Effect of hydroxyl position isomerism on flotation separation of bastnaesite from Calcium-Bearing minerals by cinnamohydroxamic acid

Hydroxyl positional isomerism significantly regulates the flotation selectivity of cinnamohydroxamic acid. • Ortho substitution induces steric hindrance and conformational constraint, reducing non-selective adsorption on Ca minerals. • DFT results reveal steric–electronic coupling as the key mechanism governing selective metal ion recognition. The molecular structure of hydroxamic acid collectors strongly affects their flotation selectivity for rare earth minerals. In this study, two hydroxyl positional isomers, p-hydroxycinnamohydroxamic acid (pHCHA) and o-hydroxycinnamohydroxamic acid (oHCHA), were synthesized and used for the flotation separation of bastnaesite from calcium-bearing gangue minerals. Single-mineral flotation, artificial mixed-mineral flotation, adsorption amount measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and quantum chemical calculations were combined to clarify the effect of hydroxyl substitution position on collector adsorption and flotation behavior. Both pHCHA and oHCHA showed effective collecting ability toward bastnaesite, with recoveries of 84.33 % and 82.46 %, respectively. However, oHCHA exhibited much lower recoveries for fluorite and calcite, decreasing to 49.33 % and 10.86 %, respectively, indicating improved relative selectivity. Adsorption amount measurements showed that oHCHA retained appreciable adsorption on bastnaesite but adsorbed less on fluorite and calcite than pHCHA. XPS and AFM results further confirmed that oHCHA produced weaker surface interaction and lower surface coverage on calcium-bearing minerals. Quantum chemical calculations revealed that ortho -hydroxyl substitution changed the electronic distribution and molecular conformation near the active region, reducing its accessibility during interaction with calcium-bearing mineral surfaces. These results indicate that hydroxyl positional isomerism regulates collector selectivity mainly by weakening non-selective adsorption on fluorite and calcite while maintaining effective adsorption on bastnaesite. Download: Download high-res image (191KB) Download: Download full-size image