Acid generation potential and kinetics of metal(loid) release from resuspended sulfidic mine waste

Abstract

Sulfidic mine waste exposed to oxidizing conditions can generate acidity and leach metal(loid)s into the environment, posing a risk to surrounding ecosystems. In the present study, four sulfidic mine waste samples were investigated using both kinetic and static experiments to determine the acid generation potential and mobilization of metal(loid)s. A long-term resuspension experiment of 821 days was performed to study the effect of oxidation on the acid generation and the release of metal(loid)s from the mine waste samples. The mineralogy of the mine waste after 821 days of oxidation was determined and compared with the original sample. A kinetic study of a pH-dependent leaching test was also performed to study the influence of time on metal(loid) release. Additionally, a static acid-base accounting test was used to gain more insight into the acid generation and neutralization potentials. The mineralogical study revealed the presence of sulfide minerals (e.g., pyrite, and sphalerite) both as free particles and embedded within other minerals (e.g., quartz). The mine waste samples exhibited a high acid generation potential, where the pH of all samples decreased to pH< 3 after 272 days. The resuspension of the mine wastes also resulted in a considerable release of As, Cd, Cu, and Zn (up to 4500, 100, 4000, and 11,500 mg/kg, respectively). However, Pb exhibited low leaching levels, due to the formation of secondary Pb-bearing minerals (i.e., beudantite and/or plumbojarosite). Overall, the samples pose an environmental risk based on the high acid generation potential and high release of metal(loid)s.