Journal of Sustainable Metallurgy最新文献

Literature regarding metals recovery from LED waste mainly focuses on semiconductor materials and precious metals, lacking data about rare earth elements. This paper explores this gap presenting an experimental study of yttrium extraction from LED waste by alkali fusion/acid leaching method. For this purpose, LED samples were obtained from tubular lamp. Chemical and thermal analyses were performed. Alkali fusion preprocessing was adopted followed by nitric acid leaching to solve difficult yttrium extraction from aluminate structure of LED phosphor. A chemical reaction mechanism in the alkali fusion involving degradation of the silicone polymer and destruction of the aluminate phosphor has been proposed as a novel approach to the subsequent easy leaching of rare earths from LED waste. Fusion conditions were 700 °C, for 3 h, NaOH/LED relation 1:1. Leaching solutions and solid residue were analyzed by energy dispersive X-ray fluorescence spectrometry, induced coupled plasma optical emission spectrometry, X-ray diffractometry and Fourier transform infrared spectroscopy. It was observed the undesirable formation of silica gel in the leaching liquor processed in temperatures below 70 °C. In that way, it is recommended the leaching at 90 °C, with formation of insoluble SiO₂. Optimal leaching conditions found were leaching time of 20 min, 1/20 solid/liquid ratio, with 91% yttrium extraction in HNO₃ 2.5 mol/L at 90 °C.

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Antimony is often used as a hardener for alloys. There are few studies on the preparation of antimony from Sb₂O₃ by microwave carbothermal reduction. In this study, Sb₂O₃ was used as the raw material, and the resonant cavity perturbation method was used to select anthracite as the reducing agent according to the microwave absorption of the material mixture. The single-factor experiment of reduction temperature, reduction time, and reducing agent ratio was carried out in a microwave tube furnace. The process parameters were optimized by response surface methodology (RSM). Under the optimized conditions, the reduction temperature was 758 °C, the reduction time was 56 min, the reducing agent addition ratio was 0.123, and the molten salt addition ratio was 0.1. An antimony ingot with a yield of 92.19% and a purity of 99.45% was obtained. The products and residue of the antimony ingot were analyzed by X-ray diffraction analysis (XRD), X-ray fluorescence (XRF), thermogravimetric (TG) analysis, scanning electron microscopy (SEM), and the mechanism of carbothermal reduction of antimony oxide powder in a microwave field was studied. The results showed that the microwave carbothermal reduction process of Sb₂O₃ under a microwave field had three stages: 25~655 °C, 655~850 °C, and >850 °C. Different stages changed with temperature. This green and energy-saving microwave heating technology can provide a feasible method for the efficient preparation of antimony.

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The study investigates the combustion-assisted synthesis of lithium orthosilicate (Li₄SiO₄) powders for potential CO₂ capture applications. Technical-grade lithium carbonate and metallic silicon powders were used as starting materials. Synthesis conditions were explored across temperatures ranging from 500 to 900 °C and different holding durations. Thermodynamic modeling using FactSage 8.2 software suggested that Li₄SiO₄ production is feasible at temperatures of 700 °C and higher with metallic silicon as the silicon source, which was confirmed experimentally. Characterization of the synthesized powders involved X-ray diffraction, specific surface area determination, particle size distribution analysis, scanning electron microscopy, and CO₂ uptake tests. Despite having the lowest Li₄SiO₄ content as 83.7%, the sample synthesized at 700 °C with 45 min of holding time showed the best CO₂ uptake performance as 12.80 wt% while having the lowest crystallite size value (126.58 nm), the highest specific surface area value (4.975 m²/g) and the lowest average particle size value (10.85 µm) which are highly effective on the CO₂ uptake performance of such solid sorbents. The study concludes that while challenges remain in achieving optimal CO₂ capture performance, it lays a foundation for utilizing lithium orthosilicate in carbon capture applications.

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The steel industry is regarded as the most critical industry in the nation and is crucial to economic prosperity; however, its high energy use and carbon emissions significantly impact climate change and global warming. In view of achieving carbon neutrality, one of the most promising technologies is using green hydrogen gas as a reductant for producing carbon emission-free direct reduced iron (H-DRI) from iron ores/pellets. Moreover, the produced H-DRI is subsequently used for steel making in the induction furnace/electric arc furnace. However, the study on the melting behavior of H-DRI, interaction among slag and metal produced from H-DRI with refractory during the steel making in induction furnace/electric arc furnace has yet to be thoroughly studied. Therefore, in this study, DRI’s dissolution/melting behavior in the liquid iron at 1600 ± 10 °C has been studied. Then, interactions among slag generated during the melting/dissolution of DRI, refractory of the induction furnace, and metal produced from H-DRI have been studied using the SEM backscatter electron method. The thermodynamics modelling for the slag formation and interactions among slag-metal-refractory systems have been studied using FactSage 8.2. The penetration of iron from a liquid melt into porous refractory and the formation of complexes like mullite, spinal, and olivine has been observed. The boundaries between the slag-metal-refractory system and the dissolution of Mg and Fe have been identified using backscattered electron mode. Thermodynamics modelling has been validated with experimental observations.

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The depletion of the Merensky ore has led the South African platinum industry into largely mining and processing Upper Group Two (UG-2) ore for the extraction of Platinum Group Metals (PGMs). However, the processing of the UG-2 material is not fully amenable to the conventional pyrometallurgical route due to the high chrome content. Therefore, in this study, a bio-based process for base metal extraction from UG-2 flotation concentrates was investigated. This study represents only part of the work done in a broader investigation to develop a completely biological two-stage process for the extraction of base metals and PGEs. In this paper, only the first stage of the process is presented. This study evaluated a mixture of indigenous thermoacidophile archaebacteria namely, Acidianus brierleyi, Sulfolobus sp., and Metallosphaera sedula. A statistical Design of Experiments (DOE) was used for finding optimal conditions. Factors investigated included particle size, pH, pulp density, inoculum dosage, and temperature. Optimal extraction efficiencies of 92% for Co, 97% for Cu, and 99% for Ni were predicted at correlation coefficients of 92.5%, 93.2%, and 88.0%, respectively, thus, verifying the fitness of the model. Optimal base metal extractions obtained were 99.3% for Co, 90.1% for Cu, 41.58% for Fe, and 99.5% for Ni. The results showed a substantial extraction of base metals from UG-2 PGM flotation concentrate suggesting a potentially feasible option for industrial bioprocessing of PGM concentrates. To the best of the authors’ knowledge, this is the first report on bioleaching of base metals from UG-2 flotation concentrates.

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The applicability of utilizing solvent extraction processes of manganese (Mn) and zinc (Zn) from chloride leachate of spent zinc–carbon (Zn–C) batteries has been studied by using di-2-ethylhexyl phosphoric acid (DEHPA) as an extractant agent. The effect of five factors (equilibrium pH, O/A ratio, temperature, extractant concentration, and diluent type) were investigated. According to the results gained, the appropriate solution pH level for DEHPA was found to be 6.5. With DEHPA (20%, v/v), 77.50% Mn and 100% Zn were extracted, within 15 min contact time at a 1:1 aqueous/organic ratio and 50 °C temperature. Also, a McCabe–Thiele diagram was drawn and one single-step extraction for Zn and a two-stage process for Mn were needed to achieve the highest extraction efficiency. ΔH as a thermodynamic parameter was calculated and found to be 18.39 kJ/mol for Mn and − 245.50 kJ/mol for Zn, respectively, indicating that the extraction process was endothermic for Mn and exothermic for Zn. A desirable stripping of Mn and Zn from the loaded organic phase could be obtained using a stripping solution of 6 M HCl.

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Pyrometallurgical processing of lateritic ore produces huge amounts of ferronickel slags, which may contain valuable metals. This paper describes a novel hydrometallurgical route to recover metals from ferronickel slag samples and reduce liability matters using oxidative acidic leaching. Hydrochloric acid and hydrogen peroxide were employed as leachants. A 2^4–1 factorial fractional design with 11 experiments was employed as a screening design to evaluate HCl concentration (3.0–6.0 mol L^–1), H₂O₂ concentration (0.5–2.5 mol L^–1), leaching time (30–240 min), and solid–liquid ratio (75–125 g L^–1). HCl and H₂O₂ concentrations were statistically significant for mass and metals leaching yields, which were studied by Doehlert design with 9 experiments with a response surface methodology (RSM). More than 80 wt% of cobalt and nickel, and ~ 75 wt% of iron were leached under the optimum region indicated by Doehlert design: 5.4–6.0 mol L^–1 HCl, 0.7–1.5 mol L^–1 H₂O₂, 25 °C, 120 min, and 100 g L^–1 solid–liquid ratio. Over 70 wt% of the slag mass was dissolved. The insoluble matter is essentially Fe₃O₄ and SiO₂. Chromium was poorly leached. The mild experimental conditions, namely temperature, leaching time, and leachant concentrations make the novel route very attractive for processing medium- to low-quality ferronickel slags and for reducing the environmental impact of this liability.

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To meet the goals of the national "Dual Carbon" strategy and reduce energy consumption in the steel industry, accurate prediction of steel composition is crucial for precise control over alloy addition in steelmaking. Several models have been created to predict the composition of the converter endpoint with a high level of accuracy. However, the different shortcomings of each have prevented large-scale application in real production environments. CBR prediction model has limited scope to solve the problem. CNN model has complex data processing and no memory. RELM model has randomly given input layer weights and hidden layer deviations. In this study, correlation analysis was used to analyze the factors influencing the carbon content at the endpoint of converter steelmaking. A feasible model was established and applied to predict the carbon content at the endpoint of converter using t-distributed stochastic neighbor embedding (t-SNE), particle swarm optimization (PSO), and backpropagation (BP) neural network. The learning rate, training times, and hidden layer nodes number of the prediction model were optimized. The prediction hit ratios for the carbon content in the error ranges of ± 0.003%, ± 0.01%, and ± 0.02% are 61%, 86%, and 98%, respectively. Meanwhile, apply the established model to actual production, the carbon content of the product can be stably controlled between the lower and median limits, the control effect is significantly better than traditional methods. The results demonstrate that the t-SNE-PSO-BP model performs better than the known models. The accurate prediction of the carbon content at the endpoint of converter can greatly contribute to realizing a “narrow composition control” of the molten steel. Realize accurate prediction of carbon content at the endpoint of converter smelting, and has been effectively applied to industrial production.

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Under the traditional method of predicting the endpoint carbon content of the converter, the hit rate of the middle and lower limits of the carbon content in the product is 48%. The t-SNE-PSO-BP model predicts the carbon content at the endpoint of the converter model, and the product carbon content can be controlled stably between 0.21–0.23%. According to the study results and actual application effects, use the t-SNE-PSO-BP model to predict the carbon content at the endpoint of the converter is appropriate, and is conducive to the “narrow composition control” of the steel composition in the converter steelmaking process.

In this paper, the vanadium extraction tailings (VT) by sodium roasting—water leaching were used to prepare the active catalyst by activate treatment to explore denitrification. The influence of activating parameters and denitrification conditions on NO_X removal of the catalyst were analyzed with selective catalytic reduction (NH₃-SCR). The surface behavior was characterized by BET, SEM, XPS, H₂-TPR, and NH₃-TPD. The results show that optimal catalyst was prepared under the conditions that acid medium was 12% (volume fraction) HNO₃, particle size of VT was less than 38 μm, and calcination temperature was 500 °C; its NO conversion rate reached 95% under the denitrification conditions of 5% O₂, 500 ppm NO, 500 ppm NH₃, and gas hourly space velocity 50000 h⁻¹. The optimal catalyst performed well for against SO₂ poisoning but bad for H₂O. The specific surface area and specific pore volume of optimal catalyst increased by 11.10 and 7.95 times compared with VT. The optimal catalyst featured a greater ratio of Fe³⁺, Mn⁴⁺, V⁵⁺, and chemisorbed oxygen, lower temperature of iron reduction, and higher H₂ adsorption peak, which were in favor of NO_X removal. Moreover, its surface acidity was enhanced reflecting in a larger NH₃ desorption peak area and a 43 °C higher desorption temperature than VT.

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The application of pressure oxidation (POX) followed by thiosulfate gold leaching is an efficient method used to extract gold from double refractory gold ores containing both sulfide and carbonaceous matter. This process is expected to result in high gold recovery rates, as it liberates gold from sulfides and eliminates the preg-robbing behavior of carbonaceous matter. Despite these expectations, the optimization study showed a maximum gold recovery of only 59% after 24 h of leaching. The optimal conditions occurred when the thiosulfate concentration was 0.14 M, the cupric ion concentration was 0.78 mM, and the temperature was set to 50 °C. To address the problem of low gold recovery, additional investigations involving kinetics tests and characterization techniques were conducted. After optimizing the conditions, it was observed that the leaching recovery was hindered at 1 h. However, this impairment did not have a significant impact on the overall recovery at 24 h. An investigation using TEM-mapping revealed that fine gold particles were disseminated within the minerals, and high concentrations of gold were also detected in locked pyritic minerals. This finding exposed the challenge of low gold recovery from alkaline POX discharge. A thiosulfate leaching test following mineral decomposition demonstrated that the complex mineralogy and poor gold liberation of the original ores were the primary factors contributing to low gold recovery. Therefore, this study suggests that increasing the degree of gold liberation is essential to address the issue of leaching recovery from alkaline POX feed.

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