Recovery of iron from red mud by selective leach with oxalic acid

Abstract

The recovery of iron from red mud by selective leach with oxalic acid was studied. In order to reduce the cost of iron recovery, the red mud was washed with diluted hydrochloric acid before it was leached. Experiment results showed that after washing with 3mol/L HCl under L/S ratio 2:1mL/g at room temperature for 1h, the loss of oxalic acid in the leached residue was decreased from about 17% to less than 1%. Under the conditions of washed red mud/H2C2O4·2H2O/H2SO4 mass ratio 3:3:2 with L/S ratio 16:1mL/g at 95°C for 1.5h, the leach ratio of iron was 94.15%, while that of aluminum was 21.12% and, the content of iron was 0.69% in the leached residue. After reducing with iron scraps at 50°C for 60min, the iron in the leached solution was completely changed into the precipitate of FeC2O4·2H2O. Then the FeC2O4·2H2O was turned into FeSO4·H2O and H2C2O4 in 9mol/L H2SO4 under the conditions: with L/S ratio 5:1mL/g at 50°C stirring for 20min. By filtering the supernatant immediately, the product of FeSO4·H2O was obtained and, the crystal of H2C2O4·2H2O was formed by cooling the filtrate at room temperature.