Sample pre-treatment and the determination of some chemical properties of acid sulfate soil materials

Abstract

This study provides a systematic analysis of the effect of common acid sulfate soil (ASS) sample pre-treatments (namely freezing, oven drying, and grinding) on chromium-reducible sulfur (SCR) and water-soluble sulfate determinations. The results show that oven drying and hand grinding of the samples prior to analysis resulted in a decrease in SCR (i.e. up to 20% compared to those of frozen samples). This lower SCR value was partly due to the oxidation of sulfides in the oven. For oven-dried ASS materials, more intensive grinding in a ring mill increased SCR values, most likely by abrading coatings from pyrite grains. For oven-dried mineral ASS materials the highest SCR values were obtained with 1 min of ring mill grinding, but for soils with appreciable organic matter (such as peat), 5 min of ring mill grinding gave the highest values. The results indicate that for some ASS materials, oven drying, regardless of the ensuing grinding procedure, results in underestimated SCR values. This study also demonstrates that an artifact of oven drying ASS materials can be greatly increased water-soluble sulfate contents.