RARE EARTH MINERAL FLOTATION – A COMPARISON OF SILICATES TO OXIDES, CARBONATES AND PHOSPHATES

Flotation is a processing method used to separate valuable minerals from gangue minerals based on differences in hydrophobicity. When applied to ores bearing rare earth minerals (REMs) variations in rare earth element (REE) concentrations within the REMs can lead to inconsistent flotation results. Prior work at Montana Technological University examined the adsorption of collectors on the surfaces of synthetic REMs to assess recovery via flotation. Previous studies showed that the results obtained for Salicyl Hydroxamic Acid (SHA) on rare earth oxides REO), rare earth carbonates (REC), and rare earth phosphates (REP) vary depending on the coordination number (CN) and the ionic diameter of the REEs (i.e., Lanthanide Contraction, LC). In this study, research was extended to synthetic rare earth silicates of La, Nd, Dy, and Eu. X-ray Diffraction (XRD) was used to confirm the synthesized rare earth silicate types. It was found that Ln4.67(SiO4)3O and NaLn(SiO4) exhibited behavior similar to RECs and therefore attributed to a CN = 10, where Ln = La, Nd, Dy or Eu. Likewise, it was found that Ln2Si2O7 behaved similar to REOs and therefore attributed to CN = 7 for light REOs (LREOs) and CN = 6 for mid REOs (MREO). Ultimately, results depend on the silicate polymerization measured by the ratio of silicon to oxygen (Si:O). Because adsorption densities appear to exceed monolayer coverages, adsorption is attributed to chemisorption and surface precipitation. To improve metallurgical performance, it is suggested the collector blends be used so that light rare earth carbonates (LRECs) and light rare earth silicates (LRESs) of the SiO4-type, as well as heavy rare earth oxides (HREOs) and heavy rare earth silicates (HRESs) of the Si2O7-type, can be targeted in aggregate