefly review the origin of elemental and compositional diversity of minerals and how microorganisms and plants connect mineralogy to biology. Thereafter, we revisit biomining from the perspective of its fundamental elements, limitations, and unexplored potentials. Finally, we make a number of indicative remarks with respect to those limitations and potentials to emphasize an existing need for the emergence of a sustainable biomining and prevent its premature application.

consensus on the very definition of the term "(co)evolution" in the scientific literature, in this paper, it refers to spaciotemporal changes which promotes complexity and diversity. Moreover, the earlier steps of evolution are logically followed by the latter steps; there is a sequence of events rather than randomness. This logical sequence can be understood in a retrospective manner and not necessarily in a predictive manner. This definition of evolution is applicable in the context of minerals which may not be in full agreement with biological definition of evolution [START_REF] Hazen | Mineral evolution[END_REF]. Yet, it is extendable to biology by including competition, mutation, and inheritance.

Strong evidences support this hypothesis that the oldest terrestrial minerals/life were formed earlier/later than the formation of the Earth [START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF][START_REF] Mccoy | Mineralogical Evolution of Meteorites[END_REF]. While this could suggest minerals to be primitive and life to be derivative, the two are intimately connected; life depended on minerals to first form and minerals depended on life to coevolve. Nonetheless, the elemental diversity of both terrestrial minerals and life mainly stems from stellar nucleosynthesis within stellar evolution [START_REF] Truran | Theories of nucleosynthesis[END_REF]. As a rule of thumb, the larger the star is, the heavier the elements that could be formed within stellar nucleosynthesis [START_REF] Truran | Theories of nucleosynthesis[END_REF]. However, formation of elements after iron, with the highest nuclear stability, is not energetically favorable even for large stars, and typically are made via explosion of large stars known as supernova (Figure 1) [START_REF] Ames | Stars and Nuclei. Part II[END_REF]. Eventually, these elements either participated in the formation of the Earth (majority) or were later on transferred by means of mediators such as comets (minority). Thereafter, chemical processes, revolving around (transferring/sharing) electrons, followed by biochemical processes mainly took over to create diversity of minerals and their chemical composition. Coevolution of minerals and life is a consequence of numerous positive and negative feedbacks.

A mineral is a crystalline compound that has a regular atomic structure, and has a well-defined chemical composition [START_REF] Povarennykh | Basic Laws of the Crystal Chemistry of Minerals[END_REF]. As far as mineralogy is concerned, this coevolution affects mineral diversity/distribution, which in turn is affected by how various factors (e.g., physical, chemical, and biological) have changed that diversity/distribution [START_REF] Hazen | Mineral evolution[END_REF]. Mineralogy includes variations in chemical compositions, sizes, and shapes (morphology) with a main focus on near-surface environment [START_REF] Povarennykh | Basic Laws of the Crystal Chemistry of Minerals[END_REF]. The concentration of mineral forming chemicals has to be high enough for them to bind together and create minerals, and the ambient temperature should be low enough for the mineral to be condensed [START_REF] Hazen | Mineral evolution[END_REF]. As the supernova envelope expands, cooling of carbon rich regions provides the minimum concentration and maximum temperature in which crystallization of any known mineral could possibly occur. Hence, diamond nanocrystals are speculated to be the first minerals that could be formed in 4000 K in the carbon rich zones of supernova envelopes via what is called vapor deposition. About 400 K below 4000 K, the condition is suitable for the formation of another allotrope of carbon; i.e., graphite [START_REF] Hazen | Mineral evolution[END_REF]. Diamond and graphite (C), and 10 other pre-solar nanocrystals are the earliest minerals formed in the cosmos, and still ubiquitous everywhere; constituting a total number of 12 minerals known as Ur minerals, namely moissanite (SiC), osbornite (TiN), nierite (Si 3 N 4 ), rutile (TiO 2 ), corundum (Al 2 O 3 ), spinel (MgA l2 O 4 ) hibbonite (CaAl 12 O 19 ), forsterite (Mg 2 SiO 4 ), GEMS (silicate glass with embedded metal and sulfide), and metallic nanoparticles (e.g., TiC, FeC, and Fe-Ni) within graphite [START_REF] Hazen | An evolutionary system of mineralogy. Part I: Stellar mineralogy (>13 to 4.6 Ga)[END_REF].

The Ur minerals are formed from 1) the most abundant elements formed in stars and 2) elements which can form crystals at very high temperatures. 10 elements satisfy those requirements, namely carbon, silicon, nitrogen, titanium, magnesium, calcium, aluminum, iron, nickel, and oxygen. We shall see how those 12 Ur minerals with only 10 different essential elements have evolved to >5000 minerals (5603 is the most recent value based on the IMA database of mineral properties) with >70 different essential elements on Earth with the aid of biology [START_REF] Hazen | Data-Driven Discovery in Mineralogy: Recent Advances in Data Resources, Analysis, and Visualization[END_REF].

Diversity of minerals increase from 12 to 60 minerals within the formation of the solar system by fusing the Ur minerals within melting cycles to form the early chondrite minerals. Those chondrite minerals start clumping together to form planets with metallic cores and silicate mantles, resulting in further diversification of minerals up to ~250 under abrupt changes, such as thermal bursts and shock waves [START_REF] Grosch | Microbes, Mineral Evolution, and the Rise of Microcontinents-Origin and Coevolution of Life with Early Earth[END_REF][START_REF] Krivovichev | Structural and chemical complexity of minerals: correlations and time evolution[END_REF]. Also, the elemental diversity in minerals increases from 10 to 20 within the latter stage; all along this evolution, complexification occurs as previously stated. It should be emphasized that primitive chondrite meteorites included the elemental diversity (>70) required for the mineral diversity of the modern Earth (>5000), but most of those elements were too rare/disperse [START_REF] Hazen | Mineral evolution[END_REF]. Mineral diversity of dry planets, such as mercury, has ceased about 250-300. On wet planets, such as Mars, this value is speculated to be as high as 400, owing to hydrological impacts. However, Earth has enough internal heat to undergo more melting cycles to concentrate some rare elements, such as uranium, cesium, and niobium, within granite formation [START_REF] Hazen | Mineral evolution[END_REF][START_REF] Hazen | Mineral Evolution: Mineralogy in the Fourth Dimension[END_REF]. Purification through a number of those melting cycles forms a very specific type of minerals called pegmatites; increasing the mineral diversity up to ~1000. Dating the oldest pegmatite (about 2.8 billion years), it can be deduced that the later stage took more than a billion years to perform those physicochemical purifications [START_REF] Hazen | Mineral evolution[END_REF][START_REF] Hazen | Genesis: Rocks, Minerals, and the Geochemical Origin of Life[END_REF]. Being unique to Earth, plate tectonics is a major physicochemical contributor to mineral diversity (increasing it up to 1500), where the upper layer is denser than its lower layer and is drawn down by gravity, reprocessing a huge volume of the Earth crust [START_REF] Hazen | Mineral Evolution: Mineralogy in the Fourth Dimension[END_REF]. This includes crystallization of the high-pressure minerals, such as diamond. It has been hypothesized that all the aforementioned minerals could have played significant roles in the formation of life [START_REF] Grosch | Microbes, Mineral Evolution, and the Rise of Microcontinents-Origin and Coevolution of Life with Early Earth[END_REF][START_REF] Hazen | Mineral evolution[END_REF]. This is from protecting prebiotic molecules and catalyzing the prebiotic processes to serving as scaffolds (to assemble smaller molecules into macromolecules) and providing selective surfaces (to concentrate chiral molecules and seed chiral life) [START_REF] Livi | Atomic-Scale Surface Roughness of Rutile and Implications for Organic Molecule Adsorption[END_REF][START_REF] Hazen | Enantioselective adsorption on rock-forming minerals: A thought experiment[END_REF]. We further discuss that life (and biological processes in general) in turn is the missing piece which fills the significant gap between ~1500 (formed by physicochemical processes) and >5000 minerals existing on the modern Earth.

Life per se neither adds any new minerals to the existing list prior to its formation nor introduces any new chemical process, but rather it catalyzes the reactions which would have been kinetically unfavorable in its absence [START_REF] Grosch | Microbes, Mineral Evolution, and the Rise of Microcontinents-Origin and Coevolution of Life with Early Earth[END_REF][START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF]. For instance, microorganisms get their energy from chemical transformation of minerals in exchange for expediting those transformations, and that is the basis of coevolution of life and minerals. In such process, microorganisms use enzymes, in which active sites have evolved for oxidation reduction (electron transfer) reactions required for metabolic processes [START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF]. Those active sites reflect the chemical environment that microorganisms are evolved in, e.g., formation of iron-rich active sites indicate the chemical composition of the oceans on the early Earth. About 2.5 billion years ago, cyanobacteria started changing the chemistry of the Earth's atmosphere by using the Sun's energy and producing oxygen, i.e., oxygenation stage [START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF][START_REF] Noffke | Earth's earliest microbial mats in a siliciclastic marine environment (2.9 Ga Mozaan Group, South Africa)[END_REF]. The latter contribution from biology to mineral diversity on Earth is more than any other previously mentioned contribution from solo physicochemical processes [START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF]. Supported by experimental evidence, it has been hypothesized that mineral diversity has drastically increased as the result of oxygenation of the Earth's atmosphere [START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF][START_REF] Noffke | Earth's earliest microbial mats in a siliciclastic marine environment (2.9 Ga Mozaan Group, South Africa)[END_REF]. This is evidently mirrored in the chemical composition of the minerals before and after the oxygenation stage. For instance, most of the iron, nickel, manganese, copper, and uranium minerals (and many more) owe their existence to life [START_REF] Grosch | Microbes, Mineral Evolution, and the Rise of Microcontinents-Origin and Coevolution of Life with Early Earth[END_REF][START_REF] Hazen | necessity and the origins of life: a physical sciences perspective[END_REF][START_REF] Noffke | Earth's earliest microbial mats in a siliciclastic marine environment (2.9 Ga Mozaan Group, South Africa)[END_REF]. After the oxygenation stage, iron was diluted away and molybdenum became more abundant in the oceans. This evolution of oceanic geochemistry is reflected by evolution of biological enzymes as well [START_REF] Moore | Geological and Chemical Factors that Impacted the Biological Utilization of Cobalt in the Archean Eon[END_REF][START_REF] Cleaves | Mineral-organic interfacial processes: potential roles in the origins of life[END_REF]. For example, nitrogenase enzymes (responsible for nitrogen fixation) have adopted iron-rich/ molybdenumrich active sites before/after the oxygenation stage [START_REF] Kendall | Transient episodes of mild environmental oxygenation and oxidative continental weathering during the late Archean[END_REF]. Moreover, after the oxygenation stage, higher oxidation states of elements such as rhenium became soluble, and thus could penetrate to subsurface regions and participate in molybdenum minerals [START_REF] Golden | Rhenium variations in molybdenite (MoS2): Evidence for progressive subsurface oxidation[END_REF]. This can be deduced from increasing the trace of rhenium in molybdenum minerals along with increasing the concentration of atmospheric oxygen in time [START_REF] Golden | Rhenium variations in molybdenite (MoS2): Evidence for progressive subsurface oxidation[END_REF]. The other significant variation in the atmospheric composition occurred in the ice age where greenhouse gases (e.g., CO 2 ) were gradually accumulated and mineral diversification ceased. Formation of the terrestrial biosphere coincided with the formation of biominerals, such as abelsonite and evenkite, as well as an increase in the formation of clay minerals [START_REF] Hazen | Clay mineral evolution[END_REF]. Living components, such as plant's roots, microorganisms, and worms mainly participated in the breakdown of rocks and extraction of their nutrients. In all the aforementioned stages, life has also affected the morphology of minerals [START_REF] Hazen | Carbon Mineral Evolution[END_REF]. For example, old uranium deposits (pre-life) are larger crystals of uranium oxide, while modern deposits (post-life) are mainly formed as nanocrystals [START_REF] Hazen | Mineral Evolution: Mineralogy in the Fourth Dimension[END_REF][START_REF] Hazen | Evolution of uranium and thorium minerals[END_REF]. Taken together, life has left its footprints from chemical composition (as in copper oxides) to morphology of minerals (as in uranium deposits) on Earth.

From the periodic table, 8 elements have more than 98% contribution in the structure of minerals on Earth, namely oxygen, silicon, aluminum, iron, calcium, sodium, potassium, and magnesium [START_REF] Yaroshevsky | Abundances of chemical elements in the Earth's crust[END_REF]. Life on the other hand is mainly based on hydrogen, carbon, oxygen, and nitrogen, and thus has to fulfil most of its needs from the Earth's atmosphere [START_REF] Urey | On the Early Chemical History of the Earth and the Origin of Life[END_REF]. Hydrogen and oxygen can be exchanged between the Earth and its atmosphere mainly through the physical processes of the hydrological cycle; evaporation, condensation, precipitation, infiltration, surface runoff, and subsurface flow [START_REF] Rast | Review of Understanding of Earth's Hydrological Cycle: Observations, Theory and Modelling[END_REF][START_REF] Devia | A Review on Hydrological Models[END_REF]. While nitrogen/carbon is exchanged within biochemical processes in plants and microorganisms via nitrogen/carbon fixation [START_REF] Salvagiotti | Nitrogen uptake, fixation and response to fertilizer N in soybeans: A review[END_REF][START_REF] Gong | Biological carbon fixation: From natural to synthetic[END_REF]. Competition between living species requires taking advantage of the fast kinetics of electron-transfer processes, which in turn is enhanced by metal ions existed in minerals [START_REF] Shi | Extracellular electron transfer mechanisms between microorganisms and minerals[END_REF]. Bioextraction of these metals is what biomining is all about as will be discussed in the following.

BIOMINING: SCIENCE AND TECHNOLOGY

Biomining is one of the broadest multidisciplinary topics where science (e.g., biology, geology, chemistry, and physics) and engineering (e.g., mining, metallurgical, and mechanical) meet. On one hand, biomining priorly deals with fundamental factors (e.g., physicochemical, microbial, and mineral factors; Figure 2). On the other hand, it posteriorly has direct and mutual impacts on the market and the environment. Although biomining is defined as extraction of minerals (metals) by the virtue of microorganisms [START_REF] Schippers | Metal Recovery from Ores with Microorganisms[END_REF], both bio and mining have much broader domains.

For instance, there is no fundamental distinction between biomining and algal-bacterial wastewater treatment in the sense that both increase the concentration of their target of interest with the aid of living beings [START_REF] Muñoz | Algal-bacterial processes for the treatment of hazardous contaminants: A review[END_REF]. As a branch of science, biomining is a subdivision of biohydrometallurgy, which has been partially used in the mining industry. However, majority of biohydrometallurgy subdivisions, such as biobeneficiation, biofloatation, and biocoagulation are yet to be commercialized [START_REF] Schippers | Metal Recovery from Ores with Microorganisms[END_REF]. Biomining itself has two subdivisions, namely biooxidation and bioleaching that are profitable for low-grade minerals (e.g., aurostibite) and secondary resources (e.g., landfill and waste dump) at their current stage [START_REF] Olson | Bioleaching review part B[END_REF]. Although biooxidation literally refers to oxidation of metals with microorganisms (that is predominant in bioextraction), it is historically named after dissolution of the matrix around the target metals, while bioleaching is used for dissolution of the target metals, making the latter more selective [START_REF] Olson | Bioleaching review part B[END_REF][START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF]. While passive bioleaching is a term used for bioextraction processes occurring once the mine waste is deposited at the surface. Selective approaches are more desirable for extraction of metals from exponentially growing low-grade resources, where the terms "biomining" and "bioleaching" are often interchangeably used [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF]. Nonetheless, biomining has also been successfully employed at the largest copper mine of the world, i.e., Escondida in Chile where high-grade resources exist [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF][START_REF] Johnson | The Biogeochemistry of Biomining[END_REF].

Figure 2. Biomining as a subdivision of biohydrometallurgy and its essential components

Microbiological factors

Physicochemical factors

Typical extractive techniques include several expensive steps such as smelting, roasting, and pressure oxidation, which are environmentally unfriendly and demand high concentrations of elements as the input [START_REF] Veiga | Mining with communities[END_REF][START_REF] Idriss | Environmental-Impact Assessment of Natural Radioactivity Around a Traditional Mining Area in Al-Ibedia, Sudan[END_REF]. However, microorganisms often gain energy by breaking the bonds between constituent elements of minerals. As the result, energy intensive components of traditional mining (e.g., grinding and extraction) become energetically favorable. Moreover, bioextractive methods do not involve digging, transporting, and disposing of large amounts of rock, unlike in traditional mining. Finally, mineral-feed weakening and breakage (i.e., crushing, grinding and pulverizing) is commonly the most energy consuming and expensive step in traditional mining process taking up to 80% of the total energy consumption [START_REF] Gadd | Metals, minerals and microbes: geomicrobiology and bioremediation[END_REF]. This becomes more highlighted considering the fact that mining sites are usually not connected to the grid; feeding on energy intensive environmentally unfriendly diesel generators [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF]. However, bioassisted pretreatment can enhance the grinding efficiency of mineral ores. The basis of this approach is that microorganisms are capable to affect rock structure through their activities during weathering process. Microorganisms, such as fungi, are significant geoactive agents that are able to modify the surface structure and chemistry of rocks [START_REF] Matthews | Holocene Chemical Weathering, Surface Lowering and Rock Weakening Rates on Glacially Eroded Bedrock Surfaces in an Alpine Periglacial Environment, Jotunheimen, Southern Norway[END_REF]. These microorganisms can survive with extreme moisture and temperature fluctuations on rock surfaces where limited nutrient is available. It has been reported that certain microorganisms, such as lichen, can accelerate the rock weathering process by an order of magnitude [START_REF] Jie | Rock-weathering by lichens in Antarctic: patterns and mechanisms[END_REF][START_REF] Chen | Weathering of rocks induced by lichen colonizationa review[END_REF]. Different from the naturally occurring process, the weathering involved with microorganisms seem to leave the rocks with different microstructures. Such example is evident where grooves along the mineral grains were created due to the activities by fungal hyphae [START_REF] Hoffland | Feldspar Tunneling by Fungi along Natural Productivity Gradients[END_REF].

In a broader academic/industrial range, microorganisms have been used in bioextraction of all sorts of elements for three main purposes: 1) increasing the concentration of target metals in the solution, i.e., dissolution, 2) decreasing the concentration of target metals in the solution, i.e., precipitation, and 3) removing environmentally unfriendly components, i.e., decontamination.

Those microorganisms include bacteria (operational pH = 0-3), archaea (operational pH = 0-5), and fungi (operational pH = 3-9), which are typically extremophiles (e.g., acidophiles and thermophiles). In terms of metabolism, typical microorganisms used in biomining are chemolithotrophs (bacteria), heterotrophs (fungi), or facultative anaerobes (bacteria and archaea) [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF][START_REF] Imhoff | Bio-mining the microbial treasures of the ocean: New natural products[END_REF]. Table 1 represents a number of microorganisms with the capability of bioextraction of metals at small academic scales (mainly transition metals). This bioextraction occurs via cell metal intake, secretion of organic acids, or metabolic use of metal in (an)aerobic respiration [START_REF] Lee | Bio-processing of solid wastes and secondary resources for metal extraction -A review[END_REF][START_REF] Ojuederie | Microbial and Plant-Assisted Bioremediation of Heavy Metal Polluted Environments: A Review[END_REF]. Traditional microbiological techniques are based on isolating and studying microorganisms existing in in-situ samples. However, only about 1% of those microorganisms can be isolated in the lab. On the other hand, genomic techniques rely on extracting the DNA of domestic microorganisms and copying their genome to develop those species that are naturally adapted to specific environmental conditions. While the ecological impacts of the modified

genes are yet to be determined, none of the industrially-used microorganisms are known to be pathogenic. In contrast to the conventional hydrometallurgical techniques, recovery of metals by biological processes is considered a "clean technology," which is based on the interactions between microorganisms and metals under mild operating conditions, leaving strikingly less carbon footprints behind [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF]. Biomining is mainly allocated to extraction of copper and gold at the industrial scale [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF]. In the case of metals such as gold, which are expensive and naturally exist in low concentrations, the lower cost of bioleaching outweighs the required time in extractive metallurgy. Low concentration of target metals is not challenging for microorganisms as they simply ignore what is not considered their food, resulting in high extraction yields; more than 90% in some cases. On top of dealing with low-grade ores, traditional gold mining includes cyanidation which produces aurocyanide complexes, Au (CN) 2 -; in turn binding to carbonaceous compounds present in the gangue material and becoming unrecoverable [START_REF] Ubaldini | Gold recovery from a refractory pyrrhotite ore by biooxidation[END_REF]. Microorganisms can be used to prevent the bond between aurocyanide and carbonaceous compounds initially, or can be used to break that bond in the tailings and release the gold [START_REF] Ubaldini | Gold recovery from a refractory pyrrhotite ore by biooxidation[END_REF]. However, biomining needs to be extended to other minerals, such as rare earth elements (REEs), where the low-grade and high industrial demand has rendered traditional mining difficult and expensive. The word "Rare" refers to dispersity (as opposed to low abundance) of REEs, making them profitable targets for biomining. Especially, the recent discovery on the role of Ce 3+ and La 3+ in oxidizing methanol to carbon and energy has drawn interests in biomining of REEs [START_REF] Pol | Rare earth metals are essential for methanotrophic life in volcanic mudpots[END_REF][START_REF] Skovran | Just add lanthanides[END_REF]. Traditional methods could be replaced by bio-assisted concentration at different stages of biomining of REEs as follows.

In the main stage of biomining (excluding mineral pre-/post-processing), microorganisms are used for liberation and/or separation of target metals. Separation processes can be biological, (electro)chemical, and/or mechanical. Biosorption, bioaccumulation and bioprecipitation are three microbial strategies to separate target metals (Figure 3, stage 3). If there are multiple target metals in a sample (natural or artificial) a proper combination of physicochemical and biological strategies should be employed. Figure 3 shows a schematic representation of bioleaching, sulfidogenic, electrochemical selective extraction, and chemical extraction (bio)reactors, in which physicochemical and biological processes recover 8 metals in 4 stages. In stage 1, the use of zero-valent sulfur (ZVS) can be used to increase bioleaching efficiency as many acidophilic bacteria and archaea commonly use ZVS as an electron donor [START_REF] Falagán | New approaches for extracting and recovering metals from mine tailings[END_REF]. In an aerobic environment, oxidation of ZVS combined with reduction of molecular can decrease the pH by generating sulfuric acid. On the other hand, in an anaerobic environment, the oxidation of ZVS can be combined with the reduction of ferric iron with the aid of some acidophiles [START_REF] Falagán | New approaches for extracting and recovering metals from mine tailings[END_REF]. These acidophiles are often autotrophs, which in turn reduce the carbon footprints of bioleaching. For instance, the autotrophic Acidithiobacillus species have been commonly-used for bioleaching of metals. However, most secondary sources have alkaline nature and/or toxic heavy metals, making the growth of acidophiles extremely difficult. Although some indigenous acidophiles have been successfully used for bioleaching of copper and iron from secondary resources more researches required to adapt microbes to alkaline environments. Sulfidogenic bioreactors (Figure 3, stage 2) can be used as a source of hydrogen sulfide to selectively precipitate copper and zinc, in the form of copper/zinc sulfide in a lower/higher pH. Selective precipitation becomes highly beneficial in metal recovery from mine drainage resources which have low concentrations of aqueous metals. While electrochemical processes are considered to be very selective in separation of some transition metals (e.g., copper, zinc, and nickel), they cannot practically reduce REEs. Therefore, a proper combination of precipitation and electrochemical methods could be employed based on the chemical composition of the solution. The metal containing leachate can be introduced to an electrochemical cell (Figure 3, stage 3) or undergo further biological processes (e.g., biosorption, bioprecipitation). Bacillus subtilis and Escherichia coli have been used in such biological processes for extraction of light and heavy REEs (La, Ce, Y, Pr, Nd, Tm, Yb and Lu) [START_REF] Dev | Mechanisms of biological recovery of rare-earth elements from industrial and electronic wastes: A review[END_REF]. REEs can be precipitated via the phosphate group released by microorganisms. Elements such as silver and gold can be recovered using (bio)chemical leaching. Cyanogenic bacteria have been commercially used for bioleaching of gold metal (Figure 3, stage 4). Accelerating exhaustion of primary mineral resources has rendered secondary recourses increasingly important [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF]. Mining tailings are one of the richest secondary resources often including copper, iron, zinc, and nickel in high concentrations (critical elements), and occasionally REEs, such as lanthanum, neodymium, and cerium, and precious metals such as silver and gold. Being ground in fine sizes, mine tailings are more susceptible to environmentally caused transformations. This is to the extent that mine tailings can be considered as significant polluting sources of ground/surface waters (e.g., acid and metal deposition of in Nevada to the Owyhee River) [START_REF] Price | Geology of Nevada With excellent rock exposures in the desert, generally good access to collecting localities on public lands, and fine tourist attractions in the towns, Nevada is a wonderful state for rock and mineral enthusiasts[END_REF]. This becomes more critical where rejects from water-treatment plants and mineral processing are deposited in the tailings. Metal value recovery from mine tailings can be carried out by conventional hydrometallurgical methods such as inorganic chemical leaching and solvent extraction. Nonetheless, these methods may require rather extreme conditions of temperature, pressure, and chemical environment.

REMARKS

Numerous studies indicate that biomining is more environmentally friendly and energy conservative. Is biomining ready to be employed with its full potential then? Despite the foregoing discussion, any premature application of biomining decelerate further developments in biomining, rather than promoting it. To avoid that, foundations of biomining must be revisited; fundamental research must be performed with respect to the multidisciplinary nature of biomining. In general terms, profitability is the major concern of engineering and not so much of science. In the field of biomining, majority of academic research (and biohydrometallurgy in general) is performed within programs other than mining and metallurgical engineering, e.g., biochemistry, microbiology, and environmental science. However, what is valuable for the market is the final product, i.e., minerals that is under the control of mining and metallurgical engineers. As far as industry is concerned, bioextraction techniques are expected to compete with traditional ones. Some of the latter techniques have been refined over thousands of years (e.g., pyrometallurgical smelting), to which investments are mainly allocated. Moreover, the slower kinetics of bioextraction introduces a substantial delay in cash flow, while technologies such as pyrometallurgical smelting benefits from higher and faster yields, justifying its higher cost.

Although biomining is considered to be more conservative about environment (as well as energy), compared to traditional mining, the negative historical impact of the mining industry on the environment has marginalized the environmentally-friendly potentials of biomining. In addition, it is hard to model and scale up biomining processes [START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF].

As already discussed, the lower grade of increasingly growing secondary resources compensates the slower kinetics of biomining. If the concertation of the desired elements is low, traditional mining will completely lose its privilege, and will be prevailed by biomining in all aspects; with respect to time, energy, and environment (Figure 4). For example, as an energy conservative approach, biomining can be more generous in exploring energy intensive methods, such as hightemperature bioextraction. Importantly, full potential of biomining can only be exploited/revealed if all bio-assisted stages are inclusively considered (e.g., bio-assisted pretreatment), rather than solely consideration of bioextraction stage. Moreover, it is extremely difficult to transfer millions of tons of mine waste into enclosures; therefore, practical posttreatment solutions are those which work outside in the environment where things are out of control. This requires developing a better understanding about interactions between domestic microorganisms and minerals under in-situ environmental conditions. From the analogy between biomining and algal-bacterial wastewater treatment, one can vividly see the self-regulating nature of microorganisms; there is mutual relationship between their survival and their environment. Regarding all those variables, one can optimize the operational condition of biomining as a whole within a multivariate analysis. Fortunately, within the current status of biomining, there is enough leeway to proceed bio-assisted stages in a parallel manner. Also, combining chemical processes (e.g., gangue chemistry) with biological ones (e.g., metabolic manipulation) could potentially help to reach the breaking point of profitability for low-grade ores. Eventually, biomining demands collaborations among scholars with various backgrounds due to its multidisciplinary nature. These collaborations not only lead to potential strategies to improve biomining as an industry to extract minerals but also help develop biomining (as well as the involved disciplines) as a science to understand the harmonious coexistence between minerals and microorganisms. Taken together, the more we invest on laying the bedrocks of biomining in a systematic way, the more science, technology, and environment can benefit from such foundational investment. Finally, biomining could practically benefit from analyzing life-mineral coevolution. For instance, higher diversity of copper oxide minerals has been demonstrated to favor copper in the biological structures existing in modern deposits. Similarly, higher oxidation state of manganese (4+) is shown to be more abundant in more recent near-surface deposits, when/where life started playing a major role [START_REF] Grosch | Microbes, Mineral Evolution, and the Rise of Microcontinents-Origin and Coevolution of Life with Early Earth[END_REF][START_REF] Hazen | Mineral evolution[END_REF]. These historical analyses could also be beneficial in roughly dating the individual biological structures and estimating the conditions they have evolved in. Another possibility is to make predictions based on mineral-microorganism network analysis; where to find new minerals. Inspired by what is called "affinity analysis", one could develop a network based on coexistence/codependency of certain mineral and microorganisms. This requires machine learning on big databases, which are rapidly being developed nowadays [START_REF] Muscente | Quantifying ecological impacts of mass extinctions with network analysis of fossil communities[END_REF][START_REF] Morrison | Network analysis of mineralogical systems[END_REF].

Figure 1 .

 1 Figure 1. Origin of elemental diversity of minerals; cosmic rays/Big Bang (white), stars/supernova (yellow), manmade (red; these are very short-lived, created only in labs). The numbers below each element correspond to its oxidation state(s).

Figure 3 .

 3 Figure 3. Schematic representation of bioleaching (stage 1), sulfidogenic (stage 2), electrochemical selective extraction (stage 3), and chemical extraction (stage 4) (bio)reactors.

Figure 4 .

 4 Figure 4. Advantages and disadvantages of biomining; the highlighted region is roughly where biomining is more economically viable

Table 1 .

 1 Different microorganisms (bacteria and fungi) for bioextraction of metals[START_REF] Shi | Extracellular electron transfer mechanisms between microorganisms and minerals[END_REF][START_REF] Schippers | Metal Recovery from Ores with Microorganisms[END_REF][START_REF] Johnson | Biomining-biotechnologies for extracting and recovering metals from ores and waste materials[END_REF][START_REF] Orell | Life in blue: Copper resistance mechanisms of bacteria and Archaea used in industrial biomining of minerals[END_REF][START_REF] Gumulya | In a quest for engineering acidophiles for biomining applications: challenges and opportunities[END_REF][START_REF] Johnson | A New Direction for Biomining: Extraction of Metals by Reductive Dissolution of Oxidized Ores[END_REF][START_REF] Mahajan | Principles and Applications of Environmental Biotechnology for a Sustainable Future[END_REF][START_REF] Jerez | Biomining in the Post-Genomic Age: Advances and Perspectives[END_REF][START_REF] Jerez | Biomining of metals: how to access and exploit natural resource sustainably[END_REF][START_REF] Liao | A new strategy on biomining of low grade base-metal sulfide tailings[END_REF][START_REF] Işıldar | Biotechnological strategies for the recovery of valuable and critical raw materials from waste electrical and electronic equipment (WEEE) -A review[END_REF][START_REF] Anjum | Biohydrometallurgy techniques of low grade ores: A review on black shale[END_REF][START_REF] Fathollahzadeh | Role of microorganisms in bioleaching of rare earth elements from primary and secondary resources[END_REF][START_REF] Donati | Thermophilic microorganisms in biomining[END_REF][START_REF] Zhang | Effect of elevated pressure on ferric iron reduction coupled to sulfur oxidation by biomining microorganisms[END_REF][START_REF] Kaksonen | The role of microorganisms in gold processing and recovery-A review[END_REF][START_REF] Jerez | Biomining Microorganisms: Molecular Aspects and Applications in Biotechnology and Bioremediation[END_REF][START_REF] Quatrini | Genomic insights into the iron uptake mechanisms of the biomining microorganism Acidithiobacillus ferrooxidans[END_REF][START_REF] Kaksonen | Recent Advances in Biomining and Microbial Characterisation[END_REF]

	Archaea	Metal	Bacteria	Metal	Fungi	Metal
						Iron
			At. ferrooxidans
	Metallosphaera sedula	Copper		Copper	Aspergillus niger	Tin
			At. Thiooxidans
						Gold
			Leptospirillum ferriphilum
	Acidianus copahuensis	Zinc		Zinc	Aspergillus niger	Cobalt
			Acidithiobacillus ferrooxidans

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