Kinetics study on the leaching of rare earth and aluminum from FCC catalyst waste slag using hydrochloric acid

• Published in: Hydrometallurgy Vol. 171; pp. 312 - 319
• Main Authors: Wang, Jinyu, Huang, Xiaowei, Wang, Liangshi, Wang, Qiang, Yan, Yannan, Zhao, Na, Cui, Dali, Feng, Zongyu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-08-2017
• Subjects: Aluminum; FCC catalyst; Leaching kinetics; Rare earths; Waste slag; FCC catalyst; Waste slag; Rare earths; Aluminum; Leaching kinetics
• ISSN: 0304-386X; 1879-1158
• DOI: 10.1016/j.hydromet.2017.06.007

During the industrial production of FCC catalyst, a large amount of FCC catalyst waste slag (FCC waste slag) containing rare earths and aluminum was generated. Landfill was commonly used to deal with the slag, which may cause serious environmental degradation and resources depletion. A novel hydrometallurgical process consisting of hydrochloric acid leaching and subsequent neutralization is proposed to recover rare earths and aluminum from the FCC waste slag. The effect of leaching temperature, hydrochloric acid concentration and leaching time on the metal extraction are studied. The leaching kinetics of aluminum and rare earths are also investigated. It is shown that 91.0% of La, 92.2% of Ce, and 94.2% of Al are extracted under optimum leaching conditions of hydrochloric acid concentration 9.00mol/L, solid to liquid ratio (S/L ratio) 0.05g/mL, leaching temperature 293K and leaching time 30min. The leaching behaviors of aluminum and rare earths follow a shrinking core model which can be expressed as 1−1−x13=kapt, and the overall leaching process is controlled by the surface chemical reaction. The activation energies for the leaching of Al, La, and Ce are 6.24, 9.71, and 9.10kJ/mol, respectively. Zeolite Na-Y and FCC catalyst presented in the FCC waste slag is leached with HCl individually. Only the FCC catalyst has a negative effect on the leaching of rare earths and aluminum. Finally, selective precipitation is employed to produce Al(OH)3 and RE(OH)3, which can be reused for the industrial production of FCC catalyst.
•A novel method to recover REEs and Al from FCC waste slag including acid leaching and selective precipitation was proposed.•Established chemical control kinetic model for leaching process.•The kinetic equations of aluminum and rare earths were determined.•Leaching mechanism was studied via individual compound leaching experiments.