Assessment of the potential of mineral sands resource exploitation in Bangladesh
Creators: name: Rahman, Md Aminur
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 370301
subject: Exploration geochemistry

description: The minerals sector of Bangladesh produces mainly cement, coal, iron and steel, natural gas, petroleum refinery products, salt, and stone, but only small amounts of industrial minerals, such as crushed granite, and processed products. More recently studies have indicated the presence of valuable heavy minerals in fluvial deposits from the major river systems such as the Brahmaputra River, Tista River etc. in Bangladesh. Since the river systems in Bangladesh are used as major transport routes, annual dredging is required to maintain open waterways and so capturing and recovering valuable HM’s from waste dredge material is may be a cost-effective, long-term source of HM’s for the country.

The mining and processing of heavy mineral (HM) sands from beach sand deposits is an established and economically viable method for recovering high value heavy minerals such as ilmenite, rutile and zircon but rare from river sand. While the major source of heavy minerals such as ilmenite, rutile and zircon are currently from mining and processing high-grade beach sand deposits, grades of such deposits are decreasing, deposits are getting smaller, more isolated, and deeper, and more slime enriched. Moreover, since beach placer mineral sand deposits are primarily located in environmentally sensitive or highly populated coastal areas many deposits have been declared as operating in environmentally critical areas. For these reasons, new sources, such as those potentially available from river sands, are now being considered for development even though the concentration of VHMs is low.
 
Sediments from stable sand bars along a 40 km section of the Brahmaputra River in northern Bangladesh were analyzed for their major, trace and rare earth element contents to determine their provenance, compositional maturity, source area weathering and tectonic setting. Following this examination, a detailed characterisation and phase analysis of the heavy mineral fraction in the sediments was conducted followed by a beneficiation study involving unit processes employing gravity, magnetic and electrostatic properties that was designed to examine the recovery, quality and assessment of potential end-use applications of the recovered VHMs.  As a significant portion of the material still remained as tailings, a flotation-based beneficiation test regime for the recovery of quartz component of the gangue mineral assemblage for glass making applications was also designed and tested. The final step in the work presented here involved examining the potential for exploiting the heavy mineral sands of the Brahmaputra River by providing a preliminary techno-economic evaluation of setting up a conceptual 1400 t/h mining and processing plant in the Brahmaputra River Basin.

Geochemically, the Brahmaputra River sediments were classiﬁed as litharenites and the Index of Compositional Variability (ICV) varied between 1.4 and 2.0, indicating low compositional and mineralogical maturity. A high mean SiO2 concentration (72.9 wt.%) and low Al2O3 (11.1 wt.%) were consistent with a low abundance of shale and clay components. AverageTiO2 values for most samples were higher than average crustal levels, consistent with the northern section of the Brahmaputra River being a potential resource for valuable Fe-Ti oxide heavy minerals.

Examination of the type and distribution of minerals present in the heavy mineral fraction of the sediments showed that 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. 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. Characterisation of the concentrates showed that further refinement of the processing conditions is required to generate concentrates that are potentially suitable for commercial applications.

The level of impurities associated with the Brahmaputra River ilmenite was higher than in the equivalent Cox’s Bazar beach fractions suggesting possible issues with liberation or the properties of the associated gangue minerals reacted differently to the separation conditions, or both. Ilmenite from both regions exhibited texturally alike grain types and chemically similar compositions with detrital ilmenite from Cox’s Bazar characterised by TiO2 contents ranging from 49 - 53 wt-% (average 51 wt-%) while the range for the Brahmaputra River was 44 - 53 wt-% (average 49 wt-%). Based on the major and minor element compositions of ilmenites from both sources, the most likely route for processing the ilmenite-rich component would be via the sulphate route to pigment.

The small component of VHMs in the Brahmaputra River sediments means that over 90% of the material constitutes rejected light minerals quartz, feldspar etc. as well as the uneconomic heavy minerals. These would usually be disposed into mined-out areas. A study into the possible application of flotation technology to separate feldspar from quartz in a Bangladesh river sand sample was undertaken with the aim of producing a high-grade quartz product for potential use in glassmaking. The test produced a quartz product assaying 99.5 wt% SiO2 and only 0.3 wt% Al2O3 with a quartz content of 98 wt%. The upgraded quartz product may be suitable for manufacturing household white glass. Further optimisation work at a larger scale is recommended.

This study demonstrate that ilmenite, magnetite, garnet, and zircon-rich concentrates can be processed from the heavy mineral-containing sand samples from the Brahmaputra River basin, Bangladesh. The technical studies such as scoping and pre-feasibility study have been carried out and mineral sands resources are characterized as inferred, indicated and measured resources. Based on the beneficiation test, a first-pass techno-economic model for mining and processing of the mineral sands was developed. A 1,400 t/h mine dredge and associated dry mineral separation plant was considered for the model. The estimated capital cost (including contingency) is approximately US$230 million and the operating costs are projected to average approximately US$20 million annually. The internal rate of return based on the first 5 years of operation (with no terminal value) is 15% and the projected payback period bis approximately 9 years after the operation commences.