Recovery of rare earths and aluminum from FCC waste slag by acid leaching and selective precipitation

This paper investigated the recovery of rare earth elements (REEs) and aluminum (Al) from the waste slag discharged by FCC catalyst factory (FCC waste slag) via acid leaching and selective precipitation. Analysis methods such as ICP-AES, XRF and XRD were applied to obtain experiment data. The maximum leaching efficiency of REEs and Al was achieved at pH value of 1 and with liquid to solid ratio of 4:1. Under such conditions, 91.01%, 92.24% and 94.77% of La, Ce and Al were extracted at 20 °C for 2 h from the FCC waste slag, respectively. The SiO2 content in the leaching residue was 88.3%, which can be used as an available silicon resource. The REEs can be precipitated in the form of REEs and sodium double sulfate (NaRE(SO4)2·xH2O) by adding Na2SO4 to the leaching solution, while Al remained in the solution. Afterwards, the pH value of the filtrate was adjusted to 4.5, and Al was precipitated as Al(OH)3. Finally, NaRE(SO4)2·xH2O and Al(OH)3 were converted into RECl3 and Al2(SO4)3 solution, respectively, which were recycled to manufacture zeolite. This process recovered REEs and Al from the FCC waste slag and reduced the emissions of waste slag simultaneously, which has an important economic and environment significance.