The Determination of Sulfide- and Sulfate-Sulfur in Igneous Rocks with Tin(II)-Strong Phosphoric Acid and Strong Phosphoric Acid

Abstract

A method for the determination of minute amounts of sulfide- and sulfate-sulfur in igneous rocks was investigated. A rock sample is easily dissolved by heating with tin(II)-strong phosphoric acid or strong phosphoric acid. When the rock sample is dissolved with tin(II)-strong phosphoric acid, total-sulfur is evolved as hydrogen sulfide. With strong phosphoric acid, sulfide-sulfur is evolved as hydrogen sulfide, but sulfate-sulfur is not. The hydrogen sufide evolved is fixed as zinc sulfide, and then determined by the photometric method, using mercuric thiocyanate and ferric iron. The conditions for separating sulfide- and sulfate-sulfur in rocks were examined by using samples which had been prepared by mixing rock or silica (each of them, <0.001% S) with sulfides or sulfates. The application of the method to some igneous rock samples gave results with a coefficient of variation of about 5% for sulfur contents of 0.01–0.02%. The sulfur in samples with more than 0.001% can be determined by using about 0.1 g of samples. The sulfide- and sulfate-sulfur in two standard rock samples were also determined: W-1 (Total-S, 0.012%; Sulfide-S, 0.005%; Sulfate-S, 0.007%) and G-1 (Total-S, 0.004%, Sulfide-S, <0.001%; Sulfate-S, 0.004%).