Mining and Processing
After site establishment, mining commences with land clearing where any vegetation and topsoil is stripped and stockpiled separately for use in rehabilitation or dust suppression. In the case of the Company’s Fungoni and Tanga South projects, the ore body begins at surface with only light vegetation and no overburden which facilitates an efficient and cost effective clearing activity.
There are various mine methods available for consideration including, but not limited to:
- Dredge mining;
- Dry mining using front end loaders (FEL) or excavator;
- Dry mining with a dozer trap;
Heavy mineral sands (HMS) deposits comprising unconsolidated sand in an area where the water table can be managed, are often suited to dry mining with heavy earth moving equipment. Dry mining also allows greater flexibility around basement irregularities and is suitable for higher slimes deposits.
With dry mining the ore is typically deposited into a mining unit or hopper, usually adjacent to the active mining area. The ore is fed to the hopper by front-end loaders, dozers, scrapers or trucks. To achieve a consistent feed grade and quality of the mined ore blending of material may be required prior to being fed into the hopper. Water may be added to the hopper to form a slurry that is pumped to the wet concentrator plant, located in close proximity (ideally less than 1000 meters from the mining face).
The valuable mineral sands (of titanium, zircon and monazite minerals) are only a small proportion of the total ore removed from the mining area (say 5%), being mixed with clays, silts, quartz sand and rock.
The land-based wet concentrator plant (WCP) is based on a modular transportable design concept making them easy to assemble and disassemble to move around a site or to other sites. Metallurgical testing in a laboratory or pilot facility is required to determine an optimal processing route for the production environment.
Wet concentration produces a high grade heavy mineral concentrate, maximising the content of valuable mineral sand whilst minimising the amount of non-valuable mineral.
The initial processing in the WCP consists of screening to coarse oversize and rock, tree roots and other organic matter, and desliming (often via hydrocyclones) to remove fines, predominantly clay and silt particles.
The deslimed material is fed to a constant density (“CD”) tank. This is then pumped, at a constant density and feed rate (to optimise performance), to the distributors above the gravity separation equipment in the form of spirals or reflux classifier.
The heavy mineral is separated from the quartz sand. In the case of spiral technology, the spiral troughs are angled and the heavy mineral sand moves to the inside and the lighter gangue minerals to the outside of the trough as the slurry travels down the spiral. Repulpers on the spirals aid in the recovery process.
The waste tailings are typically pumped directly back to into the mine void.
To maximise the recovery and grade of the valuable mineral the WCP design may consist of multiple process stages to upgrade the material including, a primary (rougher) process unit followed by middlings, cleaners, recleaner and scavenger.
Heavy mineral concentrate is stockpiled on site using dewatering cyclones and allowed to drain before being transported to the mineral separation plant (commonly referred to as the Dry-Mill or MSP).
Mineral Separation Processing
Following wet processing the heavy mineral concentrate undergoes a number of dry processing stages to separate the valuable minerals and produce saleable products..
Dry mill processing relies upon the unique physical properties of each mineral to separate the non-valuable minerals from the valuable heavy minerals.
Rare earth drum and/or roll magnets remove the ilmenite as it is the most magnetic of the minerals in the concentrate feed.
Electrostatic separation process is typically performed on the non-conductive minerals such as zircon, kyanite, staurolite, quartz and monazite from conductive minerals such as rutile, leucoxene and residual ilmenite. Further magnetic, electrostatic and/or wet gravity separation techniques may be performed to clean up (reduce contaminants) and increase the saleability of the end product.
The product is stored in a dry area and then transported to market in bag, container or bulk.