Extraction of alumina from aluminum dross by a non-hazardous alkaline sintering process: Dissolution kinetics of alumina and silica from calcined materials

作者：He, Liuqing; Shi, Lin^*; Huang, Qizhen; Hayat, Waseem; Shang, Zhongbo; Ma, Tengfei; Wang, Min; Yao, Weidong; Huang, Haoyong; Chen, Rui

来源：Science of the Total Environment, 2021, 777: 146123.

DOI：10.1016/j.scitotenv.2021.146123

• Desalination
• Mineralogical analysis
• Leaching parameters
• Desiliconization
• Ettringite

The aluminumdross (AD), which causes numerous problemsof itsmanagement and disposal to environment is a useful resource to extract alumina. This study explains a novel process to extract highly pure alumina (Al2O3) from AD at a high extraction rate without producing the residues and exhaust gases. An experimental set up was designed to perform the grinding of AD for the decomposition of aluminum nitride (AlN) and the removal of salts. Thereby, the desalted dross was used to detect the optimum alkaline (NaOH) calcination parameters and leaching conditions, as well as the dissolution kinetics of alumina and silica. The leaching residues were used to produce Ettringitemineralwith calcium-based compounds (including CaO and CaSO4) to avoid the problems of solid waste disposal from the leaching process. Moreover, to purify the alumina, slightly soluble CaSO4 was added in leaching solution to precipitate silicate and the optimumadditive/solution ratio (g/mL) was determined. The aluminumhydroxide (Al(OH)3), precipitated after the carbonizationwas calcinated at 900.0 degrees C for 2 h to produce.-alumina. Themorphological and mineralogical characterizations of AD,.-Al2O3 and the synthesized Ettringite mineralwere studied by X-ray diffraction (XRD), field emission scanning electronmicroscopy (FESEM) and X-ray fluorescence (XRF). Itwas observed that activation temperature of 1000.0 degrees C, Na2O/Al2O3molar ratio of 1.4, leaching temperature of 60.0 degrees C, leaching time of 40.0 min, and the leaching liquid/solid ratio (mL/g) of 25/1 were the optimal parameter conditions to extract alumina with the extraction rate at 86.7% and purity of more than 98%. The results of leaching kinetics' study showed that the dissolution of alumina and silicawere both controlled by layer diffusion process with the apparent activation energy of 11.4010 kJ center dot mol-1 and 2.0556 kJ center dot mol-1, respectively.