Abstract
Adsorption isotherms of octylhydroxamate and the relationship between octylhydroxamate adsorbed and phosphate released have beenmeasured against monazite. These results have been compared to those against synthetic CePO4and LaPO4. Adsorption of hydroxamate on monazite takes as long as several daysto reach equilibrium. The maximum adsorption of hydroxamate on monazite occurs at pHabout 10. Hydroxamate adsorption on monazite is much higher thanon CePO4or LaPO4and forms multilayer. Monolayer adsorption ofhydroxamate on monazite is mainly due to substitution reaction with lattice phosphate ions and makes surface hydrophobic. On the other hand, multilayer adsorption may be caused by precipitationof rare-earth metal hydroxamates and other mechanisms, such as hydrophobic bonding or hydrogen bonding between hydroxamate molecules. Hydroxamate adsorption is enhanced at elevated temperature, but flotation recoveryis not. This may be explained by a reason that the increase oftemperature promotes multilayer adsorption of hydroxamate which donot contribute to surface hydrophobicity.
