Flotation and adsorption of novel Gemini decyl-bishydroxamic acid on bastnaesite: Experiments and density functional theory calculations

Abstract

Rare earth element is an important strategic metal, but the supply of high purity rare earth ores is growing slowly, which is in sharp contradiction with the rapidly growing demand. Froth flotation has been confirmed to be an effective method to separate bastnaesite from its gangue minerls. However, the traditional collectors are facing serious problems in flotation separation of minerals, requiring the addition of excess depressant and regulator in the flotation process. Herein, we proposed and synthesized novel Gemini hydroxamic acids Octyl-bishydroxamic acid (OTBHA), Decyl-bishydroxamic acid (DCBHA) and Dodecyl-bishydroxamic acid (DDBHA) as the collectors in bastnaesite-barite flotation system. The effect of different carbon chain lengths on the molecular properties were explored by density functional theory (DFT) calculations. DCBHA possessed a stronger reactivity compared with OCBHA and DDBHA. The flotation results verified the consistency of the computational calculation about the performance prediction of Gemini hydroxamic acids. Compared with OCBHA and DDBHA, DCBHA displayed superior collecting affinity toward bastnaesite, and did not float barite. Zeta potential results showed that the presence of DCBHA increased the potential of bastnaesite, while it had almost no effect on barite, indicating DCBHA had a stronger affinity for bastnaesite. Then, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses indicated that the adsorption mechanism was due to two hydroxamate groups of DCBHA co-anchored on bastnaesite surface by forming five-membered hydroxamic―(O―O)―Ce complexes. In addition, atomic force microscopy (AFM) clearly observed that DCBHA uniformly aggregated on bastnaesite surface, which increased surface contact angle and improved the hydrophobicity of bastnaesite.