SURFACE CHEMISTRY AND MODELLING OF SALICYL HYDROXAMIC ACID ADSORPTION AT THE SURFACE OF RARE EARTH OXIDES, CARBONATES AND PHOSPHATES

The adsorption mechanism of salicyl hydroxamic acid (SHA, C7H7O3N) on rare earth minerals was investigated using two complementary methods: precipitation studies and modelling. Precipitation studies showed that SHA adsorption occurs through a displacement of the hydroxide ion at the surface in an ion exchange mechanism, leading to surface precipitation and/or chemisorption. Surface precipitation predominates in the light rare earth oxides (LREOs), while chemisorption predominates in the heavier REOs. Modelling revealed that adsorption of SHA on the REM surface is dependent upon the orientation of SHA on the surface as well as the distance between rare earth elements sites on the surface. It was concluded that surface precipitation predominates in the LREOs and in the heavy rare earth carbonates (HRECs), while chemisorption predominates in the HREOs and in the light rare earth carbonates (LRECs). With the rare earth phosphates, both chemisorption and surface precipitation are observed all across