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Sulfuric acid,when allowed to mobilize,assuming buffering,will eventually become neutralized by <br /> contacting other minerals and organics that can tie up this sulfur. Once this occurs,the ions that are <br /> contained in low pH solution are forced out as a precipitate as the pH rises. A common ion found in <br /> solution in low pH water is iron. This precipitate has a characteristic red color when deposited as an <br /> oxide. These chemical reactions occur naturally in the environment and can also be created by man as <br /> a result of disturbing materials at the surface or below the water table. <br /> The oxidation of sulfide minerals produces predictable results based on the simple chemical reactions. <br /> However,the rate of the reaction is slightly more difficult to predict without knowledge of the other <br /> minerals present and their mechanical relationships to the sulfide mineral that is to undergo oxidation. <br /> The mineral decomposition and amount of free sulfur available to become mobile can vary greatly based <br /> on the crystal habit of the mineral, and that mineral's spatial relationship with its neighboring minerals. <br /> The presence of iron sulfide in the system, increases the chances of the generation of free sulfur,over <br /> the sulfides of other metals, but certainly does not guarantee that it will be generated. In the most <br /> simple analysis,a measure of the ratio of free accessible sulfur to the whole rock volume produces a <br /> guideline for predicting the generation of sulfuric acid. This tendency to produce free sulfur is typically <br /> referred to as Acid Generation Potential (AGP). <br /> On the other side of the equation the non-sulfur containing minerals can act to chemically collect and <br /> bind the free sulfur. This process is typically referred to as Acid Neutralization Potential (ANP). One of <br /> the best and most efficient compounds used to tie up sulfur is calcium carbonate(CaCO3). Generally <br /> AGP and ANP are referred to in terms of relative weight of calcium carbonate as compared with weight <br /> of rock. The reaction results in the sulfur ion interacting with a carbonate anion,to form calcium <br /> sulfate. Calcium sulfate is stable in an oxidizing environment,and tends to produce a material that has <br /> a low permeability,tends to shed precipitation,thus it tends to protect sulfide-bearing materials that <br /> might be located below it from weathering. <br /> 2 <br />