Journal of Sustainable Metallurgy最新文献

A novel, HCl-based metallurgical process is investigated aiming at the production of α-Al₂O₃ from calcium aluminate slags. The process includes the following stages: (a) leaching of the slag with aqueous HCl to dissolve the aluminum content and separate SiO₂ as a filterable precipitate, (b) HCl_(g) purging precipitation of the dissolved aluminum in the form of aluminum chloride hexahydrate salt (AlCl₃∙6H₂O, ACH), (c) partial removal of dissolved metal impurities from the impure ACH by acetone washing and (d) calcination of the higher purity ACH to produce α-Al₂O₃. Under optimum leaching conditions, approximately 90% of aluminum is successfully extracted. An ACH purity of 97.5% was achieved after the precipitation and purification process. After calcination of the ACH, α-Al₂O₃ of 98.5% purity was produced.

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This study introduces a novel approach in sustainable metallurgy for the efficient utilization and valorization of bauxite residue, aimed at producing sustainable alumina and green steel. The integrated process combines hydrogen reduction, alkaline leaching, and smelting of the leaching residue. Initially, the bauxite residue was pelletized with calcite and quicklime to create self-hardened pellets, leveraging the cementing effect of quicklime with water. These pellets underwent hydrogen reduction, achieving over 95% reduction, resulting in the formation of metallic iron and a leachable calcium aluminate phase for alumina recovery. The reduced pellets were then subjected to alkaline leaching, extracting 62% alumina. Subsequently, smelting at 1550 °C facilitated the near-complete separation of iron and calcium-rich slag. The process was analyzed using various analytical techniques, including X-ray diffraction, electron probe microanalysis, and inductively coupled plasma mass spectroscopy, complemented by thermodynamic calculations using FactSage 8.1 software. Iron oxide reduction to metallic iron was achieved at 1000 °C for 120 min, while sodium carbonate leaching effectively extracted alumina from the calcium aluminate slag. However, residual alumina was attributed to the formation of indissoluble gehlenite and a dense calcium carbonate layer that impeded leaching kinetics. Successful iron separation during smelting required temperatures above 1500 °C, though this process was challenged by the high viscosity of the oxide matrix and the purity of the iron.

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This study evaluates the effectiveness of CO₂ nanobubble-enhanced hydrate-based desalination (HBD) to treat industrial effluents from the mining and metals industry. Testing was conducted in a high-pressure reactor apparatus that employed CO₂ as the gas hydrate former at 274.15 K and 3.58 MPa. CO₂ nanobubbles (NBs) were used to promote hydrate formation, aiming to streamline an HBD process without separation steps for the additives/chemicals used. Due to the limited studies on hydrate formation in sulfate-containing aqueous solutions, this research focused on the kinetics of hydrate formation in varying concentrations of Na₂SO₄ and MgSO₄ (0.1 and 0.5 M). The results showed that CO₂ NBs significantly enhanced hydrate formation in both Na₂SO₄ and MgSO₄ solutions, with CO₂ consumption increasing by up to approximately 51% and 35%, respectively. Additionally, a kinetics study on a real effluent from the mining and metals industry showed that the presence of CO₂ NBs increased CO₂ consumption by around 20% after 180 min. This research also evaluated water recovery and desalination efficiency in a 3-stage HBD process applied to the effluent, the concentration of which exceeded the operating range of reverse osmosis. The results indicated an improvement in water recovery from 25.13 ± 2.04% to 40.16 ± 1.43% with CO₂ NBs, underscoring their effectiveness in treating highly saline water. Moreover, desalination efficiencies of 49.54 ± 2.39% and 42.03 ± 3.43% were achieved without and with CO₂ NBs, respectively. This study represents the successful demonstration of the efficient application of the CO₂ NBs-boosted HBD method to treat high-salinity effluents and recover clean water for reuse.

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An efficient and environmentally friendly recovery of platinum group metals (PGMs) from secondary sources is necessary to ensure a sustainable supply of PGMs. In this study, contact with FeCl₂ vapor in the presence of metallic Fe was investigated as a useful pretreatment for leaching PGMs from spent automobile catalysts. Fe-PGM alloys were efficiently formed when Pt, Pd, and Rh wires and Rh₂O₃ powder were subjected to FeCl₂ vapor treatment at 1050 K (777 °C) for approximately 40 min. Further, the leachability of the PGMs in spent automobile catalyst samples increased after a similar vapor treatment was applied. When the pulverized spent catalyst sample without pretreatment was leached with aqua regia at 333 K (60 °C) for 60 min, 88% of Pt, 91% of Pd, and 37% of Rh were extracted. Meanwhile, after vapor treatment at 1050 K, 98% of Pt, 97% of Pd, and 87% of Rh were extracted under the same leaching conditions. Thus, the pretreatment with FeCl₂ vapor, followed by leaching, is a feasible and effective technique for recovering PGMs from spent catalysts.

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The existing pretreatment method for recycling spent lithium iron phosphate (LFP) batteries effectively separates most of the copper foil. However, a small amount of fine copper particles (CP) remains in the LFP battery waste, which is mainly composed of graphite and LFP, affecting the subsequent smelting. Centrifugal gravity concentration (CGC) is a physical separation method that is highly efficient and environmentally friendly and is often used for the separation of fine-grain materials. In this study, it was used for the deep removal of CP from LFP battery waste. The dynamics analysis of the particles in the CGC indicated that CP can be effectively separated from graphite and LFP. The effects of fluidizing water pressure (FWP), relative centrifugal force (RCF), pulp density, and feeding rate on Cu grade, Cu recovery, and Cu separation efficiency (SE) were investigated by single-parameter experiments and response surface methodology (RSM) in CGC. The findings indicate a substantial impact of FWP and RCF on copper recovery, contrasting with the limited influence observed for pulp density and feeding rate on the recovery of Cu. The predicted outcomes from the RSM for Cu grade, Cu recovery, and Cu selectivity (Cu SE) were 85.1993%, 70.0271%, and 67.4004, respectively, under the conditions of FWP at 39.2697 kPa and RCF at 91.9 G. By means of both theoretical analysis and experimental validation, a novel and environmentally sustainable process for the recovery of CP from waste LFP batteries has been proposed.

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A technological process for the deep removal of fine copper particles from lithium iron phosphate battery waste using centrifugal gravity concentration.

Spent lead paste (SLP) obtained from end-of-life lead-acid batteries is regarded as an essential secondary lead resource. Recycling lead from spent lead-acid batteries has been demonstrated to be of paramount significance for both economic expansion and environmental preservation. Pyrometallurgical and hydrometallurgical approaches are proposed to recover metallic lead or lead oxide from SLP. However, traditional pyrometallurgical techniques are plagued by high energy consumption and substantial environmental pollution, whereas hydrometallurgical processes suffer from excessive reagent consumption and wastewater emissions. Benefiting from the technical advantages, electrochemical techniques in the recycling of SLP have attracted extensive interest in the last few years. This review provides a comprehensive summary of electrochemical approaches, technical feasibility, and improvements in recycling SLP. These methods mainly consist of leaching-electrowinning, direct solid-phase electrolysis, suspension electrolysis, electrolysis in ionic liquids, and electrolysis in molten salt. The recent research advances in electrochemical recycling of SLP are discussed. The present state-of-the art challenges and issues including energy consumption and impurity behavior in electrochemical treating SLP are also addressed.

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For carbon neutrality, the use of sinter should be decreased owing to higher CO₂ emission in the sintering process of the blast furnace operations. This trend might contribute to the increased use of iron ore pellets with lower CO₂ emission in the fabrication process, high reducibility and gas permeability due to higher mechanical strength. The pelletizing process mostly uses high-grade iron ore such as magnetite (Fe₃O₄) as the main raw material, which has been depleted due to the increasing demand for pellet production. The current study attempted to replace magnetite ore with low-grade limonite ore (Fe₂O₃∙nH₂O) at different additional levels (10, 30, 50 and 100 wt%). The augmented limonite content influenced the increase in the porosity of pellets, which resulted from dehydration. The effect of microstructure on the compressive strength of mixed pellets before reduction and the reduction behavior of mixed pellets in a hydrogen atmosphere could be elucidated by porosity and pore size distribution analysis. The integration of limonite with magnetite facilitated the formation of small-sized pores, which in turn resulted in a significantly enhanced microstructure, with the limonite-mixed pellets demonstrating compressive strength comparable to that of magnetite pellets. The goethite phase provided a pathway for hydrogen permeability, and consequently, the reduction degree of limonite-mixed pellets in a H₂ atmosphere amounted to a reduction degree of 80%, which is similar to that of magnetite pellets. The mechanical strength of mixed pellets during reduction suggests their potential to withstand the stack layer in blast furnace operations. These findings could suggest the potential to utilize low-grade iron ore pellet process.

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Enhancing blast furnace sustainability via pellet feed optimization

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With the growing concern of environmental protection and waste recycling, recovery of high-value metal from coal fly ash (CFA) has attracted a lot of attention around the world. In our previous study, CaO was employed as an additive to react with mullite (3Al₂O₃·2SiO₂) in CFA to produce CaO·xAl₂O₃, by which the extraction of alumina was strengthened tremendously. However, the dissolving mechanism of CaO·xAl₂O₃ in alkali liquor has not yet been conducted in in-depth research, which casts a shadow for the further progress of the process. In this paper, with the aim of clarifying the alkali dissolving mechanism as well as developing an eco-friendly alumina recovery process, the effect of CaO addition on the mineralogical transformation of CFA and the dissolving behaviors of CaO·xAl₂O₃ in alkali liquor were investigated thoroughly. The results show that the mullite in CFA can be converted to Fe-Si alloys and CaO·xAl₂O₃ with the addition of CaO. Additionally, it is proved that the liquid/solid ratio, the alkali concentration, and the dissolving temperature would be the most critical impactors to decide the extraction rate of alumina. Under the optimal conditions, the extraction rate of alumina attained 93.8% and the CaO can be recycled for cyclic utilization in this process.

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This study investigates the use of graphene oxide (GO) as a nanocollector to remove Zn ions from synthetic wastewater via ion flotation. The effect of various parameters, such as pH, GO concentration, air flow rate, impeller speed, and concentration of sodium dodecyl sulfate (SDS) as an auxiliary collector, on the removal of Zn ions was examined. Under optimal conditions (pH 8.5, GO concentration 40 mg/L, SDS concentration 37.5 mg/L, air flow rate 2 L/min, and impeller speed 800 rpm), Zn ion removal and water recovery reached 90% and 36%, respectively. Characterization techniques, including FTIR, SEM–EDX, and WDX, confirmed the successful interaction between GO and Zn ions, leading to the formation of Zn–GO complexes. This research highlights the potential of GO as a promising and efficient nanocollector for the removal of Zn ions from wastewater through ion flotation, contributing to environmental remediation efforts.

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High-alumina iron ore sintering is characterized by poor sinter indices and high carbon emission due to the limited formation amount of liquid phase. In this study, the conventional Ca-bearing flux (i.e., burnt lime) was substituted by a new Ca-bearing flux with low melting point (i.e., prefabricated calcium ferrite) for the improvement of the formation ability of liquid phase during sintering. The substitution of prefabricated calcium ferrite for burnt lime contributed to the reduction of the formation temperature of liquid phase and the improvement of liquid-phase fluidity. At the optimum substitution ratio of 20%, the strength of sinter compacts was improved by 38.38% in the mini-sintering tests due to the more formation of liquid phase, especially SFCA (i.e., Silico-ferrite of calcium and alumina). In addition, the proportion of high-alumina iron ore can be appropriately increased from 10.20% to 25.20% at the substitution ratio of 20% under the premise of the similar strength of sinter compacts. High-alumina iron ore can be effectively utilized during sintering by pre-preparing the low melting-point flux, which will be further proved by the relevant sinter pot tests in our follow-up study.

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