Caustic Liquor Recovery

Caustic liquor recovery in an alumina refinery refers to the systematic process of intercepting, collecting, and recycling sodium hydroxide (NaOH) solution — whether as dilute wash liquor recovered from bauxite residue washing circuits, as liquor collected from equipment drains and spills, or as condensate and liquor recovered from evaporator and other process streams — back into the main Bayer process circuit, thereby minimizing caustic soda losses and reducing the need for fresh caustic soda make-up additions. Effective caustic liquor recovery is both an economic imperative and an environmental responsibility for alumina refineries: caustic soda (sodium hydroxide) is the single largest chemical cost in alumina refining, and any caustic lost with bauxite residue, discharged in wastewater, or otherwise escaping the circuit represents a direct financial loss and a potential environmental liability. The primary route of caustic liquor recovery in an alumina refinery is the bauxite residue washing and counter-current decantation (CCD) circuit, where a series of thickeners performs a counter-current wash of bauxite residue (red mud) — progressively diluting and recovering dissolved caustic soda from the residue using progressively cleaner water — before the washed residue is pumped to the residue storage facility. Optimization of the CCD washing circuit through control of wash water addition, thickener overflow clarity, underflow density, and flocculant dosage is critical to maximizing caustic recovery (targeting residue wash liquor soda loss of less than 3-5 g/L Na₂O). Additional caustic liquor recovery measures include installation of liquor-tight bunded areas around process equipment with sumps and sump pumps to recover spilled or drained caustic liquor; recovery of weak liquor from condensate polishers; and systematic collection and return of all caustic-bearing streams from across the refinery to liquor storage or evaporation for reconcentration.