Dear Colleagues,

Extractive metallurgy deals with the processes for the recovery of valuable metals from ores and concentrates (primary metallurgy) or waste raw materials such as slags, slime and flying ashes (recycling or secondary metallurgy). Regarding the type of obtained metals, these processes are divided in five different groups: extractive metallurgy of iron and steel, non-ferrous extractive metallurgy, extractive metallurgy of precious metals, extractive metallurgy of rare earth elements and refractory metal extractive metallurgy. These processes in extractive metallurgy include unit processes for separating highly pure metals from undesirable metals in an economically efficient system. Decarbonated processes will be considered using green hydrogen in order to promote extractive metallurgy aimed towards an environmental protection and zero-waste concept.

Unit metallurgical operation processes are usually separated into three categories: 1) hydrometallurgy (leaching, mixing, neutralization, precipitation, cementation, crystallization), 2) pyrometallurgy (roasting, smelting), and 3) electrometallurgy (aqueous electrolysis and molten salt electrolysis). In hydrometallurgy, the target metal is first transferred from ores and concentrates to a solution using selective dissolution (leaching; dry digestion) under an atmospheric pressure below 100 °C and under a high pressure (40-50 bar) and high temperature (below 270°C) in an autoclave and tube reactor. The purification of the obtained solution was performed using neutralization agents such as sodium hydroxide and calcium carbonate or more selective precipitation agents such as sodium carbonate and oxalic acid. The separation of metals is possible using liquids/liquid processes (solvent extraction in a mixer-settler) and solid–liquid (filtration in filter-press under high pressure) methods. Crystallization is the process by which a metallic compound is converted from a liquid into a solid crystalline state via a supersaturated solution. The final step is metal production using electrochemical methods (aqueous electrolysis for basic metals such as copper, zinc, silver and molten salt electrolysis for rare earth elements and aluminium). Advanced processes for metal production, such as ultrasonic spray pyrolysis and microwave-assisted leaching, can be combined with reduction processes.

Some preparation for the leaching process is performed via a roasting process in a rotary furnace, where the sulfidic ore was first oxidized in an oxidic form, which is suitable for the metal transfer to water solution. During the smelting process, the target metal is further refined at high temperatures and reduced to its pure form. The pyrometallurgical treatment of the ore was performed in an electric furnace and combined with refining during distillationCircular hydrometallurgy can be involved in this consideration, enabling the design of energy-efficient and resource-efficient flowsheets or unit processes that consume the minimum quantities of reagents and result in minimum waste. Treatment of waste water from metallurgical processes is an important subject considering the consumption of water and energy must also be reduced to an absolute minimum. 

Since metals are manly existent in the solid and liquid state, analysis of the processes involved focuses on solid–liquid, liquid–liquid, liquid–gas, solid–solid, solid–liquid–gas, and solid–gas reactions. The theory of metallurgical processes will be deeply involved in this consideration determining reaction mechanisms (reaction models) on which kinetic models are based. Designing an industrial process requires a kinetic model in the first place. Kinetic models describe at which rate a reaction is happening (reaction and reverse reaction). If or under which conditions a reaction happens is part of thermochemical calculation. Computational thermochemistry can assist in the prediction of different chemical reactions and material selection in these extreme operation conditions to select refractory materials in contact with metallic melts and high corrosive media. The FactSage thermochemical software and its specialized databases can be used to perform these simulations that are proven here to match the available data found in the literature. The OLI, HSC and other software can be used to perform these simulations for hydrometallurgical processes in order to enable the selective winning of metals from solution.

Dr. Srecko Stopic
Guest Editor

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• extractive metallurgy
• unit operations
• hydrometallurgy
• pyrometallurgy
• electrometallurgy
• precious metals
• refractory metals
• rare earth elements
• kinetics
• thermochemistry
• simulation
• iron and steel
• modelling
• environmental protection
• hydrogen
• decarbonation
• kinetics
• reduction
• oxidation