Optimal Conditions for Treating Acid Mine Drainage using Bentonite-Steel Slag Composites

Abstract

Acid mine drainage is characterised by low pH and high concentrations of heavy metal ions, such as Fe²⁺, Mn²⁺, Cu²⁺ and Zn²⁺. In this paper, composite particles consisting of bentonite and steel slags are used to dispose acid mine drainage. Bentonite is an mineral material which has an excellent capacity to adsorb heavy metal ions. Steel slags are alkaline, an industrial solid waste commonly used in the treatment of acid mine drainage. The main influencing factors, including adsorbent dosages, shaking rates, concentrations of heavy metal ions, temperature, adsorption time and pH value are examined using a static experiment. The results indicate that the removal efficiency of heavy metal ions improves when increasing the adsorbent dosages and the concentrations of the heavy metal ions, speeding up the shaking rates, raising temperature, extending the adsorption time and increasing pH value. With a consideration of removal efficiencies combining with treatment costs, the optimum reaction conditions for the four types of heavy metal ions are obtained, which are an adsorbent dosage of 21 mg/L, a rotational speed of 120 r/min, temperature 25’„ƒ, adsorption time 100 min and initial wastewater pH7. The highest initial concentration of Fe²⁺, Mn²⁺, Cu²⁺ and Zn²⁺ was 150 mg/L, 100 mg/L, 170 mg/L and 140 mg/L, respectively, and the removal rates was 93.42%, 92.64%, 93.86% and 95.17%, respectively, when the four heavy metal ions existed independently in the simulated mine wastewater. The determination of the particles‘ SEM-EDS Microscopic characterization show that the composite particles play a partial role in neutralizing, absorbing and the chemical precipitation. The acidity decreased notably and the heavy metal ions of Fe²⁺, Mn²⁺, Cu²⁺ and Zn²⁺ were adsorbed and precipitated effectively. The research results can extend the practical engineering application of the composite particles.