Acid Leaching Research Articles

Mixed rare earth metals production from surface soil in Idaho, USA: Techno-economic analysis and greenhouse gas emission assessment

Rare earth elements are crucial for the development of cutting-edge technologies in various sectors, such as energy, transportation, and health care. Traditional extraction of rare earth elements from soil and ore deposits primarily involves chemical leaching and solvent extraction. Environmental-based biological rare earth element extraction, such as bioleaching, can be a promising alternative to mitigate pollution and hazardous wastes. We investigated the sustainability aspects (techno-economic and environmental impact) of mixed rare earth metals production from soil in Idaho, USA. We focused on the bioleaching of surface soil using techno-economic analysis and “cradle-to-gate” life cycle assessment. The system boundary included collection, transportation, bioleaching, and molten salt electrolysis. Our results revealed that the mixed rare earth metals (including Nd, Ce, and La) production costs approximately $10,851 per metric ton and generates 1.9 × 106 kg CO2 eq./ton. Our results showed that most emissions are due to energy consumption during bioleaching. Over a 100-year time horizon ultrasound-assisted bioleaching can reduce greenhouse gas emissions by approximately 91 % compared to the traditional bioleaching process by decreasing the organic acid leaching process time and energy consumption. Our work demonstrates that higher solids loading in leaching with biological reactions can promote economic feasibility and reduce chemical wastes.

Synergistic valorisation of wastewater microalgae: Sulphuric acid-assisted phosphorus recovery and enhanced electrochemical performance of biochar for supercapacitors

This study proposes a strategy for phosphorus recovery from algae biomass while simultaneously enhancing the electrochemical capacitance of resulting biochar in supercapacitor applications. Use of sulphuric acid leaching process on both wastewater microalgae and seaweed biochar demonstrated high phosphorus recovery rates, ranging from 93.4% to 95.4%, while at the same time retaining 52.7% to 58.6% of Fe content in the biochars. By modifying the sequential order of leaching (L) and physical activation (A) as LA and AL, the strategy allows for the optimisation of phosphorus recovery and the electrochemical properties of activated biochars. During the LA process, a more porous structure formed and more S-containing functional groups occurred compared to AL which explained the higher specific capacitance (486.3F g−1 at a current density of 1 A g−1) of wastewater microalgae biocarbon with the LA process. Consequently, the life cycle assessment of this strategy revealed a significant global warming reduction potential of 1.34–2.94 tonnes of CO2-eq/yr for each tonne of biochar produced. This indicates that sulphuric acid-assisted biochar production could be a sustainable strategy for waste management and carbon sequestration, while simultaneously generating economic profits from valorised carbon material for energy storage applications.

Synthesis of large mesoporous silica for efficient CO2 adsorption using coal gasification fine slag

Coal gasification fine slag (CGFS), a byproduct of the coal gasification process, is currently being recognized as a resource with significant potential for value addition and sustainable applications, especially in synthesizing CO2 adsorbents. The overarching challenges in this domain include the attainment of high-efficiency, environmentally benign transformation of CGFS into useful products, and the development of cost-effective adsorbent materials featuring precisely engineered pore structures. In this study, a hierarchical porous nanostructured silica material is synthesized rapidly, efficiently, and cost-effectively through acid leaching and alkaline dissolution-assisted hydrothermal treatment, employing CGFS as the precursor. The mass ratios of sodium hydroxide (NaOH) to CGFS range from 0.4 to 1, resulting in varying morphologies and adsorption properties. Specifically, the sample with the NaOH to CGFS ratio of 0.6 (CGFS-0.6) shows the best adsorption performance. The adsorption capacities are 2.87 mmol/g and 8.49 mmol/g at 20 °C with 15 % and 45 % CO2 concentration, respectively. The material is characterized by a well-developed pore structure shaped like a bouquet of flowers, with a specific surface area of 457 m2/g and pore volume reaching 2.34 cm3/g. During the hydrothermal processing, silicate/aluminosilicate entities self-organized into a Si-O-Na/Al network structure, endowing the synthesized adsorbent with optimal internal porosity and silanol functionalities. The adsorption equilibrium is achieved rapidly within 10 min, and CO2 adsorption stability remains robust across 20 successive cycles. All isothermal models of the adsorbents conform to the Sips model. This study offers a promising pathway for the value-enhanced utilization of coal-derived solid wastes.

Recovery of rare earth elements from rare earth molten salt electrolytic slag via fluorine fixation by MgCl2 roasting

Rare earth fluoride molten-salt electrolytic slag (REFES) is a precious rare earth element (REE) secondary resource, and considerable amounts of REEs exist in REFES as REF3; they are difficult to dissolve in acid or water and impede efficient REE extraction. In REFES recovery, the REF3 species in REFES are usually transformed into acid-soluble rare earth compounds by NaOH roasting or sulfating roasting and then extracted by acid leaching. Moreover, the fluorides in REFES are released as HF gas in the roasting process or enter the liquid phase during the water washing process; both of these processes cause fluorine pollution. Fixing the fluorine into the solid slag provides a way to avoid fluorine pollution. In this study, a novel method was proposed to extract REEs from REFES via MgCl2 roasting followed by HCl leaching. Thermodynamics calculations and thermogravimetry‒differential thermal analyses (TG-DTA) were conducted to investigate the reactions occurring in the roasting process. First, MgCl2 reacts with the REF3 and RE2O3 to form RECl3 and REOCl, respectively. Second, the RECl3 absorbs water and forms RE(OH)3. Third, MgCl2·6H2O is gradually dehydrated to MgCl2·2H2O and reacts with REF3 and RE(OH)3, and REOCl, MgF2 and MgO are formed. Through HCl leaching, the REOCl in the roasting products is leached by HCl acid, while fluoride remains in the solid slag as MgF2. The optimum experimental conditions are as follows: mass ratio of MgCl2 to REFES of 30%, roasting temperature of 700 °C, roasting time of 2 h, hydrochloride acid concentration of 4 mol/L, leaching time of 2 h, leaching temperature of 90 °C and leaching L/S ratio of 20:1. The efficiencies for total leaching of the REEs, La, Ce, Pr, and Nd are 99.13%, 99.20%, 98.42%, 99.38%, and 99.08%, respectively. Moreover, the concentration of fluoride in the leaching solution is 2.191 × 10−6 mol/L. This method has a short process flow with low reagent costs, and the problem of fluoride pollution from REFES recovery is solved; thus, our study has great industrial application potential.

Sulfuric Acid Baking and Fe(III)-Cl--H2SO4 Leaching Behavior of Ni- and Cu-Containing Sulfide and Silicate Rich Suhanko Concentrate.

Ni- and Cu-rich concentrate from a new site in Suhanko, Finland, was investigated. Mineral phases identified included talc, chalcopyrite, kaolinite, and pyrrhotite with 3.2% Cu and 1.5% Ni, and the latter is associated with pyrrhotite. In addition, the concentrate contained the precious elements Pd (14.9 g/t), Ag (17.1 g/t), Pt (2.1 g/t), and Au (1.1 g/t). This concentrate was baked and leached using a Fe(III)-Cl--H2SO4 system. The results showed that the leaching efficiencies of Ni, Cu, and Si from raw concentrate were 60%, 40%, and 5%; however, those from baked concentrate were 96%, 60%, and below 0.1%, indicating that the baking process enhanced Ni and Cu extraction while simultaneously inhibiting the dissolution of Si, which was due to the baking process liberating the associated Ni and Cu by the oxidation of chalcopyrite and pyrrhotite and converting the acid-soluble silicate into an insoluble form. Sulfuric acid leaching solution with Fe(III) as oxidant and Cl- as lixiviant was shown to be effective at leaching Ni (97%), Cu (62%), and Ag (89%), while simultaneously enriching the PMs Pd, Pt, and Au in the residue.

Simultaneous multi-coordination adsorption of V(IV) and V(V) in highly acidic solution using modified amino phosphate chelating resin

To avoid harmful neutralizing slag containing toxic metals during pH adjustment of acid leaching solution, we proposed an efficient extraction method of vanadium without adjusting the pH of the vanadium-containing acid leaching solution using modified amino phosphate chelating resin DS418. In this paper, the performance of the modified resin was further characterized, the adsorption kinetics, isothermal adsorption model of V(IV) and V(V) were compared and adsorption mechanism were analyzed on the atomic and molecular level. Under the condition of 25℃, the liquid-solid ratio was 1: 20 g/ml, nV(IV): nV(V)=1: 3, the V had the best adsorption effect of 92.65 %, and the cyclic stability of the DS418 resin was good. Through FTIR, XPS, TG-DSC as well as the DFT, it shows that V(IV) interacted with-PO3H2, while V(V) chelated with the-PO3H2 and -N, the most significant interaction was the distance between phosphate group and V with an average distance of 1.8018 Å for V(IV) and an average distance of 1.8376 Å for V(V). Based on the results, it shows the prospect of efficient recovery of multivalent vanadium ions in strongly acidic solutions and has environmental significance.

Recovery of iron phosphate and lithium carbonate from sulfuric acid leaching solutions of spent LiFePO4 batteries by chemical precipitation

The recycling of lithium and iron from spent lithium iron phosphate (LiFePO<sub>4</sub>) batteries has gained attention due to the explosive growth of the electric vehicle market. To recover both of these metal ions from the sulfuric acid leaching solution of spent LiFePO<sub>4</sub> batteries, a process based on precipitation was proposed in this study. Since ferric and ferrous ions coexisted in the leaching solution, all the ferrous ions were first oxidized to ferric ions by adding H<sub>2</sub>O<sub>2</sub> to the leaching solution. About 99% iron(III) was recovered as iron phosphate by adjusting the solution pH to 2 at 25 <sup>o</sup>C for 30 mins. After the precipitation of iron phosphate, the remaining Li(I) in the filtrate was recovered as lithium carbonate by precipitation with Na<sub>2</sub>CO<sub>3</sub> as a precipitant. Addition of acetone to the filtrate at room temperature greatly enhanced the precipitation percentage of Li(I). Moreover, solid Na<sub>2</sub>CO<sub>3</sub> was better than Na<sub>2</sub>CO<sub>3</sub> solution in precipitating Li(I). About 95% of lithium ions was recovered as carbonate precipitates under the optimum conditions: solution pH = 11, 3.0 molar ratio of solid Na<sub>2</sub>CO<sub>3</sub> to Li(I), 7/5(v/v) volume ratio of acetone to the filtrate, 25 <sup>o</sup>C, 300 rpm for 2 hrs.

Development of complete hydrometallurgical processes for gold recovery from ICs and CPUs using ionic liquids

Integrated circuits (ICs) and central processing units (CPUs), essential components of electrical and electronic equipment (EEE), are complex composite materials rich in recyclable high-value strategic and critical metals, with many in concentrations higher than in their natural ores. With gold the most valuable metal present, increase in demand for gold for EEE and its limited availability have led to a steep rise in the market price of gold, making gold recycling a high priority to meet demand. To overcome the limitations associated with conventional technologies for recycling e-waste, the use of greener technologies (ionic liquids (ILs) as leaching agents), offers greater potential for the recovery of gold from e-waste components. While previous studies have demonstrated the efficiency and feasibility of using ILs for gold recovery, these works predominantly concentrate on the extraction stage and often utilise simulated solutions, lacking the implementation of a complete process validated with real samples to effectively assess its overall effectiveness. In this work, a simulated Model Test System was used to determine the optimal leaching and extraction conditions before application to real samples. With copper being the most abundant metal in the e-waste fractions, to access the gold necessitated a two-stage pre-treatment (nitric acid leaching followed by aqua regia leaching) to ensure complete removal of copper and deliver a gold-enriched leach liquor. Gold extraction from the leach liquor was achieved by liquid-liquid extraction using Cyphos 101 (0.1 M in toluene with an O:A = 1:1, 20 °C, 150 rpm, and 15 min) and as a second process by sorption extraction with loaded resins (Amberlite XAD-7 with 300 mg of Cyphos 101/g of resins at 20 °C, 150 rpm and 3 h). In both processes, complete stripping and desorption of gold was achieved (0.5 M thiourea in 0.5 M HCl) and gold recovered, as nanoparticles of purity ≥95%, via a reduction step using a sodium borohydride solution (0.1 M NaBH4 in 0.1 M NaOH). These two hydrometallurgical processes developed can achieve overall efficiencies of ≥95% for gold recovery from real e-waste components, permit the reuse of the IL and resins up to five consecutive times, and offer a promising approach for recovery from any e-waste stream rich in gold.

Erosion wear characteristics of metal seal floating ball valve in gas–solid–liquid three-phase flow

During high-pressure acid leaching, sulfuric acid slurry acts as the transportation medium in the withdrawal drum for acid pressure leaching. Over time, the metal-sealed float valve at the pipeline outlet may experience internal leakage. To address this issue, the Euler–Lagrange method for fluid dynamics is used to evaluate the corrosion wear characteristics of the valve in a three-phase flow. Specifically, we investigate the erosion and wear properties of the ball valve core as it opened and closed. To further understand how different ball valve openings impact erosion characteristics, we establish a correlation between the corrosion rate and the drag coefficient. Our research findings indicate that as the valve’s relative opening decreases from 80% to 20%, the corrosion wear rate gradually increases. In addition, the number of particles within the valve cavity also follows a similar trend. These erosion results highlight the significant influence that particle quantity has on erosion. Moreover, with an increase in particle size, both the erosion gradient range and maximum erosion rate decrease.

Recovery of rare earth elements from sedimentary rare earth ore via sulfuric acid roasting and water leaching

Rare earth elements were extracted using a sulfuric acid roasting-water leaching process. The effect of acid roasting on a new type of low-grade sedimentary rare earth ore found in Guizhou Province, China was analyzed using X-ray diffraction and scanning electron microscopy. A systematic study was conducted on process parameters such as amount of acid, roasting temperature, roasting time, water leaching temperature, and leaching time. The results reveal that the total recovery of rare earth elements reaches 81.37%, which is 3.1 times higher than that achieved through direct acid leaching, under the optimal conditions. In addition, the leaching rate of heavy rare earth elements reaches 72.53%. Rare earth elements and some other valuable metals are transformed into soluble sulfate through the local decomposition of clay minerals under the action of the sulfuric acid attack. The dissolution rates of aluminum, iron, and titanium ions are 34.94%, 17.05%, and 62.77%, respectively. The precipitation rate of Ti reaches 99%, and the loss of rare earth ions in the solution is less than 1%. Meanwhile, the results of a leaching kinetics analysis indicate that the leaching process of rare ions is controlled by diffusion. Precious metal ions such as iron and aluminum in the leaching solution can reduce the adsorption of rare earth ions by kaolinite. This study efficiently recovered rare earth ions under conditions of low calcination temperature and direct water leaching, resulting in reduced energy consumption of the extraction process and acidity of the leaching solution. These findings provide a solid foundation for the further separation and extraction of rare earth ions.

Electrochemical methods for the removal of impurities from thegraphite anode in spent ternary lithium-ion batteries

The use of lithium-ion batteries (LIBs) is becoming increasingly widespread, and a large number are reaching their end of life. The recycling and re-use of spent LIBs has attracted great attention. Because of the unchanged layer structure of the graphite anode in these batteries, their recycling does not require high-temperature graphitization, and only focuses on the removal of internal impurities. We used electrochemical treatment for the deep removal of internal metal impurities after the heat treatment, ultrasonic separation, and acid leaching of spent graphite. By comparing and analyzing the graphite in different recovery stages, it was found that the presence of organic impurities seriously affects the electrochemical performance. The presence of trace inorganic impurities such as Cu and Fe has little effect on the initial discharge specific capacity, but reduces the cycling stability of graphite. The content of the main metal impurities in the final recycled graphite was less than 20 mg/kg. The discharge specific capacity reached358.7 mAh/g at 0.1 C, and the capacity remained at 95.85% after 150 cycles. Compared with the reported methods for recycling spent graphite, this method can efficiently remove impurities in the graphite, solve the current problems of high acid and alkali consumption, incomplete impurity removal and high energy consumption. The recycled graphite anode has a good electrochemical performance. Our work provides a new recycling and regeneration path for spent LIB graphite anodes.

A novel shotcrete accelerator prepared from industrial aluminum mud waste and its influence on cement hydration

In this study, the aluminum sulfate and industrial aluminum mud solid waste were respectively used to prepare shotcrete accelerators (named as AFA and AFS, respectively). A comparative analysis of their performance was conducted, and the underlying mechanisms were investigated. Different concentrations of sulfuric acid (25 %, 30 %, 35 %, 40 %, 45 % 50 % respectively) and liquid to solid ratios (2:1, 3:1, 4:1, 5:1, 6:1) were employed for the acid leaching of aluminum mud, among which 35 % mass concentration of sulfuric acid and 3:1 of liquid to solid ratio were identified as the optimal conditions according to the setting and hardening performance of cement. AFS exhibited superior effectiveness on enhancing the rapid setting and early age strength in cement pastes and mortars compared to AFA. The working mechanisms of AFA and AFS were revealed via the examination of ionic concentrations and pH values in pore solution, as well as the evolution of hydration heat and hydration products during the hydration process. The results showed that AFS generated higher concentration of Al3+ and SO42- ions during hydration as compared to AFA thus promoted the formation of a larger amount of ettringite. Moreover, the introduction of both AFA and AFS into cement pastes significantly lowered the pH values in pore solution, and AFS was more obviously, which accelerated the cement hydration process. This study presents an innovative approach in utilizing industrial aluminum mud solid waste for the development of a novel accelerator with promising performance characteristics, opening up new opportunities for its wide range of application.

The stepwise extraction strategy for selective recovery of scandium from hydrochloric acid leachate of bauxite residue based on reactivity of metal ions

The recovery of Sc from secondary resources such as bauxite residue has received considerable interest. As the main elements in bauxite residue, Fe and Al exhibit significant interference in the selective separation of Sc. Herein this work, a stepwise extraction strategy of Sc from the hydrochloric acid leachate of bauxite residue was proposed based on the differences in reactivity of metal ions. The results show that Fe(III) and Sc(III) can be extracted sequentially with Aliquat 336 and Cyanex 272 from hydrochloric leachate. The separation factors of Fe/Sc, Fe/Al and Sc/Al were up to 4.3 × 104, 4.1 × 104 and 2.6 × 103, respectively. The results of spectroscopic characterization indicate that a cation exchange and coordination occur during the extraction of Sc(III) with Cyanex 272. The Sc(III) complex with Cyanex 272 (H2A2) is presented as ScClA2(HA)2¯. The loaded Aliquat 336 and Cyanex 272 can be stripped with acidified sodium sulfite and oxalic acid, respectively. The extraction-stripping performance of the stepwise separation route was investigated and the extraction efficiency of Fe(III) and Sc(III) can be remained above 97 % after 5 cycles. The proposed strategy has the potential to be considered industrially for the recovery of Sc from bauxite residue and other secondary resources.

The Impact of an Earthworm Digestion on the Chemical Compositions of Various Clay Minerals from Soils

Aims: The impact of living organisms activities in soils may generate various chemical and mineralogical changes. The objective of this study is to estimate the impact of earthworms on the chemistry of soil minerals such as the clay minerals. Study Design: An experiment was carried out integrating earthworms and clay minerals. The modifications due to this interaction between minerals and organic matter induced by earthworms’ digestion are discussed. Place and Duration of Study: Institut des Sciences de la Terre et de l’Environnement (UdS/CNRS), Université de Strasbourg, Strasbourg, France. Eight weeks of experiment for each type of clay. Methodology: The earthworm Lumbricus terrestris was used for digestion of illite and various smectite-type minerals, with or without peat moss, during a laboratory experiment at a constant temperature of 20°C during 8 weeks and under artificial 12 hour-light and 12 hour-dark cycles, for each digestion cycle. Results: The chemical elements extracted from smectites by the earthworm digestion appear to be mineral dependent. The behavior of K and radiogenic 40Ar is more dictated by the type of digested mineral than by the digestion process itself. The 87Sr/86Sr ratio of the acid leachates of the nontronite and peat mixture, before and after digestion, suggests that half of the digested matter corresponds to the digestive action of the earthworms, with the second half resulting from food. Digested clay material represents up to 30% and the peat moss the remainder of the mixtures. Conclusion: This study highlights the role of organic compounds generated by earthworms activities in transfer of elements to surface waters and soil fluids.

The single atom Fe loaded catalytic membrane for effective peroxymonosulfate activation and pollution degradation

A novel iron-based single-atom catalyst (Fe SAC) integrated into a catalytic membrane was developed for peroxymonosulfate (PMS) activation and organic pollutant degradation. The Fe SAC membrane was synthesized using a co-precipitation method and acid leaching treatment, and its catalytic activity was evaluated in a continuous flow-through system using nitenpyram (NPR) as a model pollutant. The Fe SAC membrane/PMS system achieved over 90% NPR removal efficiency with low iron leaching (2.85–8.05 μg/L) during 10 hours of continuous operation, and maintained over 80% NPR removal in tap water, Yellow River water, and Yangtze River water. Experimental and theoretical analyses revealed that the strong chemisorption and electron transfer between PMS and FeN4 led to the dominant production of singlet oxygen for NPR degradation. This study demonstrates the potential of SAC-based catalytic membranes for efficient and stable attenuation of refractory organic pollutants in water treatment applications.

Recycling of sludge residue as a coagulant for phosphorus removal from aqueous solutions.

Phosphorus pollution poses a significant challenge in addressing water contamination. The coagulant is one of the effective methods to remove phosphorus from wastewater. Abundant Al and Fe oxides in sludge residue make it have great potential to synthesize water treatment coagulants. However, the utilization of sludge residue for preparation of coagulant was seldom investigated. In this study, we fabricated a novel coagulant, polyaluminum ferric chloride (SM-PAC), using sludge residue as a raw material through acid leaching and polymerization processes. Characterization results confirm that the parameters of SM-PAC meet the specifications outlined in the national standard (GB/T 22627-2022). We investigated the effects of pH, dosage, initial phosphorus concentration, and contact time on the removal efficiency of SM-PAC. As anticipated, the prepared SM-PAC exhibited a significant efficacy in removing phosphorus, meeting the discharge standards set for municipal sewage. Furthermore, the adsorption kinetics analysis suggests that the predominant mode of phosphorus adsorption on SM-PAC is chemical adsorption. Furthermore, the SM-PAC was employed in the actual wastewater treatment plant and exhibited excellent efficiency in phosphorus removal. The utilization of SM-PAC can not only effectively address the issue of sludge disposal but also achieve the goal of "treating waste with waste." It is expected that the proposed method of reusing sludge residue as a resource can provide a sustainable way to synthesize a coagulant for phosphorus removal.

Sustainable recovery of rare earth elements from Ni-MH batteries: Flux-free thermal isolation and Subsequent hydrometallurgical refinement

This study details a sustainable approach for efficient recovery of highly pure rare earth elements oxides (REOs) from Ni-MH batteries. REOs (i.e., La, Ce, Sm, Nd, and Pr oxides) were thermally isolated from spent Ni-MH batteries into an oxide phase with the REO concentration of 67.4 wt%. Subsequently, separate leaching processes were conducted using sulfuric acid and hydrochloric acid solutions, and the results were compared in terms of efficiency and feasibility. Sodium REEs sulfate hydrate (NaRE(SO4)2.xH2O) was precipitated from the sulfuric acid leachate by adjusting the pH to 1.5 using sodium hydroxide, while the addition of oxalic acid to the hydrochloric acid leachate enabled the recovery of REEs as oxalate hydrate (RE2(C2O4)3.xH2O). The resulting sulfate salt was mixed with a sodium hydroxide solution, leading to the formation of REEs hydroxide. The REEs hydroxide and oxalate were calcined at 1000 °C, resulting in the production of REOs with a purity exceeding 99.7%. This research demonstrates the feasibility of developing an efficient, environmentally friendly, and sustainable approach for the recovery of highly pure REOs from Ni-MH batteries which potentially can minimize the environmental impact associated with the extraction of REOs from virgin sources, while addressing the challenge of effective recycling of end-of-life Ni-MH batteries.

Synchronous extraction of Pt, Zr and Ce from spent catalysts via SoG-Si scraps melting collection by regulating Si reduction based on a new fluorine-containing slag

Recycling the rare and precious metals from spent catalysts is critical for the sustainability of the petrochemical and automotive industries and fulfilling to close rare and precious metals materials loops. A major challenge is to extract oxidized rare earth and rare metals while collecting platinum group metals (PGM) for the widely used iron and copper smelting collection. Here, a new method for one-step extraction of Pt (PGM), Ce (rare earth metal) and Zr (rare metal) from spent petrochemical catalysts has been proposed based on collaborative melting of solar grade silicon (SoG-Si) scraps. In this process, Si serves as both a reducing agent and collector, which can reduce the oxidized Ce and Zr to metallic elements, and also collect the reduced Ce and Zr together with Pt. Through thermodynamic calculations and experimental exploration, it was demonstrated that Si can effectively reduce zirconium cerium oxide compared to traditional methods using Fe, Cu, and C. Subsequently, a CaO-Al2O3-SiO2-MgO-CaF2 slag system containing fluorine was developed by adjusting slag basicity and the ratio of silicon to slag, which can greatly improve the process of Si reduction of metal oxides. Under this optimized slag system, maximum recoveries of Ce and Zr reached 79.98% and 95.30% respectively, while Pt recovery remained high at 92.08%. Finally, Pt, Ce and Zr in the obtained Si alloy were well separated through a stepwise acid leaching process. This method offers a promising new avenue for the green, clean, and efficient collaborative processing of petrochemical/automotive catalyst and SoG-Si scraps, and also helps close rare and precious metals materials loops.

Innovative strategy for comprehensive utilization of vanadium slag: Maximizing valuable metals recovery and minimizing hazardous waste generation

Compared to traditional methods, which faced challenges such as enormous toxic waste and low efficiency, self-pressure acid leaching (SPAL) presented a promising solution for the cleaner production of vanadium slag (VS). Under controlled conditions, the structure of vanadium slag (VS) could be disrupted by SPAL. Meticulous optimization of the SPAL process parameters had resulted in remarkable recovery efficiency: 97.72 % for vanadium, 86.09 % for chromium, 90.27 % for manganese, and 94.73 % for iron at 433 K. Mechanism studies revealed that titanium and silicon followed a "dissolution before precipitation" mechanism and ultimately enriched in the non-toxic residue. Importantly, due to the absence of extra oxidants, all metal ions in the leaching solution remained in a low valence state, effectively eliminating the generation of toxic V(V) and Cr(VI). This approach holds significant promise for the efficient and environmentally friendly recovery of valuable metals from VS, while minimizing the production of toxic waste.

Geochemical evaluation and the mechanism controlling groundwater chemistry using chemometric approach and groundwater pollution index (GPI) in the Kishangarh city of Rajasthan, India.

This study is primarily focused on delving into the geochemistry of groundwater in the Kishangarh area, located in the Ajmer district of Rajasthan, India. In pursuit of this research goal, the sampling locations were divided into three parts within the Kishangarh region: Badgaon Rural (KSGR), Kishangarh Urban (KSGU), and the Kishangarh RIICO marble industrial area (KSGI). Various analytical methods have been executed to assess the suitability of groundwater for various purposes based on pH, electric conductivity, total dissolved solids, hardness, salinity, major anions, and cations. The ionic trend of anions and cations was found as HCO3- > Cl- > SO42- > NO3- > Br- > NO2- > F- and Na+ > Ca2+ > Mg2+ > K+, respectively. Applying statistical techniques such as principal component analysis (PCA) and Pearson correlation matrix analysis (PCMA) makes it evident that the physicochemical attributes of water sourced from the aquifers in the study area result from a blend of diverse origins. In addition, Gibbs, Piper, Durov, and scatter plots were used to assess groundwater's geochemical evolution. Piper plot demonstrated the two types of groundwater facies, Na-HCO3- and Na-Cl, implying significant contributions from evaporitic dissolution and silicate weathering. Also, the scatter plots have evaluated the impression of mine acid leachate, evaporitic dissolution, and silicate weathering to upsurge salt formation in the groundwater. The pollution risk evaluation within the study area was conducted using the groundwater pollution index (GPI). This index revealed a prominent concern for pollution, particularly in the northern segment of the study region. As a result, it can be inferred that the fine aeolian sand and silt formations in the northern part are relatively more vulnerable to contamination.