Several methods have been studied to overcome chalcopyrite passivation during bioleaching at atmospheric pressure. One such method is to reduce particle size to increase the reactive surface area of the mineral. However, little is known about the effect of fine particles on the performance of chalcopyrite bioleaching in terms of bacterial growth and activity. In this study, two size fractions were prepared by sieving a raw chalcopyrite concentrate to produce particles between 20 and 100 mu m and particles below 20 mu m. These three materials were used in batch bioleaching tests performed in 2 L stirred reactors at 42 degrees C, with a solid concentration of 10 %w/w and the BRGM-KCC microbial consortium. Redox potential and iron and copper concentrations were monitored over time to characterize the reaction progress. With the coarser materials, the redox potential increased to above 750 mV vs. SHE within a day, whereas particles below 20 mu m took an additional day to reach this potential. This lag phase permitted faster copper dissolution, resulting in a yield of 35 % after two days. In contrast, a yield of 10-20 % copper was achieved in 15 days using coarser materials. In contrast to previous assumptions, fine particles did not hinder bacterial growth and activity. Rather, they promoted them by increasing the availability of substrates generated by greater sulfide oxidation. Bioleaching chalcopyrite particles < 20 m produced higher copper yields thanks not only to their larger reactive surface, but also to the delayed increase in redox potential and subsequent chalcopyrite passivation.

Following the Paris agreements on climate change, CO2 emissions from large emitters have become the focus of particular attention. With a national average of 0.4 kg of fossil CO2 emitted per kg of Municipal Solid Waste (MSW) incinerated, bottom ash (BA) residues from waste-to-energy (WtE) plants in France are possible candidates for CO2 mitigation by mineralization, considering BA as feedstock for CO2 capture and production of alternative construction materials. BA samples collected from an operating WtE plant in the suburb of Lyon were carbonated under slurry or humidity-controlled conditions. It was found that 35 kg of CO2 could be captured per tonne of minus 100 mu m ground BA in 30-120 min at ambient conditions. A water pre-washing stage was necessary to prevent the production of H2 by oxidation of Al metal during carbonation and removed chlorides and sulfates that are undesirable in construction materials. While it is argued that CO2 mineralization is of limited interest for mitigating the CO2 emissions of WtE facilities, a conservative analysis of a production system that associates a WtE plant and a cement plant reveals that the net carbon footprint of such a combined production system could be reduced by 15 % with an added mineralization process.

Carbon footprint reduction and circularity are strategic goals for the concrete sector. This study presents a concrete waste recycling process that incorporates mineral carbonation and promotes the complete reuse of concrete waste for the production of new concrete. The process is a sequence of 4 steps: (1) intensive micro-cracking of the cement paste by microwave heating to promote both (a) textural separation between the original concrete constituents, natural aggregates and hardened cement paste (HCP), and (b) carbonation of the latter, (2) non-impact crushing to physically separate them, (3) abrasive screening of the concentrated cement paste into a recycled concrete fines (RCF) fraction to further reduce residual cement paste on the surface of recycled concrete aggregates (RCA), and (4) a cement paste carbonation step for RCA and RCF. Using concrete samples of controlled formulation, the performance of the proposed process is evaluated at the laboratory scale in comparison to a conventional recycling process using crushing and screening. Microwave heating experiments were conducted using a 2.45 GHz waveguide powered by a 2 kW magnetron. Settings used for the micro-cracking stage of concrete samples were a 1.5 kW incident power and a 4 min heating time. For several performance indicators, the proposed process outperforms the reference process by a factor of 2 or more for both RCA and RCF, concentrating 75

In this study, we investigated an innovative bioleaching process that aims to improve the leaching performance of chalcopyrite by in situ mechanical abrasion of passivating layers. This technology uses millimetre-sized grinding glass beads to erode particles continuously, thereby applying shear stresses that continuously remove and refresh surface layers. To this end, a hybrid bioreactor (6 L) was constructed with a stirred mill impeller to perform bioleaching and attrition concomitantly inside a single reactor. Bioleaching tests were carried out with a Cu concentrate containing 71

The overall performance of hydrometallurgical leaching operations can be limited by the presence of various types of insoluble layers coating the surface of the treated solids. The attrition-leaching process, which is carried out in a stirred reactor containing millimetric beads, can partially overcome this problem and increase the extraction yield by physically abrading the layers. Through a comparative analysis of three different systems, this work develops a constructive discussion of the attrition-leaching process. The systems of interest are (i) mineral carbonation of ferronickel slag, (ii) dissolution of a chalcopyrite concentrate in sulfuric media, and (iii) dissolution of spent Ni-MH battery black mass powder in sulfuric media. In the case of ferronickel slag and chalcopyrite, the reaction yields are improved by a factor of 10 with attrition-leaching compared to leaching only, while there is no yield improvement in the case of Ni-MH black mass batteries, highlighting that the layers observed on the grain surface do not interfere with the leaching reaction. Despite very different system chemistries and conditions, the particle size distribution is similar for the three materials, showing that particles’ behavior is controlled by the attrition environment. This work offers a simple setup for investigating the potential improvements of the kinetics and yields of leaching reaction due to concomitant attrition. It also allows a fundamental study of the physico-chemical processes involved, by testing whether a leaching reaction is hindered by an in situ passivation at the surface of a material.

This study’s aim is to fully characterize ferronickel slag from New Caledonia, considered a multiphase mineral containing amorphous material. The methodology consisted of combining chemical, mineral, and morphological characterization techniques, such as ICP-AES, TGA, Q-XRD, microscopy, spectroscopy, etc. The ferronickel slag consisted of 44 wt. % forsterite, with the inclusion of iron as a substitution for magnesium (Mg1.8Fe0.2SiO4), 1.7 wt. % chromite and 54 wt. % amorphous phase containing iron, magnesium, aluminum, and silica (Mg/Si = 0.4; Fe/Si = 0.2; Al/Si = 0.1). This material was slightly reactive in a cementitious medium, thus limiting its use as an SCM in the construction sector. The ferronickel slag was then subjected to an attrition-leaching carbonation process at 180 °C and a partial pressure of CO2 of 20 bar. The obtained product, carbonated at 80% of its capacity, was also characterized. It was composed of carbonates (37% of magnesite and 4% of siderite), remaining forsterite (7 wt. %), chromite (1 wt. %), and 50% of an amorphous phase, mainly composed of silica and aluminum. The complete characterization of those products helped in understanding the chemistry of the carbonation process and finding valorization paths for the carbonated products in the construction sector. The carbonated product may be used either as an SCM in blended cement or as a precursor of magnesium–silicate binders.

EDITORIAL article Front. Clim., 10 January 2023Sec. Negative Emission Technologies Volume 4 - 2022 | https://doi.org/10.3389/fclim.2022.1128721

We report the investigation of a chalcopyrite leaching process that implements millimeter-sized glass beads that are stirred in the leach reactor to combine particle grinding, mechanical activation, and surface removal of reaction products. The paper focuses on demonstrating the impact of the so-called attrition-leaching phenomenon on the leaching rate of a chalcopyrite concentrate and provides a first understanding of the underlying mechanisms. For this purpose, we have compared the copper leaching yield for different configurations under controlled chemical conditions (1 kg of glass beads and 84 g of chalcopyrite concentrate in 2.5 L of H2SO4-H2O solution, pH = 1.3, E-h = 700 mV vs SHE, and T = 42 degrees C). On top of elemental analysis of the leach solution with time, we provide a full characterization of the solid residue based on X-ray diffraction, elemental analysis, and sulfur speciation. We demonstrate that glass beads led to a remarkable enhancement of the leaching rate in conditions where particles were already passivated by simple leaching and even when large amounts of solid products (elemental sulfur and jarosite) were present. An in-depth evaluation of particle size distribution showed that particle breakage occurred during a rather short time (a few hours) at the beginning of the runs, transforming the initial particles with d(4/3) = 30 mu m to finer particles with d(4/3) = 15 mu m. Then, particle breakage almost stopped, while an attrition phenomenon was evidenced, inducing the formation of very fine particles (<1 mu m) and aggregates concomitantly with copper leaching.

This paper aims to provide an overview of tungsten (W) tailings properties, detrimental impacts of these tailings, approaches to mitigate these impacts, and a presentation of methods to reprocess them to capture their economic value. Since W is widely used in a variety of industries, it has been extensively mined since the 19th century, and the mining continues to generate significant volumes of tailings. Recent data show that global W production stands at 84 kt per year, and more than 100 Mt of W tailings exist containing over 100 kt of WO3. The tailings contain variable amounts of valuable products and deleterious environmental substances. Some of the contained metals are in great demand for the energy transition. However, these tailings usually contain FeS2/Pyrrhotite and FeAsS minerals, which, when exposed to air and water, can produce acid mine drainage. As such, W tailings may pose environmental and human health risks. Globally, the reprocessing of W tailings presents a potential resource that can be regarded as a paradigm of sustainability and circular economy. Flotation, enhanced gravity separation, and wet high-intensity magnetic separation have been reported to be the common approaches to reprocessing W tailings. However, W processing presents particular difficulties owing to complex material properties, such as fine particle size, surface weathering, similarity in surface properties exhibited by gangue materials (fluorite, apatite, calcite), low concentrations of the elements of interest, and poor mineral liberation.

Accelerated carbonation is recognized as a possible way to improve the quality of recycled concrete aggregates (RCA) and thus increase the possibilities of their use for concrete manufacturing. This work is a contribution to exploring high-pressure carbonation as a possible technology for carbonation of cement-based RCA. Using mortar powder and cylinders as a model for RCA, the work established that mortar with sufficient water content can be nearly fully carbonated at 138 kg of CO2 per tonne of mortar in less than 30 min with high pressure CO2. The presence of water inside the mortar's porous structure appeared to be a factor of paramount importance for carbonation of mortar, whereas using water-saturated CO2 was of no benefit. Increasing CO2 pressure and temperature both improved carbonation kinetics of mortar within the range of pressure and temperature conditions tested.

Quantitative risk assessment is required by some regulations in specific situations, such as major risk evaluations. The bowtie method, which combines fault and event trees and includes safety barriers, is a valid quantitative method for analyzing industrial risks and a tool for decision-making and safety management. At present, accounting for uncertainties associated with reliability data is not necessarily mandatory in quantitative risk assessment. The quantitative method, as currently implemented, introduces uncertainties that are not addressed in the bowtie. Input data uncertainties linked to choosing values among different sources lead to variability in the results. The possibility method, presented in this article corrects this bias by considering all scenarios, without excluding those with a very low probability. For an industrial company, this specificity can allow to ensure the completeness and the robustness of its risk analysis. This study highlights the impact of uncertainties on the quantification of a bowtie. Besides obtaining a probability, it enables decision-makers to have access to the uncertainty related to the result. This information is essential to judge the trustworthiness of the analysis and to manage risks based on uncertainties. This study allows the development of an advanced bowtie method, by considering the uncertainties associated with the input data.

The main obstacle to the aqueous carbonation of non-serpentinised magnesium silicates is the formation of surface passivation layers, which severely limits the reaction rate and thus the overall efficiency of the process. A technological solution to overcome this problem is to perform the carbonation process inside a stirred bead mill, which aims to continuously remove the surface by-product layers by attrition. In this work, the aqueous carbonation of ferronickel slag, a mineralogically complex mining waste composed of a Mg/Si rich amorphous phase and a crystalline ferrous forsterite, was studied at 150°C and under 10 bar of CO2 with different operating configurations: carbonation alone (C mode), attrition followed by carbonation (A-C mode) and concomitant attrition and carbonation (AC mode). By careful observation of the mineralogy and the surface of the secondary phases formed using complementary analytical techniques, the article allows a better understanding of the passivation phenomenon inherent to the carbonation of magnesium silicates, and confirms the effectiveness of continuous surface mechanical depassivation for reaching high carbonation rates with this type of material. Comparative analysis of the products obtained with the three operating modes shows that a true synergy takes place between attrition and carbonation due to the combined effect of continuous exfoliation and mechanical activation of particle surface, which goes far beyond the simple increase in surface area due to particle size reduction. While mechanical depassivation is here substantiated by several evidence, the additional mechanochemical activation effect cannot be delineated from experiment; however its beneficial contribution to carbonation is inferred from its observation in A-C mode. The work finds that the synergy between attrition and carbonation also yields very characteristic products. They consist in micrometric agglomerates formed by bound spherical particles a few tens of nanometers in size. These particles themselves contain an entanglement of nanometric grains of carbonates and amorphous silica dispersed inside a magnesium-depleted alumino-siliceous matrix. These results confirm that concomitant attrition and carbonation offers one of the most promising pathways for developing direct aqueous carbonation processes with non-thermally activatable magnesium silicates.

The world is facing critical technological and environmental challenges in the production of basic materials in high demand, such as aluminium and silica, whose processes were developed long ago. New production routes, involving using alternative resources and innovative technological solutions, are needed to secure access to these base materials at a lower cost to the environment, in terms of waste and carbon footprint. The European project AlSiCal is currently investigatingan environmentally friendly multi-step process for producing alumina and silica from anorthosite, an abundant feldspar mineral. The present paper focuses on the modelling strategy of the dissolution of anorthosite in concentrated hydrochloric acid, which is the first step of the AlSiCal process. The objectives of this study are (i) to give a reliable first-level prediction of the product speciation in the aqueous and solid phases, (ii) to provide the sensitivity of the process to key operating variables, and finally, (iii) to evaluate the performance of both batch and continuous leaching processes. The proposed methodology is based on the coupling of geochemical equilibrium simulations and particle reaction models, using different computational tools and relevant literature data. This makes it possible to select the favourable operation window and process configuration for the quantitative extraction of aluminium in solution and the production of amorphous silica with an acceptable purity for large-market applications.

Tangential introduction of liquid results in a swirling flow within a cylindro-conical hydrocyclone. Upon continuous feeding with water, the central axial region experiences local low pressure across the height yielding the formation of an air-core, which executes meandering motion similar to the oscillation of an elastic string. We investigated the vortical flow and the induced oscillating behavior of an air column submerged in a water flow field inside a hydrocyclone. Through a series of experiments in a transparent hydrocyclone and subsequent full scale multiphase flow simulations with the Reynolds stress model, we analyzed the morphological characteristics of the air-core (mean and fluctuating properties). Air-core oscillations are characterized in terms of spatial wavelength and frequency. We show that hydrodynamics driven oscillating behavior of the air-core shares an analogy with the vibration of an elastic beam. Following this analogy, we obtain a scaling relationship between the wavelength and air-core radius, which is in good agreement with our experimental data and numerical results.

In this work, we are interested in the sources of raw materials for mineral carbonation as well as the valorization of the products resulting from this carbonation. To achieve carbonation of waste and to obtain a valuable product we need carbonatable materials such as Fe, Mg, Mn, Ca: it is necessary to seek these compounds in the waste considered. We will focus on particular sources of waste, the residues of cement industries, bottom ash (steel mills, incineration of household waste) or building deconstruction residues. The objective of this paper is to describe the functional specifications of a carbonation unit that is both flexible enough to treat a wide variety of these materials, and compact enough to allow it to be moved from one source to another. These specifications will concern two different uses of this mobile unit: that of initial feasibility demonstration, and those corresponding to its current operation.

The world is being confronted with urgent environmental challenges such as climate change, the unsustainable use of resources and loss of biodiversity. Innovative technologies can make a significant difference in terms of resource and cost saving, but they often fail to reach the market because they cannot demonstrate a successful track record of previous applications. In this context, it has appeared the Environmental Technology Verification (ETV) with the main aim of helping innovative environmental technologies to reach the market faster and easier. ETV is an initiative that provides for third-party verification of the performance claims made by technology manufacturers in business-to-business relations. By issuing a Statement of Verification, which is the product of a successful ETV process, ETV provides credible information on the new technology to could reach the market reducing risks. Since its creation in 2011, ETV has been implemented in few European Countries (only 7 countries are Members States: Belgium, Czech Republic, Denmark, Finland, Poland, France and United Kingdom) and due to this geographical limitation, a group of different European organisations (SME, university, associations, technological centres, clusters, etc.) have created ETV4INNOVATION Consortium, with support from the Erasmus Plus Programme of 2017 (Project Reference: 2017-1-IE001-KA202-025703) whose main aim is to create a flexible learning pathway in line with the needs of learners and companies in terms of ETV. Following the competences identified by a key study on general needs by SMEs towards ETV, companies can respond to these environmental issues. In order to provide students with the key competences related to environmental planning, we have created a Joint Curriculum composed by 3 main learning outcomes: Basic aspects of verification of environmental technology The ETV programme as a commercial tool on domestic and international markets Practical aspects of the ETV verification

This work is part of the ongoing development of the attrition-leaching carbonation process, a single-step aqueous carbonation technology that integrates a stirred bead mill. The principle of the attrition-leaching carbonation process is to continuously refresh the surfaces of reactive particles so that leaching can proceed unimpeded, yielding enhanced carbonation kinetics and yield. Invariably, attrition-leaching carbonation experiments carried out under controlled temperature and CO2 partial pressure conditions with different silicate-rich carbonation feedstocks - natural ores and nickel slags - show a carbonation yield that tends towards a plateau 20–50% below the stoichiometric yield. This repeatable behaviour raises the question as to whether the carbonation limitation is due to specific equilibrium side reactions of the carbonation feedstock or to a kinetic limitation of the attrition-leaching carbonation process. To try to provide some answers to this puzzling question, this reflexive paper implements a “thermo-kinetic” modelling methodology based upon geochemical equilibrium simulations and particle reaction models. The results obtained indicate that the observed slowing down of the carbonation process can be explained either by the formation of Mg- and/or Fe-rich silicates that precipitate at the expense of carbonates, or by a decrease in the efficiency of the attrition process over time. Indeed, either one of these mechanisms could explain the observed behaviour of the attrition-leaching carbonation process. However, the cross comparison of different data sources pleads in favour of the attrition-leaching carbonation performance being limited by the attrition process. Pending further confirmation, this tentative conclusion suggests that further development of the attrition-leaching carbonation process requires new knowledge about its inner workings, and that there may be ways to optimize the performance of this process beyond that based on standard stirred bead mill operating rules.

This paper is part of a multi-disciplinary research program on development and application of an integrated CO2 mineralization (ICM) framework for development of carbon mineralization as a CO2 mitigation solution. ICM is viewed as a three concentric layer system: technological, industrial integration, and decision-making. The search for viable ICM solutions in a given societal and economic context, which could be posed as an inverse design problem, begins with the identification and characterization of every system component. As an early writing on the development and applicability of the proposed ICM framework, this contribution focuses on ICM's inner technological layer. Several technological pathways, each one defined as a set of processing and transformation steps that connect a feedstock to a specific marketable product, can coexist within this layer. The paper addresses the characterization of one such technological pathway, whose cycle is divided into three successive blocks: feedstock, carbonation and valorization. The proposed concepts are illustrated through the valorization of ferronickel slag from New Caledonia as supplementary cementitious material or cement constituent, a case study that targets the production of “greener” construction materials. The data presented in the paper confirm the feasibility of characterizing the chosen ICM technological pathway, giving credit to the proposition that ICM can be approached as an inverse design problem. While exemplifying the significance of the characterization work necessary for one particular ICM technological pathway, the paper argues that development of ICM requires working on a scale considerably larger than that of standard mineral carbonation process research. Indeed, where grams of carbonated products are sufficient to investigate mineral carbonation processes, kilograms are mandatory to test and validate the use performance of final marketable products. Without precluding the merits of seeking innovative solutions, the authors argue that unit operations and transformation processes whose validity is proven at an industrial scale should be favored for timely development of viable ICM solutions.

Mineralization is a CO2 utilization solution that can possibly meet all the CO2 mitigation criteria stated by the International Energy Agency, namely CO2 emissions reduction, economic self-sufficiency and scalability. Considered as a global niche markets solution, mineralization process development is particularly challenging, as its scope is territory dependent and combines feedstock selection, mineralization technology and undisruptive product valorization through local materials supply chains. Identification of potential mineralization pathways is a definite challenge. This paper argues that geochemical modelling is an indispensable guiding tool for mineralization process development. Owing to its capacity to predict product speciation for complex mineralization systems, the paper discusses a number of issues that illustrate and confirm the value of geochemical modelling for feedstock selection, product valorization and process engineering. Supporting arguments are provided in the context of the valorization of Ni-slags from the New Caledonian metallurgical industry. It is concluded that geochemical modelling is an undisputed building block for developing and modelling any mineralization process. Moreover, the paper argues that the full potential of geochemical modelling for mineralization process design requires its merging with high-level decision-making frameworks, such as regionalized life cycle assessment.