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

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 (S_CR) 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 S_CR (i.e. up to 20% compared to those of frozen samples). This lower S_CR 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 S_CR values, most likely by abrading coatings from pyrite grains. For oven-dried mineral ASS materials the highest S_CR 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 S_CR values. This study also demonstrates that an artifact of oven drying ASS materials can be greatly increased water-soluble sulfate contents.