Dephosphorization of unroasted oolitic ores through alkaline leaching at low temperature

Roasting followed by acid leaching has long been an established dephosphorization technique for processing the goethite iron ore in the past. However, given the high-energy requirement in the process, there still exists further room for improvement. The present study of phosphorus removal from an unroasted iron ore via alkaline leaching method examined the possibility of dephosphorization from goethite ore at low temperature. The iron ore concentrate used in this study is an oolitic type of iron ore consisting primarily of goethite, in which phosphorus does not form a discrete mineral phase, but instead is diffused throughout the entire volume of the ore. This study reveals that the reduction of particle size, the increase in both temperature and hydroxyl ion [OH¯] concentration all promote phosphorus removal. About 50% of the phosphorus can be removed in relatively low [OH¯] concentration (1.25 M), about 80% phosphorous removal was attained after further increasing the [OH¯] concentration to 15 M resulting in 0.1% phosphorus in final solids with no iron losses, which was comparable to roasting followed by acid-leaching route. The optimum conditions was identified as temperature of 85 °C, [OH¯] concentration of 15 M, 0.025–0.038 mm particle size, and 10 min of leaching time with S/L ratio of 0.25 g/ml, in which P level can be reduced from 0.73 to about 0.1 wt%P. Additionally, leaching solution was demonstrated to be readily regenerated using hydrated-lime with comparable leaching ability in terms of phosphorus removal compared to fresh solution. No significant mineralogical change observed other than the uniform removal of phosphorus during the process.