Page 22 - HUB-4 Magazine Issue 79

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Washing & Screening
The Terex Washing Systems PreWash tank allows the ability to produce sand products into specification from materials with a high silt content and is a must for recycling applications and plant operators. The principal of it is to pump less volume out than is entering the tank. It is designed to “overflow”, gently separating out extra fines, and the light density contaminants, keeping only the sand 0-4 mm, that will be sent by a centrifugal pump to the sand washing Hydro-cyclones module.
The Terex Washing Systems FM200 Sand Plant is part of the wider solution and it is fitted with separators, high performance cyclones, which are also specially design for recycling applications. The use of separators means the plant can handle the variability of material that is often the case with Construction, Demolition and Excavation material, and results in a reduction in losses of valuable sand product, and the production of an in-specification material.
The FM200 also features a double wash process. The Terex washing systems double wash process to maximum recovery of sand through the removal of silt, slimes and clays below 63μm.The sand slurry (0-4mm and water) is pumped to the primary separator for an initial wash. The underflow discharges onto the dewatering screen where it receives a further rinse. Any fine sand which passes through the screen is collected in the sump and pumped to the secondary separator for a final wash. It was necessary to double wash the material at the Albin Borer AG site due the high percentage passing 63- micron in the feed, which was identified in the initial laboratory testing.
After this double wash process, the two in specification grades of sand are dewatered onto the high frequency dewatering screen, which reduces residual water content in the final product to 10-15%. The water from both separators containing the minus 63-micron material is collected in a ground sump and pumped into the thickener tank—where the water management process begins.
Aquaclear Water Management
The waste water is pumped into a low level thickener with flocculent added, from the central control room housing unit. Within the low level thickener, the waste particles of silt (minus 63-micron ) and clay combine with the “co-polymer”, or flocculent, to create a larger heavier particle that sinks towards the base of the cone. The flocculent dramatically speeds this process up and allows the clean water to weir over the top weir of the thickener into a collection tank, where it is recycled back into the wash plant.
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www.hub-4.com March/April - Issue 79