Effect of oxalate on seed precipitation of gibbsite from sodium aluminate solution

Abstract

The precipitation performance and kinetics of gibbsite from sodium aluminate solution with different sodium oxalate concentrations as well as the corresponding influence mechanism of oxalate during the seed precipitation process were systematically investigated by physicochemical properties test, using SEM and Raman spectra. As the concentration of sodium oxalate increases, both the precipitation rate and particle size of gibbsite decrease. The presence of sodium oxalate not only increases the viscosity of sodium aluminate solution, but also promotes the transformation of Al(OH)4- to Al2O(OH)62. The overall reaction rate constant decreases and the apparent activation energy of gibbsite increases with the increasing sodium oxalate concentration, the rate controlling step of which is chemical reaction. The needle-like sodium oxalate precipitates on the gibbsite crystals and covers the active Al(OH)3 seed sites, which leads to the lower precipitation rate and the finer particle size of gibbsite during the seed precipitation process.