Leaching Mechanism Research Articles

Synergistic leaching of lithium from clay-type lithium ore using sulfuric acid and oxalic acid

With the escalating market demand for lithium, the development and efficient utilization of lithium resources have become crucial. This study introduced a method for leaching lithium from raw clay-type lithium ores using a composite sulfuric acid oxalic acid system. The experimental results revealed that the optimal conditions for the leaching process included roasting temperature of 600 °C, sulfuric acid concentration of 0.8 mol/L, liquid-solid ratio of 5 mL/g, leaching temperature of 90 °C, leaching duration of 90 min, and oxalic acid dosage of 2 g. Under these conditions, the leaching efficiency of lithium reached 93.45 %. The structural changes during the lithium leaching process and leaching mechanism were analyzed by XRD, SEM, TOF-SIMS. It was found that the minerals after mixed-acid leaching showed a loose morphology, a decrease in the average particle size, and a significant increase in the specific surface area as well as the pore volume, leading to improved lithium leaching efficiency. Furthermore, the mechanism underlying the mixed-acid leaching of lithium from clay-type lithium ores was explored. According to this mechanism, sulfuric acid first dissociated H+, which disrupted the mineral structure, allowing further destruction by oxalic acid. During this process, Li+ was continuously replaced by H+ and reacted with C2O42− dissociated from oxalic acid to form water-soluble Li2C2O4.

Investigation of the emission and leaching behavior of characteristic heavy metals in sintered bricks prepared from oil-based drill cutting residues

Oil-based drill cutting residues (OBDCR) are hazardous waste generated by the thermal desorption of oil-based drill cuttings. Recently, the utilization of OBDCR as building materials has attracted extensive attention, but the environmental risks during preparation and long-term usage remained unclear. In this study, OBDCR with a 40 % (wt./wt.) mixing ratio was used to prepare sintered bricks, and the emission and leaching behaviors of Ba, Mn, Zn, Ni, Cr, and Pb were investigated. The results indicated that the addition of OBDCR in bricks showed insignificant increase in the emission of Ba, Mn, Zn, Ni, and Cr, whereas the emission of Pb slight decreased from 10.5 to 8.6 μg/m3. The volatilization rates of these heavy metals were considerably low, with Ni showed the highest volatilization rate of only 1.45 % in OBDCR bricks. Moreover, the leaching behavior of Ba, Mn, Zn, Ni, Cr, and Pb in bricks were studied. The results indicated that surface wash-off was the main controlling leaching mechanism of Ba and Cr, whereas the leaching of Mn, Zn, Ni, and Pb was controlled by diffusion. The Elovich and second-order kinetic equation were identified as the leaching models for Mn, Zn, Pb, and Ni. The life-time leaching predictions of OBDCR bricks indicated that the leaching of Ni and Mn after 10 and 20 years of leaching were 0.1529, 0.257, 0.1530, and 0.274 mg/L, respectively, exceeding the relevant standards. Therefore, the leaching risks of Ni and Mn should be emphasized when using OBDCR bricks with a 40 % OBDCR mixing ratio.

High-Value Resource Utilization of Steel Waste to Prepare Uniform Micronano LiFePO4/C Cathode Material.

Steel slag is a promising secondary resource necessitating recycling and high-value utilization. This study innovatively converted steel slag into micronano FePO4 and well-performing LiFePO4/C through a selective two-step leaching process followed by fast coprecipitation in HMCRR under superior mass transfer, and a subsequent in situ carbothermal reduction afterward, thereby realizing a waste-to-resource conversion pathway. Besides, a metal leaching mechanism was proposed based on comprehensive slag composition analysis, affirming the process selectivity. Thermomechanical analysis for precipitation underscored the importance of controlling reaction pH to prevent the formation of impure sediments. Leveraging efficient leaching and superior mass transfer during precursor preparation, the further-made carbon-coated LiFePO4/C derived from steel slag exhibited favorable morphology and enhanced discharge capacity, especially at high rates, owing to fast ion diffusion kinetics, minimized Li+ migration distance, and improved structure stability. Notably, the discharge capacity could reach 167.44, 153.56, and 119.62 mAh/g at 0.1, 1, and 10 C, respectively.

A novel acid-free combined technology to achieve the full recovery of crystalline silicon photovoltaic waste

To achieve the global carbon neutrality commitment, photovoltaics, a clean and renewable source of energy, is increasingly deployed. Photovoltaic panels are core components of photovoltaic systems. As these panels reach the end of their life, recovering the photovoltaic waste becomes crucial. Currently, strong acid reagents are commonly used in the recovery of silver from crystalline silicon photovoltaic waste, posing environmental risks and restricting the industrialization of their recycling. In this study, a novel acid-free technology to achieve the full recovery of crystalline silicon photovoltaic waste was proposed. A pyrolysis process was first conducted for decapsulation, with carbon dioxide being the main gas component at 60.64 %. Next, bioleaching technology was employed to leach silver from waste crystalline silicon photovoltaic cells. The silver leaching rate in a single leaching cycle reached 44.7 %. Meanwhile, the mechanism of silver leaching was further analyzed. Finally, high-velocity fluid frictional separation, a technique that uses high-speed fluid flow to separate material, was chosen to obtain silicon wafers. The reclaimed silicon samples had a total thickness variation of 6.64 µm to11.62 µm, with average carrier lifetimes exceeding 4.9 µs, higher than that obtained by wet etching. This study is expected to advance the industrialization of the recovery of photovoltaic waste, which is also beneficial for the sustainable development of the photovoltaic supply chain.

The synergistic interaction of fungi with different structural characteristics improves the leaching of lithium from lepidolite

The aim of this study was to explore the improvement of lithium leaching from lepidolite by microbial co-culture, focusing on the synergistic effect of different structural fungi in improving the leaching performance of biological systems. The results showed that in the single leaching experiment, the multicellular fungi and the unicellular yeast showed weak effects. Multicellular fungus is limited by insufficient EPS secretion, while unicellular yeast is non-mycelial organisms with weak acid production capacity and limited effect on minerals. However, in the combined leaching experiment, the interspecific collaboration promoted the synthetic and metabolic activity of the two strains, resulting in changes in the type and content of organic acids, polysaccharides, proteins and humus. The content of citric acid reached the highest value of 16.98g·L-1 at about 22 d, and the EPS secreted by unicellular yeast promoted the mycelium adhesion and mineral wrapping of multicellular fungi. The combined action of the two enhanced the effects of acidification, complexation and mycelium destruction, and improved the leaching effect. This study revealed the synergistic metabolic mechanism of lepidolite leaching by fungi with different structures, verified the effectiveness of microbial co-culture to improve the leaching rate, and provided a basis for industrial application. In addition, the use of co-culture technology has a positive impact on commercial production and environmental protection.

Efficient leaching of valuable metals from spent lithium-ion batteries using green deep eutectic solvents: Process optimization, mechanistic analysis, and environmental impact assessment

The accumulation of over 11 million tons of spent lithium-ion batteries (LIBs) by 2030 highlights a critical environmental challenge posed by their large-scale retirement. The efficient recycling valuable metals from spent LIBs can both reduces environmental impact and mitigates the pressing issue of metal resource scarcity. In this context, deep eutectic solvents (DESs) have become a promising option as an eco-friendly solvent, exhibiting great potential for recycling spent LIBs. Therefore, this work proposed an innovative green DES system consisting of choline chloride (ChCl), DL-malic acid (MAL), and glycerol for the efficient leaching of valuable metals from spent LIBs. Comprehensive experiments were conducted to determine the optimum leaching conditions (130 °C, 60 g/L, MChCl:MAL:Glycerol of 1:1:3, 3 h), achieving high leaching efficiencies of 94.6% for Ni, 96.8% for Co, 93.8% for Mn, and 96.4% for Li. Through characterization techniques, kinetics studies, and density functional theory (DFT) calculations, the leaching process was predominantly governed by surface chemical reaction (1-(1-x)1/3 = kt) within the shrinking core model, exhibited activation energies of 49.89 kJ/mol, 47.66 kJ/mol, 50.51 kJ/mol, and 22.24 kJ/mol for Ni, Co, Mn, and Li, respectively. The propensity for DES to leach metal ions followed the order: Li > Co > Ni > Mn, determined by binding energy and energy gaps. Cl− and −COOH within the DES were capable of forming stable complexes with reduced transition metal ions, revealing an efficient coordination leaching mechanism. Additionally, a life cycle assessment (LCA) was conducted on the environmental impacts of the DES leaching process, confirming it as an effective and environmentally friendly method for recycling spent LIBs. This work avoided the employment of corrosive acids and alleviated the generally harsh conditions associated with DESs leaching, providing a viable solution for recovering spent LIBs.

Ginger powder as sustainable and eco-friendly corrosion inhibitor for the protection of steel reinforcement bars

In the present studies, ginger powder has been used as an eco-friendly admixture for the cement mortar. Different amounts i.e. 0 wt% (M1), 0.10 wt% (M2), 0.25 wt% (M3) and 0.50 wt% (M4) ginger powder was mixed in the cement mortar (M1) and assessed the durability. The ginger powder with 0.50 wt% (M4) improves the compressive strength by 17 % owing to the water reducing capability, which enhance the hydration reaction and fill the pore matrix of the cement mortar. The active ingredient of ginger powder i.e. shogaol adsorbs on the steel rebar surface through leaching mechanism by interaction of oxygen (O) and п-electrons with iron (Fe) and provide corrosion protection at longer duration of continuous immersion in 3.5 wt% NaCl solution. Following 173 d in a 3.5 wt% NaCl solution, the M4 sample exhibits 82.10 % corrosion inhibition efficiency. Therefore, it is suggested that ginger powder could be a potential eco-friendly admixture to be used in construction industries to get high durability performance in the coastal areas.

Evolution of activation energy for boron dissolution in the borosilicate glass during the initial leaching stage

Borosilicate glass is widely used for immobilizing high-level radioactive waste. In this study, two types of borosilicate glasses, Na-borosilicate and Zr-Na-borosilicate, were subjected to leaching within a temperature range of 50-90°C, at 10°C intervals. The rate of boron consumption was measured by Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES) and Fourier-Transform infrared spectroscopy (FTIR) techniques, and the boron activation energy was determined through the Arrhenius equation. The boron activation energies for Na-borosilicate and Zr-Na-borosilicate glasses are approximately 46 kJ/mol and 42 kJ/mol, respectively. The activation energy, which FTIR calculated, was consistent with that obtained by ICP-OES during the initial leaching time and decreased as the leaching time increased. The decrease in activation energy of boron is because the [BO3] structure was replaced by molecular water. The FTIR method offers an alternative approach for calculating the boron activation energy and contributes to understanding the leaching mechanism in the initial leaching stage.

Study of the kinetics and mechanisms of rare earth elements leaching from end-of-life NdFeB magnets through Hydro-Nd process

With the growing demand for REEs in numerous high-tech and energy transition-related applications, recycling these elements from secondary sources, mainly from end-of-life permanent magnets, has become crucial for responsible sourcing of raw materials from a circular economy. To date, numerous processes have been developed and optimized to allow this recovery to be sustainable from both an economic and environmental point of view. In this context, hydrometallurgy is one of the most promising avenues. Through an innovative hydrometallurgical process (Hydro-Nd), this research investigated the kinetics and mechanisms involved in leaching REEs from end-of-life permanent magnets. This process involves the use of citric acid in the leaching phase. Through systematic experimentation and analysis, the article elucidates key factors influencing leaching kinetics, providing insight into critical mechanisms of the process. In particular, ANOVA was used to study the influence of important factors (temperature, particle size, and agitation) on the recovery yields of the elements of interest. The shrinking core model studied the leaching mechanisms to identify a possible rate-determining step. Thanks to the results obtained, the Arrhenius parameters were estimated for the different heterogeneous reactions involved in the process, and the trend of the time constants versus the average diameter of the solid particles was identified. Also, the results showed that 100 % of Nd, Fe, Dy, B, and Pr from small PM particles (0–40 µm) in 4 h and more than 90 % of the mentioned metals from large particles (1000–1700 µm) within 5 h of leaching time were dissolved by citric acid solution. This research not only contributes to the development of an even more sustainable rare earth recovery process thanks to the optimization of several factors but also clarifies fundamental aspects of leaching kinetics and mechanisms, paving the way for future advances in the recovery of REEs from different sources.

Changes in the structure of alkali activated slag mortars subjected to accelerated leaching

The chemically induced degradation of alkali-activated materials exposed to the surrounding environment is a critical concern for durability. In this study, the leaching of alkali activated slag mortars (AASs) subjected to a 6M NH4NO3 solution was investigated by integrating techniques including ICP-OES, XRD/QXRD, TGA/DSC, ATR-FTIR, and 29Si MAS-NMR. The results revealed that the main leachable elements from the AASs and their leaching rates decreased in the following order: Na, K, Ca, and Mg. In contrast, Si and Al, the key elements in the C-A-S-H gel, displayed a remarkable resistance to leaching. Upon NH4NO3 attack, the primary phase (C-A-S-H) becomes more siliceous and has a greater mean chain length through decalcification and dealumination. The second phase, Mg, Al-layered double hydroxide (Mg, Al-LDH, or hydrotalcite), incorporated nitrate from the surrounding solution, sulfate from precursor dissolution, and Ca from gel decalcification to form nitrate/sulfate-bearing Ca, Al-LDH phases. Remarkably, the water-to-binder ratio exerted a nuanced influence, dictating the pace of element leaching, while exhibiting a relatively modest impact on the stability of the solid phases after 28 days of exposure. This work proposes a leaching mechanism for understanding the leaching process occurring in AASs based on an in-depth experimental exploration of mineralogical alterations.

Application of a simple organic acid as a green alternative for the recovery of cathode metals from lithium-ion battery cathode materials

Industrialization, technology, and population growth have on one hand resulted in the rapid rise for energy demand and on the other hand led to the pursuit for alternative carbon neutral energy sources to satisfy demand, address climate change and promote sustainable development. The transition to renewable energy sources has resulted in the rapid rise in energy storage options with battery technologies at the forefront. Lithium-ion batteries (LIBs) have emerged as a leading battery energy storage option. The rise in LIB technology demand has resulted in a proportional increase in the demand for the various materials used in their manufacture. Primary sources of several of the LIB component materials largely consist of mining activities, however, recycling has emerged as a promising secondary material source. In this work, we evaluate the application of a green, organic acid treatment approach utilizing propionic acid in the recovery of key metals from LIB cathode materials. The study delved into exploring the application of both commercially sourced virgin LIB cathode powder (VCP) and recovered spent LIB cathode powder (SCP) and investigating the system leaching characteristics. The highest metal recoveries were obtained on leaching the SCP, with metal recoveries determined as 92.9%, 87.4%, 92.7% and 94.0% for Co, Li, Mn and Ni respectively. The difference in the recoveries on leaching metals from the VCP and SCP was under 5% for each metal. Further, the leaching model was determined as chemical reaction-controlled on using the SCP, and the activation energies were evaluated as 60.37 kJ/mol, 53.38 kJ/mol, 63.98 kJ/mol and 60.20 kJ/mol for Co, Li, Mn and Ni respectively, agreeing with the deduced chemical reaction-controlled leaching mechanism. By application of a simple organic acid, propionic acid, for organic acid leaching operations we contribute to the diversification of the lixiviant options for LIB waste treatment.

Impact of mechanical activation and mechanochemical activation on microstructural changes, leaching rate and leachability of natural chalcopyrite

The influence of mechanical activation (MA) and mechanochemical activation (MCA) with Fe and Fe2O3 on the microstructural changes, leachability and leaching rate of natural chalcopyrite was investigated and compared. MCA pretreatments were carried out by chalcopyrite co-milling with Fe and Fe2O3 for 20 and 50 min. The XRD analysis indicated that even after 50 min MA and MCA, constituent phases of chalcopyrite, Fe and Fe2O3 could be detectable beside the newly formed bornite. Regarding the peak broadening and peak intensity reduction, MCA generally intensified the microstructural changes of chalcopyrite in comparison with MA. The microstructural study performed by the Rietveld method also proved that all microstructural parameters changed in favor of reactivity, such that the amorphization degree and microstrain were increased to 96 % and 0.164 (%), respectively, while crystallite size was reduced to 14.6 nm after 50 min MCA of chalcopyrite with Fe2O3. It could be concluded from the leaching tests that MCA along with Fe and Fe2O3 addition could promote the leachability and leaching rate of chalcopyrite, as compared to MA and nonactivated chalcopyrite. Although both the MCA of chalcopyrite with Fe and Fe2O3 could enhance copper extractions in the 1 M sulfuric acid leaching tests at 80 °C, Fe addition was slightly more effective than Fe2O3. The results obtained from the kinetic study also revealed that the leaching mechanism of nonactivated chalcopyrite, mechanically activated chalcopyrite and mechanochemically activated chalcopyrite with Fe2O3 changed from diffusion control to chemical control due to MCA with Fe. Finally, the combination of kinetic and microstructural studies proved that all microstructural parameters, except for the microstrain parameters of chalcopyrite MCA with Fe2O3, could be effective in chalcopyrite reactivity promotion.

Leaching behavior and release mechanism of pollutants from different depths in a phosphogypsum stockpile

Phosphogypsum (PG), a byproduct during the production of phosphoric acid and phosphate fertilizers, is predominantly stockpiled with a height greater than hundreds of meters. In this study, the leaching behavior of pollutants from PG stored at different depths was systematically investigated through batch tests, column tests, and geochemical modeling. PG samples were collected at different depths within a range of 48 m from a large-scale PG stack in China. The results showed that the pH, electrical conductivity, and elemental concentration of the leachate exhibited spatial variability in terms of the depth distribution, with evident bottom enrichment effects for metals and soluble salts. The pH-dependent leaching tests investigated the impact of pH variations on the solubility of various elements in PG, with a specific focus on elements precipitation occurring within the natural pH range. The geochemical modeling of leaching tests conducted by PHREEQC enabled the identification of the dominant phases controlling the solubilization of the elements, as well as the dynamic process of changes in element forms and concentrations with pH variation. Column leaching tests reveal the differences in pollutant properties between the unsaturated and saturated zones within the PG stack and categorize the leaching mechanisms of elements into three models including dissolution, diffusion, and wash-off. This study aims to reveal the leaching characteristics of PG at different depths, so as to provide a data foundation for the design of liner system, leachate management strategies, and remediation of heavy metal pollution of PG stack sites.

Investigation of hydrohalic acids as lixiviants for the leaching of cathode metals from spent lithium-ion batteries

The exploration of alternative energy sources is inextricably linked with energy storage considerations. Current high density energy storage options on the market rely heavily on lithium (Li)-based technologies. A projected increase in energy storage technology demand has sounded the alarm on a need to develop suitable approaches for the recovery of the various constituent metals from spent Li-ion batteries (LIBs). This, coupled with urgent consideration for the environment has necessitated the investigation of various LIB metal recovery techniques. In this work, we explore the novel application of the hydrohalic acids, hydrobromic (HBr) and hydroiodic (HI) acid, as lixiviants in a series of leaching experimental investigations on LIB cathode powder. A methodology for battery disassembly and cell cathode material recovery is presented leading up to the metal leaching. Our results indicate that the lixiviants can be utilized in the absence of a reducing agent which is typically present in conventional LIB leaching systems. The highest recoveries of the constituent metals, Co, Li, Mn and Ni in the HI system were 92.9 %, 93.6 %, 93.1 % and 94.5 % respectively, at an operating temperature of 60 ℃ and with a 1.5 M HI concentration. The HBr system achieved metal recoveries of 90.6 %, 89.1 %, 83.1 % and 96.4 % for Co, Li, Mn and Ni respectively, at 60 ℃ and using 2 M HBr. Kinetic studies showed that the leaching mechanism for both acids follow a chemical reaction-controlled model.

Mechanism of ultrasonic-enhanced leaching for separating organic impurities from the surface of bauxite and H2O2 oxidation-CaO precipitation for purifying the leaching solution

The existence of organic impurities in bauxite significantly hampers the regular production of alumina. This study proposes a low-temperature ultrasonic-enhanced alkali leaching to directly separate organic impurities from bauxite, and purify the leaching solution through H2O2 oxidation and CaO precipitation. Under the optimal conditions of 550 W ultrasonic power, 80 °C, 60 min, and 200 g/L NaOH concentration, the leaching rate of organic carbon in bauxite is 91.02 %, which is 19.01 % higher than conventional alkali leaching, and the organic carbon content in the bauxite decreased from 0.59 % to 0.06 % after leaching. Kinetic studies indicate that the limiting factors of the leaching rate vary under different leaching temperatures and leaching times. Characterization of bauxite before and after leaching using various detection techniques demonstrates the effective separation of organic impurities while basically no loss of alumina and increasing the alumina to silica ratio to 34.13. Subsequently, H2O2 and CaO are introduced to the leaching solution with 20 % and 800 mL/g, respectively. The oxidation process under 550 W ultrasonic power at 90 °C for 60 min achieves an 71.35 % removal rate of organic carbon. GC-MS analysis confirms the successful removal of the main organic substances in the leaching solution, while XRD analysis of the oxidation residue indicates that organic substances are ultimately removed as CaC2O4·H2O and CaCO3. Additionally, a proposed free radical reaction mechanism of H2O2 oxidizing organic substances is discussed. In conclusion, this study providing valuable insights for the removal of organic pollutants in the alumina production process.

New insights into selective leaching and ferritization in 15-15Ti austenitic steel in lead-bismuth eutectic through parent phase reconstruction

Selective leaching accompanied by ferritization is widely observed in the dissolution corrosion of austenitic steels exposed to lead-bismuth eutectic. This study proposes a refined mechanism for selective leaching involving solid-state diffusion followed by dissolution-reprecipitation processes. Pole figure analysis reveals that ferritization follows the Nishiyama-Wassermann orientation relationship, independent of corrosion environment or corrosion behavior. Moreover, austenite reconstruction analysis shows that the growth of ferrite is hindered by the misfits at random high-angle grain boundaries. Hence the above results suggest that ferritization is initially driven by solid-state diffusion. As LBE channels open within the grains, further growth of ferrite is assisted by the dissolution-reprecipitation mechanism. Additionally, the formation of dual-oriented ferrite grains at Σ3 twin boundary is observed, and the selectivity of this formation with respect to grain boundary and ferrite orientation is discussed.

Environmental assessment of alkali-activated materials based on agro-industrial waste as alkaline activators through leaching tests

Global circular economy drives the development of sustainable alkali activated materials (AAM) for use as construction material from industrial by-products and wastes. The assessment of the potentially hazardous substances release of these new material combinations into the soil and groundwater over time is essential. In this study, the aim is the environmental assessment of three AAMs based on blast furnace slag (BFS), activated with almond shell biomass ash (ABA) as potassium source and three solid sources of silica from the agricultural industry, rice husk ash (RHA), spent diatomaceous earth (SDE) and bamboo leaf ash (BLA), using European horizontal leaching tests proposed for construction materials, for monolithic form, Dynamic Surface Leaching Test (DSLT) and for granular form, Up-flow Percolation Test and the Compliance leaching test, by simulating different scenarios of their entire life cycle. The leaching results of the AAM showed the effectiveness of the inertization of all the recycled materials studied, which exceeded some inert materials limits, by means of the activation process. Despite the absence of significant differences in the leaching mechanisms of the oxyanions As, Cr, Mo, Sb, Se and V between the three AAMs developed, they presented different long-term leaching behavior depending on their form, monolithic, or granular, and therefore in their different life cycle stages. Therefore, it is concluded that although the incorporation of agro-industrial waste as alternative activators in BFS based AAM according to the Dutch Soil Quality Decree (for unrestricted use of monolithic and granular materials) is an environmentally acceptable option, the design of waste derived AAMs should be assessed by means of a combination of leaching tests that cover their expected life cycle.

Ultrasound-assisted enhanced leaching of lithium and fluoride compounds from waste cathode carbon: Comprehensive recovery and leaching mechanism

Due to the rapid development of the aluminum industry, waste cathode carbon, as a hazardous solid waste, is inevitably generated during the production process of the aluminum electrolysis industry. Improper treatment of waste cathode carbon will inevitably result in significant environmental damage, affecting both flora and fauna. Therefore, ultrasound-assisted leaching was employed to extract the waste cathode carbon, using a sodium hydroxide solution as the leaching medium to recover valuable metals and electrolytes, thereby mitigating environmental risks and reclaiming resources. Optimal conditions for ultrasonic-assisted alkali leaching were determined through a single-factor experiment: a leaching temperature of 70 °C, a liquid-solid ratio of 7:1, a leaching time of 50 min, an alkali concentration of 100 g/L, and ultrasonic power of 250 W. Under these conditions, the fluoride leaching efficiency reached 89.17 %, and the lithium ion leaching efficiency was 86.33 %. Comparative analyses between traditional leaching methods and the optimized experiments revealed that the advantages of ultrasonic action and cyclic leaching contributed to an increase of 5.28 % in the fluoride leaching efficiency and 11 % in the lithium ion leaching efficiency. Furthermore, ultrasonic-assisted leaching significantly reduces the leaching time to 50 min while achieving a higher rate of impurity removal.

Comprehensive recovery of valuable metals from spent LiCoO2 cathode material by a method of NH4HSO4 roasting- (NH₄)₂S leaching

With the retirement of rechargeable lithium-ion batteries (LIBs) entering peak period, the recycling of LiCoO2 has become a hot topic. The spent LiCoO2 batteries are rich in carcinogenic metal Co and high-value metal Li, so they are needed to be recovered in time before causing serious environmental pollution and resource waste. Thus, a clean and efficient process is proposed for the comprehensive recovery of Li, Co, and Mn from the spent LiCoO2 cathode material. It is an integrated pyro-hydrometallurgical process, mainly consisting of sulfation roasting with NH4HSO4 and selective sulfurizing leaching with (NH4)2S solution. Using low melting point ammonium salt as roasting auxiliary, 99.7 %, 99.1 %, and 99.8 % of Li, Co, and Mn in the spent LiCoO2 powder can be converted into sulfate when roasting under 400 ℃ for 75 min. Then 99.5 % of Li in the sulfation roasting product can be selectively leached with an aqueous (NH4)2S solution, which is also a precipitator for Co, Mn, and impurity Al. In addition, 96.4 % of Co and 96.0 % of Mn in the sulfurized precipitate can be separated with impurity elements Al and C via oxidation roasting–water leaching process. Compared to traditional recycling, this method can achieve a higher Li leaching rate at a low roasting temperature, and the recovery of Co and Mn can be realized without adding any acid/base reagents or impurity cations. More importantly, the circulation of NH3/NH4+ and S element in the recycling system has been taken into account, making it an environmental-friendly and economical process. In this study, the sulfation reduction roasting and selective sulfurizing leaching mechanisms were both revealed in details, and the behavior of the valuable elements was also elucidated.

Leaching phosphorous from the lime mud of kraft pulp mills: Towards sustainability

AbstractThe optimum conditions needed to separate phosphorus from the lime mud generated in kraft pulp mills were identified using different leaching solutions including carbonate, bicarbonate, and green liquor under variety of conditions. Carbonate ions seemed to be the active ion in the phosphorus leaching process. Bicarbonate solution seems to be the most effective leaching agent by removing 84% of phosphorus under the optimum operating conditions of 95°C, 2.92 m, and solution‐to‐ mud mass ratio of 3.6. The shrinking core model was used to determine the leaching mechanism and it showed that the leaching process is controlled by a mix of chemical reaction and diffusion through the particle. Two empirical models were developed to predict the leaching efficiency as a function of carbonate concentration and temperature. Counter‐current leaching was shown to be beneficial in increasing the leaching efficiency with the carbonate solutions.