The transformation of potential into actual acid sulphate soils studied in column experiments

Abstract

The transformation of potential into actual acid sulphate soils was studied in a 450 day column experiment to determine the rate and extent of pyrite oxidation and accompanying buffering processes. One potential acid sulphate soil was derived from the lower section of a Typic Sulfaquept (Soil Survey Staff, 1987) or Thionic Fluvisol (FAO, 1988) near the village of Nieuwkoop, the Netherlands, and the other from beneath the acidified upper part of a Typic Sulfaquent (Soil Survey Staff, 1987) or Thionic Fluvisol (FAO, 1988) of the Pulau Petak region in South Kalimantan, Indonesia. Drainage of both the potential acid sulphate soils caused a strong acceleration in pyrite oxidation, i.e. approximately 10 g FeS 2 per kg soil in the Dutch soil and more than 20 g in the Indonesian soil. In both columns, iron, released by the oxidation of pyrite, is immobilized instantaneously due to the precipitation of jarosite and/or iron hydroxides. The presence of carbonates prevented acidification of the soil solution upon pyrite oxidation in the Dutch soil, whereas severe acidification of the soil solution occurred in the Indonesian soil. The cationic composition of the adsorption complex is seriously affected in layers where pyrite oxidation occurred; main exchange reactions are Al 3+ against Ca 2+ and Mg 2+ for the drained Dutch and drained Indonesian soils, respectively. The experimentally obtained actual acid sulphate soils show a high similarity with the actual acid sulphate soils found in the regions under consideration.