Nutrient-dependent bioturbation of calcium ions in acid mine drainage simulations: Thresholds for inhibition and promotion of jarosites-schwertmannite mineral synthesis

Abstract

In this study, the effect of Ca^2 + concentration on the biosynthesis of secondary iron minerals in two different nutrient environments was analyzed by simulating acid mine drainage using shake flask tests, one with a liquid medium containing 9 K and another without it. The Ca²⁺ concentrations in both systems were set at 0, 30, 60, 120, 240, and 480 mg/L. We analyzed pH value(s) level, Fe²⁺ oxidation rate, total Fe precipitation rate, and relevant parameters of secondary iron minerals throughout the mineral formation mediated by Acidithiobacillus ferrooxidans (A. ferrooxidans). The results showed that in the system containing 9 K medium, adding Ca²⁺ inhibited the oxidation of Fe²⁺ during the A. ferrooxidans–mediated mineral formation process. In that case, as the concentration of Ca²⁺ increased, the pH value(s) decreased more slowly, resulting in lower rates for both Fe²⁺ oxidation and total Fe precipitation. The minerals produced from each treatment were primarily jarosites and a small amount of schwertmannite. The overall mineralization process in the system without 9 K medium was significantly slower than in the system with 9 K medium. However, compared to the control group, Ca²⁺ still had a certain positive effect on the biological oxidation process within the system.