Separation technologies for metals recovery from industrial wastes

Three hydrometallurgical processes for industrial wastes treatment are presented. The main separation techniques are: solvent extraction, leaching-precipitation, electro-oxidation, and ion exchange. Recovery of gold from solid wastes generated in the electronic and jewellery industries consists of thermal degradation, two-stage leaching with nitric acid solution to remove silver and other metals and then with aqua regia to dissolve gold, selective solvent extraction of gold with diethyl malonate, and reduction of gold from the organic phase. Vanadium recovery from residue ashes after burning heavy oil fractions consists of alkaline leaching of vanadium, filtration, neutralization of sodium vanadate solution, precipitation of ammonium metavanadate, drying of the precipitate, and adsorption of the remaining vanadium from the filtrate on an anionite. From the remaining ashes nickel is recovered using acidic leaching, filtration, precipitation of ammonium-nickelous sulphate, filtration, and drying. The third process concerns processing of electroplating sludges and waste waters containing chromium and copper. The waste waters are electro-oxidized to transform Cr(III) into chromate. Then metal cations are separated on a cationite. The purified electroplating baths are recycled directly to electroplating; other solutions are first concentrated using anionite, followed by sodium chromate eluate conversion into concentrated chromic acid solution. The sludges accumulated from waste water processing by hydroxide precipitation are re-dissolved in chromic acid solution generated progressively by circulation between the dissolving and electro-oxidation steps. The concentrated chromic acid solution obtained is purified on the cationite and recycled.