Separation of lepidolite from hard-rock pegmatite ore via dry processing and flotation

Abstract

A mineralogical study of Gonçalo lithium-bearing mica-rich pegmatite ore (Portugal) indicated that lepidolite occurs in coarse-grained textures, which allows an appreciable liberation of gangue minerals (quartz, k-feldspar, and albite) from lepidolite. However, the intergrowth of these gangue minerals results in uncomplicated liberation (i.e., inclusions). Taking advantage of this coarse gangue liberation, optical ore sorting through image analysis was attempted in order to predict the grades of different-sized fractions using a random comminution algorithm. The ore-sorting process allowed the production of a marketable Li pre-concentrate product for metallurgy. Moreover, this method also highlighted the possible valuation of the reject as low-Li-content quartz–feldspar mixtures for the ceramic industry (reduction in the temperature of porosity closing). Furthermore, a scaled approach of grinding and sieving allowed the formation of a lepidolite-rich fraction (>210 μm), which was processed using an electrostatic separator by varying key process parameters. The lepidolite and muscovite were separated to obtain a Li pre-concentrate assaying 3.5 % Li2O from a feed grade containing 1.8 % Li2O. Nevertheless, according to the zeta-potential measurements, the flotation test performed with the finer-sized fraction (–210 + 63 μm) showed that lepidolite flotation was optimised between pH 3 and 5. In this pH range, concentrates from the rougher stage assayed 4.2–4.5 % Li2O, corresponding to 87–95 % Li recovery. At pH > 5, the selectivity decreases, and SiO2 analysis suggests the flotation of quartz and other silicates rather than lepidolite. Feldspar/quartz flotation was also tested using lepidolite flotation rejects to promote the separation of feldspars from quartz and obtain products for ceramic applications.