Long-term neutralisation potential of red mud bauxite with brine amendment for the neutralisation of acidic mine tailings

Acid mine drainage is an environmental problem produced when sulphide in mine tailings dams comes in contact with O2, bacteria and water. Oxidation occurs and a succession of reactions is responsible for producing acid and metals in the environment. One solution proposed is to use red mud bauxite (RMB) that is very alkaline to neutralise acidic tailings. Previous experiments showed that RMB has a good neutralisation capacity for a short time, but the long-term neutralisation potential is uncertain. So brine was added to RMB to verify if it can improve long-term alkalinity retention of RMB. Some authors have presented results where seawater or other natural or artificial Ca- and Mg-rich brines were used with RMB to convert the basicity (mainly NaOH) and other soluble alkalinity into low solubility hydroxide, carbonate and hydroxycarbonate minerals. Results showed that neutral pH conditions were maintained over the entire test for RMB and a mixture of RMB with brine. Addition of brine to RMB slightly lowered the pH compared to RMB alone. RMB alone lost a lot of dissolved alkalinity at the beginning of the test. Most of the alkalinity was lost in water after a few flushes for RMB samples. The addition of brine helped to keep neutralisation potential over more cycles of leaching.