Safe Preparation of Ultrafine White Gibbsite from Secondary Aluminum Dross through the Efficient Removal of Harmful Elements

Safe, comprehensive utilization of hazardous secondary aluminum dross (SAD) remarkably contributes to the green aluminum industry. A novel approach to preparing the ultrafine white gibbsite was provided after economic transformation of the reactive aluminum-bearing substances and efficient removal of salts. The simultaneous roasting process for the transformation of AlN with sodium-bearing additives was adopted through the utilization of the waste heat in the recovery of aluminum from the primary aluminum dross. Increasing roasting temperature, prolonging duration, and adding additives all notably raised the conversion efficiency of AlN. The oxidant Na2O2 and mineralizer NaF contributed to a 96.95% conversion efficiency of AlN at 750 °C owing to the formation of α-Al2O3, NaAlO2, and Na2SiO3. Meanwhile, the roasting process also promoted the removal of fluorides. Compared to the 58.6% removal efficiency of fluorine from the roasted SAD without additives, 100 g/L Na2O in solution contributed to a 92.52% removal efficiency of fluorine. Without β-2CaO·SiO2, the sodium aluminate clinker was produced from a Cl-free SAD residue with minor F at 950 °C for 1 h. Extraction efficiencies of Al2O3 and Na2O from the sodium aluminate clinker at 5 min reached 96.88% and 98.56%, respectively. Less than 8% residue was composed of MgO, CaTiO3, and CaCO3 with less than 0.045% F. 48.19% precipitation efficiency was achieved at the initial temperature of 75 °C for 48 h from the purified sodium aluminate solution. No organics, low content of Fe2O3, and good growth from the solution with less than 75 g/L Na2O at high temperature all contributed to the high quality of the ultrafine plate-like gibbsites with low content of impurities, 99.02 luminance, and 95.81 CIE whiteness.