The salt extraction process is an

electrolytic An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon d ...

method which may be used to extract valuable metals from

slag Slag is a by-product of smelting ( pyrometallurgical) ores and used metals. Broadly, it can be classified as ferrous (by-products of processing iron and steel), ferroalloy (by-product of ferroalloy production) or non-ferrous/ base metals (by ...

low-grade ore Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also r ...

s, or other materials by using molten salts. This method was developed by S. Seetharaman, O. Grinder, L. Teng and X. Ge at the

Royal Institute of Technology The KTH Royal Institute of Technology ( sv, Kungliga Tekniska högskolan, lit=Royal Institute of Technology), abbreviated KTH, is a public research university in Stockholm, Sweden. KTH conducts research and education in engineering and technol ...

in Sweden as part of a large Steel Eco-Cycle Project in 2005.

Description

In the first step of this process, the slag or other raw materials containing metal values of interest, e.g. chromium, is dissolved into the molten salt phase at a suitable temperature. A suitable flux must be found in order to achieve the dissolution of oxides. According to the

Fajans' rules In inorganic chemistry, Fajans' rules, formulated by Kazimierz Fajans in 1923, are used to predict whether a chemical bond will be covalent or ionic, and depend on the charge on the cation and the relative sizes of the cation and anion. They can be ...

, AlCl₃, as a covalent metal chloride, is able to release chloride ions, which then can effectively break the chemical bonds between metal and oxygen atoms, leading to the formation of corresponding soluble metal chlorides and capture of oxygen in Al₂O₃. AlCl₃ was proved indeed to be a powerful fluxing agent in this regard. In the second step, the salt phase is subjected to electrolysis in order to recover the metal of interest as a cathode deposit. The salt melt used for extraction can be recycled. The metals can be selectively electrodeposited from the salt melt. There is also the option of aqueous processing of the salt phase containing the metal values. The process can design to be continuous by combining the two steps. The anode off-gas from electrolysis, Cl₂ can be reused for accentuating the dissolution of the raw materials. On the other hand, the residue after processing, which consists essentially of Al₂O₃, can safely be used for landfill, building construction or as a raw material for the refractory industry.

Application

This process had been successfully employed for the recovery of

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and h ...

and

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in ...

from the electric furnace slag generated from the stainless steelmaking process, or from low-grade chromite ore. It is also extended to extract copper or iron from both copper oxides and sulfides. The electrochemical behaviors of the metal ions (Cr, Cu, Fe, Mg, Mn) in the molten salts (NaCl-KCl-(CaCl₂))with respect to this process were also extensively investigated. Those results are also useful for the industrial

electrowinning Electrowinning, also called electroextraction, is the electrodeposition of metals from their ores that have been put in solution via a process commonly referred to as leaching. Electrorefining uses a similar process to remove impurities from a ...

processes of related metal or alloy production.

References

{{Reflist Electrolysis Chemical processes Extraction (chemistry)