Caustic Soda Recovery refers to the process of reclaiming, reconcentrating, and recycling sodium hydroxide (NaOH) from spent process liquors within mineral processing and refining operations. In alumina refineries using the Bayer Process, caustic soda is consumed during the digestion of bauxite ore to extract aluminium hydroxide. After precipitation of aluminium trihydrate (ATH) and filtration of red mud, the remaining liquor — called "spent liquor" — still contains significant concentrations of sodium hydroxide and sodium aluminate. Rather than discarding this liquor, the recovery system reconcentrates it through evaporation, removing excess water and restoring the caustic concentration to levels suitable for re-use in the digestion circuit. Caustic soda recovery is economically vital because NaOH is expensive, and losses directly impact production costs. Technically, recovery involves multi-effect evaporators, flash tanks, and crystallizers that progressively concentrate the liquor while managing sodium carbonate and other impurity build-up. Green liquor treatment processes may also be employed to causticize sodium carbonate back into usable NaOH. In gold mining, caustic soda used in the elution (stripping) of gold from activated carbon is similarly recovered and reused. Effective caustic soda recovery reduces chemical consumption, lowers environmental discharge loads, and supports overall sustainability targets in bauxite, gold, iron ore, and other mineral processing operations.
