Distribution, separation and characterisation of valuable heavy minerals from the brahmaputra river basin, Kurigram District, Bangladesh

Abstract

Bangladesh’s heavy minerals deposits in river systems remain largely unexplored with past research restricted to beach placer deposits along the south-eastern coastline of the country. In this study, 64 samples were collected from stable sand bars from the northern Brahmaputra River. The average total heavy minerals (THM) from all sample sites was 10.73 wt%, with the THM concentrations generally highest at the outermost edges of the river and lowest within the mid-channel regions. There was no variation in THM content from north (upstream) to south (downstream). Valuable heavy minerals (VHMs) magnetite, ilmenite, garnet and zircon made up around 25–30 wt% of the THM content, with other heavy minerals including amphibole, pyroxene, kyanite, sillimanite, monazite, apatite and xenotime making up the remaining 70–75 wt%. A VHM distribution map showed that the upstream division of the studied area appeared to be the most prospective for valuable heavy minerals. A bench scale heavy mineral sands beneficiation flowsheet involving unit processes employing gravity, magnetic and electrostatic properties was designed and based on a detailed characterisation and phase analysis of the resulting fractions, it was determined that VHMs made up ~2 wt% of the material recovered. Of these, garnet and ilmenite made up the bulk of the VHMs at levels of 0.88 and 0.51 wt%, respectively, with recoveries of >83%. Characterisation of the concentrates showed that further refinement of the processing conditions is required to generate concentrates that are potentially suitable for commercial applications.