1996 Volume 45 Issue 11 Pages 1051-1058
A method to determine the chemical forms of As and Sb in geological reference samples is described. It combines a sequential extraction procedure with hydride generation and AAS. The sequential extraction solutions were classified into the following five types: 1) 1 M magnesium nitrate of pH 7 for the ion exchange and adsorbed fraction; 2)0.05 M ethylendiaminetetraacetic acid disodium salt(EDTA)for the EDTA soluble fraction; 3) a mixture of 0.2 M ammonium oxalate, 0.2 M oxalic acid, 0.1 M ascorbic acid and 0.01 M HCl for the oxide fraction; 4) 0.7 M sodium hypochlorite for the sulfide fraction;and 5) a mixture of HF, HNO3, HClO4 and KMnO4 for the residual fraction.For samples treated with the 0.05 M EDTA, almost all of the As and Sb in the carbonate minerals and small amounts of both elements in the oxide phases were extracted. In some cases sulfides such as As2S3 and Sb2S3 were changed to oxides and/or EDTA soluble forms during sample processing. In the speciation of As and Sb in geological reference samples, igneous rocks are dominated by residual forms reflecting their mineral composition, whereas sediments and sedimentary rocks are generally richer in oxide forms. This method was successfully applied to the speciation of As and Sb in a variety of geological reference samples.
