Additive action on boehmite precipitation in sodium aluminate solution.

Precipitation of boehmite (Al(2)O(3)·H(2)O) instead of gibbsite (Al(2)O(3)·3H(2)O) from sodium aluminate liquor can be an energy saving option for alumina production. Gibbsite is stable at precipitation temperature lower than 90 °C. Thus when boehmite is precipitated below 90 °C it is always accompanied with a gibbsite phase. However, the addition of certain organic additives favours precipitation of a monophase product i.e. boehmite at a temperature lower than 90 °C. At a temperature as low as 60 °C additives like tartaric acid, xylose and glucose could favour the precipitation of single phase boehmite precipitation. The role of the additive is proposed to be complete inhibition of gibbsite formation and facilitation of boehmite nucleation through different extent of complex formation by multidentate ligands.