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

Abstract

The Acid Mine Drainage has characteristics of low pH, high concentrations of heavy metal ions, such as Fe 2+ , Mn 2+ , Cu 2+ and Zn 2+ . In this paper, the composite particles that consisted of bentonite and steel slags were used to dispose the Acid Mine Drainage. Bentonite is the mineral materials and can adsorb heavy metal ions excellently. The steel slags are alkaline and industrial solid waste for the treatment of the Acid Mine Drainage. The main influencing factors, such as adsorbent dosages, shaking rates, concentrations of heavy metal ions, temperatures, adsorption time and pH value were studied by the static experiment. Increasing the adsorbent dosages and the concentrations of the heavy metal ions, speeding up the shaking rates, raising the temperatures, extending the adsorption time and improving pH would improve the removal efficiencies of heavy metal ions. Through considering the removal efficiencies and the treatment costs, the optimum reaction conditions for the four kinds of heavy metal ions were obtained. The adsorbent dosage 21 mg/L, the rotational speed 120 r / min, the temperature 25℃, adsorption time 100 min and the initial wastewater pH 7. The four kinds of heavy metal ions existed independently in the simulated mine wastewater. The highest initial concentrations of Fe 2+ , Mn 2+ , Cu 2+ and Zn 2+ were 150 mg/L, 100 mg/L, 170 mg/L and 140 mg/L respectively. The removal rates were 93.42%, 92.64%, 93.86% and 95.17% respectively. The determination of the particles’ SEM-EDS Microscopic characterization showed the composite particles could play a part in neutralizing, absorbing and the chemical precipitation. The acidity decreased notably and the heavy metal ions of Fe 2+ , Mn 2+ , Cu 2+ and Zn 2+ were adsorbed and precipitated effectively. The research results can extend the practical engineering application of the composite particles.