A Methodology to Determine the Acid-neutralization Capacity of Rock Samples

Chemical calculations based on the molar quantity of neutralizing cations (Na, K, Mg, Ca, Mn) released to solution associated with the acidic dissolution of minerals provide a method to chemically quantify the acid-neutralization capacity (ANC) of carbonates, silicates, simple assemblages of mixed minerals, and waste-rock samples obtained from international mining operations. The acidity neutralized by each cation is equivalent to its valence within the mineral structure. Fe and Al are hydrolyzed during the ANC back-titration and thus are effectively non-acidneutralizing cations. Sulfur derived from pyrite oxidation is equivalent to the release of two moles of H+, although non-acid-forming S (e.g., gypsum) should be addressed. Calculations based on these principles for the samples tested correlate well with the ANC determined by titration-type tests.