A simple and inexpensive chromium-reducible sulfur method for acidsulfate soils

Edward D. Burton, Southern Cross University
Leigh A. Sullivan, Southern Cross University
Richard T. Bush, Southern Cross University
Scott G. Johnston, Southern Cross University
Annabelle F. Keene, Southern Cross University

Abstract

A new chromium-reducible sulfur (CRS) method suitable for the quantification of reduced inorganic S (RIS) in acid-sulfate soils is presented. The new method utilises the reduction of RIS by an acidic Cr(II) solution within a sealed reaction chamber and diffusion of the produced H₂S_(g) into an alkaline Zn solution. It offers rapid sample processing times, without the need for large volumes of high-purity N_2(g) or for specialized, expensive glassware. Examination of pyrite-talc mixtures containing up to 11.8% pyrite, revealed that the method achieves 95–98% recovery of RIS. A comparison between CRS measured by the new diffusion-based method and that measured by a standard purge-and-trap method for 25 pyritic soil samples shows a very strong (r² = 0.996) linear relationship with a slope of 0.995. The ability of the new diffusion-based CRS method to achieve accurate and precise quantification of RIS in acid-sulfate soils is demonstrated.