A local innovation is helping to dredge sediment more efficiently from water cleaning reactors, contributing to the treatment of acid mine drainage (AMD) from historic mine workings in Gauteng.

Water in deep underground mining areas around Johannesburg, has become contaminated through contact with broken rock containing sulphur-bearing minerals. As the water rises and decants on the surface, it poses a serious health risk and contaminates other water resources.

Two AMD treatment plants have deployed IPR’s SlurrySucker dredging units to more effectively dredge sediment and silt.

IPR business development manager Ruaan Venter explains that the highly acidic water is treated with lime and flows through two reactors at the AMD plant, where sediment settles and gradually fills up the concrete channels of each reactor. This was causing extensive downtime for the plant, as each reactor had to be emptied of water before the acidic silt could be excavated.

“To allow one reactor to be cleaned, it had to be closed off – reducing plant throughput and placing extra strain on the other reactor,” Venter explains. “The customer needed a solution that would allow them to gain more uptime from the plant, as digging out the silt was disruptive and time consuming.”

The SlurrySucker dredging system suspends a heavy duty submersible slurry pump from a specially designed flotation raft, allowing continuous dredging with minimal supervision. For the AMD plant, a customised solution was required due to the specific structure of the reactors.

IPR designed a custom-engineered mini SlurrySucker to pass under the walkways of the reactor, allowing it to manoeuvre through the channels. To resist the acidic water, the construction frame is stainless steel.

“We equipped the unit with a Toyo heavy duty GR20 submersible slurry pump, which is part of our range – as the official distributor in Southern Africa,” says Venter. “This heavy duty pump, with its solids handling capability of up to 30 mm particles, is ideally suited to this application, where the slurry comprises about 60% water and 40% solids.”

This 15 kW pump can deliver up to 190 m3 an hour at a maximum head of 30 m, although the plant will be required to meet the volume limits of the downstream gold processing plant.

In addition, the SlurrySucker is equipped with an Atlas Copco Weda D50 pump which will be used to force clean water to the main slurry pump assisting with agitating the slurry. This unit is capable of handling dirty water with a specific density of up to 1,1 and has a solids handling capability up to 12 mm particles.