Dephosphorization of high phosphorus oolitic hematite by acid leaching and the leaching kinetics

It is highly difficult to remove phosphorus from high phosphorus oolitic hematite by the usual dressing process. Acid leaching is an effective method for the dephosphorization of high phosphorus oolitic hematite. The acid leaching experiments were conducted to study the effect of acid concentration, temperature, leaching time, solid-liquid (S/L) ratio and the stirring speed on the dephosphorization of the high phosphorus oolitic hematite. The results demonstrate that hydrochloric acid is the best selection for leaching acid for the dephosphorization, and treatment of the sample in 0.2 mol/L hydrochloric acid at 298 K for 10 min with the S/L ratio of 0.03 g/mL and a stirring speed of 300 rpm is optimum. Thus, the dephosphorization can reach 90% with < 0.18% iron loss. We also investigated the hydrochloric acid leaching kinetics. There were two distinct stages in the leaching process for dephosphorization, and the kinetics of both stages followed a shrinking core model. The apparent activation energy for leaching in leaching stage one (initial 10 min) and stage two (10-60 min) was estimated to be 2.51 kJ/mol and 5.59 kJ/mol, respectively. The results demonstrated that leaching of the two stages was controlled by acid diffusion through the solid product layer. The leaching with iron dissolution was mostly controlled by chemical reaction between Fe2O3 and acid.