MechChem Africa

Reliable level measurement under extremely harsh conditions is now possible thanks to VEGApuls 64 radar level sensors. This article highlights the 80 GHz instruments’ use in diamond ore processing and the advantages one operator was able to gain by switching to radar level measurement at

VEGAPULS small antennaThe dense media separation (DMS) process is a special flotation process in diamond ore processing. Dust and dirt are, among other things, the major factors that adversely affect level measurement in the flotation tank.

The Maluti Mountains in the Kingdom of Lesotho is home to the highest diamond mine in the world at 3 200 metres above sea level. The environmental conditions there are correspondingly rough with frequent, abundant snowfalls, temperatures that fluctuate between -18 °C and +20 °C and strong winds that intensify the low temperatures being part of everyday life.

The conditions in the ore preparation process are also pretty rough. The mine transports the ore to the surface through two kimberlite pipes. These are vertical chimneys of volcanic origin that extend deep into the earth's crust. The source rock is crushed and further processed to extract diamonds. This whole procedure is extremely laborious. Worldwide production of natural diamonds is now about 20 t per year but covers only about 23% of industrial demand. The rest is manufactured industrially.

The two pipes in the Lesotho mine contain only a very small proportion of diamonds. Their yield is less than two carats per hundred tonnes of rock. A huge effort is required to get at these diamonds. In the mine, 70% of which belongs to Gem-Diamonds and 30% to the Lesotho government, 5.8-million tonnes of ore are processed per year in two plants. An additional 1.2-million tonnes are mined and processed by a contractor at a separate plant. The combined tonnage produces approximately 100 000 karats per year. Approximately 18-million tonnes of rock that cannot be used for anything are left over each year.

Separating diamonds from kimberlite

In a DMS plant, ferrosilicon – an alloy of iron and silicon – in powdered form is suspended in water to obtain a fluid with the same density of diamond, about 3.52 g/cm³. To this is added the previously crushed diamond bearing material, in order to separate the heavier minerals from the lighter rock. The DMS process produces a concentrate, which generally amounts to less than one percent of the original material fed into the plant at the beginning of the process.

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