Recovery of aluminum oxide and iron oxide from aluminum electrolysis iron-rich cover material and preparation of aluminum fluoride.

In aluminum electrolysis, the iron-rich cover material is formed on the cover material and the steel rod connecting the carbon anode. Due to the high iron content in the iron-rich cover material, it differs from traditional cover material and thus requires harmless recycling and treatment. A process was proposed and used in this study to recovery F, Al, and Fe elements from the iron-rich cover material. This process involved aluminum sulfate solution leaching for fluorine recovery and alkali-acid synergistic leaching for α-Al2O3 and Fe2O3 recovery were obtained. The optimal leaching rates for F, Na, Ca, Fe, and Si were 93.92, 96.25, 94.53, 4.48, and 28.87%, respectively. The leaching solution and leaching residue were obtained. The leaching solution was neutralized to obtain the aluminum hydroxide fluoride hydrate (AHFH, AlF1.5(OH)1.5·(H2O)0.375). AHFH was calcined to form a mixture of AlF3 and Al2O3 with a purity of 96.14%. The overall recovery rate of F in the entire process was 92.36%. Additionally, the leaching residue was sequentially leached with alkali and acid to obtain the acid leach residue α-Al2O3. The pH of the acid-leached solution was adjusted to produce a black-brown precipitate, which was converted to Fe2O3 under a high-temperature calcination, and the recovery rate of Fe in the whole process was 94.54%. Therefore, this study provides a new method for recovering F, Al, and Fe in iron-rich cover material, enabling the utilization of aluminum hazardous waste sources.

Removal of sulfur by adding zinc during the digestion process of high-sulfur bauxite.

This paper proposes a novel approach to sulfur removal by adding zinc during the digestion process. The effects of zinc dosage on the concentrations of different valence sulfur in sodium aluminate solution were investigated at length to find that high-valence sulfur (S2O32-, SO32-, SO42-) concentration in sodium aluminate solution decreases, but the concentration of the S2- in the sodium aluminate solution increases as zinc dosage increases. This suggests that zinc can react with high-valence sulfur to generate S2- at digestion temperature, which is consistent with our thermodynamic calculation results. In this study, as zinc dosage increases, sulfur digestion rate decreases while sulfur content in red mud markedly increases when zinc dosage was below 4%; the digestion rates of sulfur and sulfur content in red mud remains stable when zinc dosage was above 4%; the alumina digestion rate, conversely, increased slightly throughout the experiment. This suggests that high-valence sulfur in sodium aluminate solution can be converted to S2- and then enter red mud to be removed completely by adding zinc during the digestion process.