Acid Leaching Research Articles

Effect of Al(OH)3 on the Properties of Silica-based Ceramic Cores Prepared by Laser Powder Bed Fusion Combined with Vacuum Infiltration

Silica-based ceramic cores, with low coefficients of thermal expansion, low sintering temperatures, and excellent acid and alkali leaching capabilities, are essential materials for the production of hollow blades. However, their mechanical properties are suboptimal, and they present various processing challenges. In this study, silica-based ceramic cores were prepared using a combination of vacuum infiltration (VI) and laser powder bed fusion (LPBF) techniques. Al(OH)3 was employed as a mineralizer to enhance the post-sintering mechanical properties and improve the efficiency of the vacuum infiltration process, thereby enhancing the overall performance of the silica-based ceramic cores. The VI process facilitated the penetration of nano-SiO2 into the samples, increasing their density and promoting the formation of cristobalite during sintering at 1225°C. Additionally, the Al(OH)3 powder, through pyrolysis into Al2O3 during sintering, reduced microcracks, inhibited excessive cristobalite transformation, and improved the VI process, resulting in enhanced room-temperature flexural strength. By optimizing the Al(OH)3 content and the VI process, significant improvements in the microstructure and properties of the silica-based ceramic cores were achieved. After three rounds of vacuum infiltration and the addition of 4wt.% Al(OH)3, the samples exhibited a high-temperature creep of 0.17mm, with flexural strengths of 15.23MPa at room temperature and 23.55MPa at high temperature.

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.

Effect of pH neutral on the separation of nickel and cobalt from laterite leaching solution using cyanex 272

Abstract Nickel and cobalt are the most common elements in the earth’s crust that naturally occur in laterite ores. Nickel and cobalt from laterite ores are recovered as products such as mixed hydroxide precipitate (MHP) and mixed sulphide precipitate (MSP). This research focuses on how the nickel laterite leach solution can be processed directly for solvent extraction without going through the precipitation stage. The nitric acid leach solution obtained from the laterite ore is used to extract nickel and cobalt. A cyanex 272 extractant and kerosene mixture will be used as an organic solvent for direct extraction. The raw material used was Indonesian laterite ore from Halmahera Island, which contained Ni (1.72%), Co (0.155%), Fe (26.17%), and other minor elements. The effect of pH in a neutral condition was investigated on the extraction efficiency, distribution coefficient, and separation factor. Nitric acid (1M) was applied as the leaching reagent. The variables include pH variations (6.8; 7.0; 7.2; 7.4; 7.6), 20% cyanex 272, and O/A ratio (1:1/v:v) at 20 minutes with a stirring speed of 500 rpm. Optimum results were obtained at pH 7.4 variation with an extraction efficiency of 69.26% for cobalt and 0% for Ni, respectively. At these optimum conditions, the highest distribution coefficient value is the element cobalt at pH 7.4, and the result is 2.253 with a separation factor (∞). The optimum condition focuses on removing cobalt from the organic phase, not nickel.

Intrasample osmium isotope disequilibrium in young volcanic rocks: Insights from a new progressive digestion procedure

Some young volcanic rocks have been found to possess intrasample Os-isotope heterogeneity. This has important implications for source tracing and dating. Here, we use a new procedure through which it is possible to sequentially extract, from a single aliquot, the 187Os/188Os ratio of: i) the surface contaminant(s) (hydrobromic acid leachate); ii) the residual bulk rock powder (Step I) and iii) the Os-bearing phases entrapped within silicates (Step II). We applied this technique to two young basaltic reference materials (RMs), USGS BHVO-2 and EN026 10D-3. The former samples the 1919 lava from the Kīlauea summit crater (Hawaii) and the latter is a basalt sample dredged from Mohns Ridge (Greenland Sea). Both rock standards have previously been shown to display large intrasample Os isotope heterogeneity. In addition to analyzing these RMs, we also analyzed the RM USGS BHVO-1 for comparison, as well as another sample from the Kīlauea 1919 summit eruption (Kil 1919-6) along with a picritic tholeiite from the Kīlauea Iki 1959 eruption.Our leaching results show that BHVO-2 is contaminated with a highly radiogenic and labile contaminant with 187Os/188Os ratio of 0.525 ± 0.021. Without leaching, the Step I 187Os/188Os ratios varied from 0.1399 ± 0.0013 to 0.1568 ± 0.0014 while those for Step II were uniform (average = 0.1286 ± 0.0006, N = 5). A comparison of Re, Mo concentrations and 187Os/188Os ratio of the leachates of BHVO-2 and its predecessor (BHVO-1) indicates that BHVO-2 was contaminated during preparation. After leaching, the Step I and Step II 187Os/188Os ratios of BHVO-1 and another sample (Kīlauea 1919-6) from the same lava flow are identical within error to that of the Step II ratio of BHVO-2. A picrite from the 1959 Kīlauea Iki eruption also analyzed using the new technique gives homogenous results for both the steps with an average 187Os/188Os ratio of 0.1302 ± 0.0005. The 187Os/188Os ratio of recent Kīlauea lavas is identical within error to that of the primitive upper mantle (=0.1296). The Kīlauea Os-isotope composition could represent a “common component” that occurs globally in many plumes. The Step I 187Os/188Os ratio of EN026 10D-3 is 0.136 with Step II ratio being 0.131 (N = 2). The Step II 187Os/188Os ratios are more radiogenic than the nearby Jan Mayen lavas (187Os/188Os = 0.124–0.129) that have been argued to influence the chemistry of the Western section of the Mohns Ridge basalt but fall within the range of the Primitive Upper Mantle. We also discovered that BHVO-1, KIL 1919-6, 1959 Kīlauea Iki picrite, and EN026 10D-3 show Os-isotope disequilibrium between the leachate and Step I, suggesting wall rock assimilation during magma ascent. The data set presented here indicates a need for re-evaluating the extent to which mantle heterogeneities influence the Os isotope composition of ocean basalts.

Recycling of secondary aluminum dross to make alumina by hydrometallurgy: A review

Secondary aluminum (Al) dross (SAD) is a hazardous waste discharged from Al production, processing and recycling. Over 6.7 million tons of SAD was discharged on the planet in 2023. SAD is consisted of 40–60 wt% of alumina (Al2O3), 10–30 wt% of AlN, 5–15 wt% of salts and 3–10 wt% of heavy metal oxides. Currently, recycling of SAD to make Al2O3 by hydrometallurgy is a promising method for disposal of SAD. Hydrometallurgy method is mainly divided into acid leaching and alkali leaching. In acid leaching, Al, AlN and Al2O3 react with acid to form aluminum sulfate and aluminum chloride. In alkali leaching, Al, AlN and Al2O3 react with alkali to form sodium aluminate. High-purity Al2O3 is obtained after precipitation, washing, drying and calcination from the leachate. Resource consumption and emission was calculated to evaluate the economic and environmental benefits. About 147.9 and 172.6 dollars was earned after making Al2O3 from a ton of SAD by alkali and acid leaching process, respectively. And carbon emissions of a ton of Al2O3 was risen about 596.5 and 2216.0 kg CO2, respectively, compared with the Bayer process with bauxite. We proposed a calcination pre-treatment with quicklime on SAD to reduce the carbon emission. The Al and AlN are oxidized into Al2O3 after calcination, and the Al2O3 reacts with CaO to form CaO·Al2O3. The Al in CaO·Al2O3 can be leached out easily with a low concentration of alkali. This review provides a guidance for the recycling of SAD by hydrometallurgy, and proposes a novel idea for the energy and consumption reduction in alumina (Al₂O₃) production.

Approach towards the Purification Process of FePO4 Recovered from Waste Lithium-Ion Batteries

The rapid development of new energy vehicles and Lithium-Ion Batteries (LIBs) has significantly mitigated urban air pollution. However, the disposal of spent LIBs presents a considerable threat to the environment. Recycling these waste LIBs not only addresses the environmental issues but also compensates for resource shortages and generates substantial economic benefits. Current recycling processes primarily focus on the extraction of valuable metals, often overlooking the treatment of residual waste post-extraction. This project targets the iron phosphate (FePO4) derived from waste lithium iron phosphate (LFP) battery materials, proposing a direct acid leaching purification process to obtain high-purity iron phosphate. This purified iron phosphate can then be used for the preparation of new LFP battery materials, aiming to establish a complete regeneration cycle that recovers lithium carbonate and iron phosphate from waste LFP materials for the production of LFP. The study investigates process parameters such as acid types and concentrations, leaching time, and the number of leaching cycles. The results demonstrate that, after purification, the levels of impurity metals decrease while the iron content increases correspondingly. Under optimized experimental conditions, the dilute sulfuric acid leaching rates of Al, Cu, Ca, and Ni reached 36.0%, 51.4%, 89.5%, and 90.9%, respectively. Furthermore, hydrothermal treatment in dilute phosphoric acid achieved leaching rates of 87.9%, 85.8%, 98.4%, and 99.1% for Al, Ca, Cu, and Ni, respectively. The microstructure characterization revealed significant changes in phase and grain morphology during the leaching process in dilute phosphoric acid, which are likely associated with the liberation of impurity atoms from the lattice. These findings indicate that acid leaching is highly effective in removing impurities from the iron phosphate recycled from waste LIBs.

Synthesis and Characterization of Silicon Nanoparticles from Coal Fly Ash Using Ultrasonication as a Battery Anode

Fly ash, a byproduct of coal combustion, is rich in silica, alumina, and other minerals, making it a valuable resource for extracting high-purity silicon. The synthesis of silicon nanoparticles from coal fly ash involves several critical steps, including the extraction of silica (SiO2) via the sol-gel method, reduction of silica to silicon using the metallothermic method, and subsequent ultrasonication to achieve nanoscale particles. Studies have shown that fly ash can contain up to 49.21% silica, which can be further purified to 93.52% via chemical extraction methods such as acid leaching and alkali dissolution. The reduction of silica to silicon is carried out using the metallothermic method, which involves the use of magnesium-reducing agents to convert SiO2 to elemental silicon. This process produces silicon with a purity of about 61.3%, which can be further increased through ultrasonication. Ultrasonication is a technique that uses high-frequency sound waves to break particles into smaller sizes, resulting in more uniform and homogeneous nanoparticles. In this study, ultrasonication for 60 and 120 min reduced the average particle size of silicon from 208.94 nm to 58.87 nm and 20.13 nm, respectively, and increased the silicon content to 74.6% and 72.7%. X-ray diffraction (XRD) and distribution particle analyses confirmed the particle size reduction and homogeneity of silicon nanoparticles, indicating the effectiveness of ultrasonication in producing high-quality silicon nanoparticles. The synthesized silicon nanoparticles have significant potential applications, particularly as anode materials in lithium-ion batteries, due to their increased surface area and improved electrochemical properties. Furthermore, the use of fly ash as a raw material for the synthesis of silicon nanoparticles not only provides a cost-effective and environmentally friendly alternative to traditional silica sources but also helps in reducing the environmental impact of fly ash disposal. The integration of the methods and findings of this study underscores the feasibility and benefits of using coal fly ash for the sustainable production of silicon nanoparticles, which can be utilized in energy storage as anode materials in lithium-ion batteries.

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.

Preparation of imprinted cryogels of cellulose cross-linked ionic liquids for selective separation of Gd(III) from rare earth leachate

The development of high technology has elevated industry’s dependence on rare earth resources. The hydrometallurgical process is widely used for the separation of rare earth elements (REEs) from rare earth ores, producing acidic leachate with trace amounts of REEs. Recovery of REEs from rare earth leachate not only mitigates the negative impact of leachate on the environment, but also contributes to the realization of sustainable resource utilization. In this study, two novel imprinted cryogel adsorbents, methyltrioctylammonium chloride-derivative carboxymethylated cellulose nanocrystal imprinted cryogel (LR-ICMC) and ethylmethylimidazolium bromide-derivative carboxymethylated cellulose nanocrystal imprinted cryogel (LM-ICMC), were constructed by using carboxymethylated modified cellulose nanocrystals as a backbone structure, and successfully branched ionic liquids (ILs) methyltrioctylammonium chloride-derivative and ethylmethylimidazolium bromide-derivative, respectively, for the separation of gadolinium ions (Gd(III)) from rare earth leachate. Firstly, SEM and TEM results showed that the incorporation of ILs retained part of the pore structure of carboxymethylated cellulose nanocrystals (CMCNCs). BET and TG results illustrated that the incorporation of ILs effectively increased the specific surface area and thermal stability of LR-ICMC and LM-ICMC. FT-IR and XPS results showed that LR-ICMC and LM-ICMC could adsorb Gd(III) by electrostatic and chelating effects. Secondly, adsorption isotherm experiments demonstrated the adsorption capacities of 66.880 mg/g and 75.895 mg/g for LR-ICMC and LM-ICMC, respectively; adsorption kinetic experiments demonstrated the ability of LR-ICMC and LM-ICMC to rapidly adsorb 85.152 % and 87.989 % of the maximum adsorption capacity, respectively, within the initial first 40 min. Finally, cycling experiments demonstrated the advantages of LR-ICMC and LM-ICMC in reuse, maintaining 89.245 % and 90.734 % of the original performance after five adsorption–desorption cycles, respectively. Based on these results, LR-ICMC and LM-ICMC were demonstrated to be highly efficient and reusable adsorbents for selective recovery of Gd(III) from rare earth leachate. This study deepens the application of ILs in solid-phase adsorbents and highlights the great potential of LR-ICMC and LM-ICMC in the field of REEs recovery.

Integration of CO2 sequestration with the resource recovery of red mud and carbide slag

Red mud and carbide slag, strongly alkaline solid wastes, are produced during the manufacturing of alumina and acetylene gas, respectively. Improper management of these wastes can pose significant environmental hazards. This study proposed a novel method for the collaborative treatment of red mud and carbide slag, enabling the recovery of constituent elements with CO2 sequestration. During the hydrochloric acid leaching process, Si was reclaimed as Si-rich residue, whereas Ti, Al, Ga, Fe, and Sc were stepwise recovered as Ti-rich product, Al/Ga-rich filtrate, and Fe/Sc-rich product via the subsequent hydrolysis, co-precipitation, and alkali leaching processes, respectively. Utilizing carbide slag to replace the energy-intensive NaOH for pH adjustment in the leaching solution resulted in a Ca2+ concentration of 21,922 mg/L in the filtrate after co-precipitation. Through further mineralization process, CO2 sequestration was achieved alongside the production of CaCO3 with the content reaching 98.5 % along with a whiteness of 94.4 %. Furthermore, by adjusting the experimental parameters in the mineralization process, controlled manipulation of the phase and morphology of the CaCO3 product could be achieved to meet various industry requirements. To summarize, the complete resource recovery of red mud and carbide slag was achieved in this study, demonstrating the promising potential in practical applications.

Zirconium titanium phosphonates for enhanced lanthanide recovery from acidic wastes

Metal phosphonates show promise for recovery of valuable lanthanide (Ln) elements from acidic waste streams due to their selectivity, high capacity, fast kinetics and chemical stability. To optimise these properties, a balance is needed between free phosphonate groups available to bind Ln and P-O-metal linkages to provide stability. This work demonstrates how astute choice of metal precursors can be used to control the phosphonate structure and maximise both sorption and stability. Relative to single metal zirconium phosphonate, mixed metal zirconium titanium phosphonate sorbents had more free phosphonate groups and greater porosity, increasing Ln capacity by 30 % and the kinetic rate constant by 90 %. Acid stability was also improved upon Ti inclusion. Use of metal propoxide and tert-butoxide precursors were also compared, revealing different reactivities with Zr versus Ti. Specifically, the tert-butoxide precursor increased P-O-Zr linkages and acid stability with Zr, but increased formation of leachable P-O-Na2 groups in the presence of Ti that decreased acid stability. The optimised zirconium titanium phosphonate sorbent used metal propoxide precursors and a Zr:Ti molar ratio of 1:1 to achieve (1) selectivity for Ln over Co, Sr and Cs, (2) sorption capacity of approximately 70 mg Eu/g, (3) fast kinetics with > 99 % sorption in 10 min and (4) retention of 60 % sorption capacity after contact with 5 M nitric acid. The enhanced chemical stability, capacity and kinetics achieved via incorporating Ti drastically improves the practicality of these sorbents for Ln recovery from acidic leachates of magnets, phosphors and other wastes.

Nitrogen recovery from biogas slurry with high ammonia nitrogen concentration through struvite precipitation utilizing acid leaching solution of collophanite tailings

ABSTRACT The high concentration of ammonia nitrogen (NH4+) and chemical oxygen demand (COD) in biogas slurry pose great challenges to the efficiency of traditional wastewater treatment systems. Collophanite tailings are solid waste, characterized by significant concentrations of phosphorus (PO43-) and magnesium (Mg2+), represent a potential resource for the reduction and recovery of NH4+ in biogas slurry via struvite precipitation. This study systematically explored the optimal leaching parameters employing sulfuric acid for the extraction of PO43− and Mg2+ from collophanite tailings. The effect of [PO43-]:[NH4+] molar ratio and pH on the recovery of NH4+ in biogas slurry was investigated. The physicochemical properties of the precipitates were confirmed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and chemical analysis. Results suggested that the highest removal efficiency of NH4+ (88.5%) was achieved when employing a [PO43-]:[NH4+] molar ratio of 1.0 at pH 9.5. Evaluation of effluent quality demonstrates a significant enhancement in the biodegradability of the treated biogas slurry, evidenced by an increase in the COD/TN ratio increased from 2.1 to 10.4. Economic analysis shows that the net income would be approximately 21.33 USD/m3 for proposed produces. These findings underscore the potential of utilizing collophanite tailings for NH4+ recovery from biogas slurry.

Rapid precipitation of vanadium from solution using melamine as precipitant with high efficiency

AbstractBACKGROUNDSelective catalytic reduction (SCR) can effectively remove NOx from flue gas in a coal‐fired power plant. As the core of SCR technology, the catalyst has a limited lifespan. The process of reducing acid leaching and roasting water leaching can efficiently extract vanadium and tungsten from spent SCR catalyst. For vanadium recovery in solution, the traditional vanadium precipitation process by NH4Cl has the disadvantages of consuming high precipitant dosage and producing large amounts of waste water.RESULTSThis study focused on the vanadium precipitation process using a solution containing vanadium obtained from adopting some steps to handle the spent SCR catalyst. First, melamine was screened out as the vanadium precipitant. Then, the vanadium precipitation conditions were optimized as follows: solution pH value of 1.0, n(C3H6N6)/n(V) = 0.8, 110 °C and 30 min. Under the best precipitation conditions, the vanadium precipitation efficiency of melamine can reach 99.32%. Finally, the mechanisms of vanadium precipitation by NH4Cl and melamine were discussed, respectively.CONCLUSIONThe results showed that the vanadium precipitation process by NH4Cl followed the chemical reactions between NH4+ and vanadium ions, while the vanadium precipitation process by melamine followed the redox and complexation reactions which essentially belonged to the types of chemical adsorption. The vanadium precipitation product was roasted at 550 °C for 2 h to obtain the vanadium product. The main component of the vanadium product was V2O5, with a purity of 93.27 wt%. The total recovery efficiency of vanadium from spent SCR catalyst was 78.24%. © 2024 Society of Chemical Industry (SCI).

Preparation of polymeric aluminum chloride from secondary aluminum dross and its water purification effect

ABSTRACT Aluminum dross is solid waste generated by the aluminum industry. Currently, a large amount of aluminum dross is produced annually year. Aluminum dross, a hazardous waste, contains harmful substances such as aluminum metal, aluminum nitride, fluoride and chlorine salts, which pose a serious threat to human health and also cause damage to the ecological environment. Thus, it is important to recycle secondary aluminum dross and realise its high-value utilisation. Polymeric aluminum chloride (PAC) is a polymer flocculant, at present, China's annual use of PAC in the field of water treatment is about 5 × 105 t, and with the continuous improvement of water purification requirements, the annual use of PAC increased year by year. Here secondary aluminum dross was used as a raw material to prepare PAC by hydrochloric acid (HCl) leaching, followed by the addition of sodium carbonate. The optimal conditions for the acid leaching of secondary aluminum dross for the preparation of PAC were as follows: HCl concentration, 18%; liquid-to-solid ratio, 4.5:1; stirring rate, 200 r/min; reaction temperature, 90 °C; and 60 min. An aluminum leaching rate of 85.5% was obtained under these conditions. The results showed that the acid leachate after adding sodium carbonate, under the conditions of polymerisation temperature of 70 °C, polymerisation time of 6 h, and polymerisation pH value of 3.0, the PAC prepared had an alumina content of 10.19%, salinity of 32.37%, density of 1.32 g/cm3, 1% aqueous solution pH 4.3. The water purification effect of the prepared PAC surpassed that of the commercially available PAC. The utilisation of secondary aluminum dross can reduce the environmental pollution caused by aluminum slag.

Efficient extraction of rare earth elements from coal-series kaolin by combining alkali fusion and sulfamic acid leaching

As a solid waste produced by coal mining, the comprehensive utilization of coal-series kaolin is the focus of attention. In this paper, the extraction of rare earth elements (REEs) from coal-series kaolin was carried out by alkali fusion and sulfamic acid leaching. The occurrence modes of REEs in coal-series kaolin was analyzed by means of inductively coupled plasma-mass spectrometry analyse and sequential chemical extraction. The influence of alkali fusion conditions on the leaching of REEs was investigated, and the activation mechanism of alkali fusion was revealed by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and field emission scanning electron microscope (FESEM) analysis. In addition, the effect of key operating parameters on the leaching efficiency of REEs from coal-series kaolin was further investigated. The results show that REEs mainly existed in silicate & aluminosilicate state of coal-series kaolin. The mineral structure was destroyed by alkali fusion, and the leaching efficiency of REEs was increased by 59.08 %. At the sulfamic acid concentration of 0.5 mol/L, H2O2 concentration of 0.2 mol/L, solid to liquid ratio of 1/50, the leaching efficiencies of total rare earth elements, light rare earth elements and heavy rare earth elements were 84.91 %, 88.43 % and 71.03 %, respectively.

Production of amorphous aluminosilicate and vaterite from acid leaching of hydrated cement paste

Acetic acid has been used to leach Portland cement paste, and the effect of acid concentration, liquid/solid ratio, temperature, and time on leaching of Ca, Al, Fe and Si is reported. The silica-rich solid residue (SR) remaining after leaching was washed, dried, and ground. This amorphous aluminosilicate has comparable pozzolanic reactivity to commercial supplementary cementitious materials (SCM) such as coal fly ash. The 28-day compressive strength of 0.5 w/b mortar containing 20% CEM 1 replaced with SR extracted from cement paste (63.6 MPa) was higher than the reference (51.2 MPa). The leachate from acid leaching contains high levels of Ca2+ ions, and these can sequester CO2 under controlled conditions to form vaterite, a spherical polymorph of CaCO3. Cement paste present in waste concrete can therefore be used to form a reactive silica-rich SCM in a process that sequesters carbon. The research has implications for the development of circular concrete.

New insight into the contribution of Ca, Mn, and Mg component to vanadium extraction from vanadium slag

The contribution of Ca, Mn, and Mg component to vanadium extraction from vanadium slag after calcium roasting−acid leaching was rarely investigated. In this study, vanadium slag was adopted to explore the vanadium extraction behavior, contribution of calcium, manganese and magnesium component to vanadium extraction in blank roasting and calcium roasting by X-ray diffraction analysis (XRD), Scanning electron microscope (SEM), and inductively coupled plasma (ICP). Furthermore, quantitative analysis of different vanadate was clarified in calcium roasting process. The results show that Ca2V2O7, Mn2V2O7, and Mg2V2O7 were mainly generated in blank roasting and calcium roasting. For blank roasting, 79.17 % of vanadium, 60.03 % of manganese and 44.33 % of magnesium was maximally extracted after roasting at 850℃ and leaching with pH of 2.2. The contribution of calcium, manganese, and magnesium component to vanadium extraction namely the ratio of vanadium dissolved by corresponding vanadate to total vanadium in leachate occupied 26.39 %, 49.61 %, and 24.00%. For calcium roasting, after roasting at 900℃ for 1.5 h with n(CaCO3)/n(V2O3) of 1 (molar ratio), vanadium leaching efficiency was 91.23 %. The contribution of calcium, manganese, and magnesium component to vanadium extraction occupied 61.37 %, 28.37 %, and 10.26 %. At least 55.99 %, 25.88 %, and 9.36 % of vanadium generated as calcium vanadate, manganese vanadate, and magnesium vanadate during roasting process.

Recovery of cadmium, lead, strontium and zinc from jarosite waste by using a combinatory approach of bioleaching and acid leaching

ABSTRACT Metallurgical processes commonly generate substantial volumes of hazardous waste, and the extraction of zinc is no exception, yielding a byproduct known as jarosite. This study aims to establish an environmentally conscious and economically viable method for recuperating residual metals from jarosite waste. Comprehensive morphological and physico-chemical characterisation of jarosite was performed using XRD, FTIR, SEM and EDS. To facilitate the selective biorecovery of cadmium, lead, strontium and zinc, Shewanella putrefaciens was employed. The efficacy of biorecovery was systematically assessed using both solid-state and liquid-state leaching methodologies. The results indicate that liquid-state leaching outperformed solid-state leaching for all four heavy metal ions. Notably, biotreated jarosite demonstrated markedly superior metal recovery (Cd, Pb, Sr and Zn) compared to non-biotreated jarosite. This investigation advocates for a hybrid approach, involving bioleaching followed by acid treatment, as a more efficacious strategy for the sustainable recovery of heavy metals from jarosite-like waste. These findings not only underscore the potential of environment-friendly biorecovery techniques but also offer a promising avenue for enhancing the ecological sustainability of waste management practices within the metallurgical industry.

Effects of active silicon amendment on Pb(II)/Cd(II) adsorption: Performance evaluation and mechanism

In this study, a high-Si (Si) adsorbent (APR@Sam) was prepared by acid leaching slag (APR) from lead-zinc (Pb-Zn) tailings based on high-temperature alkali melting technology. The synthesized Si-based materials were applied to aqueous solutions contaminated with Pb and cadmium (Cd) to investigate the crucial role of active Si in sequestering heavy metals. The adsorption capacities of APR@Sam and the Si-depleted material (APR@Sam-NSi) were studied under different pH and temperature conditions. The results showed that as the pH increased from 3 to 7, the adsorption capacity increased, the active Si content in the solution increased by 63 %, and the maximum pH of the solution after adsorption was 7.12. After the removal of active Si, the Pb (II) and Cd (II) adsorption capacities of APR@Sam decreased by 45 % and 11.96 %, respectively. OH- promoted the release of Si into the solution, enhancing the material's adsorption efficiency. The reaction mechanism is mainly attributed to surface complexation guided by Si-O and Si-O-Si bonds, metal cation exchange, and bidentate coordination. The results indicated that the Si component is critical for the removal of Pb (II) and Cd (II) by APR@Sam and provide valuable insights into resource recovery strategies from leaching residues.

Hydrochloric acid leaching of rare earth elements from a novel source of deep-sea sediments and advantage of reduction with H2O2

In this study, the mineralogy of a novel resource of deep-sea sediments containing rare earth elements (REEs) was investigated, along with the leaching of REEs using hydrochloric acid. The results revealed that, apart from 62.0% of the Ce found in the Mn oxides, the other REEs in the deep-sea sediments mostly existed in hydroxyapatite mineral which can be easily decomposed via a hydrochloric acid leaching. An optimized REEs leaching percentage of 89.5% was achieved using 2.0 mol/L hydrochloric acid as the leaching agent, with a liquid-solid ratio of 4:1, at 60 °C for 30 min. However, Mn oxides remained stable during the leaching process, resulting in a low Ce leaching percentage of 30.7%. Under the optimized conditions, Mn oxides could be decomposed by adding 30% H2O2 as a reducing agent, leading to improved leaching percentages of Ce and REEs to 86.6% and 93.2%, respectively. The high leaching efficiency of REEs may further increase the utilization potential of this novel resource.