Phosphorus sorption by red mud residue as affected by concentration and reaction time

This study was undertaken to evaluate the phosphorus (P) sorption potential of a red mud residue from Alcan, Jonquiere (Quebec) as a function of the P added and the reaction time. Batch sorption experiments were undertaken using P concentrations ranging from 2.5 to 50 mg of P per g of red mud and equilibration times ranging from 12 hours to 83 days. These experiments showed that the red mud residue has a very high sorption potential, with a maximum sorption between 40 and 45 mg g(-1). P sorption with time by the red mud was biphasic, with a fast sorption phase followed by a slower one. The present results show that ligand exchange is involved in the rapid P sorption by the red mud, with possible P precipitation. Furthermore, P sorption was Found to be concentration dependent, which is due to concentration gradient and change in the range of diffusion coefficients, which increased with increasing amount of P added. The present results show that one major problem in the establishment of a vegetative cover on this residue is due to the very high sorption potential, which depends on the amount of P added and the time of reaction.