Modern Mining Marchh 2017

DIAMONDS

come into their own, as they can efficiently extract recyclable water from the desired end-product of mining, as well as from tailings or waste. Excessive water in the end-product or tailings also makes it expensive – and in many cases problematic – to transport, and in the case of some commodities penal- ties are applied. “There are a number of commodities which have to be dried to a certain degree before they are acceptable to the customer, making dewatering an operational

dams, Kwatani offers fine screening solutions by Derrick Corporation, whose dewatering screens can be used as a precursor to thick- eners and filter presses. This technology from Derrick has been successfully used in a number of dewatering applications for diamond mines, as well as in a diverse range of other commodi- ties worldwide. Derrick’s HI-G performance, linear motion dewatering screen is able to recover solid mate- rial including particles as small as 25 microns. This allows slurry to be successfully screened, releasing valuable water resources while con- verting the slurry into material dry enough to be conveyed and stacked. These screens are designed for high volu- metric capacity, which they achieve through the use of two 2,5 horsepower vibrating motors rotating at 1 750 rpm in opposite directions, creating high G-forces. The effectiveness of this solution is enhanced by using very high open area, patented Polyweb urethane screen panels. “The open area of the screen is critical for successful dewatering, and the high open area of these panels results in a superior dryness of up to 90 % solids in the oversize,” says Schoepflin. “The lifespan of these products is lengthened by the urethane panels’ resistance to abrasion. At the same time the sealed-for- life Derrick vibrators ensure low maintenance operation.” The benefits of effective dewatering impact positively not only on the financial bottom line, but help mines to manage a range of environmental risks associated with water man- agement. As environmental controls tighten in various countries, dewatering screens are likely to become a valuable element of mines’ tailings and water recycling strategies. 

imperative,” Schoepflin says. “In terms of waste product or tailings, the material must be dry enough to be transported on a conveyor to be stacked.” What the dewatering screen is able to accom- plish is to drain ‘free moisture’ from a wet slurry through the screen media while retain- ing as much of the fine particle material in the screen bed, creating a product that can be con- veyed and stockpiled with minimal handling and environmental impact. The drained mois- ture can then be re-used by being recirculated into the processing plant. The key principle at work in a dewatering vibrating screen is the entrapment of solid fine particles in a thick layer on the screen, creating a ‘cake’ that acts as a filtration bed. The incom- ing feed forms a pool in the angle between the back of the screen and the slightly upward- sloping deck, where most drainage takes place until the feed particles form a cake. The G-forces resulting from the screen’s action enhance the adherence of the particles to one another, effectively squeezing water out of the material. At the same time, the linear action of the screen conveys the cake up the slightly inclined deck – which on Kwatani dewatering screens can be up to a 5 degree angle. “At Kwatani, we achieve higher G-forces by generating an ideal combination of stroke and speed, which in turn squeezes more water out of the bed,” she says. “We also ensure that the material is retained for sufficient time on the deck of the screen – requiring a more vertical stroke angle and an alignment of the exciter drive’s speed. At the same time, we ensure the required tonnage passes across the deck.” To enable mines to recover more water and reduce the need to pump slurry onto slimes

The combination of a dewatering cyclone cluster and a Derrick HI-G dewater- ing machine in a diamond tailings application.

“There are a number of commodities

which have to be dried to a certain degree before they are acceptable to the customer, making dewatering an operational imperative.”

March 2017  MODERN MINING  31