Rare earth (La, Ce, Nd) and rare metals (Sn, Nb, W) as by-product of kaolin production, Cornwall: Part1: Selection and characterisation of the valuable stream
Résumé
This paper analyses output streams of a kaolin plant to select the most valuable waste stream for metal recovery. The results indicate that rare metals (Sn, Nb, W) and Light Rare Earth Elements (LREEs) are pre-concentrated in the micaceous residue which contains a relatively high LREE (La, Ce, Nd) concentration of around 170 ppm. This residue have been characterised using a two-stage gravity pre-concentration process involving a Falcon concentrator and a shaking table to obtain concentrates suitable for mineralogical study. A statistical analysis, combined with qualitative mineralogy, highlights the main mineralogical associations and identifies monazite, cassiterite, Nb-rutile and wolframite as the main metal-bearing minerals. Estimation formulas for Nb and LREE using only the TiO2 and SiO2 content of the wastes, obtained by binary and multiple linear regression, show very accurate results suggesting a possible on-line application. This will provide tools to select the most valuable waste streams or the associated tailing dams (using historical data) for metals recovery. These selected wastes will be used for metallurgical test works to assess the potential for by-product recovery of these metals.