-

Until recently, reclaiming construction-grade silicas, particularly sand, was a labor- and time-intensive operation. These methods are changing, as one of South Africa's leading building materials suppliers recently demonstrated. The equipment chosen for a unique application of sand extraction was the Mud Cat™ portable dredging system.

Non-traditional use
Charles Fourie, Managing Director of Sand Bar (Pty)., Ltd., South Africa, is said to be the first to use the portable dredging system in a unique way on the African continent: extracting sand from a swampy region.

Fourie first saw the system at work at a dredging project near Randforntein, South Africa, where it was being tested for the Transvaal Provincial Administration. Fourie saw the system as an answer to the problems he had in extracting sand in the usual way.

Previously, Fourie's extraction method was slow and arduous. A front-end loader scraped the sand from the surface deposits. A dump truck transported it about 2.4 km to washing and grading plant. A second loader was used to feed the sand into the plant. Apart from the time element, major drawbacks to this approach were its machine and labor requirements, the equipment's limited ability to operate in the site's more swampy areas, and the fact that the sand needed extensive washing before it could be processed.

The Mud Cat™ is able to work in swampy sand quarries, and in water as deep as 4.5 m. Its auger head digs out the sand while its powerful centrifugal pump drives the water-borne sand through flexible pipes to a pre-selected storage area. Generally, the system requires only two people - one on board and another on shore tending the pipes. This cuts down on labor expenses. Since the Mud Cat™ uses water as a transport medium, the sand is already prewashed when it arrives at the plants. "After processing, the sand we're providing now is of a better quality than was possible before," Fourie said.

Handles different grades
According to Fourie, the Mud Cat™ is able to handle different grades of sand very well. A large portion of Sand Bar's annual $1.4-million revenues are from sales of sand to the South African Railways (SAR). The coarsest grade, called the locomotive sand, is used on the railways' lines to improve traction during rainy weather. Grade 'A' sand is used to make rough castings for wheels, rail lines and large objects. SAR uses the finer grades for more sophisticated metal castings, while the finest grade goes onto delicate aluminum castings. In addition, Sand Bar also supplies SAR with building and plaster-grade sand.

Increased production
The system increased sand production from 40.5m3/hr to more than 76.4 m3/hr in its first year of use. Fourie also said the Mud Cat™ is producing 1500 m3 of sand every 24 hours, operating on two 12-hour shifts. "At this point, the Mud Cat™ is not working at full output because our process plant's capacity was designed to accommodate the old extraction method," Fourie said. He added that his plans now include expanding the washing and grading plant and increasing the sand storage capacity.

Reprinted from World Construction