Recovery of Gallium from Bauxite Residue Using Combined Oxalic Acid Leaching with Adsorption onto Zeolite HY

摘要

Bauxite residue, the byproduct of alumina production, may potentially be a valuable source of strategically important metals, e.g. Gallium. Ga is considered critical element for the EU. To ensure adequate supply of Ga for the future, secondary sources such as bauxite residue should be exploited with efficient extraction methods. Therefore, in this study, mineral acids (H_2SO_4, HC1, and HNO_3) and an organic acid (H_2C_2O_4-oxalic acid), were evaluated for their efficiencies to extract Ga from bauxite residue. Using H_2C_2O_4, the highest Ga leaching efficiencies were achieved, compared to other acids. The achieved leaching experimental results were considered for the construction of a design of experiment (DOE) model to achieve optimal conditions for Ga extraction using H_2C_2O_4. These values were validated by experiments which resulted in ~ 94% accuracy. In the second part of the study, using pure Ga solution, the adsorption of Ga onto zeolite HY was studied. The effects of adsorbent dosage, temperature, and contact time on the adsorption of Ga from solution by zeolite HY were studied. The obtained adsorption experimental results were used to construct a DOE model to achieve optimal conditions for Ga adsorption on to zeolite HY. The DOE-achieved optimal conditions were evaluated by experiments in pure Ga solution, which resulted in an efficiency of ~ 99.4 %. In the third stage, the bauxite residue was leached in H_2C_2O_4 under the optimal DOE conditions which resulted in 71 % efficiency; thus the resulting bauxite residue solution was subjected to adsorption using zeolite HY under the optimal DOE conditions achieved. The Ga adsorption onto the zeolite was only 16% compared to the Ga adsorption of 99.4 % under the pure Ga solution, thus, representing the influences of the other leachates in the solution, which are minimizing the Ga adsorption onto the zeolite HY and providing an opportunity for future studies on the different mechanisms involved.