Metal Adsorption on Clays from Pyrite Contaminated Soil

A clayey soil contaminated with pyrite was treated with the addition of a base in laboratory experiments. The subsequent rise in pH is an efficient mechanism to retain the metals released by the sulfide weathering. Iron concentrations decrease as pH increases owing to the formation of secondary hydroxide phases, such as ferrihydrite. Aluminum and the aqueous divalent metals, such as Cu, Zn, Ni, Co, Cd, and Mn also decrease in concentration as pH increases. The fall in concentration can be accounted for by the formation of complexes on the surface of illite, which forms about 20 wt % of the soil. Given the proportion of illite and the thickness of clayey soils in the Aznalcollar region, the addition of a base such as lime or lime-containing flying ash could be an efficient remediation process. By contrast, the addition of more efficient exchangers such as zeolite continues to be recommended for sandy soils and gravels from the area with low clay contents.