What is solvometallurgy?
The SOLVOMET Centre provides novel solutions in the domain of solvometallurgy. In contrast with the established domains of pyrometallurgy and hydrometallurgy, solvometallurgy is an emerging brand within the general metallurgy domain, which offers a number of unique advantages. Prof. Koen Binnemans is one of the world-leading experts in this new domain. A milestone review paper by Prof. Koen Binnemans and Dr. Peter Tom Jones, published in the Journal of Sustainable Metallurgy ((2017) 3:570–600), provides a comprehensive overview of the benefits of solvometallurgy. This open-access paper can be downloaded here.
Setting the scene
Solvometallurgy is the extraction of metals from ores, tailings, industrial process residues, production scrap and urban waste using non-aqueous solutions. Solvometallurgy differs from hydrometallurgy by the absence of a discrete water phase. The solvents are either organic or inorganic solvents (excluding water). Sustainable solvometallurgical processes must be based on green solvents. Therefore, toxic or environmentally harmful solvents must be avoided. Most of the unit processes in solvometallurgy are very similar to those in hydrometallurgy, with the main difference being that the water is replaced by a non-aqueous solvent (see figure). The Table below shows a comparison of the hydrometallurgical and solvometallurgical processes.
Table. Comparison of hydrometallurgical and solvometallurgical processes.
|Leaching||Leaching with aqueous solutions of acids or bases, or aqueous solutions of chelating agents||Leaching with acid-saturated neutral or basic extractants, acidic extractants, chelating extractants diluted in non-polar organic solvents; acid-saturated polar solvents; halogens in organic solvents|
|Solvent extraction||Distribution between an aqueous phase and an immiscible organic phase||Distribution between two immiscible organic phases|
|Ion exchange||Ion exchange between the resin and aqueous solutions||Ion exchange between the resin and non-aqueous solutions|
|Precipitation||Precipitation by reagent addition, control of pH, evaporation of water||Precipitation by reagent addition, addition of anti-solvent, evaporation of solvent|
|Electrolysis||Electrodeposition of metals at the cathode from an aqueous electrolyte||Electrodeposition of metals at the cathode from a non-aqueous electrolyte|
10 reasons to use solvometallurgy
Solvometallurgy is complementary to pyrometallurgy and hydrometallurgy. However, this new approach offers several advantages. The reader is referred to the Binnemans & Jones position paper on solvometallurgy where the benefits of solvometallurgy are described in greater detail. [K. Binnemans & P.T. Jones, Solvometallurgy: an emerging branch in metallurgy, Journal of Sustainable Metallurgy (2017) 3:570–600] Amongst the ten good reasons to use solvometallurgy (see Table), four stand out in particular. Firstly, the consumption of water is very limited offering a major advantage in regions where there is a shortage of water. Secondly, the leaching and solvent extraction can be combined in a single step, which leads to simplified process flow sheets. Thirdly, solvent leaching can be more selective than leaching with acidic aqueous solutions, leading to reduced acid consumption and less purification steps. Fourthly, solvometallurgy is useful for the treatment of ores that are rich in soluble silica (such as eudialyte) as no silica gel is formed. Hence, solvometallurgy is in a position to help develop near-zero-waste metallurgical processes, and with levels of energy consumption that are much less than with high-temperature processes.
Table. Ten good reasons to use solvometallurgy
|Reason 1. Very limited water consumption|
|Reason 2. Reduced energy consumption|
|Reason 3. Process intensification|
|Reason 4. Reduced consumption of acids|
|Reason 5. Higher selectivity for leaching|
|Reason 6. Fewer problems with silica gel formation|
|Reason 7. Suitable for the treatment of low-grade ores, mine tailings and industrial process residues|
|Reason 8. Useful for the treatment of urban waste|
|Reason 9. Compatibility with bioleaching|
|Reason 10. New separation processes|