Reductive-Sorption Methods for Noble Metals Extraction from Solutions

Active carbons combining the properties of ion exchangers and reductive sorbents, take a special place among sorption materials for noble metal extraction from solution. Electrochemical mechanism is the specific feature of the noble metals sorption by active carbons. In the present work on the natural phenomena of reductive sorption of electropositive metals (Cu sub-group, platinoids) using synthetic active carbons of SCN or SCS type are studied. Synthetic carbons have been indicated to extract electropositive metal ions both from concentrated and diluted media (solutions of hydrometallurgy conversion, sewage and rinse flushes of galvanic production, etc.) Synthetic carbons were shown to have high selectivity in extracting gold and silver from alkaline cyanide solutions of gold-containing raw material processing. Synthetic carbons of SCN type make it possible to extract palladium and platinum from hydrochloric acid solutions up to the overflow decantation level 100-fold against the background. Using the technique of internal electrolysis (systems: Carbon/Zn, Carbon/Al) gives the possibility, with reductive sorption method, to select rhodium and ruthenium from solutions of complex salt composition with the formation of metallizing carbon granules. It was indicated that the selectivity and high extraction of these metals from fluid media are connected with the possibility of using sorption to reduce ions to metallic phase formation. Carbons coated by noble metals or metal complexes can be used as a catalyst. The proposed approach (reductive sorption) and applied new materials (synthetic carbon) give the possibility to solve important tasks of noble metal hydrometallurgy, environmental protection, and catalyst production.