Alternative neutralisation materials for acid mine drainage treatment

Abstract

This study reports the novel use of alkaline waste material from the alumina refining industry (Bayer liquor and precipitates formed by the seawater neutralisation of Bayer liquor), for the neutralisation of acid mine drainage (AMD) water. The hypothesis was that utilization of waste to treat waste can potentially result in environmental and economic benefits. The performance of Bayer liquor and Bayer precipitate was compared with conventional alkalis used for AMD neutralisation such as lime (Ca(OH)2), sodium hydroxide (NaOH), and sodium carbonate (Na2CO3). Target ions to remove from the AMD solution included Al (1233 mg/L), Cu (77.26 mg/L), Fe (16.7 mg/L), Ni (1.54 mg/L), Mn (161.5 mg/L) and Zn (48.89 mg/L)). Both alumina industry wastes were shown to produce treated water with acceptable discharge limits for all metals except Mn. Nevertheless, Bayer precipitate was shown to have an enhanced ability to remove manganese at lower pH (6.5–7.5) relative to lime, with residual Mn concentrations of 32.30 and 85.40 mg/L, respectively. Manganese discharge limits were challenging to meet due to pH values >9 being required wherein not only aluminium species redissolved but also the pH was not compatible with discharge regulations. Mechanistically, larger precipitates were found to positively influence the removal of heavy metals, with lime and Bayer precipitates forming the largest precipitates. Overall, Bayer precipitate was found to be a potential alternative for the treatment of AMD water.