Feature Papers in Extractive Metallurgy II

Dear Colleagues,

Extractive metallurgy covers the processes involved in 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). Based on the type of metals obtained, these processes are divided in five different groups: the extractive metallurgy of iron and steel, non-ferrous extractive metallurgy, the extractive metallurgy of precious metals, the extractive metallurgy of rare earth elements, and refractory metal extractive metallurgy. These processes include unit processes for separating highly pure metals from undesirable metals in an economically efficient system. Decarbonated processes which use green hydrogen in order to promote extractive metallurgy, aiming to enable environmental protection and zero waste, will be considered.

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 then under a high pressure (40-50 bar) at high temperatures (below 270 °C), in an autoclave and tube reactor. The purification of the obtained solution is 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 liquid–liquid (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, and silver and molten salt electrolysis for rare earth elements and aluminum). Advanced processes for metal production, such as ultrasonic spray pyrolysis and microwave-assisted leaching, can be combined with reduction processes.

Some of the preparation for leaching is performed via a roasting process in a rotary furnace, where the sulfidic ore is first oxidized, which makes it suitable for transferring to a water solution. During the smelting process, the target metal is further refined and reduced to its pure form. The pyrometallurgical treatment of the ore is performed in an electric furnace and it is refined during its distillation. Circular hydrometallurgy can be considered at this stage, enabling the design of energy-efficient and resource-efficient flowsheets or unit processes that consume minimal quantities of reagents and result in minimum waste. The treatment of waste water from metallurgical processes is an important subject, as the consumption of water and energy must also be reduced to an absolute minimum.

Since metals mainly exist in solid and liquid states, analyses of the processes involved focus on solid–liquid, liquid–liquid, liquid–gas, solid–solid, solid–liquid–gas, and solid–gas reactions. The theory of metallurgical processes is always at the heart of determining the reaction mechanisms (reaction models) on which kinetic models are based. Designing an industrial process requires a kinetic model. 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 the thermochemical calculation. Computational thermochemistry can assist in the prediction of different chemical reactions and material selection in these extreme operating conditions in order to select the refractory materials that will be in contact with metallic melts and highly corrosive media. FactSage thermochemical software and its specialized databases can be used to perform these sorts of simulations, which are proven to match the data available in the literature. OLI, HSC and other software can be used to perform these simulations for hydrometallurgical processes in order to enable the selective gain of metals from solutions.

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

• Feature Papers in Extractive Metallurgy in Metals (10 articles)