Modern Quarrying Q3 2020

bucket elevator scoops the sand from the tub and drains the water from the sand during transfer. The wastewater flows over the weir at the back of the bucket wheel and the solid fraction is separated in the wastewater slurry. “The limited capacity at the feed point of these technologies means that control over the volumes of water required for accurate material classification is difficult,” says Du Plooy. “The inability to use sufficient volumes of water means that fines are not efficiently removed and 100 – 300 micron fractions are lost to ponds or to the water treatment phase, along with the overflow, mak- ing the sand product coarser.” He says the bucket wheel’s settings must be adjusted regularly to mitigate the risk of inaccurate material classification. As this method of classification depends on settling time, the cut point must often be chosen above the threshold to obtain a maximum amount of allowable silt in the final product. Diverting excess material to settling ponds requires considerably more space to accommodate them, and the classification inefficiencies increase as the proportion of fines in the feed material increases. Clearing out settling ponds to recover lost material requires plant downtime in addition to the operat- ing costs incurred when reprocessing waste material. High maintenance and restricted throughput aside, the sand product typically discharged contains between 23% and 25% moisture, placing stockpiles at risk of contamination if located in proximity to one another. “As a consequence, stockpiling the final product requires double or even triple handling to move the material to separate stockpile areas. Stockpiles take long to build and to dry to saleable standards, and return on investment becomes a significant issue,” says Du Plooy. Cyclone technology He says cyclone technology is now replacing bucket wheel technology as a “natural evolution” of materials processing brought about by modern innovations. CDE has developed cyclonic materials technology to the point where it guarantees the

Switching from the bucket wheel system to the Combo has resulted in production gains for Ground Breakers.

KEY TAKEAWAYS

Bucket wheel technology is fast becoming a much less attractive proposition when compared to new systems

The limited capacity at the feed point of bucket wheel technologies makes control over the required volumes of water difficult

Cyclone technology is now replacing bucket wheel technology as a ‘natural evolution’

Return on investment is fast thanks to a reduced spares requirement, efficient water management and longer and running time

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QUARTER 3 - 2020 MODERN QUARRYING