Metal partitioning dynamics during the oxidation and acidification of sulfidic soil

The oxidation and acidification of sulfidic soil can lead to changes to metal mobility that can have far-reaching environmental consequences. In this study, we examined changes in the partitioning and mobility of Fe, Cr, Cu, Mn, Ni and Zn in four sulfidic soils, due to sulphide oxidation driven acidification, over a 90 day period. These changes were examined using a novel six-step sequential extraction procedure specifically developed for acid sulphate soil materials. The results demonstrate two distinct steps for the mobilisation of metals in disturbed acid sulphate soil materials, associated with (i) oxidation and (ii) acidification. Initially, oxidation causes metals to be redistributed from the “pyritic” and “organic” fractions to the “acid-soluble” fraction. Subsequent acidification, due to exceedance of the acid neutralising capacity of the soil, drives the release of metals to the “labile” fraction. This study demonstrates the importance of these metal pools in understanding the short-term processes which mobilise metals in sulfidic soils.

Research Highlights
► Metal partitioning changes during oxidation of sulfide-rich sediments.
► We examined changes during short-term oxidation events.
► Two major metal mobilisation pathways were observed.
► i) Metals are mobilised from the sulfidic and organic to the acid-soluble fraction.
► ii) Extreme acidification mobilises metals from the acid-soluble to the labile fraction.