Acidification adjacent to an elemental sulfur stockpile: I. Mineral weathering

Abstract

Soil pH values below 3.0 are measured in soil material located adjacent to stockpiles of elemental sulfur on sour gas plant sites. The objective of this study was to examine the influence of extreme acidity on the changes and redistribution of major chemical and mineralogical components in soil along the side of a 25-year-old elemental sulfur block. Soil samples, obtained from pits located 2 m from the side of the sulfur block, were analyzed for total content of Al, Fe, Ca, Mg, Na, K, and Ti. Sand and clay separates were analyzed by X-ray diffraction, and physical and chemical methods to identify and quantify mineral phases. Carbonate, Fe-containing primary minerals, chlorite, smectite, and plagioclase feldspars were either partially or completely dissolved in soil having pH values of about 2.1. Clay-sized mica and kaolinite were apparently not affected by the acidity. Calcium carbonate and Ca-feldspars dissolved in the presence of H2SO4 to form gypsum. Iron dissolved from minerals in the acidified surface layer was deposited primarily as oxyhydroxides at the interface of acidic and calcareous materials to form an indurated layer about 10–15 cm thick. Jarosite precipitated within the acidic material just above the indurated layer. Key words: Elemental sulfur, anthropogenic acidification, mineral weathering, acid soils