Closure of Mining Pond B at Richards Bay Minerals, South Africa

Closure of Mining Pond B at Richards Bay Minerals, South Africa

In 2007 when Richards Bay Minerals (RBM) decided to close their Mining Pond B, SRK was appointed to manage the project. Prior to removing the pond and rehabilitating the pond area, the dredger had to be docked for transfer to another mining pond and the floating concentrator had to be demolished. The possibility of relocating the concentrator was also considered, but an SRK study showed that this was not cost effective.

Working with the RBM operating personnel, the team excavated a docking area by creating a slot in the end of the pond, using the dredger. The neck of the slot was then closed by bulldozing sand in from each side to form a sand wall between the pond and the docking area. The water in the dock was then pumped back to the main pond and the docking area was kept dry by pumping from sumps and a well point system, which had been installed in the sand wall.

The floor of the dock area was strengthened by placing a half-meter-thick layer of crushed stone enclosed in geofabric, half a meter below the sand surface of the floor. Concrete strip foundations were then cast to accommodate a structural steel cradle, on which the dredger would be placed. Once the cradle had been assembled, pond water was pumped back into the dock until the water in the pond and the dock were the same level. Breaching the sand wall between the dock and the pond without adjusting the water levels would have caused a rush of slimes from the bottom of the pond into the docking area. The dredger then cut through the sand wall and positioned itself above the submerged cradle using a laser positioning system. The sand wall was re-installed and the dock once again pumped dry, with the dredger settling on to the cradle.

After docking the dredger, the plant, comprised of the concentrator and surge bin, sanded itself in and a platform was built around the plant using black topped gravel as a surface layer to support cranes and demolition equipment. Pumps and other electrical and mechanical items that could be re-used were carefully removed before the main demolition started. The sheeting was then removed before the demolition, using cutting torches and cranes, starting at one end of the plant. Once the superstructure had been removed, the supporting pontoons which were about 3.5m deep were dragged out of the sand and cut up. The scrap value of the plant covered the cost of the demolition.

The dunes around the pond and the pond area were then reshaped using bulldozers, front-end loaders and articulated dump trucks before re-vegetating the site, following RBM’s tried and tested methods. The project was completed successfully within budget due to the close teamwork between RBM, SRK and the demolition contractor.

Peter Labrum: plabrum@srk.co.za

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