A STUDY OF THE DEPHOSPHORIZATION OF KOTON KARFE IRON ORE BY ACIDIC LEACHING

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Department of Engineering

ABSTRACT
In this work an attempt was made to dephosphorize Koton-karfe iron ore by leaching with Sulphuric (H2SO4), Hydrochloric (HCl) and Citric (C6H8O7) acids. The work involved carrying out chemical and mineralogical characterization of the ore, size/assay analysis (+355μm to -50μm) followed by leaching at different particle sizes (-355 +250 and -180 +125μm) and varying time (20 – 120minutes at an interval of 20 minutes), concentration of the acids (0.5M – 2.5M at an interval of 0.5M for hydrochloric and citric acid and 0.15 – 1.2M for sulphuric), temperature (30 - 80oC at an interval of 10oC) and agitation (100 – 500rpm at an interval of 100rpm) in order to develop the optimum leaching conditions for the acids under study. The ore after calcinations at 700, 800 and 900oC was also leached at optimum conditions attained. The results of the chemical analysis revealed that the iron ore head sample had a total iron content of 46.91% Fe (67.02% Fe2O3) and phosphorus content of 0.79% P (1.81% P2O5). The results of the mineralogical analysis reveal that Goethite (FeO(OH)), Quartz (SiO2), Alumina(Al2O3) and Phosphorus are the minerals present in the ore while Magnetite (Fe3O4), Hematite(Fe2O3) e.t.c are present in minute amounts. The mineralogical analysis also showed that the phosphorus is uniformly distributed in the iron ore in the form of berlinite (AlPO4) and in solid solution with goethite. The leaching shows that the highest percentages of phosphorus removal prior to calcination of 45.40, 35.31 and 29.73% were attained at particle size fraction -180 +125μm for sulphuric, hydrochloric and citric acids respectively. Generally calcination of the iron ore prior to leaching increased the rate of removal of Phosphorus from the ore. The kinetic study of the leaching mechanism of the phosphorus removal by the acids revealed that leaching with citric acid has an activation energy of 12.6KJ/mol, and hence it is diffusion controlled, while leaching mechanism of the phosphorus by hydrochloric and sulphuric acids are intermediate (chemical and diffusion) controlled with activation energies of 29.56 and 26.9KJ/mol respectively. Based on the results obtained, it can be concluded that Sulphuric acid gave the best results with 73.51% of the total phosphorus in the ore being removed.