| Abstract Scope |
In the Bayer process, a concentrated sodium aluminate solution is produced by digesting bauxite in a caustic solution, followed by recovery of aluminum hydroxide by precipitation and calcination of the hydroxide to produce alumina. After calcination, the spent liquor is recycled to digest more bauxite. With each cycle, the concentration of sodium carbonate and other inorganic non-alkaline compounds keeps increasing, which in turn decreases the efficiency of bauxite digestion. The concentration of these undesirable side-products is typically controlled by causticization of the process liquors with lime. The reaction of lime with sodium bicarbonate however results in formation of tricalcium aluminate (TCA), which reduces process yield. We demonstrate the TCA formation can be minimized or eliminated by using sugar derived molecules, specifically gluconic acid and sodium gluconate. Experiments conducted with synthetic Bayer liquor showed an almost 10% increase in the C/S ratio, which will directly lead to higher production yield. |