Selective preparation of lithium carbonate from overhaul slag by high temperature sulfuric acid roasting - Water leaching.

An efficient recycling process is developed to recover valuable materials from overhaul slag and reduce its harm to the ecological environment. The high temperature sulfuric acid roasting - water leaching technology is innovatively proposed to prepare Li2CO3 from overhaul slag. Under roasting conditions, fluorine volatilizes into the flue gas with HF, lithium is transformed into NaLi(SO4), aluminum is firstly transformed into NaAl(SO4)2, and then decomposed into Al2O3, so as to selective extraction of lithium. Under the optimal roasting - leaching conditions, the leaching rate of lithium and aluminum are 95.6% and 0.9%, respectively. Then the processes of impurity removal, and settling lithium are carried out. The Li2CO3 with recovery rate of 72.6% and purity of 98.6% could be obtained under the best settling lithium conditions. Compared with the traditional process, this work has short flow, high controllability, remarkable technical, economic, and environmental benefits. This comprehensive recycling technology is suitable for overhaul slag, and has great practical application potential for the disposal of other hazardous wastes in electrolytic aluminum industry.

Innovative methodology for comprehensive utilization of arsenic-bearing neutralization sludge.

Arsenic-bearing neutralization (ABN) sludge is a classical hazardous waste commonly found in nonferrous metallurgy. However, the current storage of these hazardous wastes not only has to pay costly hazardous waste taxes but also poses significant risks to both the environment and human health. To address these issues and achieve the comprehensive utilization and minimization of ABN sludge, this study proposes a new combined process. The process involves selective reduction roasting, leaching, and carbonation, through which, the arsenate and gypsum in the ABN sludge were recovered in the form of As(s), high-purity CaCO3, and H2S. The selective reduction behaviors of arsenate and gypsum were investigated through thermodynamic analysis and roasting experiments. The results indicated that the 95.35 % arsenate and 96.55 % gypsum in the sludge were selectively reduced to As4(g) and CaS at 950 °C by carbothermic reduction. The As4(g) was condensed to As(s) and enriched in the dust (As, 96.78 wt %). In the leaching process, H2S gas was adopted to promote the leaching of CaS, and resulted in 97.41 % of CaS in the roasted product was selectively leached in the form of Ca(HS)2, leading to a 74.11 % reduction in the weight of the ABN sludge. Then, the Ca(HS)2 was subjected to capture CO2 for the separation of Ca2+ and S2-. The result depicted that 99.69 % of Ca2+ and 99.12 % of S2- were separated as high-purity (99.12 wt %) CaCO3 and H2S (24.89 vol %) by controlling the terminal carbonation pH to below 6.55. The generated H2S can be economically converted to sulfur by the Clause process. The whole process realized the comprehensive resource recovery and the minimization of the sludge, which provides an alternative solution for the clean treatment of hazardous ABN waste.

Recovery of zinc and extraction of calcium and sulfur from zinc-rich gypsum residue by selective reduction roasting combined with hydrolysis.

A novel process that includes selective reduction roasting followed by hydrolysis was proposed in this work to recover zinc, and efficiently extract calcium and sulfur from hazardous zinc-rich gypsum residue (ZGR) waste for high-purity of CaCO3 and sulfur production. The selective reduction behaviors of ZGR during the reduction roasting were investigated in detail based on thermodynamic analysis and roasting experiments. The effect of roasting temperature, carbon dosage and time on the selective reduction of ZGR was comprehensively investigated, and the results indicated that ZnO and CaSO4 in the ZGR can be selectively reduced to Zn(g) and CaS, respectively. The volatile Zn(g) was oxidized to ZnO and enriched in the dust, which can be used as a secondary zinc resource. Moreover, the hydrolysis behaviors and leaching kinetic of CaS during hydrolysis were studied intensively. Results depicted that in the H2S-H2O system, the CaS in the roasted product can be selectively and efficiently dissolved into the leachate. Furthermore, the kinetic analysis revealed that the hydrolysis of CaS conformed to the internal diffusion reaction control model in the shrinking core model and the apparent activation energy Ea = -12.02 kJ/mol. The obtained hydrolysate with low impurities could be used to capture CO2 for the production of high-purity sulfur and CaCO3. Iron and other impurities in the roasted product were concentrated into the leaching slag in the form of metallic iron and akermanite. The whole process realized the recovery of zinc, and the selective and effective extraction of calcium and sulfur, which could provide an alternative process for the large-scale treatment of these hazardous wastes.

The Role of Nanobubbles in the Precipitation and Recovery of Organic-Phosphine-Containing Beneficiation Wastewater.

Dissolved air flotation (DAF) is broadly applied in wastewater treatment, especially for the recovery of organic pollution with low concentration. However, the mechanism of interaction between nanoscale gas bubbles and nanoparticles in the process of DAF remains unclear. Here, we investigated the role of nanobubbles in the precipitation of styryl phosphoric acid (SPA)-Pb particles and recovering organic phosphine containined in beneficiation wastewater by UV-vis (ultraviolet-visible) spectra, microflotation tests, nanoparticle tracking analysis, dynamic light scattering, and atomic force microscopy measurements. As suggested from the results, nanobubbles can inhibit the crystallization of SPA-Pb precipitation, which makes the sediment flotation recovery below 20%. After the precipitation crystallization is completed, nanobubbles can flocculate precipitated particles, which can promote the flotation recovery of precipitated particles to 90%. On the basis of the results, we proposed a model to explain the different roles of nanobubbles in the process of precipitation and flotation of SPA-Pb particles. This study will be helpful to understand the interaction between nanobubbles and nanoparticles in the application of flotation.

Human cytomegalovirus triggers the assembly of AIM2 inflammasome in THP-1-derived macrophages.

Absent in melanoma 2 (AIM2) inflammasome is a multiprotein complex which plays a pivotal role in the host immune response to multiple pathogens. The role of AIM2 in human cytomegalovirus (HCMV) infection is poorly studied. Thus, using a small inference RNA (siRNA) approach and THP-1 derived macrophage cells infected with HCMV AD169 strain, we investigated the impact of HCMV infection on AIM2-mediated molecular events. Compared to wild-type cells, AIM2-defiecient macrophages showed a limited ability to activate caspase-1, process IL-1ß, and induce cell death. In addition, AIM2-defiecient cells were unable to efficiently control HCMV infection, as the transcription of virus DNA polymerase gene UL54 and major tegument protein gene UL83 were higher compared to wild-type cells. In conclusion, HCMV infection induces an AIM2 inflammasome response, which negatively influences viral life cycle.

Novel nitrogen-rich hydrogel adsorbent for selective extraction of rare earth elements from wastewater.

Efficient recovery of rare earth elements (REEs) from wastewater is crucial for advancing resource utilization and environmental protection. Herein, a novel nitrogen-rich hydrogel adsorbent (PEI-ALG@KLN) was synthesized by modifying coated kaolinite-alginate composite hydrogels with polyethylenimine through polyelectrolyte interactions and Schiff's base reaction. Various characterizations revealed that the high selective adsorption capacity of Ho (155 mg/g) and Nd (125 mg/g) on PEI-ALG@KLN is due to a combination of REEs (Lewis acids) via coordination interactions with nitrogen-containing functional groups (Lewis bases) and electrostatic interactions; its adsorption capacity remains more than 85 % after five adsorption-desorption cycles. In waste NdFeB magnet hydrometallurgical wastewater, the recovery rate of PEI-ALG@KLN for Nd and Dy can reach more than 93 %, whereas that of Fe is only 5.04 %. Machine learning prediction was used to evaluate adsorbent properties via different predictive models, with the random forest (RF) model showing superior predictive accuracy. The order of significance for adsorption capacity was pH > time > initial concentration > electronegativity > ion radius, as indicated by the RF model feature importance analysis and SHapley Additive exPlanations values. These results confirm that PEI-ALG@KLN has considerable potential in the selective extraction of REEs from wastewater.

An unconventional approach for the efficient recovery of iron, cobalt, copper and silicon from copper slag.

High-grade heavy metal elements in copper slag (CS) are worth recovering. Unfortunately, the high viscosity of leaching solution, low leaching efficiency, difficult filtration and low separation efficiency of valuable components exist in the traditional sulfuric acid leaching process. In this study, the above problems are solved by sulfuric acid pretreatment + curing + water leaching. Moreover, iron, cobalt and copper ions in solution are separated by stepwise precipitation. The final iron, cobalt, copper and silicon recoveries are 99.01 %, 98.45 %, 93.13 % and 99.52 %, respectively. Thermodynamic calculations show that H4SiO4 can be converted to insoluble SiO2 to improve filtration properties under curing conditions of sulfur dioxide partial pressures of 10-20∼0 atm, oxygen partial pressures of 10-20∼0 atm and 400-600k. Simulation studies of the phase equilibria of the components of the leach solution by Visual MINTEQ showed that the oxidation of Fe2+ to Fe3+ is necessary for the removal of Fe2+ from the solution by precipitation. This study provides a new idea for the efficient utilization of CS.

Resource recovery and regeneration strategies for spent lithium-ion batteries: Toward sustainable high-value cathode materials.

Traditional cathode recycling methods have become outdated amid growing concerns for high-value output and environmental friendliness in spent Li-ion battery (LIB) recycling. Our study presents a closed-loop approach that involves selective sulfurization roasting, water leaching, and regeneration, efficiently transforming spent ternary Li batteries (i.e., NCM) into high-performance cathode materials. By combining experimental investigations with density functional theory (DFT) calculations, we elucidate the mechanisms within the NCM-C-S roasting system, providing a theoretical foundation for selective sulfidation. Utilizing in situ X-ray diffraction techniques and a series of consecutive experiments, the study meticulously tracks the evolution of regenerating cathode materials that use transition metal sulfides as their primary raw materials. The Li-rich regenerated NCM exhibits exceptional electrochemical performance, including long-term cycling, high-rate capabilities, reversibility, and stability. The closed-loop approach highlights the sustainability and environmental friendliness of this recycling process, with potential applications in other cathode materials, such as LiCoO2 and LiMn2O4. Compared with traditional methods, this short process approach avoids the complexity of leaching, solvent extraction, and reverse extraction, significantly increasing metal utilization and Li recovery rates while reducing pollution and resource waste.

New Insight into Elastic Mechanical Properties and Anisotropies of Crystal Defect α-Quartz from DFT Calculation.

To reveal the cleavage mechanism of α-quartz in the grinding process of nonferrous metal ores, mechanical and charge properties of α-quartz crystals are investigated using the density functional theory. Based on the elastic constant matrix, the bulk and shear moduli were calculated before and after the α-quartz with oxygen atom defects. The results show that the ratios of bulk and shear moduli (B/G) were 0.87 and 0.95, respectively, which indicated that at the same stress level, it was easier to fracture without O-vacancy defects than with O-vacancy defects. The mapping surfaces indicated that the O-vacancy defect increased the bulk-, shear-, and Young's moduli, and Poisson ratio while decreasing the hardness. The anisotropy index (AL and AU) was calculated which illustrated that the O-vacancy can result in an increased anisotropy; meanwhile, the bulk anisotropy index (AB) increased strongly about two times. The anisotropy analysis shows the dominance crystal cleavage of the (011) plane in the shear stress and the dominance crystal cleavage of the (111) plane in the normal stress. The electron localization function α-quartz show that the O-vacancy defect can decrease the Si-Si length from 3.703 to 2.442 Å, which indicated that the O-vacancy formed the new covalent bonds between silicon atoms. Our work provided a systematic approach containing the mechanical, anisotropic, and electronic properties of mineral crystals to explain the cleavage behavior of crystals.

Closed-loop recycling of spent lithium-ion batteries based on selective sulfidation: An unconventional approach.

The facile recycling of spent lithium-ion batteries (LIBs) has attracted considerable attention because of its great importance to environmental protection and resource utilization. A novel process is developed for cyclic utilization of spent LiNixCoyMnzO2 (NCM) batteries. The spent NCM was converted into water-soluble Li2CO3, acid-dissolved MnO, and nickel-cobalt sulfides through selective sulfidation, based on roasting condition optimization and thermodynamic calculation. More than 98 % of lithium is extracted preferentially from calcined NCM through water leaching, and over 99 % of manganese is extracted selectively from water leaching residue with H2SO4 solution of 0.4 mol/L in the absence of additional reductant. The nickel and cobalt sulfides were concentrated into the leaching residue without metal impurities. The obtained Li2CO3, MnSO4, and nickel-cobalt sulfides can be regenerated as new NCM, showing good electrochemical performance, and its discharge capacity is 169.8 mAh/g at 0.2C. After 100 cycles at 0.2C, the discharge specific capacity can still be maintained at 143.24 mAh/g, and its capacity retention ratio is as high as 92  %. An environmental assessment and economic evaluation indicate that the process is an economical and eco-friendly approach for green recycling of spent LIBs.

Facile separation and regeneration of LiFePO4 from spent lithium-ion batteries via effective pyrolysis and flotation: An economical and eco-friendly approach.

The facile recycling of spent lithium-ion batteries (LIBs) has attracted much attention because of its great significance to the environmental protection and resource utilization. Hydrometallurgical process is the most common method for recycling spent LIBs, but it is difficult to economically recover spent LiFePO4 batteries, because of the complicated metal separation process and low added value of its products. Herein, a novel and facile approach has been developed to achieve the direct regeneration of LiFePO4 from spent LIBs. By employing a flotation process after effective pyrolysis, it is found that 91.57% of LiFePO4 can be recovered from spent LIBs. Different surface hydrophobicity of cathode and anode active materials could be achieved via the selective adsorption of causticized soluble starch on the surfaces of spent LiFePO4, which effectively enhances the separation performance in flotation process. The recovered LiFePO4 barely contains metal impurities, which can be directly regenerated as new LiFePO4 materials with the first discharge capacity of 161.37 mAh/g, and their capacity retention is as high as 97.53% after 100 cycles at 0.2C. A technology assessment and economic evaluation indicate the developed regeneration approach of LiFePO4 is environmentally and economically feasible, which avoids the complex element separation process and achieves the facile recycling of spent LiFePO4.

Investigation of energy gene expressions and community structures of free and attached acidophilic bacteria in chalcopyrite bioleaching.

In order to better understand the bioleaching mechanism, expression of genes involved in energy conservation and community structure of free and attached acidophilic bacteria in chalcopyrite bioleaching were investigated. Using quantitative real-time PCR, we studied the expression of genes involved in energy conservation in free and attached Acidithiobacillus ferrooxidans during bioleaching of chalcopyrite. Sulfur oxidation genes of attached A. ferrooxidans were up-regulated while ferrous iron oxidation genes were down-regulated compared with free A. ferrooxidans in the solution. The up-regulation may be induced by elemental sulfur on the mineral surface. This conclusion was supported by the results of HPLC analysis. Sulfur-oxidizing Acidithiobacillus thiooxidans and ferrous-oxidizing Leptospirillum ferrooxidans were the members of the mixed culture in chalcopyrite bioleaching. Study of the community structure of free and attached bacteria showed that A. thiooxidans dominated the attached bacteria while L. ferrooxidans dominated the free bacteria. With respect to available energy sources during bioleaching of chalcopyrite, sulfur-oxidizers tend to be on the mineral surfaces whereas ferrous iron-oxidizers tend to be suspended in the aqueous phase. Taken together, these results indicate that the main role of attached acidophilic bacteria was to oxidize elemental sulfur and dissolution of chalcopyrite involved chiefly an indirect bioleaching mechanism.

Global transcriptional analysis of stress-response strategies in Acidithiobacillus ferrooxidans ATCC 23270 exposed to organic extractant--Lix984n.

Acidithiobacillus ferrooxidans (A. ferrooxidans) ATCC 23270 is a model bacteria for bioleaching research. Because of the use of extractant in metal extraction industry, A. ferrooxidans needs to cope with the water-organic two-phase system. To get insight into the molecular response of A. ferrooxidans to organic solvent, global gene expression pattern was examined in A. ferrooxidans ATCC 23270 cells subjected to Lix984n (an organic extractant) using the method of whole-genome DNA microarray. The data suggested that the global response of A. ferrooxidans to Lix984n stress was characterized by the up-regulation of genes involved in pentose phosphate pathway, fatty acid and glutamate biosynthesis. In further study, compared to heterotrophic bacteria in dealing with short-time stress, A. ferrooxidans has a special strategy of continuously enhancing the expression of genes encoding proteins involved in electron transport, such as petI, petII, cyo and cyd. Besides, acrAB-tolC operon encoding organic solvent efflux pump and its positive regulator gene ostR were addressed.

Production and resource utilization of flue gas desulfurized gypsum in China - A review.

Flue gas desulfurized gypsum (FGD gypsum), mainly originates from thermal power plants, smelters, and large-scale enterprise boilers. This article reviews the production in China and the latest beneficial utilizations of FGD gypsum. China is a large coal-consuming country and has always had serious SO2 emissions. Therefore, the Chinese government has implemented a large number of desulfurization measures since 2006. With continually increasing energy consumption and increasingly stringent environmental requirements, the production of FGD gypsum has exceeded 108 tons. The basic properties and the current beneficial applications of FGD gypsum are summarized here. The practical application of FGD gypsum in four fields-building materials, agriculture, material synthesis, and soil-and its impact on the environment, are analyzed. Finally, a new direction is proposed for the future utilization of FGD gypsum.

Metabolic changes of Acidithiobacillus caldus under Cu²(+) stress.

Metabolic changes were investigated by measuring the depletion of dissolved oxygen and the enzymatic activities of sulfur metabolism in Acidithiobacillus caldus (A. caldus) before and after copper stress. The results showed that high concentrations of Cu²(+) have an indirect negative effect on the sulfite oxidase and the APS reductase involved in sulfur metabolism when A. caldus is cultured in medium with elemental sulfur as its growth energy. This leads to a decrease in the respiration rate and the growth rate. The changes of activity are negatively correlated with the intracellular Cu²(+) concentration through an indirect interaction mechanism. A. caldus was able to induce an efflux of copper ions by forming an ATPase-dependent pump, which transported copper ions by consuming ATP. The negative effect of Cu²(+) on the bacterial metabolism could be minimized by the copper efflux when the bacteria were adapted in medium containing Cu²(+) for a long time. However, this bacterial rejuvenation became weaker when grown in medium containing higher concentrations of copper ions.

Pneumatic separation for crushed spent lithium-ion batteries.

Pneumatic separation was used to separate the valuable current collectors and harmful separators in spent lithium-ion batteries (LIBs) to avoid the plastic pollution caused by the separators in this study. Theoretical calculations for suspension velocities of the current collectors and separators indicate that they could be separated under special conditions. Furthermore, a special Z-shaped pneumatic separator was used to separate the current collectors and separators for the first time. Experiments for manually cut samples indicate that the efficiency of pneumatic separation is approximately 100% with the sizes and airflow velocities in the range of 3-4 cm and 6.96-7.8 m/s, respectively. Furthermore, industrial experiments of pneumatic separation indicate that the recoveries of the current collectors and separators are approximately 99.23% and 98.64%, respectively. Computer simulations of the separation process indicate that the turbulence and the changes in high-speed zones in the pneumatic separator benefit the separation of current collectors and separators. In conclusion, pneumatic separation is a promising technology to separate crushed current collectors and separators.

Thermal degradation behaviors and evolved products analysis of polyester paint and waste enameled wires during pyrolysis.

The thermal degradation behaviors and evolved products analysis of polyester paint and waste enameled wires during pyrolysis were studied. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were performed to investigate the mass loss characteristics. The pyrolysis solid residues generated during the process under optimal condition were detailedly analyzed by Fourier-transform infrared spectroscopy (FTIR). Meanwhile, the pyrolysis gas and oil generated were analyzed by gas chromatography-mass spectrometry (GC-MS). Kinetic analysis adopted the Ozawa-Flynn-Wall (OFW) model to confirm the reaction series by the variation pattern of activation energy. The results indicated that the pyrolysis of polyester paint and waste polyester enameled wires can be divided into three stages. The average activation energy of polyester paint and waste polyester enameled wires pyrolysis was 323.34 kJ/mol and 215.95 kJ/mol, respectively. The optimized pyrolysis temperature for polyester paint and waste polyester enameled wires was 500 °C and 900 °C, respectively. The chemical compositions of the pyrolysis residues of polyester paint and waste polyester enameled wires were basically same, mainly containing the compounds with CH, CO, aromatic ring, methyl, and aromatics bonds. The pyrolysis gas of polyester paint was mainly composed of C2H6, while that of waste polyester enameled wires mainly consisted of C2H6 and C4H8O. The main components of the pyrolysis oil polyester paint and waste polyester enameled wires were basically same, mainly containing long chain hydrocarbons, long chain alkenes, alcohols, phenol, ketone, aldehyde, and aromatic.

Combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans.

Although jarosite and visible light are important factors for the formation of acid mine drainage (AMD), the effects of combined jarosite and visible light on chalcopyrite biodissolution have not been explored until now. In order to fill this knowledge gap, the combined effects of jarosite and visible light on chalcopyrite dissolution mediated by Acidithiobacillus ferrooxidans were investigated. The results indicated that jarosite and visible light could significantly accelerate chalcopyrite biodissolution, thus releasing more copper ions, iron ions and producing more acid. This in turn suggests enhanced generation of AMD under these conditions. Biodissolution results, mineral surface morphology, mineralogical phase and elemental composition analyses revealed that the promotion of chalcopyrite dissolution by additional jarosite and visible light was mainly attributed to the acceleration of ferric iron/ferrous iron cycling and the inhibition of the formation of a passivation layer (jarosite and Sn2-/S0) on the surface of chalcopyrite. This study provides a better understanding of the effects of jarosite and visible light on chalcopyrite biodissolution. In the future, the influences of jarosite and visible light on chalcopyrite dissolution should be considered in AMD evaluation to ensure reliability.

Pyrolysis and physical separation for the recovery of spent LiFePO4 batteries.

In this study, a novel process consisting of pyrolysis and physical separation was proposed to comprehensively recycle spent lithium ion batteries (LIBs). The discharge and pyrolysis behaviors of spent LIBs, the recovery of electrolyte from the spent LIBs by low-temperature volatilization, and the recovery of valuable materials from the pyrolytic residues through physical separation were studied in detail. The results indicated that approximately 99.91% of the organic electrolytes was recycled, and the lithium salt (LiPF6) in the batteries was disposed by pyrolysis process. The active materials could be effectively separated from current collectors after the pyrolysis under N2 at 550 °C for 2 h. The pyrolytic gas was mainly composed of light alkenes, and the pyrolytic tar was mainly composed of aromatic long chain alkenes and light alcohols. Pyrolytic residues were recycled by color sorting, high-pressure water cleaning and flotation processes, and about 99.34% of Al, 96.25% of Cu, and 49.67% of cathode active materials were recovered from the spent LIBs. Finally, electrochemical tests indicate that the cathode active materials obtained by the process can be used to produce new batteries.

Influence of Mixing and Nanosolids on the Formation of Nanobubbles.

The generation of nanobubbles (NBs) by replacing different dissolved gas solutions has been widely adopted. Recently, we have found that mixing solutions with different gas contents can also produce a large number of NBs. However, the mechanism of the formation of NBs during mixing has not been well explored. Here, we designed a series of experiments to investigate the influence of mixing of different solutions on the concentration and size contribution of formed NBs via the help of nanoparticle track analysis. The effect of nanosolids was also investigated. The pressurization and depressurization were used to produce NBs. The results indicated that NBs can be influenced by the gas contents and nanosolids. The addition of nanosolids is beneficial to produce more NBs. Both the nanosolids and gas contents together are expected to substantially increase the concentration of NBs. These results will be very helpful to understand the formation and stability of NBs.