Chemical Leaching Process Research Articles

Study on the Deashing of Lignite with Hydrochloric Acid/Sodium Fluoride Leaching, Assisted by Microwave and Ultrasonic Waves.

This study was aimed at investigating the effects of adding sodium fluoride (NaF) and using the assistance of ultrasonic and microwave energy on the removal efficiency of ash content during the hydrochloric acid (HCl) chemical leaching process of lignite samples from Zhaotong, Yunnan, China. Chemical leaching was conducted on lignite samples from Zhaotong, Yunnan, China, under the experimental conditions of time (30-120 min), temperature (55-95 °C), microwave power (240-800 W), ultrasonic power (25-100%), and NaF addition concentration (0.2-1.2 M). The addition of NaF greatly improved the removal efficiency of ash content from lignite. Under optimized conditions, the addition of NaF increased the removal rate of ash content from lignite from 25% to 65.27%. The microwave-assisted deashing of lignite can significantly improve the deashing efficiency, with positive implications for the microstructure regulations of lignite. Ultrasonic-assisted deashing can lower the temperature for coal powder burnout and enhance the combustion performance of coal.

Direct lithium extraction from spent batteries for efficient lithium recycling

The flourishing expansion of the lithium-ion batteries (LIBs) market has led to a surge in the demand for lithium resources. Developing efficient recycling technologies for imminent large-scale retired LIBs can significantly facilitate the sustainable utilization of lithium resources. Here, we successfully extract active lithium from spent LIBs through a simple, efficient, and low-energy-consumption chemical leaching process at room temperature, using a solution comprised of polycyclic aromatic hydrocarbons and ether solvents. The mechanism of lithium extraction is elucidated by clarifying the relationship between the redox potential and extraction efficiency. More importantly, the reclaimed active lithium is directly employed to fabricate LiFePO4 cathode with performance comparable to commercial materials. When implemented in 56 Ah prismatic cells, the cells deliver stable cycling properties with a capacity retention of ∼90% after 1200 cycles. Compared with the other strategies, this technical approach shows superior economic benefits and practical promise. It is anticipated that this method may redefine the recycling paradigm for retired LIBs and drive the sustainable development of industries.

Application of an integrated pyrolysis and chemical leaching process for pulper waste conversion into coal, hydrogen and chemical flocculating agent

This work aims to investigate the potentials of integrating slow pyrolysis and chemical leaching to recycle pulper waste (PW), the waste generated by paper mills, and consists of plastics, metallic films, and biobased polymers. The concentration of chlorine and metals is a barrier against PW valorisation by combustion or high temperature thermochemical processes. In this study, PW was tested by slow pyrolysis at 400 °C and 500 °C. Chemical leaching tests were performed by processing both chars in a 1.4 M HCl solution, at 80 °C for 2 h, to remove inorganic compounds and upgrade the char to a coal-like material. Then, precipitation by NaOH was conducted on the leachate. Slow pyrolysis led to a char mass yield around 30 %. Due to the high inorganic matter concentration (almost 36 %, mainly including chlorine, calcium, and aluminium), the char retained only 25 % of the feedstock’s chemical energy, while the remaining 75 % was recovered in the pyrogas. Leaching of the 500 °C pyrolysis char led to extract 93 % of aluminium, and almost 100 % of calcium and chlorine, resulting in an upgraded char containing 15.5 % ash, comparable to a fossil coal. By char leaching, the oxidation reaction of aluminium could produce 8 kg hydrogen per dry ton PW. The effectiveness of the precipitated compounds as flocculating agents was demonstrated, enabling a closed-loop recycling in the same paper mill. In conclusion, the proposed process demonstrated to be an effective solution to convert PW into high quality products.

Geochemical evolution of the Doushantuo economic phosphorite in Central Guizhou, South China: Quantified multi-stage metallogenic process

Economic phosphorite from Ediacaran Doushantuo Formation is the first true phosphorite giant and represents the onset of the Precambrian-Cambrian global phosphogenic event. The Doushantuo phosphorite may have deposited during the early-middle Ediacaran (ca. 632–574 Ma) according to the latest radiochronological data. Petrographically, in central Guizhou, it can be subdivided into two types of lithofacies: pristine phosphorite (micritic phosphorite, phosphatic shale, banded phosphorites) and reworked phosphorite (intraclastic phosphorite, vuggy intraclastic phosphorite, unconsolidated phosphorite). Geochemical data show that chemical/biochemical enrichment is the most effective process to condense the phosphatic sediments and obviously improve the grade of P2O5 (can reach 38.8 wt%). Hydrodynamic reworking may not play an important role in the further enrichment of P2O5 content but effectively got rid of SiO2 and Al2O3 components in phosphorite by the removal of lighter terrigenous particles and clays. Mass change calculation shows that Ca and Mg are heavily depleted in the chemical leaching process, implying it is a key process to upgrading the quality of phosphorite by separating the carbonate constituents from phosphorite. Therefore, a multi-stage metallogenic model of chemical/biochemical enrichment, hydrodynamic reworking, and chemical leaching is proposed, quantified the composition changes and elucidated the constrained factors in the formation of high-graded phosphorite. Such a metallogenic process effectively produced high-quality phosphorite deposits and bring great benefits to metallurgy.

Leaching of Ibute-Nze kaolin iron-oxide impurity with oxalic acid process optimization of dissolution conditions using response surface methodology

The goal of this research was to remove iron oxide from Ibute-Nze kaolin by dissolving the clay mineral in an aqueous oxalic acid solution and optimizing the process. The chemical composition of the raw and modified clay was determined using x-ray fluorescence, and the morphology of the solid sample was determined using a scanning electron microscope. The best conditions for the oxalic acid leaching of iron-oxides impurity from Ibute-Nze kaolin were determined using response surface methodology based on Box-Behnken design. The studies were carried out within the following process parameter ranges: 40–90 leaching temperature; 0.075-0.355mm particle size; 1–6 mol/dm3 acid concentration; 0.02–0.12 g/cm3 kaolin sample to acid ratio and 30-240 min contact time. The characterization revealed that Ibute-Nze clay is kaolinitic in nature and calcination at 750 opens more pores for its leaching. According to the analysis of variance, a second-order polynomial regression equation provided the best fitting for the experimental data. The predicted and experimental response values were shown to be correlated (R2 = 0.9276) in the experimental runs. The following were found to be the best conditions for the leaching process variables: 83.2051 leaching temperature, 0.0827mm particle size, 3.6179mol/dm3 acid concentration; 0.0287g/cm3 kaolin to acid ratio and 217.932min reaction time. The chemical leaching process was 92.6035 per cent under these conditions, which made the clay good for industrial applications.

Turbostratic Carbon/Graphene Prepared via the Dry Ice in Flames Method and Its Purification Using Different Routes: A Comparative Study.

Although the dry ice method used to synthesize turbostratic carbon/graphene is little known and used, it has significant advantages over others, such as the following: it is low cost, simple, and a large quantity of material can be obtained using some inorganic and highly available acids (which can be reused). Despite the above advantages, the main reason for its incipient development is the resulting presence of magnesium oxide in the final product. In the present work, three different treatments were tested to remove this remnant using some acid chemical leaching processes, including hydrochloric acid, aqua regia, and piranha solution. Based on the experimental evidence, it was determined that using aqua regia and combining the leaching process with mechanical milling was the most efficient way of removing such a remnant, the residue being only 0.9 wt.%. This value is low compared to that obtained with the other acid leaching solutions and purification processes (2.8–29.6 wt.%). A mandatory high-energy mechanical milling stage was necessary during this treatment to expose and dissolve the highly insoluble oxide without secondary chemical reactions on the turbostratic carbon. High-energy mechanical milling is an effective route to exfoliate graphite, which allows the magnesium oxide to be more susceptible to acid treatment. A yield of turbostratic carbon/graphene of 1 wt.% was obtained from the metallic Mg. The obtained surface area was 504.8 m2g−1; this high value resulting from the intense exfoliation can potentiate the use of this material for a wide variety of applications.

Reshaping the Module: The Path to Comprehensive Photovoltaic Panel Recycling

The market for photovoltaic modules is expanding rapidly, with more than 500 GW installed capacity. Consequently, there is an urgent need to prepare for the comprehensive recycling of end-of-life solar modules. Crystalline silicon remains the primary photovoltaic technology, with CdTe and CIGS taking up much of the remaining market. Modules can be separated by crushing or cutting, or by thermal or solvent-based delamination. Separation and extraction of semiconductor materials can be achieved through manual, mechanical, wet or dry chemical means, or a combination. Crystalline silicon modules are currently recycled through crushing and mechanical separation, but procedures do exist for extraction and processing of intact wafers or wafer pieces. Use of these processes could lead to the recovery of higher grades of silicon. CdTe panels are mostly recycled using a chemical leaching process, with the metals recovered from the leachate. CIGS can be recycled through oxidative removal of selenium and thermochemical recovery of the metals, or by electrochemical or hydrometallurgical means. A remaining area of concern is recycling of the polymeric encapsulant and backsheet materials. There is a move away from the use of fluorinated backsheet polymers which may allow for improved recycling, but further research is required to identify materials which can be recycled readily whilst also being able to withstand outdoor environments for multi-decadal timespans.

Understanding gangue acid consumption in copper sulfide heap leaching: Predicting the impact of carbonates, silicates and secondary precipitates

A geometallurgical model, linked to simple ore body characteristics, was established to understand short- and long-term gangue acid consumption (GAC) variability for a new copper sulfide chemical heap leaching process under standard metallurgical conditions, including an acid dose of 12 kg/t sulfuric acid during agglomeration at a particle size of 80% passing ¾”. Carbonate availability, or liberation, defined as a function of feed grade and alteration type, enabled the calculation of short-term GAC when combined with mineral abundance, assuming stoichiometric behavior. An adjustment to the acid balance needed to be applied for jarosite formation, which was made possible via a linear correlation, again related to carbonate feed content. The long-term GAC component of the ore could then be determined by difference, comparing data from the column program to the estimation of the two previous variables, resulting in the identification of biotite and chlorite as key drivers of long-term acid consumption during leaching. Final inputs for the three-stage approach to predict overall GAC were simplified to carbonate (CO3), magnesium (Mg), and iron (Fe), facilitating implementation in the 3D resource block model. Application of this methodology indicated that the magnitude of long-term GAC is reduced when higher levels of acid are consumed during the initial phases of processing. The study clearly shows how a holistic knowledge of the ore body can provide an in-depth understanding of future processing response, enabling key investment decisions to be made appropriately, prior to mine construction.

Effect of cleanup of spiked sludge on corn growth biosorption and metal leaching

A chemical leaching process was used for the cleanup of two municipal biosolids (MOS and BES) spiked with Cd, Cu, Zn or their mixture prior to agricultural use. Non-cleaned, cleaned and washed biosolids were compared as soil amendments for corn cultivation in greenhouse. Corn growth, biosorption and metal leaching were measured. Results showed that biosolid amendments tend to produce more aerial biomass. Cleanup and washing of BES biosolid significantly increased total biomass of roots and stalks, respectively. Regarding biosorption of metals, Cd accumulated in roots (0.06–1.13 mg kg−1) and leaves (0.06–0.63 mg kg−1), but not in seeds nor in stalks. Larger amounts of Cu were detected in roots (10.7–18.2 mg kg−1), stalks (1.29–3.78 mg kg−1) and leaves (6.77–20.2 mg kg−1). However, Zn was more accumulated in roots (17.9–74.9 mg kg−1), stalks (6.15–17.1 mg kg−1) and leaves (47.9–90.1 mg kg−1). Whereas Cd and Cu decreased in the order roots > leaves > stalks, Zn decreased from leaves > roots > stalks. Cleanup and washing of MOS and BES biosolids significantly lowered biosorption of Cd (up to 84%), Cu (up to 38%), Zn (up to 63%), and other metals. Concentrations in leachate draining into outlet water varied over time, but on average were moderately low. Significant amounts of metal leached from MOS biosolid. The effects of cleanup and washing of both biosolids on biosorption and leaching depended on the initial metallic charge and the biosolid type.

Deashing and desulfurization of subbituminous coal from the East field (Bogovina Basin, Serbia) - insights from chemical leaching

The study is focused on the determination of the most effective chemical leaching process for the simultaneous demineralization/deashing and desulfurization of subbituminous coal from the Bogovina Basin. Coal was treated for 30 min, at different temperatures, using variable concentrations of hydrochloric, nitric, acetic and citric acids; hydrogen peroxide, mixture of hydrogen peroxide and nitric acid (pH 2), as well as by the stepwise leaching process (nitric acid + mixture of hydrogen peroxide and nitric acid, pH 2). The changes in mineral composition, caused by the chemical leaching, are followed using X-ray diffraction, whereas alterations of coal organic matter are tracked by Fourier-transform infrared spectroscopy and the content of fixed carbon. Inorganic acid leaching, regardless of the temperature and acid concentration, enabled the successful deashing of coal, whereas the percent of desulfurization was insufficient. The organic acid leaching was not satisfactory for both, deashing and desulfurization. Leaching by H2O2 and H2O2/HNO3 mixture (pH 2) resulted in moderate desulfurization, but the ash reduction was low. The most suitable method for the simultaneous effective ash (78 wt.%) and the sulfur (66 wt. %) removal from Bogovina coal is the two-step leaching, combining 10 vol. % HNO3 and mixture of 35 vol. % H2O2/10 vol. % HNO3 of pH 2 at 60?C.

Cleanup of sewage sludge spiked with Cd, Cu, and Zn: Sludge quality and distribution of metals in the “soil-plant-water” system

Corn was grown under greenhouse conditions in the presence of uncleaned versus cleaned municipal sewage sludge to assess the effectiveness of a chemical leaching process that uses an inorganic acid and strong oxidants to clean biosolids (i.e., to remove metals without reducing their agronomic potential). Specifically, our study analyzed physicochemical sludge from the Montreal (MSL) wastewater treatment plant (WTP) and biological sludge from the Becancour (BSL) WTP. Both biosolids were spiked with individual metals (dry weight basis): Cd (100 mg kg-1), Cu (3000 mg kg−1), and Zn (5000 mg kg−1), or their mixture. MSL biosolid enrichment led to the solubilization of added metals and removed 84–88% of Cd, 78–79% of Cu, and 79–81% of Zn. Similarly, BSL biosolid enrichment resulted in the removal of 86–88% of Cd, 80–81% of Cu, and 88–89% of Zn. The fractional distribution of metals varied between biosolids depending on their production process, stabilization, and initial metal concentration. In the MSL biosolids, only Cu partitioning was influenced by spiking, cleanup, and washing. The three metals (Cd, Cu, and Zn) occurred either in their crystalline phase or were linked to Fe oxide, organic matter, or carbonate. In the BSL biosolids, the metals that were not in their crystalline phase were only associated with Fe oxide. This study demonstrated that 99% of Cd and Cu and 97% of Zn contents remained in the soil; however, biosolid cleanup generally decreased metal concentrations in plants, leachate, and/or soil.

Recovery of valuable metals from spent mobile phone printed circuit boards using biochar in indirect bioleaching

Improving the bioleaching efficiency of metals from spent mobile phone printed circuit boards (PCBs) in a short time has been of major interest in recent years. In this paper, a novel cheap catalyst (oak wood biochar) was used to improve the copper and nickel bioleaching efficiency from spent mobile phone PCBs. The biochar was derived from oak wood through slow pyrolysis at a low temperature of 500 °C for 1h. The results of RSM optimization indicated that the optimum conditions to maximize copper and nickel recovery were 1.6 g/L biochar and 16 g/L pulp density. The findings indicated that compared to without the presence of biochar, the leach yields of copper and nickel were high. As much as 98% of copper and 82% of nickel were leached by indirect bioleaching under optimum conditions. The better performance in the presence of biochar is due to both galvanic interactions between biochar and solid waste. The biochemical characterization of bioleaching solution suggested that the high concentration of biochar (> 1.6 g/L) led to copper absorption by functional groups on the surface of biochar. Compared to chemical leaching, the bioleaching has better performance. Under optimum conditions, the copper and nickel recovery by indirect bioleaching was 36% and 64% more than that by chemical leaching. Also, it is found that biochar has a positive effect on the chemical leaching process. Therefore, in this paper, the function of biochar was elaborated not only in bio-hydrometallurgy but also in the hydrometallurgy process.

An effective process for the recovery of valuable metals from cathode material of lithium-ion batteries by mechanochemical reduction

To improve the recovery of valuable metals (Li, Co, Ni, and Mn) from the cathode material of waste lithium-ion batteries (LIBs), a mechanochemical reduction technique is proposed in this research. The cathode material was mechanochemically ball milled with various reductive agents as a pretreatment and then subjected to a chemical leaching process for the recovery of valuable metals. The influence of mechanochemical ball milling parameters and leaching conditions on metals recovery, and the changes in physicochemical properties of cathode materials before and after mechanochemical ball milling were investigated. The results show that Zinc (Zn) powder was an effective co-grinding reagent forimproving the recovery of valuable metals from cathode materials. The crystal structure of the cathode material gradually shifted to an amorphous state with an increase in ball milling speed and time. Mn(IV) and Co(III) in the cathode material were mechanochemically reduced to Mn(III) and Co(II) after co-grinding with Zn, which was beneficial to their leaching. The activation energies of Ni and Co decreased from 30.47 KJ/mol and 31.99 KJ/mol to 5.58 KJ/mol and 7.15 KJ/mol, respectively. The leaching rates of Li, Ni, Co, and Mn increased from 72.0%, 42.5%, 31.2%, and 15.2% to 99.9%, 96.2%, 94.3%, and 91.0% under the optimum conditions of a cathode material to Zn powder mass ratio of 7:3, a rotational speed of 500 rpm, a milling time of 2 h, and a ball-to-powder mass ratio of 19: 1. This research presents a highly efficient and feasible approach for recovering valuable metals from waste LIBs.

Effective Utilization of Coal Processing Waste: Separation of Low Ash Clean Coal from Washery Rejects by Hydrothermal Treatment

ABSTRACT Handling and disposal of high volume of fine coal tailings is a biggest challenge for coal washeries. Separation of clean coal by density separation and flotation shows limited yields of 23–28% and 13–14% respectively. Chemical leaching process has a challenge with the formation of insoluble salts. The present investigation aimed to separate clean coal by a combination of chemical-physical separation technique, i.e. alkaline hydrothermal process followed by density separation. Hydrothermal extraction of humic substance causes dissociation of coal aggregated structure (Mineral-Maceral-Pore structure), thus improves the separation. Experiments performed as per design of experiments and reduced design of experiments, where 100 µ particle size, 50% (w/w) pulp density, 4.5% KOH (w/w), and 140°C reaction temperature found to be optimum, at which 16.2% ash clean coal at 40.7% yield and humic acid by-product at 18.3% yield were obtained. Use of swelling agent such as tetrahydrofuran shown negative impact on clean coal recovery. Material balance and cost data were presented to show the techno-commercial viability of this technology.

Recovery of rare earth elements from coal fly ash through sequential chemical roasting, water leaching, and acid leaching processes

The majority of rare earth elements (REEs) in coal fly ash (CFA) are associated with the aluminosilicate glassy phase, hindering their solubility in the acid leaching process. In this study, a sequential chemical roasting, water leaching, and acid leaching process was developed for the recovery of REEs from CFA. The effect of several roasting additives on the transformation of CFA phases into water or acid soluble phases was first studied. The reaction conditions for chemical roasting were selected based on a thermodynamic analysis. The selected reaction conditions were then validated experimentally. NaOH and Na2CO3 were the most effective additives to break the glassy phases to sodium silicate and sodium aluminosilicate, which can then be readily dissolved in water or acid. The reactions with NaOH was found to be spontaneous at ambient temperatures, while the reactions with Na2CO3 were spontaneous at elevated temperatures. Water leaching was very effective for the dissolution of the sodium silicate product, removal of the majority of silica, and for turning the glassy phases into a porous structure. As a result, mass transfer limitations were reduced, and acid could easily diffuse into the particles, dissolve the majority of remaining, and extract REEs along with other elements such as Al. This process significantly enhanced the REE recovery to 79% and 89% using NaOH and Na2CO3 roasting, respectively, compared to 20% REE recovery in baseline acid leaching.

Utilization of secondary agricultural products for the preparation of value added silica materials and their important applications: a review

Silica and its compounds are widely used in the industries like pharmaceutical, chemical, agricultural, and research sectors. Generally, silica is obtained from natural precursors available in the form of silicates. Extensive use of silica makes it necessary to find the new sources and methods of synthesis. Secondary agricultural products and by-products like rice husk, sugar cane bagasse, corn cabs, wheat straw, rice straw, grasses, and coconut husk contains considerable amount of silica. The methods for the extraction of silica includes burning of materials to make it ash, acid treatment, base treatment, ionic liquids, and sol-gel methods. Among all the methods, sol-gel is an important method of silica synthesis. Highly pure and desirable silica materials can be synthesized by the chemical leaching process, where metallic impurities can be removed by the acid treatment. This review describes the selected secondary agricultural products and their utilization for the value-added silica synthesis.

Stirred-tank and heap-bioleaching of shredder-light-fractions (SLF) by acidophilic bacteria

End-of-life vehicles are usually crushed in large scaled shredders in order to increase the surface area for further processing. During the shredding process, the so-called shredder-light-fraction (SLF), containing mainly plastics and other synthetic polymers, is discharged. However, this fraction still contains up to 20% metals such as iron (Fe), copper (Cu), nickel (Ni) and zinc (Zn), making them an interesting substrate for bioleaching and source of high-value metal traces. To develop a bioleaching process for metal recovery from shredded fractions, two experimental approaches including a heap- and a stirred-tank reactor were tested. The acidophilic, iron- and sulfur-oxidizing bacteria Acidithiobacillus ferrooxidans and the iron-oxidizing bacteria Leptospirillum ferrooxidans were investigated as pure and co-culture for their ability to solubilize trace metals. A. ferrooxidans proofed to be the more suitable bioleaching organism resulting in leaching efficiencies of up to 100% for Zn and Ni in batch experiments. Furthermore, in the stirred-tank reactor using A. ferrooxidans about 100, 80 and 55% of Cu, Zn and Ni have been recovered from 50 g l−1 of the SLF, respectively. Bioleaching of 3000 g SLF in the heap-reactor resulted in a recovery of about 100% Zn, 60% Cu and ~ 55% Ni after 33 days without the need of external sulfuric acid addition for pH regulation. The high leaching efficiencies in both experimental setups confirmed the potential of bioleaching for a sustainable metal recovery from shredder residues (i.e. SLF) making it a profitable, eco-friendly alternative to conventional chemical leaching processes.

An integrated approach combines hydrothermal chemical and biological treatment to enhance recycle of rare metals from coal fly ash

Coal fly ash rich in rare metals accounts for a large amount of solid waste released from coal-fired power plants. However, rare metals, the components of coal fly ash with the highest economic value, are not fully recycled due to the lack of an effective, low-cost approach. Therefore, it is urgent to develop a new approach, aiming at increasing the recycling efficient, decreasing the cost and strengthening the high economic value of fly ash. Here, we developed an integrated approach combines hydrothermal chemical treatment process (HTCP) and biological leaching process (BLP) to improve recycle of rare metals from coal fly ash. The results showed that the one-step bioleaching method could obtain more kinds of rare metals and dramatically improve bioleaching rate after hydrothermal-alkali treatment (HAKT) using Acidithiobacillus thiooxidans. After HAKT, the leaching rates of metals V, Sr, Y, La, and Ce were higher than those of the untreated pure fly ash (UPFA) with the maximum values of 51%, 70.52%, 37.48%, 64.77%, and 76.37%, respectively; after hydrothermal-acid treatment (HTAT), the bioleaching rates of rare metals Ni, Sr, and Y, were higher than those of the UPFA with the maximum values of 70.24%, 20.26%, and 34.54% respectively. The results also showed that, for most rare metals, the recovery rate following HAKT was higher than that following HTAT. This result can be demonstrated via analyzing adsorption quantity, adsorption kinetics and diffusion model of fly ashes for A.thiooxidans. Our study provides an important pathway for recycling rare metals from coal fly ash.

Ex-ante Life Cycle Assessment of Bioleaching in Indium Recovery from LCD-Waste

ABSTRACTIn light of growing demand and pollution versus a finite amount of resources, electronic waste recycling is a way towards material circularity. New recycling technologies not only face technical difficulties but also need to overcome challenges of feasibility in both economic and environmental aspects. An assessment regarding environmental impacts and economic factors at the early development stages of such technologies is necessary to ensure a successful establishment. A batch lab-scale process using bioleaching to win indium from electronic waste was drafted using recent research in the field. Life Cycle Assessment (LCA) was used to determine the environmental impacts in four different categories at the lowest Technology Readiness Level (TRL). The findings were then compared to two existing chemical leaching processes to put them in perspective. Results show that the electricity consumption is the major contribution to environmental impacts. The assumed bioleaching process has a higher environmental impact than the two chemical processes due to its high duration and resulting high electricity consumption. However, the research has also proven, that an LCA during the conceptual phase has a high uncertainty due to lack of data and knowledge about the process.

An XAS study of silver species evolution in silver-catalysed chalcopyrite bioleaching

The catalysing effect of Ag+ or Ag nanoparticle (AgNp) on chalcopyrite (bio)leaching at 30 °C was studied in this paper, and the change of Ag speciation was investigated by Ag K-edge X-ray Absorption Near-edge Spectroscopy (XANES). The solution studies indicate that the addition of 0.2% Ag (fraction of Ag to chalcopyrite) can effectively improve the dissolution of chalcopyrite in both bioleaching and chemical leaching. Further increasing the silver concentration to 1% only marginally increase the rate of chalcopyrite dissolution compared with the rate with 0.2% Ag added. No obvious difference has been found between the catalytic effect of Ag+ and AgNp (Silver Nanoparticle). XRD studies indicate the formation of jarosite, elemental sulfur in both bioleaching and chemical leaching. However, the speciation of Ag in the residual cannot be confirmed by XRD analysis. Ag k-edge XANES spectra show that Ag+ or AgNp have completely changed to Ag2S within 7 days in both bioleaching and chemical leaching process. In-situ XANES analysis shows that the Ag+ or AgNp changed to Ag2S very rapidly in the absence of Fe3+. In contrast, AgCl was firstly detected with the presence of 3 g/L Fe3+, which only partially changed to Ag2S in about 36 h, which is likely because the stability of Ag2S was decreased by Fe3+.