SEPARATION TECHNOLOGIES FOR METALS RECOVERY FROM INDUSTRIAL-WASTES

Three hydrometallurgical processes for industrial wastes treatment are presented. ?The main separation techniques are: solvent extraction, l eaching-precipitation, electro-oxidation, and ion exchange. Recovery o f gold from solid wastes generated in the electronic and jewellery ind ustries consists of thermal degradation, two-stage leaching with nitri c acid solution to remove silver and other metals and then with aqua r egia to dissolve gold, selective solvent extraction of gold with dieth yl malonate, and reduction of gold from the organic phase. Vanadium re covery from residue ashes after burning heavy oil fractions consists o f alkaline leaching of vanadium, filtration, neutralization of sodium vanadate solution, precipitation of ammonium metavanadate, drying of t he precipitate, and adsorption of the remaining vanadium from the filt rate on an anionite. From the remaining ashes nickel is recovered usin g acidic leaching, filtration, precipitation of ammonium-nickelous sul phate, filtration, and drying. The third process concerns processing o f electroplating sludges and waste waters containing chromium and copp er. The waste waters are electro-oxidized to transform Cr(III) into ch romate. Then metal cations are separated on a cationite. The purified electroplating baths are recycled directly to electroplating; other so lutions are first concentrated using anionite, followed by sodium chro mate eluate conversion into concentrated chromic acid solution. The sl udges accumulated from waste water processing by hydroxide precipitati on are re-dissolved in chromic acid solution generated progressively b y circulation between the dissolving and electro-oxidation steps. The concentrated chromic acid solution obtained is purified on the cationi te and recycled.