Two-stage process for the safe utilization of secondary aluminum dross in combination with the Bayer process

• Published in: Hydrometallurgy 2022-03, Vol.209, p.105836, Article 105836
• Main Authors: Tang, Jie, Liu, Guihua, Qi, Tiangui, Zhou, Qiusheng, Peng, Zhihong, Li, Xiaobin, Yan, Huaqian, Hao, Hongjie
• Format: Article
• Language: English
• Subjects: Alumina; Bayer process; Hydrogen; Secondary aluminum dross; Sodium aluminate solution
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2022.105836

Secondary aluminum dross (SAD) is a hazardous waste produced from Al electrolysis, casting, and regeneration. A two-stage process for the safe utilization of SAD was proposed by combining with the Bayer process liquor. In the first stage, approximately 32%, 100%, and 27% of Al, Cl, and F, respectively, from the reactive substances were dissolved into the saturated sodium aluminate solution. A kinetic synergy with a considerable amount of SAD at high temperatures led to an uncontainable reaction, and the frequent addition of SAD at a low dosage was determined for the separation and utilization of H2 and NH3. The inert alumina-bearing compounds and CaF2, which accounted for 50% of the mass of SAD, remained in the residue after the first stage. Efficient conversion of the inert alumina-bearing compounds and elimination of impurities from the Bayer process were both achieved by sintering at 1000 °C for 1 h in the second stage. An alumina extraction efficiency of 99% was obtained at 85 °C after the as-prepared sinter was leached into the saturated sodium aluminate solution. The saturated sodium aluminate solution obtained in the two-stage process was incorporated into the Bayer liquor to produce alumina. Furthermore, cl− and F− were removed by forming sodalite in the desilication process and precipitating CaF2 in the dilute sodium aluminate solution, respectively. Using this novel approach, an estimated 30,000 t/a of SAD has been processed in an alumina refinery in China since 2019. These results provide a novel short process for the safe and efficient utilization of SAD [Display omitted] •A kinetic synergy led to the uncontainable reaction of the reactive substances.•The H2 and NH3 can be released and separated for recycling in a controlled manner.•Cl and F are economically removed in the form of sodalite and CaF2, respectively.•Both recovery of Al2O3 from SAD and removal of organics from the Bayer process.•A two-stage process for the safe utilization of SAD has been applied since 2019.