Abstract: A process for purifying at least a fraction of a solution in the Bayer cycle, which is preferably taken off after decomposition of the sodium aluminate, before or after concentration thereof, by causing the precipitation of the sodium oxalate in solution by the introduction of an agent for destabilization of the state of supersaturation of the sodium oxalate, which is characterized in that the supersaturation destabilization agent introduced into the Bayer solution to cause precipitation of the sodium oxalate is selected from the group comprising calcium oxalate and barium oxalate and that, in the case of solutions charged with degraded organic materials which generally result from high-temperature attack on bauxites with high proportions of humic materials, an anionic synthetic polyelectrolyte of high molecular mass is previously introduced into said solutions in order to increase the efficiency of the purification effect.