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

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 Ca 2+ concentrations in both systems were set at 0, 30, 60, 120, 240, and 480 mg/L. We analyzed pH value(s) level, Fe 2+ 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 Ca 2+ inhibited the oxidation of Fe 2+ during the A. ferrooxidans –mediated mineral formation process. In that case, as the concentration of Ca 2+ increased, the pH value(s) decreased more slowly, resulting in lower rates for both Fe 2+ 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, Ca 2+ still had a certain positive effect on the biological oxidation process within the system. • In 9 K medium, Ca 2+ inhibits A. ferrooxidans activity, slowing pH drop and Fe oxidation, but not final Fe precipitation. • Without 9 K, Ca 2+ boosts A. ferrooxidans activity and Fe precipitation rate, though formed minerals lower than with 9 K. • Ca 2+ effects diverge: mild suppression in 9 K vs. stimulation without 9 K, different strains (ATCC 23270 & LX5) were consistent. • In system with 9 K medium forms jarosites and schwertmannite; without 9 K forms only schwertmannite. Ca 2+ doesn't alter main mineral phases. • Ca 2+ inhibits schwertmannite transformation and weakens grain boundaries, causing surface cracks in system without 9 K medium.