Liquor recovery in hydrometallurgical processing refers to the suite of unit operations and strategies employed to capture, recycle, and reuse process liquors — aqueous solutions containing dissolved valuable reagents or metal species — from various streams within a processing plant, thereby minimizing reagent consumption, reducing effluent volumes, lowering operating costs, and improving the overall sustainability of the operation. It is a critical performance parameter in bauxite refining, gold processing, and other hydrometallurgical operations.
In the Bayer Process for alumina production from bauxite, liquor recovery is primarily concerned with the efficient recirculation of spent caustic soda (sodium hydroxide) solution from the precipitation circuit back to the digestion circuit. After aluminum trihydrate (ATH) crystals are precipitated from the supersaturated sodium aluminate liquor in large precipitation tanks, the spent liquor — now depleted in dissolved alumina but still containing a high concentration of caustic soda — must be recovered and recycled to the digestion stage. The efficiency of this caustic recovery is a key economic driver in alumina refining, as sodium hydroxide is an expensive and energy-intensive reagent.
An important component of liquor recovery in Bayer refining is the counter-current decantation (CCD) wash circuit, where red mud (bauxite residue) is washed with water in a series of thickeners to recover the caustic liquor entrained in the residue before it is pumped to the residue storage area. Optimizing the wash efficiency of the CCD circuit minimizes caustic soda losses and reduces the demand for purchased caustic.
In gold mining cyanide circuits, liquor recovery involves the efficient stripping of gold from loaded activated carbon, the electrowinning of gold from the eluate solution, and the regeneration and recycling of barren cyanide solution back to the leach circuit. In both contexts, liquor recovery is integral to achieving competitive operating costs and meeting environmental discharge standards.