Passive remediation of acid mine drainage using cryptocrystalline magnesite: A batch experimental and geochemical modelling approach.

Acid mine drainage is generated when mining activities expose sulphidic rock to water and oxygen, leading to the generation of sulphuric acid eluents rich in Fe, Al, SO4, and Mn, with minor concentrations of Zn, Cu, Mg, Ca, and Pb depending on the geology of the rock hosting the minerals. These eluents must be collected and treated before release into surface water bodies. Mining companies are in constant search for cheaper, effective, and efficient mine water treatment technologies. This study assessed the potential of applying magnesite as an initial remediation step in an integrated acid mine drainage (AMD) management system. Neutralization and metal attenuation were evaluated using batch laboratory experiments and simulations using geochemical modelling. Contact of AMD with cryptocrystalline magnesite for 60 min at a 1 g: 100 mℓ S/L ratio led to an increase in pH and a significant increase in metals attenuation. Sulphate concentration was reduced to approximately 1910 mg/ℓ. PHREEQC geochemical modelling results showed that metals precipitated out of solution to form complex mineral phases of oxy-hydroxysulphates, hydroxides, gypsum, and dolomite. The results of this study showed that magnesite has potential to neutralize AMD, leading to the reduction of sulphate and precipitation of metals.