Ex-situ mineral carbonation: resources, process and environmental assessment (Carmex project)

This article presents the main results of the Carmex project (2009-2012), whose purpose was to review the feasibility of ex-situ mineral carbonation in terms of resource availability, performance of the aqueous mineral carbonation process and life cycle analysis criteria. This collaborative project looked at a wide range of generic issues about this CO2 mitigation option, with particular views on assessing its potential in the context of New-Caledonia. Indeed, insularity and local abundance of 'carbonatable' rocks and industrial wastes (i.e. rich in MgO, CaO, if not Fe(II)O), coupled with significant GHG emissions from first-class nickel pyrometallurgical industries, make it a potential candidate for application of ex-situ mineral carbonation. The project conducted a worldwide analysis of the potential of ex-situ mineral carbonation using a dedicated SIG-based tool. Using a variety of materials the project also reviewed a number of critical issues associated with the aqueous mineral carbonatation process itself, with promising perspectives. Finally, through life cycle analysis of the system as a whole, ex-situ mineral carbonation was compared to mainstream CSC solutions. It was concluded that the viability of this CO2 storage option is located at the level of the process itself and lies with the optimisation of its operating conditions

Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model

High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis. Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted. Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant, or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results. The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully applied to recent experimental results on the release of arsenic from Bengal delta sediments

Comprehensive analysis of direct aqueous mineral carbonation using dissolution enhancing organic additives.

Direct aqueous mineral carbonation using organic anions has been presented by many as a promising strategy for mineral carbonation, on the basis that additives such as oxalate increase the rate and extent of dissolution of magnesium silicates several folds. Through geochemical modelling and detailed solid characterization, this paper discusses and extends our current understanding of this process. The role of disodium oxalate as a dissolution enhancing agent for olivine is thoroughly examined through experiments in which all phases are carefully analysed. We show that under 20 bar of CO2 pressure formation of strong oxalate-magnesium complexes in solution and precipitation of MgC2O4,2H2O (glushinskite) impede any chance of obtaining significant amounts of magnesium carbonate. Other promising ligands from a dissolution perspective, namely citrate and EDTA salts, are also investigated. Contrary to oxalate, these ligands do not form any solid by-products with magnesium, and yet they do not produce better carbonation results, thereby casting strong doubts on the possibility of developing a direct aqueous mineral carbonation process using organic salts. Geochemical modelling permits successful simulation of the dissolution kinetics of magnesium silicate using a shrinking particle model that accounts for the precipitation of glushinskite, amorphous silica and a magnesium phyllosilicate at advanced stages of the dissolution process

Development of an attrition-leaching hybrid process for direct aqueous mineral carbonation

Mineral carbonation is the single most eligible companion solution to geosequestration for mitigation of anthropic CO2 emissions on a large scale. Amongst its possible pathways, direct aqueous mineral carbonation stands out as one of the most promising ones. The originality of the present work lies in the transposition of the concomitant exfoliation/mineralisation concept, which was first proposed by the mineral carbonation research group from the Arizona State University in early 2000s, inside a dedicated attrition environment, more specifically inside a stirred bead mill. Experimental results and analyses bring definite proofs about the possibility and synergy of concomitant exfoliation and mineralisation. Given high carbonation yield for olivine and serpentinised ores (up to 35% in 5 h and 80% in 24 h in water, and 70% in 5 h with inorganic additives) and the capacity of stirred mills to process mining size throughputs, this work leads to real perspectives for developing large scale robust solutions for direct aqueous mineral carbonation

Ex situ mineral carbonation for CO2 mitigation: Evaluation of mining waste resources, aqueous carbonation processability and life cycle assessment (Carmex project)

This article presents the main outputs from the multidisciplinary Carmex project (2009–2012), which was concerned with the possibility of applying ex situ mineral carbonation concepts to mafic/ultramafic mining wastes. Focus points of the project included (i) matching significant and accessible mining wastes to large CO2 emitters through a dedicated geographical information system (GIS), (ii) analysis of aqueous carbonation mechanisms of mining waste and process development and (iii) environmental assessment of ex situ mining waste carbonation through life cycle assessment (LCA) methodology. With a number of materials associated with the mining sector, the project took a close look at the aqueous carbonation mechanisms for these materials and obtained unexpected carbonation levels (up to 80%) by coupling mechanical exfoliation and reactive carbonation. Results from this work support the possibility of processing serpentine-rich peridotites without applying the classical first step of heat activation. Perspectives are also given for the carbonation of Ni-pyrometallurgical slag available closed to ultramafic mining residues. LCA of the mining waste carbonation system as a whole made it clear that the viability of this CO2 storage option lies with the carbonation process itself and optimisation of its operating conditions. By combining the body of knowledge acquired by this project, it is concluded that New Caledonia, with its insularity and local abundance of ‘carbonable’ rocks and industrial wastes coupled with significant greenhouse gas (GHG) emissions from world-class nickel pyro and hydrometallurgical industries stands out as a strong potential candidate for application of ex situ mineral carbonation

Influence of the cooling conditions on the nature and the size of the mineral phases in a Basic Oxygen Furnace (BOF) slag

This paper presents the influence of different cooling conditions on the nature and size of the major mineral phases present in a BOF slag. XRD, SEM and image analysis are used. The objective of this work is to optimise the industrial process in order to better recycle BOF slag.Les laitiers sont des déchets produits par les procédés de fabrication de la fonte et de l’acier. Alors que les laitiers de hauts fourneaux ont un taux de valorisation proche de 100 %, ce taux est beaucoup plus bas pour les laitiers d’aciérie de conversion. Les tonnages produits sont extrêmement importants, puisque environ 100 kg de laitiers sont générés lors de la fabrication d’une tonne d’acier.Les voies de valorisation actuelles des laitiers d’aciérie sont principalement les marchés de granulats pour les routes, remblais ou travaux portuaires. Cette application, très bas de gamme, permet principalement d’éviter la mise en décharge mais ne consiste pas réellement en une vraie valorisation. Elle se heurte de plus, pour les applications enrobées (asphalte, bétons,…), au problème de gonflement dû à l’hydratation et à la carbonatation de la chaux et de la magnésie libres contenues dans les laitiers. Les laitiers non valorisés en France représentent environ un tiers de la production, soit 330 000 tonnes par an, qui sont généralement stockés sur site. Pourtant, les laitiers d’aciérie contiennent des éléments chimiques très intéressants pour la valorisation comme matières premières (Fe, Si, Ca notamment)

Primary phases and natural weathering of old lead-zinc pyrometallurgical slag from Príbram, Czech Republic

Pyrometallurgical slag, produced 100-150 years ago from lead-zinc ores in the smelting region of Príbram, Czech Republic, contains elevated amounts of Zn and Pb. Knowledge of the distribution of these elements in the main phases and an investigation of natural weathering features represent the first step in the environmental assessment related to dumping of metallurgical slag. Optical microscopy, scanning electron microscopy (SEM/EDS), X-ray diffraction (XRD) and electron-beam microanalysis (EMPA) were used to identify the silicate, oxide, sulfide and metallic phases. The study focused on silicates and oxides, and the major constituents of the slag proved to be clinopyroxene, melilite, olivine, spinel and glass. A substantial amount of zinc, initially dissolved in the silicate melt, is held by zinc-rich end members of the spinel (gahnite, up to 19.9 wt% ZnO) and silicates (e.g., hardystonite, up to 10.5 wt% ZnO). Lead, by contrast, behaves as an "incompatible element" and is likely to be concentrated in the residual matrix glass. Two distinct glasses were identified: (i) transparent (surface) glass from the quenched borders of slag fragments, and (ii) opaque (matrix) glass, which forms a black matrix in the center of the fragments. These glasses contain important amounts of lead and zinc, up to 3.72 wt% PbO and 9.80 wt% ZnO, partly in the form of droplets (generally <1 µm) composed of galena, metallic lead, ZnS and other sulfide and metallic phases and alloys. Two features attributed to natural weathering, found mainly on the surface of chilled-glass borders, were identified in the slag: (i) deposition of a Fe- and Pb-rich veneer, and (ii) selective leaching of superficial glass revealing, with respect to unaltered glass, the mobilization of Ca, Fe, Na, K, and Zn

Monitoring the stabilization of municipal solid waste incineration fly ash by phosphation: Mineralogical and balance approach

The application of a micro-characterization protocol coupled with a balance approach has allowed the relevant monitoring of a phosphation process for fly ash produced by municipal solid waste incineration. The three main steps of this process consist in removing the salts (chlorides, sulfates) by dissolution at basic pH, phosphation of the residue to trap metals, and its calcination to destroy dioxin-like compounds. The chemical and mineralogical balances compiled on the samples after each step of the process validate these main objectives and highlight the wide phosphorus distribution throughout the sample during the phosphation process, as well as the formation of apatite-type crystallized phosphates. During calcination, the increase in the proportion of crystallized phosphates apatite and whitlockite is largely attributable to the presence of an available calcium source, corresponding to the calcite formed during washing. The metals Pb and Zn, initially distributed in the silicate and carbonate phases, are broadly redistributed in the phosphate neoformations after carbonate dissolution, thus guaranteeing a more permanent stabilization. © 2002 Elsevier Science Ltd. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Evaluation of mineral processing techniques to concentrate metals (Pb, Zn, Cu, Au) in mining residues at Baia Mare, Romania

International audienceRehabilitation of historical mining sites is a great matter of concern in the world. In European countries, under 2006/21/CE Directive, national inventories were performed and dedicated management regarding environment and sanitary issues proposed. Mining residues are usually present on these sites; depending on their type and nature, they can be in particular source of acid and metallic drainage. More recently economic circular issues have listed mining waste as possible secondary resources containing metals and materials. Their reprocessing could be of some interest especially if strategic or critical elements are present. Benefit could then help rehabilitation purpose. At Baia Mare, Romania, polymetallic sulphide mine produced Pb, Zn, Cu. In particular the Central flotation pond operated for 13y (1962-75) to stock 8.5 Mt (5.7 Mm3) of residues. It is now located in an urban area with need of management. A technical program was established to: 1) prepare representative samples and characterise them-chemical/ mineralogical composition, acid potential, particle size and metal distribution; 2) evaluate the possibility of concentrate metals by physical separation techniques to facilitate the leaching step. The tailings consist of fine materials (d50: 73 µm) rich in quartz with silicates, carbonates, sulfides and sulfates. Metals are Pb, Zn, Cu (<1%) and Au (0.6-0.7 ppm). Gravity separation using laboratory Mozley table showed a slight concentration of base metals within the heavy fraction but Au is disseminated in all size-fractions. Further separation tests are planned and Au speciation will be studied. Further experiments will concern hydrometallurgy by testing thiosulfates and ionic liquids. NB: The study is performed under MINTECO project (2018-20) with Eramin2 cofunding

Compilation of mining waste databases to prioritize site study for metal recovery. Perspectives.

International audienceIn a global context of growing raw materials scarcity, the Valodem project, conducted by the French Geological Survey (BRGM) aimed identifying national mining wastes that could possibly be reprocessed to recover metallic commodities (base- but also strategic or critical metals). To achieve this goal, French data on mining wastes have been compiled from various databases, and analyzed to identify most interesting mining wastes and evaluate their potential for reprocessing. Twelve waste deposits were selected for further capitalisation of data and one for sampling, analyses and pilot operation. The present paper briefly presents the methodology, results and perspectives of this work, at both national and European levels