Leaching Mechanism Research Articles

Leaching of heavy metal(loid)s from historical Pb–Zn mining tailing in abandoned tailing deposit: Up-flow column and batch tests

This study aims to investigate the water-leaching characteristics of heavy metal(loid)s (HMs) from historical Pb–Zn mine tailing of an abandoned tailing deposit in eastern China. Up-flow column and batch leaching tests were conducted at different liquid-to-solid (L/S) ratios to estimate the releases of HMs and investigate the controlling mechanisms. Calcite and silicate were the dominant minerals in the tailing and the HMs contents followed the order of Zn (2371 mg/kg) > Pb (2061 mg/kg) > Cu (109 mg/kg) > Cr (47.8 mg/kg) > As (15.9 mg/kg) > Cd (5.1 mg/kg). Moreover, considerable fractions of Pb, Zn, and Cd existed in the acid-soluble forms (41–47%). Column and batch leaching tests consistently showed that limited quantities (<0.002%) of HMs could be leached from this historical tailing. In particular, variations in column conditions (e.g., length, flow rate, and initial saturation) significantly affected the release fluxes from the columns but had a relatively limited effect on the leaching mechanisms. The estimated results of HM release suggested that the leaching process was predominantly solubility-controlled and the dissolution of Ca-bearing minerals (e.g., calcite) primarily controlled the release of HMs. The studied tailing had a limited impact on the quality of the surrounding aquatic environments because the water-leaching concentrations of HMs were generally lower than the Chinese standards for drinking water. Only for Pb, the leaching results in column tests were significantly lower than those in batch tests; whereas the results in column tests for other HMs were comparable to those in batch tests to a certain extent. Based on the column test results, the amounts of HMs potentially released from the abandoned tailing deposit (height, 10 m; footprint area, 30,000 m2; tailing dry density, 1.9 × 103 kg/m3) followed a decreasing order of Zn (4.2 × 105 kg) > Cu (2.3 × 104 kg) > Pb (1.4 × 104 kg) > Cr (2.3 × 104 kg) > Cd (1.6 × 103 kg) > As (1.2 × 103 kg) over the 75-year assessment period (corresponding to an L/S ratio of 10 L/kg with an annual precipitation of 1500 mm).

A comprehensive study on the extraction of transition metals from waste random access memory using acetic acid as a chelating solvent

The reduced lifespan of electrical and electronic equipment results in the generation of electronic waste (e-waste), one of the fastest-growing solid waste streams. A systematic and practical approach is needed for the sound management of e-waste and metal recovery. We report an effective and comprehensive study for metal extraction from waste random access memory using acetic acid as a chelating solvent. Under the optimized conditions, Cu, Pb, Zn, and Ni extraction was 97.5%, 88.2%, 79.3%, and 83.7%, respectively. Subsequently, the kinetic study revealed that the diffusion-controlled mechanism governs the metal extraction. The calculated activation energy for Cu, Pb, Zn, and Ni are 11.3, 12.6, 17.6, and 13.3 kJ/mol, respectively, which indicates Cu-extraction could be more favourable than the rest of the metals. Furthermore, the metal leached salt was recovered from the leached solution and was thoroughly characterized to understand the nature of the compound formed and the corresponding leaching mechanism. It was observed that the leached salt could be comparable with standard copper acetate, revealing the acetic acid's ligation property. Finally, the Cu-content in the cathode was recovered as 92.7 wt% from the leached solution using the electrowinning process. We believe, our contribution can be a paradigm for promoting the effective extraction of transition metals from waste random access memory.

Selective leaching of lithium ions from LiFePO4 powders using hydrochloric acid and sodium hypochlorite system

AbstractHigh‐efficiency and selective leaching of lithium ions from spent lithium iron phosphate (LiFePO4) batteries is currently an urgent problem to be solved. Hydrochloric acid and sodium hypochlorite were used as acidic media and oxidant for recycling LiFePO4 powders based on the stoichiometric ratio. The effect of operation conditions on leaching performance was investigated. The leaching yield of Li and Fe were higher than 95% and lower than 0.1% within 20 min at 15°C. In addition, X‐ray diffraction, X‐ray photoelectron spectroscopy, scanning electron microscopy, and laser particle size analysis characterizations were applied for revealing the selective leaching mechanism, the results of which indicated that the crystal structure of powders remained basically unchanged during the leaching process. Finally, an efficient and cost‐effective recycling process for LiFePO4 powders was proposed, and lithium carbonate products with purity higher than 99.7% were obtained. The proposed recycling process shows strong industrial application potential for LiFePO4 powders.

Influence of Biochar Application on Soil Nitrate Leaching and Phosphate Retention: A Synthetic Meta-analysis

How to control non-point source pollution caused by leaching of soil nitrate and phosphate from agricultural land is currently an extremely important global environmental problem facing human society. Biochar, a carbon-rich material produced from various organic feedstocks using thermochemical technologies, has attracted much attention because of its great potential in soil improvement. Many studies have been carried out to investigate the effects of biochar application on the retention, utilization, and use efficiency of soil nutrients. Unfortunately, the results from individual experimental studies regarding the effects of biochar on soil nitrate leaching and phosphate retention differed greatly. Consequently, the underlying mechanisms related to reduction in nitrate and phosphate leaching/retention by biochar application, as well as the appropriate preparation conditions (or biochar type), remain unclear. In this study, the effects of biochar application on soil nitrate leaching and phosphate retention were systematically examined using the method of Meta-analysis (MA); based on these results, the inhibition mechanisms for nitrate leaching and enhancement mechanisms for phosphate retention were also explored. In total, 149 paired datasets from 41 articles and 180 paired datasets from 36 articles were collected for nitrate and phosphate, respectively. The MA results demonstrated that, regardless biochar and soil properties, biochar application could significantly reduce soil nitrate leaching by 37.1% and increase soil phosphate retention by 20.8%. Furthermore, the C/N ratio of biochar, heating treatment temperature, and biochar application amount indicated a significant effect on the response of soil nitrate leaching to biochar application. The specific surface area of biochar, heating treatment temperature, and soil organic carbon content had a significant effect on the response of soil phosphate retention to biochar application. Based on the results from MA, the potential mechanisms of soil nitrite leaching reduction and phosphate retention enhancement were further explored from different perspectives. Lastly, the biochars prepared from straw or wood materials and pyrolyzed at a medium temperature (400-600℃) or high temperature (>600℃) were recommended for reducing soil nitrate leaching and improving soil phosphate retention, respectively. In sum, the results presented in this study can provide a scientifically theoretical basis for the practical application of biochar in the control of soil non-point source pollution of nitrate and phosphate.

Response of Nd3+ and Sm3+ precipitating into rhabdophane and the leaching mechanism of associated monazite ceramics

AbstractRhabdophane has been considered an important permeable reactive barrier to isolate groundwater radionuclides, and evaluating its precipitation response to different species of radionuclide in acid solutions is critical. In this work, the effects of pH values on the precipitation behavior of Nd3+ and Sm3+ into La‐rhabdophane are systematically investigated. Some specific issues such as ions removal, precipitation reaction kinetics, and crystal growth affected ions incorporation are discussed in detail, along with uncovering the veil of the Ln (La, Nd, and Sm) leaching mechanism of associated La0.666Nd0.167Sm0.167PO4 monazite ceramic based on dissolution experiments and density functional theory. The results reveal that Nd3+ and Sm3+ can be removed more than 98% in pH = 1 solution within 12 h, whereas uneven precipitation process to form unexpected stoichiometric ratio of rhabdophane has been observed in 30–50 nm short crystal. Grain growth effects based on spark plasma sintering can contribute to homogenize the materials composition with obtaining La0.666Nd0.167Sm0.167PO4 monazite ceramics. Furthermore, the binding energy of Ln–O in (1 0 0) surface of monazite plays an important role in controlling the leaching stability of Ln3+, associated with the leaching activities are energetically favorable in the order of La &gt; Nd &gt; Sm for La0.666Nd0.167Sm0.167PO4 monazite.

Transformation and leaching behavior of Pb in hazardous waste incineration fly ash after thermal treatment with addition of Fe2O3

This study investigated the leaching behavior of Pb in hazardous waste incineration fly ash (HWIFA) after adding Fe2O3 thermal treatment and revealed the leaching mechanism of Pb from the perspective of phase transformation. The static leaching results showed that at 600 °C-1300 °C, with the addition of Fe2O3 increased, the Pb leaching toxicity continued to decrease. The dynamic results indicated that as the thermal treatment temperature was higher than 1100 °C, the addition of Fe2O3 can effectively inhibit the dynamic leaching of Pb in HWIFA. Meanwhile, the inhibition effect was not very closely related to the amount of Fe2O3. The addition of Fe2O3 can react with PbO to form PbFe12O19, which has a better stability. The appearance of PbFe12O19 was the main reason for adding Fe2O3 to enhanced the immobilization of Pb. However, the amount of Fe2O3 should be carefully controlled to avoid an excessive reducible fraction of Pb in the thermal treated HWIFA, which will affect the long-term stability of Pb.

A classical modelling of abandoned mine tailings' bioleaching by an autochthonous microbial culture

The aim of this study was to study and model the bioleaching of abandoned mine tailings at different pulp densities 1–20% w/v by using an autochthonous mesophilic microbial culture. Because of the importance of the ferrous-iron oxidation as sub-process on the bioleaching of sulphide mineral ores, the ferrous-iron oxidation process by the autochthonous microbial culture was studied at different ferrous-iron concentrations. A mathematical model fitted to the experimental results and the main kinetic and stoichiometric parameters were determined, being the most relevant the maximum ferrous-iron oxidation rate 5.1 (mmol Fe2+/mmol C·h) and the biomass yield, 0.01 mmol C/mmol Fe2+, values very similar to that of mixed cultured dominated by Leptospirillum strains. This autochthonous culture was used in the bioleaching experiment carried out at different pulp densities, obtaining a maximum metal recovery in the tests carried out at 1% w/v, recovering a 90% of Cd, 60% of Zn, 30% of Cu, 25% Fe and 6% of Pb. Finally, the different leaching mechanisms were modelled by using the pyrite as ore model obtaining a bioleaching rate of 0.316 mmol Fe2+/(L·h) for the direct mechanisms and a bioleaching rate for the indirect and cooperative leaching mechanisms of 0.055 Fe2+/(L·h).

Patterns of long-term variations of nitrate concentration – Stream discharge relationships for a drained agricultural watershed in Mid-western USA

Nitrate Concentration–discharge (C-Q) relationshipshave been used to infer nitrate sources, storage, reactions, and transport in watersheds, and to reveal key processes that control runoff chemistry. Yet, studies on long-term nitrate C-Q relationships are limited due to scarce high frequency (e.g., daily) concentration data. In this paper, using a long-term high-frequency dataset (1976–2019) comprising stream flow and nitrate concentrations, we quantitatively analyzed the long-term variations of event-scale hysteresis patterns (quantified by hysteresis index, HI, and flushing index, FI) to infer the leaching mechanisms of nitrate in an artificially drained agricultural watershed in Mid-western U.S. Our results revealed that most events exhibited anti-clockwise behaviors (HI < 0), regardless of whether nitrate was flushed or diluted during events. This means that water with high levels of nitrate-N reaches the stream network slower than water with lower nitrate concentrations. Long-term mean FI was close to zero but had strong seasonal patterns with dilution patterns observed during Winter and Summer, and flushing patterns during late Spring and Fall. The consistently negative HI values regardless of the FI value gave a strong indication of the preponderant role of the near-drain zone that usually exhibits accelerated leaching and less accumulation of nitrate in the soil profile in these drained agricultural watersheds. Both HI and FI depicted strong but opposite seasonality because of weather patterns and agricultural activities, particularly N fertilization. Overall, our findings suggest a little evidence of the role of deep groundwater and instead a strong evidence of the role of subsurface drainage as the primary pathway for nitrate transport in drained agricultural watersheds. Therefore, artificial drainage could dampen N legacy caused by the historically intensive N fertilization in drained agricultural landscapes.

Biological resistance and leaching mechanism of alder camellias prepared by impregnation with Tanalith E and Celcure AC 500

Dünya nüfusunda meydana gelen artışa bağlı olarak orman ürünlerinin kullanımı yaygınlaşmıştır. Ancak, artan orman ürünleri ihtiyacını ekosistemi tehlikeye sokmadan karşılamak dikkat edilmesi gereken en önemli husus olmaktadır. Bu bakımdan ormanlardan elde edilen ağaç malzemelerin kullanım sürelerinin arttırılması araştırmacıların ilgi duyduğu konular arasında yer almaktadır. Bu çalışma ile ülkemizde doğal olarak oldukça fazla yayılış alanı gösteren, Karadeniz bölgesinde bolca bulunmasına rağmen endüstriyel olarak bir değeri bulunmayan kızılağacın (Alnus glutinosa subsp. barbata) kullanım ömrünün arttırılarak endüstriyel alanlara kazandırılması hedeflenmiştir. Çalışmada referans ürün olarak endüstride sıklıkla kullanılan sarıçam (Pinus sylvestris L.) odunundan elde edilen emprenyeli kamelyalar kullanılmıştır. Tanalith E ve Celcure AC 500 ile emprenye edilmiş kızılağaç ve sarıçamdan hazırlanan kamelyalar dış ortam koşullarına maruz bırakılmıştır. Daha sonra örneklerin biyolojik dayanımı (Coniophora puteana ve Poria placenta) ve yıkanma mekanizması incelenmiştir. Çürüklük testi EN 113 standardına göre, yıkanma testi AWPA E11 standardına göre yapılmış, yıkanmış su örnekleri ICP-MS cihazı ile bakır analizine tabi tutulmuştur. Elde edilen sonuçlara göre çürüklük testinde emprenyeli ağaç malzemenin ağırlık kaybı kontrol gruplarına göre çok daha düşük oranda tespit edilmiştir. Bununla birlikte, en düşük yıkanma ve bakır oranları ise sarıçam odunu esaslı kamelya örneklerinde belirlenmiştir.

Genome mining to unravel potential metabolic pathways linked to gallium bioleaching ability of bacterial mine isolates.

Gallium (Ga) is considered a high-tech Critical Metal, used in the manufacture of several microelectronic components containing either gallium arsenide (GaAs) or gallium nitride (GaN). The current high demand for this critical metal urges the development of effective recovery processes from secondary resources such as mine tailings or electronic recycling material. The importance of bioleaching as a biotechnological process to recover metals prompted this study, where an integrative approach combining experimental and genomic analysis was undertaken to identify potential mechanisms involved in bioleaching ability and strategies to cope with high metal(loid)s concentrations in five mine isolates. The Clusters of Orthologous Group (COG) annotation showed that the “amino acid transport and metabolism” [E] was the most predominant functional category in all genomes. In addition, the KEEG pathways analysis also showed predicted genes for the biosynthetic pathways of most amino acids, indicating that amino acids could have an important role in the Ga leaching mechanism. The presence of effective resistance mechanisms to Ga and arsenic (As) was particularly important in GaAs bioleaching batch assays, and might explain the divergence in bioleaching efficiency among the bacterial strains. Rhodanobacter sp. B2A1Ga4 and Sphingomonas sp. A2-49 with higher resistance, mainly to As, were the most efficient bioleaching strains under these conditions. In bioleaching assays using cell-free spent medium Arthrobacter silviterrae A2-55 with lower As resistance outperformed all the other stains. Overall, higher efficiency in Ga leaching was obtained in bioleaching assays using GaAs when compared to GaN.

Rich microbubbles modifying the leaching mechanism of aluminum and aluminum nitride of secondary aluminum dross in sodium aluminate solution

An understanding of the mechanisms of reactive Al and AlN in a sodium aluminate solution contributes to the safe and effective utilization of secondary aluminum dross (SAD). This study demonstrates that the slurry temperature increased exponentially with an increase in the SAD dosage. Synergistic kinetic phenomena in the form of a large dosage and high temperature occurred initially in relatively stable microbubbles and later in the slurry. The leaching efficiencies of pure Al and AlN powders were greater than that of Al and AlN in SAD, respectively. Meanwhile, the leaching rate became higher for Al in SAD but lower for AlN in SAD compared to that of pure Al and AlN powder. The AlN particles in SAD were covered by Al(OH)3 precipitated from the saturated solution in the bubbles. As a result, the relatively stable microbubbles with a thick border accelerated the reaction of Al and AlN and produced a saturated solution thereby changing the leaching efficiency and leaching rate of AlN in SAD. The embedded Al and AlN grains in the SAD, relatively stable microbubbles, and the SAD particles covered by Al(OH)3, synergistically changed the leaching mechanism. These results provide further understanding of the reaction mechanism of rich bubbles and facilitate the optimization of the comprehensive utilization of SAD.

Enhancement and mechanisms of micron-pyrite driven autotrophic denitrification with different pretreatments for treating organic-limited waters

Pyrite-driven autotrophic denitrification (PAD) represents a cheap and promising way for nitrogen removal from organic-limited wastewater, which has obtained increasing attention in recent years. However, the limited denitrification rate and unclear mechanism underlying the process have hindered the engineered application of PAD. This study aims to shed light on the impacts of different pretreatments (i.e., ultrasonication, acid-washing and calcination) on micron-pyrite surface characteristics, denitrification performance and biofilm formation during PAD in batch reactors. A series of solid-phase analyses revealed that all pretreatments could significantly promote biofilm attachment on pyrite granules, but impacted the proportion, distribution and chemical oxidation state of sulfur (S) and iron (Fe) at varying degrees. Batch tests showed that ultrasonication and acid-washing could enhance the total nitrogen reduction rate by 14% and 99%, and decrease the sulfate production rate by 51% and 42%, respectively, when compared with untreated pyrite. Microbial community analysis indicated that Thiobacillus and Rhodanobacter dominated in PAD systems. Two types of indirect mechanisms (i.e., contact and non-contact) for pyrite leaching may co-occur in PAD system, resulting in ferrous iron (Fe2+), thiosulfate (S2O32−) and sulfide (S2−) as the main electron donors for denitrification. A PAD mechanism model was proposed to describe the PAD electron transfer pathway with the aim to optimize the engineered application of PAD for nitrogen removal.

Preparation of titanium mineral from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching

Titanium mineral was prepared from vanadium titanomagnetite concentrates by hydrogen reduction and acid leaching. The leaching behaviors of elements like Fe, V, Mn, Al, Mg, Ca, and Si were highly related to the reduction degree. The phase compositions of the reduced materials and the leached residues were analyzed by XRD to identify the effect of reduction degree on the leaching mechanisms. The results showed that the concentrates were reduced to iron metal and titanomagnetite at 800−1000 °C for 0.5 h, and the above elements of Fe and impurities were easily leached. Deeper reduction led to the formation of ilmenite and Mg−Al spinel, which hindered leaching. Mg-bearing anosovite appeared in the further reduced materials, and the leaching rates of impurities became much lower. An upgraded titanium mineral with a normalized TiO2 grade of 70.3% was achieved by H2 reduction at 850 °C for 0.5 h and acid leaching, which is a satisfactory Ti resource for the preparation of titanium oxide by sulfate process.

Genetic Relationship between Granite and Fluorite Mineralization in the Shuanghuajiang Fluorite Deposit, Northern Guangxi, South China: Evidence from Geochronology, REE, and Fluid Geochemistry

Hydrothermal vein-type fluorite deposits are the most important metallogenic type of fluorite deposits in South China, most of which are closely related to granitoid in space; however, the genetic relationship between granitoid and fluorite mineralization remains controversial. The Shuanghuajiang fluorite deposit in northern Guangxi of South China is a typical vein-type fluorite deposit hosted in a granite pluton, with the orebodies occurring within brittle faults. Zircon U-Pb dating of the hosting Xiangcaoping granite yields an emplacement age of 228.04 ± 0.76 Ma (MSWD = 0.072). Fluorite Sm-Nd dating yields an isochron age of 185 ± 18 Ma. The new age data indicate that the fluorite deposit was precipitated significantly later than the emplacement of the hosting Xiangcaoping granite pluton. The fluorite and granite exhibit similar rare earth element (REE) patterns with negative Eu anomalies, suggesting that fluorine (F) was derived from the granite. The fluorite fluid inclusions show a homogeneous temperature mainly ranging between 165 °C and 180 °C. Salinity is typically less than 1% NaCl eqv, while the δ18OV-SMOW and δDV-SMOW values are between −5.2‰–−6.1‰ and −17.35‰–−23.9‰, respectively. These indicate that the ore-forming fluids were a NaCl-H2O system with medium-low temperature and low salinity, which is typical for meteoric water. Given the combined evidence of geochronology, REE, and fluid geochemistry, the mineralization of the Shuanghuajiang fluorite deposit is unrelated to magmatic-hydrothermal activity but achieved via hydrothermal circulation and leaching mechanisms. Our study presents a genetic relationship between the fluorite deposit and granitoids based on an example of northern Guangxi, providing a better understanding of the genesis of hydrothermal vein-type fluorite deposits in granitoids outcropping areas.

Recovery of rare earth elements from coal flyash using deep eutectic solvents as leachants and precipitating as oxalate or fluoride

This paper presents results of the study on the applicability of deep eutectic solvents (DES) for the recovery of rare earth elements (REE) from coal flyash (CFA) assaying REE 0.22%. The combination of DES used was choline chloride (ChCl) with lactic acid (LA) and ChCl with para toluene sulphonic acid monohydrate (pTSA). Besides the synthesis and characterisation of the DES systems, detailed study on their flow behaviour as a function of temperature and viscosity was also made. Screening studies indicated better leaching performance when the molar ratio of ChCl:pTSA and ChCl:LA were 1:1 and 1:2 respectively. Influence of various process parameters like temperature, solid to liquid ratio, reaction time and dilution ratio of DES with water on the leaching efficiency of REE and other impurity ions was investigated using the best molar ratio combination identified for the two systems. Performance of the DES systems were compared with that of individual hydrogen bond donors (HBD) namely, LA and pTSA, hydrogen bond acceptor (HBA) viz. ChCl as well as with H2SO4. The dissolved REE from the DES medium were selectively and quantitatively recovered by chemical precipitation. The DES systems gave REE leachability of about 85–95%. The mixture of ChCl:pTSA(1:1) showed higher leach recovery and faster kinetics compared to ChCl:LA(1:2). Both DES systems gave a decisive 5–8% higher leachability than the individual HBDs (LA and pTSA) and HBA (ChCl) which constitute the respective eutectic. Comparison of leaching performance of REE using DES with that of H2SO4 indicated significant enhancement, about 35%, with the former over the inorganic acid. A probable leaching mechanism of REE with the DES used is also proposed. Precipitation of REE from the DES medium was near complete with oxalic acid and NaF reagents.

Selective extraction of precious metals in the polar aprotic solvent system: Experiment and simulation

The traditional hydrometallurgical process is the mainstream technology to recover precious metals from e-waste, which usually adopts strong acid/base and strong oxide with high environmental cost and energy consumption. In the present study, the selective extraction of precious metals was simulated and experimented with DMF as the solvent and Cl− ions provided by CaCl2 and CuCl2 (oxidizing agent). The leaching and precipitation rates of precious metals (Au, Ag, Pd) can reach more than 98% under optimization conditions. Kinetic data shows that the control model of the leaching process on precious metals was determined by linear fitting of the shrinkage model. The complex trace precious metals were extracted selectively using dimethylglyoxime and deionized water as precipitators by the leaching-precipitation-cycle method. Meanwhile, the waste liquid produced by this reaction process could be cyclically utilized. Furthermore, the leaching mechanism of precious metals was proposed. DMF could be complexed with the metals as well as coordination ions (Cl−), which can reduce the redox potentials. Cu(II) could be easily reduced to Cu(I) in the DMF system due to the higher second ionization energy of copper, which is not influenced by the hydration effect, thus shifting the equilibrium to the metal leach side. Oppositely, the addition of water promoted the conversion of Cu(I) to Cu(II) since the higher hydration energy of Cu(II) compensates for the second ionization energy. This research opens up a new path of sustainable development and provides basic theory and practical experience for environmentally friendly recovery of precious metals from e-waste.

Insight into leaching of rare earth and aluminum from ion adsorption type rare earth ore: Adsorption and desorption

Clay minerals are inferred to be the primary host materials for ion-exchangeable rare earth in ion adsorption type rare earth ore (IAREO). During the rare earth leaching process, the adsorption and desorption reactions of the cations controlling the leaching process continue to occur at the clay minerals-leaching agent solution interface. In order to understand the leaching mechanism and behavior of rare earth and co-leached aluminum, adsorption, competitive adsorption, and desorption experiments were carried out using kaolin as a typical clay mineral. The powerful electrostatic attraction and concentration driving forces facilitate the adsorption of cations. The adsorption ability and competitive adsorption ability of cations depend on their charge, hydration radius, and hydrolysis properties, and decrease in the order of La3+, Y3+, Al3+, Mg2+, and NH4+. The desorption of rare earth and aluminum is positively affected by the concentration-driving force exerted by high concentrations of Mg2+ and NH4+, with the order of the desorption ability being opposite to the adsorption ability. However, unspecified interactions between clay mineral particles enhanced by high-concentration desorbents, especially by Mg2+ than NH4+, will adversely affect desorption reactions, which result in lower desorption efficiencies of rare earth and aluminum obtained with magnesium sulfate compared to those obtained with ammonium sulfate at high concentrations. Solid-phase Al(OH)3 generated at a high peak aluminum concentration leads to a considerably delayed aluminum efflux, thereby partially separating the rare earth from aluminum during the actual column leaching process. To advance the mining technology of IAREO by selectively improving the rare earth leaching efficiency with minimal leaching agent consumption, higher charged cations with concentrations limited to suitable levels should be preferred as leaching agents.

Selective extraction of lithium from spent LiNixCoyMnzO2 cathode via in-situ conversion of ethylene glycol in subcritical water system

The resources scarcity and explosive growing demand of lithium have made the selective extraction of lithium from spent lithium-ion batteries (LIBs) more and more widely concerned. Yet the current lithium recovery routes still suffer the problems of complex process, low efficiency and unfriendly environment. In this study, a strategy of selective lithium extraction from spent LiNixCoyMnzO2 cathode with ethylene glycol (EG) in subcritical water system is proposed. The in-situ conversion pathway and lithium extraction mechanism in this new system are investigated in detail. Benefit from the reducibility of EG and the dynamic strengthening of the subcritical water system, more than 99% of lithium can be selectively extracted into the solution under the optimal conditions. The leaching kinetics show that the selective leaching process is controlled by chemical reactions and the leaching mechanism suggests that EG plays a dual role of reducing and donating protons in subcritical environment. Furthermore, the lithium-containing leachate can be applid to prepare Li2CO3 products with high purity, and the transition metals (Ni, Co, Mn) in the lithium extraction residue are recovered by acid leaching without adding reducing agent. This process puts forward a innovative idea for preferentially extracting lithium from spent LIBs and even lithium-containing wastes, which has the significant advantages of high efficiency, environmental protection and simplicity.

Simultaneous stabilization/solidification of arsenic in acidic wastewater and tin mine tailings with synthetic multiple solid waste base geopolymer

Stabilization/Solidification (S/S) is considered as a feasible technology for the treatment of arsenic (As) in acidic wastewater (AW) and tin mine tailings (TMTs); however, high cost, high carbon footprint, and strict reaction conditions are the main limitations. Herein, a novel alkali-activated geopolymer material (AAGM) for S/S As was synthesized by combining AW, TMT, gypsum (GP), and metakaolin (MK). At room temperature, an initial As concentration of 3914 mg/L, a NaOH content of 4.98%, and an MK content of 20% decreased the As leaching concentration to 1.55 mg/L (<5 mg/L). The main S/S mechanisms of As included physical encapsulation of C-(A)-S-H and geopolymer structures, ion exchange of ettringite, and formation of Fe–As and Ca–As precipitates. Further studies showed that increasing initial As concentration and MK content facilitated the formation of Ca–As precipitates and C–(A)–S–H gels. The semi-dynamic leaching tests revealed that the leaching mechanism of As was surface wash-off. The effective diffusion coefficients of the samples were less than 10−13 cm2/s, and the respective leachability indexes were greater than 9, indicating that AAGM was effective in preventing the leaching of As. Therefore, this study provides a green and low cost solution for the synergistic utilization of AW, TMT, GP, and MK.

Enhancement of leaching copper by organic agents from waste printed circuit boards in a sulfuric acid solution

Leaching copper from waste printed circuit boards (WPCBs) by hydrometallurgy has always been a hot research topic. At atmospheric pressure, hydrogen peroxide (H2O2) was used as an oxidant to study the leaching behavior of copper from WPCBs in sulfuric acid (H2SO4) solution with ethylene glycol (EG). To elucidate the leaching mechanism of copper from WPCBs, the effect of various parameters on the leaching performance with or without EG was investigated. The results showed that the copper leaching process from WPCBs in the presence of EG was found to conform to the ash diffusion-controlled shrinking core model according to the kinetic curve and a activation energy of 18.38 kJ/mol. Moreover, the presence of EG strengthened the stability of H2O2, improved dispersity and increased electrical activity of WPCBs, which enhanced the leaching of copper from WPCBs in the high leaching temperature (>323.15 K). As a result, apart from the fact that the optimal leaching concentration of H2O2 was reduced by the addition of EG, the improved copper leaching efficiency from WPCBs was achieved by the addition of EG, as demonstrated by a maximum copper leaching efficiency of 98.01% and a maximum loss rate of 29.68%. Besides, the mineralogical and morphological properties of leaching residue validated the leaching results. Based on this, our findings confirmed the enhanced leaching performance of copper from WPCBs by EG, which benefited for the efficient recovery of copper from WPCBs.