Advances in Process Metallurgy

Over the past several decades, extensive research and developmental activities have led to the emergence of new methods, processes, and engineering flowsheets in hydro(bio)-, pyro-, and electrometallurgy. Incorporation of new modifications into conventional techniques has shown promise in many metallurgical practices.

These best practices and research advances in the areas of materials electrochemistry, chemical metallurgy of secondary resources and strategic (waste) materials, recovery of critical elements, and fundamental physical chemistry processed through modeling and molecular simulation, are described in this collection of manuscripts on the topic of Advances in Process Metallurgy. With 12 articles focused on the electrochemical and thermodynamics of molten salts, metallurgy process modeling as well as recycling and secondary resource utilisation, this topic has been allocated into two parts. Part I has already been published in April with seven papers, and the remaining papers are included in Part II in the June issue.

Organized thematically, the papers can be broken into three subject areas. First, covering the high temperature of molten salt, four articles are presented, as described below.

To reduce the greenhouse gas concentrations of the earth and realizing in situ utilization of Mars atmosphere, the molten salt CO₂ capture and electrochemical transformation (MSCC-ET) process is a highly desirable method to convert CO₂ gas to solid carbon. In “Electrochemical Decomposition of CO₂ in a Fluoride Melt”, Liu et al. proved the feasibility of electrochemical decomposition of CO₂ into carbon materials and oxygen gas in a fluoride melt.

In “Low-temperature Molten Salt Synthesis and Characterization of Nanowire-like TaB2 Powders” (published in April), Liaqat Ali Shah et al. present the preparation of nanowire-like TaB2 nano-powders in the system of the Ta₂O₅-MgB₂ reaction using KCl/NaCl molten salt as the reaction media. The effect of the synthesis temperature, firing time, and the reactants to salt ratios on TaB2 nano-powder formation was examined to optimize the synthesis conditions.

For the third paper (published in April), Jiang Diao et al. present “Study on Saturated Solubility of MgO in Converter Vanadium Slag,” combining theoretical calculation and dissolution equilibrium experiments. This study provides a further theoretical proof of their previous research that increasing the MgO content in vanadium slag would not have a negative impact on the vanadium conversion in the subsequent roasting process.

In the fourth paper, by Hongyang Wang et al. (published in April), the “Liberation and Enrichment of Metallic Iron from Reductively Roasted Copper Slag” was investigated. The main phases in the slag were identified. Furthermore, it was found that iron, present in its metallic form, was covered by silica. An alkali leaching–magnetic separation process was studied and found to be suitable to liberate the iron from the slag.

Next, two articles are presented on the topic of the application of modeling for the metallurgy process.

To understand the influence of FeO content on the slag structure and properties, Shufang Ma et al. implement molecular dynamics simulation to theoretically calculate the structure and properties of a CaO-SiO₂-Al₂O₃-FeO quaternary slag system by the LAMMPS software with classical force field parameters. In their article “Structural Characteristics of CaO-SiO₂-Al₂O₃-FeO Slag with Various FeO Contents based on Molecular Dynamics Simulation,’’ simulated data indicating that, as the FeO content increases, the diffusion coefficient of each atom increases, and the system viscosity decreases. These findings proved that FeO in blast furnace slag has a great influence on the structural characteristics of CaO-SiO2-Al2O3-FeO slag.

In “Modeling and Simulation Study of Goethite Process for Iron Removal in Zinc Leaching Solution,” Tianxiang Nan et al. conducted a finite element analysis of the goethite process for iron removal by using COMSOL Multiphysics simulation software. The results showed that the stirring has a significant effect on the distribution of the fluid field. The reaction rate and mass transfer were greatly influenced by the gas inlet flow rate.

Finally, six papers cover secondary resource utilization.

“Study on Refining Mechanism of Doped Molybdenum Powder in Reduction Process”, by Chaopeng Cui and Xiangwei Zhu, aims to elucidate the influence mechanism of the second phase on molybdenum powder based on the preparation of Mo-ZrO₂ alloy powder. The findings may indicate that nano-sized ZrO₂ particles adsorbed on the surface of micro-sized MoO₃ and MoO₂ powders during the reduction process hinders the growth and fusion of the powder, and thus refines the reduction product, Mo powder.

Next, “Thermodynamics and Synthesis of Cu Powder from CuO in Waste Tire-derived Pyrolytic Gas Atmosphere” by M. Altay and S. Eroglu (published in April) investigates the reduction behaviour of CuO particles under the gaseous atmosphere generated by waste tire pyrolysis. The results indicated that CuO could be reduced to the metal via a tire (rubber) pyrolysis route in the temperature range 700–900 K.

“Comparison of Biomass and Coal in Recovery Process of Silicon in an Electric Arc Furnace” by H. Hasannezhad and A. Meysami, (published in April) studied the silicon recovery of silica ore (SiO₂) in an electric arc furnace using two types of carbon materials: charcoal as a biomass and coal as a fossil fuel. The data indicated a higher electrical resistance of charcoal in compression comparison with coal, increased efficiency of the furnace and decreased electric energy consumption.

Julien Comel et al. explored “Use of Phytic Acid for the Removal of Iron in Hot Acidic Leachate from Zinc Hydrometallurgy” in their paper. Different precipitation conditions were investigated by DOE methodology in laboratory scale and then scale-up to laboratory pilot to validate the optimal condition and also the environmental impact of waste.

Joona Petteri Rajahalme et al. investigated “Effective Recovery Process of Copper from Waste Printed Circuit Boards Utilizing Recycling of Leachate” in their April paper. An optimized leaching and electrowinning process was presented where the leachate was recirculated. Response surface methodology was used to investigate the combined effect of hydrogen peroxide and sulfuric acid concentration, pulp density, leaching temperature, and time on copper recovery. In the optimized process with recirculation, acid consumption could be reduced by 60% compared to a process with no recirculation.

“Leaching Behavior and Kinetics of Light and Heavy Rare Earth Elements (REEs) from Zircon Tailings in Indonesia” by Gyan Prameswara et al. studied the leaching characteristics and kinetics of rare earth elements from zircon tailings in their work published in April. Leaching with hydrochloric acid was studied at varying temperatures, hydrochloric acid concentrations, and pulp densities. Furthermore, different kinetic models were evaluated for the experimental results, and the activation energy for leaching of heavy and light rare earth elements, respectively, were determined. The leaching process was best described using the Zhuravlev, Lesokhin, and Templeman (ZLT) kinetic model. The results indicated that the leaching of both light and heavy rare earth elements was diffusion-controlled.

All manuscripts published under Part II of the topic Advances in Process Metallurgy in the June 2021 issue (vol. 73, no. 6) of JOM can be accessed at: http://link.springer.com/journal/11837/73/6/page/1.

All manuscripts published under Part I of the topic Advances in Process Metallurgy in the April 2021 issue (vol. 73, no. 4) of JOM can be accessed at: http://link.springer.com/journal/11837/73/4/page/1.