Insight into the chemical and biochemical mechanisms governing inorganic contaminants removal by selective precipitation and neutralization in acid mine drainage treatment using MgO: A comparative study

Neutralization and selective precipitation of chemical species are regarded as the most promising techniques to actively treat and valorise acid mine drainage (AMD). In this study, the different chemical and biochemical process controlling the attenuation of inorganic pollutants during AMD treatment are reported. Specifically, magnesium oxide (MgO) was used as neutralizing agent to attenuate chemical species in AMD using two different techniques: neutralization and selective precipitation. Firstly, MgO was used to gradually increase the pH of AMD, precipitate chemical species in stepwise fashion. Secondly, the effect of varying dosage of MgO on AMD water quality was investigated and the fate of metals and SO₄^2[sbnd] was traced using the state-of-the-art analytical techniques. Findings revealed that MgO played a significant role in the depletion of inorganic pollutants from AMD, which resulted on the pH increment of 7.7 for both techniques. The removal efficiency (RE) after treatment using selective precipitation technique was as follows: Ni (99.99 %) > Al (99.96 %) > Fe (99.93 %) > Zn (99.75 %) > Cu (92 %) > Mn (91 %) > electrical conductivity (EC) (82 %) > SO₄^2[sbnd] (75 %) > total dissolved solids (TDS) (65 %). After treatment using neutralization technique, the RE in inorganic pollutants removal revealed the following sequence: Ni (100 %) > Zn (99.98 %) > Fe (99.96 %) = Al (99.96 %) > Cu (98.8 %) > Mn (97 %) > EC (87 %) > SO₄^2[sbnd] (78 %) > TDS (67.4 %). The characterization studies were used to briefly underpin the fate of chemical species in pure and AMD reacted MgO.