Prediction of the acid generating potential of coal mining spoils

Abstract

The sulfide oxidation impact on mined land reclamation mades it necessary for mine spoils to be classified according to their acidifying potential. In this paper predictions were made of the acid generating potential of sulfide-containing spoils from the Puentes lignite mine (Galicia, NW Spain), and the limits of sulfur contents allowable for their storage in aerobic conditions, were established. Using samples of fresh spoils, analyses were made of the content and speciation of sulfur, pH was measured after oxidation of the sample with H2O2 (pH of oxidation=pHox), and titration of the oxidation extract with 0.1 N NaOH to pH = 7 was carried out (Net Acid Production=NAP). The total sulfur content (ST) varied between <0.0l% and >3 %, with pyritic-S being the most common form (>80%). pHox varied between 1.6 and 6.4 and NAP between 1.2 and 85.0 Kg CaC03 t−1. A high correlation was found between the NAP and the ST(r=0.98, p<0.001). Spoils with ST>0.15% cause high risks of mine-soil acidification., and create the need for large doses of CaCO3 to be used on final surface of the mine dump. Use of fly ash, produced from the combustion of lignite, as an alternative to commercial lime is more effective in the control of acidity generated by spoils with high ST.