Yu Zheng

Compared with vanadium extraction by sodium roasting followed by water leaching, the calcification roasting–sulfuric acid leaching method is considered a promising approach for the comprehensive utilization of vanadium titanomagnetite, as it avoids the introduction of alkali metals. However, during vanadium extraction by sulfuric acid heap leaching, the diffusion of leaching reagents and leaching products was hindered by the deposition of leaching solid products. To address this issue, this study systematically investigated the leaching kinetics and the mechanisms underlying the deposition of leaching solid products. The results indicated that vanadium leaching was governed by a combination of liquid film diffusion and internal diffusion through solid-phase products during days 0–2, and by internal diffusion alone from day 2 to day 9. The primary solid products formed during leaching were calcium sulfate and silica gel. Calcium sulfate precipitated and grew within the pore via two-dimensional nucleation, while silicates formed silica gel through dehydration. By optimizing the sulfuric acid leaching conditions—specifically, maintaining an H⁺ concentration of 2 mol/L, a leaching temperature of 40 °C, and a liquid-to-solid ratio of 5:1—the formation of calcium sulfate and silica gel was effectively suppressed. Under these conditions, the vanadium leaching efficiency reached 75.82%.

The Jinbaoshan Pt-Pd deposit is China’s largest independent PGM deposit. However, the deposit has not been utilized until now because of the low grade of precious metals, the complex mineral composition, and, notably, the presence of precious metals in the microgranular material disseminated to other minerals. Its high MgO content, in particular, is regarded as a challenge for efficiently recovering precious metals via mature pyrometallurgical methods. In this research, the feasibility of a smelting process to recover precious metals from Jinbaoshan Pt-Pd concentrates at a conventional smelting temperature (1350 °C) with the addition of iron ore as a metal collector and SiO₂ and CaO as fluxes was verified on the basis of thermodynamic slag design and experimental analyses. Under the optimal conditions of 100 g of the Pt-Pd concentrates, 32.5 g of SiO₂, 7.5 g of CaO, and 30 g of iron ore at 1350 °C for 1 h, the extraction efficiencies of Au, Pt, and Pd were 94.66%, 96.75%, and 97.28%, respectively. This strategy enables the rapid collection of PGMs from Jinbaoshan Pt-Pd concentrates at the conventional temperature within a short time and minimizes the use of fluxes and collectors, contributing to energy and cost conservation.

Vanadium tailings from vanadium extraction by a sodium roasting process are solid waste and cannot be used in sintering and ironmaking due to their high sodium content. In this paper, a calcification and reduction roasting process was proposed to remove sodium from vanadium tailings. The effects of Ca(OH)₂ addition, reduction temperature, and roasting time on the sodium removal behavior and compression strength of pellets were studied. The addition of Ca(OH)₂ and the reduction of iron oxides promoted the sodium-containing phases to transform to be simpler, which could enhance sodium removal. The sodium removal rate was up to 93.47% and the compression strength of the reduced products was 4497 N/P, and the metallized ratio of the product was higher than 70% under the optimal conditions: roasting at 1200 °C for 2 h with the Ca(OH)₂ addition of 35%. The treated product after removing sodium can be recycled in the ironmaking process in a steel company.