Purification of sodium aluminate solutions of the Bayer process by elimination of sodium oxalate

摘要

Purificn. of at least a fraction of an alkaline soln. in the Bayer cycle is claimed in which Na oxalate is pptd. by addn. of Ca or Ba oxalate to destabilise the supersaturation state of the Na oxalate, pref. at a temp. of 20-80 (partic. 50-70) deg.C, and, in the case of solns. charged with als degraded organic materials resulting from high-temp. attack on bauxites with high proportions of humic materials, an anionic synthetic polyelectrolyte that is a polyacrylic acid, polyacrylamide, Na polystyrene sulphonate or a copolymer of Na polyacrylate and polyacrylamide is pe previously introduced into the solns. at any point in the Bayer cycle, pref. before the Al(OH)3 pptn. step. - The solid phase contg. the Na oxalate produced by this process is opt. partially dissolved, pref. at 70-90 deg.C, in either water and then treated with lime wash to produce Ca oxalate or in an alkaline soln. and then treated with Ba aluminate to produce Ba oxalate. Opt. all the Ca oxalate or opt. a portion of the Ba oxalate so produced are recycled to the Bayer soln. to be purified. The remaining Ba oxalate is discharged and opt. used to regenerate the Ba aluminate.