A novel steady-state model to quantitively assess the effect of pH elevation by dissimilatory sulfate reduction process in acidic waters in mining areas

Abstract

Acidic waters such as groundwater, drainage and lakes in mining area contain high-strength acids and metal ions, posing serious threats to aquatic ecosystems and human health. Dissimilatory sulfate reduction (DSR)-based processes are attractive technologies for remediating acidic waters because it produces alkalinity and sulfide for metal precipitation and acid neutralization. However, the effects of pH elevation achieved by DSR-based processes are case-sensitive and difficult to be quantitively assessed, which limits the application of DSR process for acidic water remediation. Therefore, in this study, a Sulfidogenic Acid mine water Remediation Model (SARM) considering the DSR process, weak acids balance, metal sulfide and hydroxide precipitations, and gas-liquid exchanges of H2S and CO2, was developed to quantitatively assess the effects of various environmental factors on the pH elevation by a DSR process in acidic waters. A long-term trial of a DSR reactor was conducted to calibrate and validate the SARM. The experimental results revealed that the DSR-based process is effective to relieve acidity. The calibrated SARM demonstrated the excellent performance to predict the pH variation in the DSR reactor, under the varied conditions of influent pH and organic concentration. The calibrated SARM was further validated with data collected from literatures, and the results verified that the proposed model is capable to accurately assess the effect of DSR process on acid neutralization and metal removals under various conditions in steady state. The model was employed to systematically evaluate the impacts of environmental factors on acid remediation within a DSR-based process. The results revealed that the background alkalinity plays an important role in acid neutralization. However, with an increase in sulfate reduction, biogenic sulfide and carbonate become the dominant buffering substances to neutralize acidity. Furthermore, the SARM was used to evaluate the applicability of the DSR-based process for the remediation of acidic waters by evaluating the sulfide production thresholds for acid neutralization and metal removal. The simulation results demonstrated that, the DSR-based process is recommended for the remediation of acidic waters with low background alkalinity. Collectively, the SARM proposed in this study was found to be a useful and efficient tool for quantitatively assessing the potential of DSR-based processes for neutralizing acidic waters, which is vital for biogeochemistry and environmental engineering research.