Synthesis of hydrotalcite by neutralization of bauxite residue mud leachate with acidic saline drainage water

Bauxite residue (‘red mud’) storage areas discharge alkaline, saline leachate which is collected and presents a challenge for management well after closure of residue deposit areas. The alkaline and saline (sodic) nature of leachate limits opportunities for treatment or reuse. Mixing alkaline, saline bauxite residue leachate with acidic, saline drainage waters from deep drains installed in the Western Australian Wheatbelt harnesses the unfavorable pH and salinity of these waters to achieve neutralization and decrease salinity through precipitation of hydrotalcite-like minerals. A mixing ratio of 1:5 bauxite residue leachate:acidic saline drainage was required to achieve circumneutral pH (8.5); and though the electrical conductivity of the mixed solution was still high (81.5 mS/cm), it was significantly lower (α = 0.05) than predicted in the case of simple mixing, indicating that mineral precipitation lowers solution salinity.