Effects of sodium-salt on Al-Fe separation by reduction roasting for high-aluminum content limonite

The effects of different sodium salts on Al-Fe separation in limonite were studied during reduction roasting process.The results show that when the ore is reduced directly,the metallization rate of iron in roasted ore is 87.13%,and the total iron grade and Al2O3 content of metallic iron concentrate is 68.07%and 7.94%,respectively,but the iron recovery rate is only 19.77%when the roasted products are treated by magnetic-separation.The metallization rate of Fe in the roasted ore is up to 95.69%when reducing with addition of 14%(mass fraction) Na2SO4 and 2.5%BS.The total iron grade of metallic iron product increases to 91.3%,and the Al2O3 content decreases to 1.27%,the iron recovery rate reaches 93.64%when the roasted products are treated by magnetic-separation.The XRD,EDX and microstructure results indicate that,when limonite is reduced without sodium salts,the iron oxides are reduced to nonmagneticγ-Fe,and most of the iron granules combine with aluminum and silicon gangues closely,which results in difficulties during magnetic separation.The sodium salts react with gangues bearing Al2O3 and SiO2 and form sodium aluminosilicates,thus,the structure of the ore is destroyed,and the reduction effect is greatly enhanced.However,the sizes of metallic iron grains obtained during the reduction with addition of sodium carbonate are relatively small and combined with gangue tightly. When reduced with sodium sulplate,the metallic iron grains grow and can be easily liberated from gangue.Therefore,Al-Fe separation is more effective after adding sodium sulphate.