Preparation of large specific surface rare earth oxides from calcium-containing rare earth solution by carbon dioxide carbonization method

Abstract

The calcium-containing rare earth solution is generated during the recovery processes of NdFeB waste, which is treated as wastewater by enterprises. In this paper, the carbon dioxide carbonization method was applied to the separation of rare earths and calcium in the solution, as well as the preparation of rare earth oxides with a large specific surface. It is shown that the process of CO₂ carbonization of solution includes reactions such as the dissolution, diffusion and ionization of CO₂, the carbonate precipitation of rare earth ions, and the neutralization of hydrogen ions. At a pH of 4.5, the carbonization precipitation rate is effectively controlled, enabling homogeneous precipitation and ensuring both high precipitation yield and rare earth oxides purity. In this way, the crystallization of carbonization products is a process dominated by the oriented attachment theory and coexisting with the Ostwald ripening theory, resulting in abundant pores formed by multiple layers of stacking in the products. With the optimal carbonization conditions, the rare earth precipitation yield solution reaches 99.32%. The obtained carbonization products are crystalline (LaCe)(CO₃)₃·8H₂O, and the purity of the rare earth oxides is as high as 99.22 wt%. The specific surface area of the rare earth oxides reaches 94.7 m²/g, and its adsorption efficiency for tetracycline hydrochloride in solution can reach 92.6% in a short time. The rare earth oxides are expected to be used as an adsorption material for wastewater treatment and other adsorption environments.