Hydrometallurgy Process Research Articles

Direct synthesis of nickel oxide nanoparticles from pregnant leach solution by using electrodeionization and Fenton processes in the presence of EDTA

This paper presents the results of a novel study on the direct synthesis of nickel oxide nanoparticles from a synthetic pregnant leach solution (PLS) as a middle stage product of hydrometallurgy process of nickel production. To increase the nickel proportion in the initial PLS, electrodeionization was utilized in the presence of EDTA to form an anionic complex ([Ni-EDTA]2−) with Ni2+ cations, allowing their separation from cobalt cations through the EDI process. Subsequently, the Fenton process was applied to synthesize nickel oxide nanoparticles from the complex containing solution. The proposed hybrid process was conducted in two different modes of one-stage and two-stage EDI process followed by the Fenton process. Different analysis methods including AAS, XRD, FE-SEM, and ICP were used for qualitative and quantitative evaluations. The analyses’ results revealed that by implementing one-stage EDI process followed by Fenton process resulted in producing nickel oxide nanoparticles with an average particle size of 45 nm and purity of about 98 %. Also, it was seen that about 81 % of initial nickel content of the initial PLS was recovered as nickel oxide nanoparticles. In the case of two-stage EDI process, 100 % pure nickel oxide nanoparticles with average size of 55 nm and recovery of 65 % was produced. The results showed that the innovative hybrid EDI/Fenton process can be considered as a promising approach for direct synthesis of high purity nickel oxide nanoparticles from PLS. However, it should be noted that there was a trade-off between purity of nickel oxide and nickel recovery from PLS.

Green Approaches to Extractive Metallurgy: A Novel Synthesis of Sustainable Practices

The realm of extractive metallurgy, a cornerstone for diverse industrial applications, has traditionally grappled with environmental challenges stemming from conventional extraction methods. This thorough literature review delves into the realm of innovative green approaches within extractive metallurgy, with the overarching goal of synthesizing sustainable practices. The introduction casts a spotlight on the environmental quandaries associated with traditional metallurgical practices, underscoring the imperative for ecologically friendly alternatives. The research methodology meticulously entails a comprehensive review of peer-reviewed literature, applying stringent criteria to handpick studies that delve into sustainable metallurgical practices. The results and discussion section intricately categorizes and dissects an array of green approaches in metal extraction, including bioleaching, ionic liquids, supercritical fluid extraction, green hydrometallurgy, electrochemical methods, and hybrid processes, providing nuanced insights into their efficacy and sustainability. Through the lens of case studies, the study sheds light on recent strides made by industries that have wholeheartedly embraced these sustainable practices, with a keen focus on unraveling their consequential environmental and economic impacts. Moreover, the study conscientiously addresses the challenges encountered in the adoption of green metallurgy and adeptly identifies latent opportunities for further development in this transformative field. The findings resonate with a resounding call for the widespread adoption of sustainable practices within extractive metallurgy, emphasizing their profound implications for both industrial application and the trajectory of future research endeavors. This expanded exploration underscores the pivotal role of environmentally conscious approaches in reshaping the landscape of extractive metallurgy, paving the way for a more sustainable and responsible future.

Polymer-Based Extracting Materials in the Green Recycling of Rare Earth Elements: A Review.

Rare earth elements (REEs) are becoming increasingly important in the development of modern and green energy technologies with the demand for REEs predicted to grow in the foreseeable future. The importance of REEs lies in their unique physiochemical properties, which cannot be reproduced using other elements. REEs are sourced through mining, with global exploration of additional commercially viable mining sites still ongoing. However, there is a growing need for recycling of REEs due to the current supply of REEs not matching the growing demand, the environmental impact of REE mining and processing (the so-called "balance problem"), and the generation of large volumes of harmful electronic waste (e-waste). Industrial REE processing is mainly carried out by hydrometallurgy processes, particularly solvent extraction (SX) and ion exchange (IX) technologies. However, these methods have a significant environmental impact due to their intensive use of harmful and nonsustainable reagents. This Review highlights the development of approaches involving polymer-based extracting materials for REE manufacturing as more sustainable alternatives to current industrial REE processing methods. These materials include supported liquid membranes (SLMs), solvent impregnated resins (SIRs), macro and micro capsules, polymer inclusion membranes (PIMs), and micro polymer inclusion beads (μPIBs). Polymer-based extracting materials have the advantage of more economical regent usage while applying the same extractants used in commercial SX, enabling applications analogous to the current industrial process. These materials can be fabricated by a variety of methods in a diverse range of physical formats, with the advantages and disadvantages of each material type described and discussed in this Review along with their applications to REE processing, including e-waste recycling and mineral processing.

Cyclability Improvement of Recycled Graphite Materials in Lithium-Ion Batteries Via Conductive Polymer Coating

In recent years, lithium-ion batteries have been widely adopted in electric vehicles and electronics. However, the growing number of retired lithium-ion batteries poses a significant environmental challenge, generating substantial material waste and potential pollution. In most commercial batteries, graphite is the prevalent choice for anode material, owing to its high electrical conductivity and mechanical stability. Therefore, recycling graphite from spent lithium-ion batteries is a potential solution to eliminate the waste and meet the increasing demand.While considerable attention has been directed toward recovering metallic components of the spent lithium-ion batteries, limited effort has been dedicated to recycling graphite. Some previously developed methods include the pyrometallurgy process and hydrometallurgy process. However, due to high energy consumption and environmental pollutions, these methods have not been applied in large scales. Additionally, graphite particles have experienced various aging mechanisms during charge and discharge cycles, such as the formation of a solid electrolyte interface (SEI) and the intercalation of solvent molecules, potentially leading to structural alterations and degradation. Hence, it is advisable to implement surface treatment to enhance capacity stability if the recycled graphite does not perform optimally following the recovery treatment.In this study, we developed a simple process to recycle spent graphite utilizing aqueous and organic wash with N-Methylpyrrolidone (NMP) and toluene, followed by surface coating with the conductive polymer poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic ester) (PFM). The surface coating served as a protective layer of graphite particles and a charge transport agent to enhance conductivity. The morphologies and structures of the pristine, recycled, and PFM-coated recycled graphite samples were measured by X-ray diffraction (XRD) and scanning electron microscope (SEM) analysis.To investigate the impact of employing PFM as a binder, electrochemical tests were done using anodes with both recycled graphite and PFM-coated recycled graphite. In recycled-graphite||NMC532 full cell testing, cells with PFM-coated recycled graphite exhibits higher coulombic efficiency (>99.90%) than cells without PFM coating at a rate of 0.33 C. A capacity retention of 77.49% was achieved for PFM-coated cells after 300 cycles, whereas the ones without coating have a capacity retention of 70.21% in average. Rate tests were also conducted on both the cells with and without PFM-coating. It shows that both types of cells support high-rate cycling. About 85% of charge capacity was delivered for cycling at 1 C for both cells with and without PFM-coating.Overall, the recycling method can be easily operated with minimal waste production, low energy consumption, and low economical costs. The PFM coating on the recycled graphite particles leads to enhancement of mechanical strength and efficiency in battery cycling.Fig. A, The process scheme of recycling graphite; B, Pictures of an electrode from spent lithium-ion batteries (left) and an electrode fabricated with recycled graphite (right); C, Capacity retention of recycled graphite without PFM coating (blue) and with PFM coating (green); D, Coulombic Efficiency of recycled graphite without PFM coating (blue) and with PFM coating (green). Figure 1

Desalination of mother liquor generated from the precipitation of lithium carbonate during the recycling of retired lithium ion battery

Generally, hydrometallurgy process is adopted in factory to recover valuable metal from anode materials in lithium ion battery. The mother liquor generated from the precipitation of lithium carbonate in this process is often managed by evaporative crystallization process which is high energy-consuming and expensive. The methodology employed in this research involves pretreatment and bipolar membrane electrodialysis to partition salts within the mother liquor into acids and bases, thereby achieving cost savings. The findings reveal that a significant 76.5 % reduction in COD is achievable through the application of potassium permanganate and activated carbon in the treatment of the mother liquor. Subsequently, the treated mother liquor can be transfer to electrodialysis process for further treatment. During this process, desalination of the mother liquor occurs, leading to the decomposition of sodium sulfate into sulfuric acid and sodium hydroxide. Analysis of the experimental data reveals that optimizing the initial concentrations of sulfuric acid and sodium hydroxide within the acid and alkali collection chambers, along with the application of elevated electric current density and maintaining a high pH value of the mother liquor, yields improvements in current efficiency and concomitant reductions in energy consumption. Under optimal conditions, the current efficiency of acid and alkali preparation is 52.53 % and 62.12 % respectively, along with energy consumption of acid and alkali preparation is 8.68kWh/kg and 8.99kWh/kg respectively. The pretreatment and bipolar membrane electrodialysis process is low-energy consumption and inexpensive, facilitating a reduction in processing expenses to $6.659 per ton of mother liquor.

Research on the optimal ratio of improved electrolytic manganese residue substrate about Pennisetum sinese Roxb growth effects

Electrolytic manganese slag (EMR) is a solid waste generated in the manganese hydrometallurgy process. It not only takes up significant land space but also contains Mn2+, which can lead to environmental contamination. There is a need for research on the treatment and utilization of EMR. Improved EMR substrate for Pennisetum sinese Roxb growth was determined in pot planting experiments. The study tested the effects of leaching solution, microorganisms, leaf cell structures, and growth data. Results indicated a substrate of 45% EMR, 40% phosphogypsum, 5% Hericium erinaceus fungi residue, 5% quicklime, and 5% dolomite sand significantly increased the available phosphorus content (135.54 ± 2.88 μg·g−1) by 17.95 times, compared to pure soil, and enhanced the relative abundance of dominant bacteria. After 240 days, the plant height (147.00 ± 0.52 cm), number of tillers (6), and aerial dry weight (144.00 ± 15.99g) of Pennisetum sinese Roxb increased by 5.81%, 200%, and 32.58%, respectively. Analyses of leaves and leaching solution revealed that the highest leaf Mn content (46.84 ± 2.91 μg·g−1) being 3.38 times higher than in pure soil, and the leaching solution Mn content (0.66 ± 0.13 μg·g−1) was lowest. Our study suggested P. sinese Roxb grown in an improved EMR substrate could be a feasible option for solidification treatment and resource utilization of EMR.

A green recyclable process for selective recovery of Li and Fe from spent lithium iron phosphate batteries by synergistic effect of deep eutectic solvent and oxygen

This work designs a new method for recovering spent LiFePO4 cathode materials, aiming to address issues with traditional hydrometallurgy processes such as complex operations, low lithium recovery rates, and high wastewater discharge. The method involves using a deep eutectic solvent (DES) composed of chloroacetic acid and ethanol, and oxygen as an oxidant, for the cooperative leaching of LiFePO4 powders. Based on the acidic nature of the DES and the oxidizing properties of oxygen, LiFePO4 was undergone an in-situ transformation into solid FePO4, while 100% of lithium was dissolved in the DES with high selectivity. The FePO4 product can be recovered by filtration, and the addition of oxalic acid to the filtrate allows for lithium recovery. Importantly, the structure of the DES remained unchanged after use, allowing for three recycling cycles without a significant decrease in LiFePO4 recovery efficiency. This process is environmentally friendly, with no generation of acidic or alkaline wastewater, and boasts high metal recovery rates, showcasing its huge potential for application.

Comparison of life cycle assessment of different recycling methods for decommissioned lithium iron phosphate batteries

The rapid development of China’s new energy industry has dramatically increased the sales of electric vehicles. Frequent charging and discharging will lead to a decline in the service life of the battery, and consequently a large number of lithium iron phosphate (LFP) batteries are discarded. Batteries contain a large number of toxic substances, and the wrong recycling method will produce a large amount of pollution. In China, the question of how to improve the technology for recycling LFP batteries more environmentally friendly is still under investigation. Life Cycle Assessment (LCA) methodology was employed to analyze the environmental impacts of the whole process of recycling LFP batteries by the conventional recycling technologies used in traditional factories in China. The results of the study show that the hydrometallurgy process is superior to the physical recycling process though environmental benefits of the physical recovery process with complete recovery are better than those of hydrometallurgical process with incomplete recovery. Incomplete hydrometallurgical methods release more toxic substances into the environment, whereas traditional physical process only need to focus on the pollution caused by the battery crushing process. The results of the calculation and analysis provide a new direction for the technological update of power battery recycling in China.

Synthesis of Fe3O4/ZnO from Zinc Dross Waste as an Active Material for Dye-Sensitized Solar Cells

Abstract Zinc oxide (ZnO) is an attractive active material in emerging solar cell technologies, such as dye-sensitized solar cells (DSSCs), due to its high stability and electron mobility. The activity of ZnO can be enhanced by adding a small amount of impurity, such as iron oxide. Since zinc dross contains Zn as the primary element and Fe as the minor element, it can be used as a precursor to obtain iron oxide/ZnO. In this study, ZnO was prepared from zinc dross through a hydrometallurgy process and utilized as the active material for DSSCs. For comparison, pure ZnO was also prepared using zinc acetate as the precursor through the sol-gel process. X-ray diffraction (XRD) results show that pure ZnO was observed in the sample prepared using zinc acetate as the precursor, while ZnO with a Fe3O4 phase was observed in the sample prepared using zinc dross. Scanning electron microscopy (SEM) examinations reveal that the thickness of ZnO layer that was deposited onto fluorine-doped tin oxide glass was 11.3 ± 0.4 μm. The solar cell performance tests showed that the presence of dyes that adsorbed on ZnO synthesized from zinc dross could increase the efficiency of DSSCs up to 26.5 times while the ZnO synthesized from zinc acetate has 11.5 higher efficiency compared to the non-sensitized counterpart. Moreover, ZnO from zinc dross exhibited 1.2 times higher efficiency than ZnO from pure Zn precursor, indicating the feasibility of converting zinc dross waste into valuable materials.

A highly efficient clean hydrometallurgy process for gold leaching in a Fenton oxidation assisted thiourea system

Clean hydrometallurgy processes, formed by “oxidant-ligand” systems, present promising strategies for gold leaching to mitigate the environmental impact of cyanidation. In this work, a Fenton oxidation-assisted thiourea system was proposed, employing reactive oxygen species (ROS, generated from Fenton reaction) as oxidant and thiourea as the ligand, respectively. By precise parameters control, 100% leaching of gold was rapidly achieved within 30 min from a roasted gold concentrate, highlighting extremely fast kinetics. Furthermore, this system was optimized by incorporating nitrilotriacetic acid (NTA) as an additive, which significantly reduced the thiourea consumption and produced the same gold leaching (100%, 60 min). Experimental results demonstrate that NTA lowers the solution potential (ORP) and eliminates the side reactions between iron ions and thiourea, thereby reducing thiourea decomposition. Surprisingly, the combination of Fenton oxidation and thiourea showed a high selectivity of the generation of ROS, with superoxide radical anion (•O2−) dominating, singlet oxygen (1O2) co-existing, but hydroxyl radical (•OH) absenting. Importantly, the moderate •O2− primarily contributes to gold leaching, which is generated through a chain reaction pathway between iron complex and H2O2 (Fe3+-Ligand+H2O2 → Ligand-Fe3+-OOH → Fe2+-Ligand+•O2−). Besides, the generation process of •O2− can be regulated by adding NTA. This work presented a prospective way in establishing the clean hydrometallurgy processes for efficient gold leaching.

Silicon and Quartz Recovery and Purification from Waste Quartz Crucible Ash with a Combined Process of Electric Separation and Hydrometallurgy

Silicon and Quartz Recovery and Purification from Waste Quartz Crucible Ash with a Combined Process of Electric Separation and Hydrometallurgy

A Gaussian-mixture-model based peak splitting method in X-ray fluorescence for high concentration ratio solution

Simultaneous detection of multi-heavy metal ions in zinc sulfate solution facilitates the zinc hydrometallurgy process control. X-ray fluorescence spectrometry is widely used for composition detection due to its high detection speed and no sample pre-treatment. However, the high matrix ion-to-trace impurity ion ratio in zinc sulfate causes severe spectral overlap, hindering pure peak area acquisition—a vital feature in ion concentration detection. To address this, a peak-splitting method based on the Gaussian mixture model was proposed. Initially, two ion mixing spectra were obtained with optimized reagents. Subsequently, Gaussian models were established for the characteristic peak regions with varying distributions. Finally, the proposed model was combined with Chaotic Sparrow Search Algorithm to handle the overlapping peaks. The experimental results demonstrated superior stability and additivity compared to other methods. All coefficients of determination between single peak areas and ion concentrations exceeded 0.99, confirming the method's efficacy in resolving heavily masked overlapping peaks.

Separation of TiO2 and Fe2O3 from Indonesia Ilmenite Minerals and their Application as Photocatalysts for Eriochrome Black‐T Dye Degradation

AbstractAnatase‐TiO2 and α‐Fe2O3 were successfully separated from Indonesia ilmenite minerals using a modification of the hydrometallurgy process. Sodium salt was used as an initiated roasting before hydrochloric leaching. The study investigated parameters that affect separation such as mass ratios of sodium salt to ilmenite and leaching temperature. The results revealed that Ti composition in residue‐TiO2 increased to 76 % while Fe‐composition in filtrate‐Fe2O3 was 87 %. The XRD diffractogram analysis confirmed that main phase formed in residue of separation was anatase‐TiO2 whereas in hydrolysed of filtrate from separation was hematite. Both residue‐TiO2 and filtrate Fe2O3 had high thermal stability. The photocatalytic activity of anatase‐TiO2 and α‐Fe2O3 showed about 97 % and 85 % of Eriochrome Black‐T dye solution was degraded, respectively, when conducted to 4 hours of UV light irradiation. Photocatalytic kinetics study of anatase‐TiO2 and α‐Fe2O3 in degradation process followed pseudo‐first order with reaction rate at 0.0144 and 0.0070 min−1, respectively.

Effect of inorganic anions on hydrothermal removal of impurities Fe/Al from Cu-bearing polymetallic leachate.

Hydrometallurgy recycling of heavy metals from electroplating sludge is of hot spot in recent decades. Such recycling was tedious in the separation of impure Fe/Al prior to heavy metals from acid leachate after sludge dissolution. Herein, a facile hydrothermal route was developed to separate Fe/Al from Cu-bearing leachate. The results showed that when the leachate was directly hydrothermally treated at 160°C in the presence of nitrate and ethanol, Al/Cu were stable in the leachate, but nearly 100% Fe was removed as hematite nanoparticles. With the addition of chloridion, the removal efficiencies of Fe/Al/Cu did not change apparently, but the corresponding precipitate was akageneite, not hematite. By replacing chloridion with sulfate, nearly 100% Fe and 98.6% Al were separated as natrojarosite/natroalunite block, while the Cu loss was only 1.7%. However, with the supplementary of phosphate, the Fe/Al removal achieved nearly 100%, but the Cu removal also achieved by 92.6%. The thermodynamic analysis showed that Cu was precipitated rapidly via the phosphate/Cu oxyhydroxide route by adding phosphate but removed slightly via the coordination route on the Fe/Al precipitates with the addition of nitrate, chloridion, and sulfate. In summary, Fe was effectively separated as hematite, akageneite, natrojarosite, and phosphate halite, in the presence of nitrate, chloridion, sulfate, and phosphate, separately. But the removal of Al as natroalunite and AlPO4 only started by adding sulfate and phosphate, respectively. Such results enabled a short hydrometallurgy process to effectively recycle heavy metals from electroplating sludge.

The Pitfalls of Deep Eutectic Solvents in the Recycling of Lithium‐Ion Batteries

The exponentially increasing demand for lithium‐ion batteries and their limited lifetime lead to a significant increase in spent batteries. With the goal to address the sustainability and recyclability to minimize negative effects for the environment, an efficient process is vital to recover valuable materials from spent batteries by recycling. In this regard, deep eutectic solvents (DESs) have attracted huge interest, due to their unique ability to efficiently extract valuable metals from spent batteries, while also being rendered greener and more cost‐effective compared to current pyrometallurgy and/or hydrometallurgy. However, the DES approach also has its own set of challenges and drawbacks, which hinder the widespread use in the industry, including its restricted recyclability, high viscosity, low thermal and chemical stability, complex chemistry, as well as limited scalability. In this perspective, it is claimed that ongoing future research on the recycling of lithium‐ion batteries requires the exploration of alternative processes including modification of current hydrometallurgy processes, if the consistent improvements cannot be achieved in DES system for recycling valuable elements.

Recovery of NixMnyCoz(OH)2 and Li2CO3 from spent Li-ionB cathode leachates using non-Na precipitant-based chemical precipitation for sustainable recycling

The interest in recycling spent lithium-ion batteries (Li-ionB) has surged due to the rising demand for valuable metals (e.g., Co, Ni, Li and Mn) and concerns about environmental repercussions emanating from conventional battery waste disposal. Conventional precipitation-based hydrometallurgy recycling processes utilise Na-based or metal-based precipitants. The Na, from Na-based precipitants, is present in high concentrations in the process effluent since they are not recovered during the recycling process. The Na-rich effluent cannot be discarded since it doesn't meet environmental regulations as per the U.S. Environmental Protection Agency (EPA) (2023) therefore creating a storage and disposal problem. It is therefore imperative to utilise non-Na-based precipitants to eliminate the effluent disposal problem. This paper focuses on the recovery of NixCoyMnz(OH)2 and Li2CO3, main precursors for Li-ionB cathode production, from a typical spent Li-ionB cathode (NMC 532) using non-Na precipitant-based chemical precipitation. This study reports NixCoyMnz(OH)2 and Li2CO3 recovery from spent Li-ionBs for closed-loop Li-ionB cathode recycling through an integrated hydrometallurgy and chemical precipitation process. Through the utilisation of leachate solutions comprising 2 M H2SO4 + 6 vol.% H2O2, and a 75 g/L S/L ratio and conducting leaching for 120 min at a temperature of 60 °C and IS of 350 rpm, the recovery efficiency of 98.1 % for Li, 97.1 % for Co, 96.1 % for Ni, and 95.7 % for Mn. The pH of the NMC leachate was initially adjusted to 5 to precipitate Fe, Al and Cu impurities. Thereafter, active metal species (Ni, Mn and Co) were precipitated at a pH of 13 as Ni0.5Co0.2Mn0.3(OH)2 composite microparticles by adding LiOH precipitant. Thereafter, the Li-rich resultant liquor was further used to recover the Li by adding 3.4 mol of CO2 bubbled at 0.068 mol (CO2)/L.min and 40 °C for 45 min. The Li2CO3 precipitates were separated from the suspension through filtration followed by washing using deionised water and hot air drying. The reaction time is 45 mins, and the agitation speed is 150 rpm. Through this multi-stage precipitation process, >98 % of Ni, Co, Mn and > 91 % of Li can be recovered in the form of Ni0.5Mn0.3Co0.2(OH)2 and Li2CO3 respectively. The process exhibits great potential for recovery of valuable materials from spent Li-ionBs. The recovered Ni0.5Co0.2Mn0.3(OH)2 and Li2CO3 materials will be used as precursors in the anhydrous NMC cathode production process.

Bifunctional solid-state ionic liquid supported amidoxime chitosan adsorbents for Th(IV) and U(VI): Enhanced adsorption capacity from the synergistic effect

Uranium and thorium of symbiotic relationship commonly appear in one kind of raw or spent ore. The simultaneous enrichment toward both metals in the first step is essential during many hydrometallurgy processing. Therefore bifunctional solid-state ionic liquid supported amidoxime chitosan (ACS) adsorbents were developed to simultaneously adsorb the two metal from the aqueous solution. The adsorption capacity of the bifunctional adsorbents toward uranium and thorium were significantly superior to the ionic liquid-free amidoxime chitosan, obviously proving the synergistic effect. For both uranium and thorium, the adsorption capacity in the consequence of ACS-[N4444][DEHP], ACS-[N4444][EHEHP], ACS-[N1888][DEHP] and ACS-[N1888][EHEHP] prove the steric effect and PO bonding played important roles in the adsorption. Study on isotherms and kinetics demonstrated the adsorption of ionic liquid-ACS adopted monolayer and chemical way. The ΔGo of very small negative values highlighted ionic liquid-ACS were prone to adsorb uranium and thorium. The study showed feasibility of bifunctional solid-state ionic liquid supported amidoxime chitosan adsorbents for Th(IV) and U(VI).

Selective recovery of gold and silver from electronic wastes through a sequential process of Qalkari and room-temperature hydrometallurgy

This work was focused on the selective recovery of gold and silver from electronic wastes using a sequential process of pyrometallurgy (Qalkari) and room-temperature hydrometallurgy. In the first step, electronic wastes underwent Qalkari recycling, yielding tablets containing precious elements (Qalkari furnace product) and melting slag (Qalkari furnace waste). In the subsequent hydrometallurgy phase, the nitric acid concentration and the input solid amount were optimized for the effective room-temperature recovery of gold. Due to the successful separation of precision elements and disturbing substances in Qalkari, the gold recovery efficiency of 99.99% was obtained at the acid concentration of 50% (v/v) and the solid input of 15% (w/v). Afterwards, HCl, NH4Cl, and NaCl were used for silver recovery from the Qalkari-processed gold-recovered leaching solution, leading to the efficiency of 99.99%. But NH4Cl was recognized as the most effective precipitant as it promises the most enhanced potential for the possible subsequent recovery of palladium. In conclusion, this study draws the effectiveness of Qalkari in recycling electronic wastes, with a significant impact on the efficiency of succeeding room-temperature hydrometallurgical processes for gold and silver recovery within a reasonable leaching time.

Co-recovery of Mn and Fe from pyrolusite and copper slag with hydrometallurgy process: Kinetics and leaching mechanisms.

With the shortage of high-quality raw materials and increasingly strict environmental regulations, the recovery of metals from copper slag and pyrolusite has become a research hotspot. A novel method for simultaneously extracting Mn and Fe from pyrolusite and copper slag has been proposed. Under the optimal conditions (Copper slag / Pyrolusite = 2, H2SO4 = 2M, liquid-solid ratio = 10, T = 90 ℃, holding time = 60min), the leaching efficiencies of Mn and Fe can reach 98.28% and 99.04%, respectively. In addition, the treated residue containing 60.04 wt% SiO2 can be used as a raw building material. Through chemical kinetics and mineralogical transformation analyses, Fe2SiO4 in copper slag decomposes to release Fe2+, which can reduce and leach Mn from pyrolusite. The unreacted shrinkage nuclear reaction model under the control of the surface chemical reaction is the most suitable model to describe the process, and when the apparent activation energy is 35.50kJ/mol, the apparent rate equation is: [Formula: see text].

Migration behavior of germanium and its related elements in zinc hydrometallurgy process

Lead-zinc sulfide ore is one of the raw materials for the recovery of strategic germanium resources. Due to the complexity of its mineralization and the diversity of elements, the occurrence and migration of germanium and its related elements in the process of zinc hydrometallurgy is still a mystery. This leads to the recovery efficiency of germanium is always in a disappointing state, which seriously reduces the economic benefits and resource recovery rate in the process of germanium recovery, and limits the development of some cutting-edge industries. Therefore, in view of the above problems, based on the properties of germanium compounds in lead–zinc sulfide minerals, this study analyzed the occurrence state and quantity of germanium in the products of each stage in the process of zinc hydrometallurgy by ICP, XRD, FT-IR, SEM, XPS, Raman spectrum and TG, so as to reveal the reaction behavior and migration law of germanium compounds in the process of zinc hydrometallurgy. The results indicate show that the two roasting will lead to the mutual transformation of GeO2 crystal form between soluble and insoluble, especially in the process of reduction and volatilization of zinc leaching residue. The phenomenon of soluble GeO2 to insoluble GeO2 is particularly significant, and the germanium-containing silicate cannot be reacted in the whole process. In addition, zinc blende, zinc ferrite, tin dioxide and other substances that exhibit isomorphism with germanium compounds will carry germanium into lead slag due to their low solubility. Finally, in view of the problems existing in the current germanium recovery process, positive solutions are proposed to introduce green additives in the two roasting stages to improve the phase of germanium, and to add oxidants or reducing agents in the leaching stage.