Integrated acid mine drainage treatment using Mg(OH)2 or Mg(HCO3)2 and Ca(OH)2: Implications for separate removal of metals and sulphate

Abstract

In this study, the influence of mole ratio dosage of Mg(OH)2 and Mg(HCO3)2 to that of Fe2+ and factors influencing the rate of Fe2+ oxidation were studied using simulated AMD. In addition, the consequence of AMD treatment first with Mg(OH)2/Mg(HCO3)2 and then Ca(OH)2 were evaluated. The optimised method was applied to real AMD. The result shows mole ratio of Mg(OH)2/Mg(HCO3)2 to Fe2+ 2:1 in which aeration accompanied with stirring was found the best proportion for complete removal of Fe2+ and other metals in the form of metal hydroxide precipitate in <30min. Unlike the conventional method, pre-treatment of AMD either with Mg(OH)2 or Mg(HCO3)2 prevent gypsum precipitation along with metal hydroxides. Thus, the metal hydroxide and gypsum were obtained from AMD treatment separately. The metal hydroxides and gypsum could be used for different industrial applications. Furthermore, the possibilities of recovery and reuse of magnesium hydroxide from the sludge were also developed. Generally, the analysis results confirmed the importance of treatment order and possibility of applying the optimised method at the plant scale.