Potential for application of alkali roast acid leach technology for removal of phosphorus from iron ore

The present study deals with the effect of sodium hydroxide and sodium carbonate used as additives during oxidizing roasting of oolitic limonite iron concentrate and more precisely upon the change in its magnetic susceptibility. Further, the efficiency of Alkali Roast Acid Leach (ARAL) technology for dephosphorisation of the concentrate is compared with the case when sodium hydroxide was added in alkali leach after roasting. The treatment without additives in roasting resulted in obtaining iron concentrate with 58 % iron and 0.21 % phosphorus, while the ARAL approach yielded concentrate with 63 % iron and 0.09 % phosphorus. The influence of combination of coke as reducing agent and sodium hydroxide in roasting at 900°C is also investigated and results displayed in 3D form. The combination of ARAL with reductive roasting, grinding of the clinker to 80 % - 0,075 mm, flotation of the non-reacted coke and magnetic separation before and after the acid leach resulted in iron concentrate with 66 % iron and 0.05 % phosphorus. The study has shown that the application of the ARAL approach with low addition of alkalis followed by 10 to 15 minute acid leaching at ambient temperature could substantially reduce phosphorus, thus offering the possibility for efficient treatment of high phosphorus iron ores.