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Radar Level Measurement

Reliable Radar Level Measurement under Harsh Conditions Thanks to 80-GHz Sensors

| Author / Editor: Sabine Mühlenkamp / Dr. Jörg Kempf

Diamond in level measurement: Vegapuls 64 provides higher accuracy, reproducibility and reliability in diamond ore processing.
Diamond in level measurement: Vegapuls 64 provides higher accuracy, reproducibility and reliability in diamond ore processing. (Source: © everythingpossible/Fotolia.com, Vega, [M]-Sahlmüller)

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The 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. Read the exciting example of diamond ore processing and find out what advantages one operator was able to gain by switching to radar level measurement at 80 GHz.

In the Maluti Mountains in the Kingdom of Lesotho in southern Africa, there is located the highest diamond mine in the world at 3,200 meters above sea level. The environmental conditions there are correspondingly rough — frequent, abundant snowfall, temperatures that fluctuate between -18 °C and +20 °C and strong winds, which intensify the low temperatures, are 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 tonnes 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 tons of rock. A huge effort is required to get 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 (Dense Media Separation) plant, ferrosilicon (an alloy of iron and silicon) in powdered form is suspended in water to obtain a fluid with the 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.

An alternative processing method is centrifugation, where the denser material is swirled at low and high speeds in cyclones. In the process, the diamonds and other dense minerals are pressed to the walls and then out the bottom of the cyclone. The waste water rises at the centre of the cyclone and is sucked out and screened to remove the remaining particles.

Both methods have their advantages and disadvantages. The investment costs for a DMS plant are ten times higher than for a cyclone. The DMS plant, however, provides better yields. The water consumption and operating costs for a DMS plant are also significantly higher than is the case with centrifuge processing. However, the service life of kimberlite mining facilities is very long, which makes it worthwhile to build stationary infrastructure that, in the long run, leads to higher productivity of the overall process. Of course the efficiency of a plant also depends on the skill of the operator and the applied technology. Decisive factors for the smooth operation of a DMS plant and, ultimately, the whole process, are, among other things, a high level of automation and measurement technology that delivers reliable measured values.

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