Optimisation of leaching procedure to recover La3+ from spent FCC catalyst of Dung Quat refinery using HNO3

Abstract

This work aims to determine the optimum condition of acid leaching procedure to recover La³⁺ from spent FCC catalyst of Dung Quat Refinery. The response surface method was then applied on the basis of a three-level Box-Behnken experimental design. The leaching yields of La³⁺ and aluminum were taken as the response variables, whereas the concentration of nitric acid (X₁, mol/L), leaching temperature (X₂, °C) and leaching time (X₃, min), were considered as the independent variables (factors). A mathematical model to describe the relationship between the response variables and the independent ones was proposed. 91% of La³⁺ was recovered while the Al³⁺ leaching yield was 52% under the optimum conditions of leaching time 180 min, HNO₃ concentration 4mol/L, and leaching temperature 80^oC. The most influential factors on the leaching yield of La³⁺ and Al³⁺ were determined as HNO₃ concentration and the leaching temperature. The proposed model equations using response surface methodology show a good agreement with the experimental data, with the correlation coefficients (R²) of 0.967 for La³⁺ recovery and 0.923 for Al³⁺ recovery. The solid waste after La³⁺ leaching can be used as raw material for gamma alumina synthesis.