Phase equilibria in the K2O–Al2O3–H2O system at 40 °C

Phase equilibria for the K2O–Al2O3–H2O system were investigated at 40 °C. In the concentrated alkali region of the phase diagram, only the equilibrium solid-phase K2O·Al2O3·3H2O was found besides KOH·H2O. This is different from the fact of the similar system Na2O–Al2O3–H2O. Two invariant points with their respective equilibrium solid pairs (Al2O3·3H2O versus K2O·Al2O3·3H2O and K2O·Al2O3·3H2O versus KOH·H2O) were identified with their corresponding compositions. These findings can provide a significant database for the removal of alumina from the concentrated alkali solution that was produced in the cleaner manufacturing process for chromium compounds.