PYRITE OXIDATION, CARBONATE WEATHERING, AND GYPSUM FORMATION IN A DRAINED POTENTIAL ACID SULFATE SOIL

To quantify the rate of pyrite oxidation, weathering of carbonates and the formation of gypsum in a potential acid sulfate soil exposed to d rainage, a column experiment was executed for 175 d. During the experi ment, 24 g of FeS2, of the originally present 1327 g, oxidized within 70 d. Weathering of carbonates prevented acidification; an estimated 2 1 g of CaCO3 and 17 g of CaMg(CO3)2 dissolved simultaneously within th e first 70 d. Rising Ca2+ and SO2-4 concentrations initiated gypsum pr ecipitation from around Day 70 until the end of the experiment. A nume rical model was used to simulate the experimental results. Estimated a nd simulated quantities of pyrite oxidation and carbonate weathering, and measured and simulated soil solution concentrations appeared to ag ree well. Model simulations indicate the formation of 63 g CaSO4 betwe en Days 70 and 175 in the upper 60 cm of the soil profile.