The colourimetric determination of trace elements in pyrrhotite

Abstract

A sample of pyrrhotite, mechanically separated from it's host rock, is dissolved in excess concentrated hydrochloric acid. Iron and any traces of copper present are oxidised by potassium chlorate. The strength of the hydrochloric acid solution is adjusted to 8.0 Molar and the bulk of the iron is extracted with iso-propyl ether. Traces of cobalt, copper, zinc, cadmium and residual iron are separated from lead and nickel by passing the extracted solution through a column containing Dowex 1-X10 - a strongly basic quaternary amine anion exchange resin. The traces are adsorbed as anionic chloro-complexes. The adsorbed metal traces and residual iron are then separated one by one by elution of the resin with hydrochloric acid of diminishing concentrations. The trace metals thus separated are determined quantitatively by simplified colourimetric techniques. The absorption of the coloured solutions is determined with a Beckman Model D.U. Quartz Spectrophotometer, corrected for reagent absorption and compared with the results obtained by using known quantities of the particular metal. A sensitivity of 1 to 2 ppm., may be expected, with results accurate to ±10 per cent at all but the lowest concentrations. By making suitable chemical or ion exchange separations of the macro elements, the method may be extended to a variety of other sulphides and acid extracts from crushed rocks, soil samples and others. Carefully purified reagents must be used throughout.