New heavy mineral spiral for recovery of ultrafine chromite

Spiral concentrators are gravity separation units which are cost and energy efficient. They are widely used to treat various minerals such as coal, iron ore and chromite ore.

Separation is based on the difference in the specific gravity of the compounds in the mineral ore. Low recoveries and mass yield are obtained when processing ultrafine chromite with conventional spirals. It has been seen that spiral concentrators are efficient between particle sizes of 45 μm and 1000 μm. Particles less than 45 μm tend to be suspended in water and thus report to the tailings fraction on the spiral. When a significant amount of ultrafine particles below 45 μm is present in the feed, the efficiency of the spiral deteriorates. This is why alternative processing methods, such as shacking tables and flotation, are used.

Traditionally de-sliming using a hydrocyclone is recommended prior to spiral processing. This helps reduce the amount of ultrafine particles and enhances efficiency. However, this could result in losses of ultrafine chromite in the hydrocyclone overflow.

The aim of the internal spiral development study is to evaluate the effect of geometrical change on the spiral concentrator on the processing of ultrafine South African chromite ore. The spiral was tested on the rougher application with an UG2 chromite ore. The particle size of the material was 100% passing 850 μm and 60% passing 45% μm. The change in geometry of the spiral showed an effect on mass yield and recovery. The spiral offers approximately 2% additional mass yield and recovery than the conventional spiral. Additional tests are underway to further improve the mass yields and recoveries.

Testing is underway at Multotec to improve mass yields and recoveries

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