A MODIFIED HYDROGEN-PEROXIDE OXIDATION METHOD FOR DETERMINATION OF POTENTIAL ACIDITY IN PYRITIC OVERBURDEN

Acidity that develops in mine spoil after exposure to the environment commonly results from oxidation of iron disulfides, mainly the minerals pyrite and marcasite. It is often necessary to quantify the acid-producing potential of overburden sediments prior to surface mining or during the reclamation process. To prevent excessive acidity problems from occurring on the spoil surface, or to correct acidity problems that may have occurred after leveling of the spoil, a rapid, accurate, and reproducible potential acidity method is required. Potential acidity determinations made by the rapid peroxide oxidation procedure were highly variable for east Texas overburden samples. Potential acidity determinations of overburden using a modified method were found to be accurate and reproducible. Modifications included grinding of the sample to < 149 μm, leaching with 1 M CaCl2 to remove residual acid prior to oxidation with H2O2, increasing the volume of H2O2 used to oxidize the sample, the use of Cu as a catalyst to decompose excess H2O2, and the removal of acidity from the sample with 1 M CaCl2 prior to titration. Recovery of standard pyrite addition by the original potential acidity method was 61 to 171% and by the modified method it was 97 to 102%. Potential acidity values obtained from samples using the modified method were compared with potential acidity values calculated from nonsulfate S, pyritic Fe, and total S data. The modified potential acidity method gave the lowest acidity estimate of three alternative methods investigated.