DIAMINE EXTRACTANTS IN METAL SEPARATION. AN ILLUSTRATION OF THE POTENTIAL OF THE CHELATE EXTRACTION MODE IN THE PLATINUMrtV)-PALLADIUM(n>BASE METAL SYSTEM

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Abstract
The potential of the chelate extraction mode displayed by diamine extractants is illustrated by using two tertiary diamine extractants to extract palladium(II) and platinum(IV) from a base metal solution containing copper(II), nickel(IT), cobalml) and iron(III) in 1 mol/dm3lithium chloride. The extraction behaviour of the diamine extractants is compared with that of the commercially-available extractants Alamine 336 (a tertiary monoamine extractant) and Aliquat 336 (a quaternary monoammonium chloride salt). By exploiting the chelate extraction mode, specific to diamine extractants, separation of palladium(IT) from platinum(lv) can be achieved. The only base metal ion that is extracted is iron(III). Iron(III) can be stripped with 1 mol/dm3sulphuric acid or the extraction can be performed under mildly acidic conditions, e.g. pH 4.7. Under the latter conditions ironflll) precipitates quantitatively as a hydroxide complex and can be removed by filtration. The selective back-extraction of palladium(II) and platinum(lV) by thiourea in hydrochloric acid and sodium thiocyanate respectively is demonstrated.