LAUSR

Abstract This paper, which is the second in a series of three, follows a previous study that showed that Light Rare Earth Elements (LREE), hosted in monazite and rare-metals (Sn, Nb, W), hosted in cassiterite, rutile and wolframite, respectively, are pre-concentrated in the micaceous residue of a kaolin plant. However, the low grade and fine size range of the metal-bearing minerals make their recovery difficult using unique gravity concentration methods. An enhanced gravity concentration flowsheet was tested, which began by screening the residue into three size fractions: +180 μm, 180–53 μm and −53 μm. The 180–53 μm fraction was treated with a spiral as a roughing unit and then a shaking table as a cleaning unit, whereas the fine −53 μm processing is addressed in the third publication. The design of experiments (DOE) methodology was used to set the best operating parameters. The best heavy mineral recoveries for the spiral concentrate were obtained at a low wash water flow rate and low pulp density. The spiral scavenging tests showed that up to 80% of the heavy minerals can be recovered. However, the mineralogical analysis showed that after three passes, middlings began to be recovered, suggesting that the scavenging operations should not be further continued. Furthermore, up to 70% monazite could be recovered in a single pass. Shaking table testing on the spiral concentrates showed that heavy mineral concentrates with up to 98.5% of heavy minerals can be recovered. However, the concentrate grades were still low for most metals (Sn, Nb and W), with the exception of LREEs, which reached up to 1.6% LREE in the shaking table concentrate. Given the reasonable overall recoveries, the main reason for the low concentrate grades could have been the very low grade of the feed material, which was two to three times less enriched in metals than the average micaceous residues grades. This suggests that the cut-off grade for those metals should be above 100 ppm and points to the critical aspect of metal grade variability in the micaceous residue as a major issue if potential industrial applications are to be considered.