There are three geological components – rock, clay and sand.
A simple mining unit involves screening out rock to leave sand and clay fractions.
A more complex mining unit is when heavy minerals may be distributed within clay and sand agglomerates, which then need to be liberated.
In such cases, a higher energy input is required, so some beneficiation separates the sand and the clay into the separate components.
Technical considerations in mining unit design relate to the clay characterisation, as clay is the most variable in nature and affects the behaviour of material most significantly.
After rock has been screened out of the heavy minerals, and the sand and the clays into their discrete components, the clay is separated from the sand using generally hydro-cyclones.
The sand fraction is then separated from the light fractions.
Generally, a heavy mineral from quartz is recovered in most cases by gravity separation. The concentrator may contain magnetic separation circuits.
- If ilmenite in the deposit is of low value, such that the cost of hauling it and processing is not economic, the concentrator design can separate it at the mining stage. lluka adopts this approach at its Murray Basin operations through a wet high intensity magnetic separation process.
The concentrator design is based on achieving the highest utilisation possible.
Generally, wet concentrators are stationary while the mining units can be mobile. Accordingly, approaches such as pre-concentrators or rougher head stockpiles are employed to maximise utilisation and maximise capital efficiency of the mining unit.
Heavy mineral extraction is about the recovery of the heavy mineral in relation to the gangue or waste, the upgrade ratio, how many stages required, the need for magnetic separation, process water conditions and potentially surface conditioning, which may require attrition scrubbing circuits in the process.
HM or VHM recovery is the most significant controllable NPV driver of any project.
- mineralogy, plasticity, bulk properties and work index influence mining unit configuration
- mineralogy, abundance and distribution
- contained HM and mineralogical value of HM contained
Slurry Handling Systems
- liquefaction demand, pumping system duties and water recovery
- mass and maneuverability
- power supply, control and communications
- pumping system duty range
- recoveries need to approach 100% of HM
- rock charge recycling into scrubbers to maintain charge
- water demand, water recovery and behaviour of non-newtonian fluids
Suboptimal design has deleterious effects on margins
- high fixed cost burden (maintenance, power and labour)
- unfavourable performance outcomes increasing mining unit costs (low mobile equipment utilisation)
- performance is critical to utilisation of downstream processes which have high fixed cost ratios