Gypsum carbonate-rock effect

Not all mine drainage or natural runoff from rock outcrops are acidic, even when extensive sulfide oxidation is present. Synthetic cyanide solutions, which are often used to extract gold and other metals from ores, can greatly increase the alkalinity of mining wastes and neutralize sulfuric acid (Craw et al., 1999). In other cases, the sulfuric acid is effectively neutralized by alkaline soils, limestones, dolostones, marbles, shams, or other carbonate-rich rocks (Pfeifer et al., 2004, 219 Razo et al., 2004 Lee, Lee and Lee, 2001, 491 Mendoza et al., 2006). Reactions between calcium carbonate and sulfuric acid may precipitate gypsum (CaS04 2H20). 

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