Beckton, G.L., Bhargava, S.K., Hartshorn, A.

The red mud lime sinter process can be used in combination with the Bayer process to recover sodium and aluminium from the red mud waste and direct it back to the process stream. This is facilitated by the high temperature reaction of lime and DSP in the red mud to produce an insoluble dicalcium silicate and a soluble sodium aluminate. A variation of the red mud lime sinter process using half the limestone of existing methods has been investigated. The calcium to silicon ratio was reduced from 2 to 1 producing a sodium calcium silicate (Na2CaSiO4) rather than the dicalcium silicate (Ca2SiO4) insoluble phase produced in the existing lime sinter method. Synthetic lime sinter products were investigated to understand the phases produced during calcination at varying temperatures and the chemistry of extraction. The target phases were seen in XRD and the highest extractions were produced from a sinter temperature of 1100ºC. A two-stage (65ºC/2 mins, 95ºC/16 hrs) water leaching process was found to be most effective for extraction. Sodium and aluminium extractions were 99% and 91% respectively. The experimental method devised was then used to treat red mud and the target phases were produced. An extraction of sodium and aluminium of 94% and 87% respectively was achieved. Silicon extractions were below 2%. Production benefits include sodium hydroxide and lime savings, liquor burning, increased aluminium extraction and reduced cost of waste handling.