New water treatment dredger refines sludge at copper mine

2nd May 2008 By: Desislava Tzoneva

Water treatment company SAME Water sales director Frank Schulz says that one of the company’s most recent research and development technologies manu-factured, the Imvubu dredger, has been used to dredge settling pond silt on a copper mine, in Zambia.

The Imvubu unit was sold to the copper mine, in Zambia, where sludge from mine water is processed and pumped out to extract copper from the settled silt. The Imvubu, developed for the mining and municipal industries, is a dredger used for removing sludge and silt from settling ponds in mines, waste water and industrial applications.

SAME Water project manager Brandon Conradie says that, at the copper mine, SAME Water was required to provide equipment that would extract silt from the mine’s settling pond and redirect it to the mining extraction process, in order to reuse refined settled metals.
“The copper-mining process is detailed and often similar to other mining process, where, through a series of refining processes, the final effluent is pumped into tailings or settling ponds that still contain a percentage of mined material,” says Conradie.
The Imvubu dredger, developed locally by SAME over a two-year period, is a sludge dredger, that collects sludge through a travelling floating device, which is manufactured from steel, two flotation tanks and a balancing tank at the front of the machine. The flotation tanks are filled with high-density foam to prevent leaks on the tank.

The Imvubu dredger moves in a sedimentation basin. The unit travels slowly in order not to resuspend settled solids. It uses a submerged scraper assembly, which houses a screw system that drives the sludge to the centre of the scraper system. From the scraper, the sludge is pumped through a sieve screen and a lobe pump to shore, through a floating hose assembly, where the sludge and water are further processed for separation.

The drive mechanism for the dredger is a base plate-mounted electrical winch, which is bolted to a concrete slab located adjacent to the basin. A base plate-mounted return sheave wheel is fixed to a corresponding concrete slab on the other side of the basin.

About 50 m3/h of sludge or silt can be pumped from depths of up to 4 m on this unit. A hydraulic pack on the front of the dredger, which controls the balancing tank and auger, is controlled by a 380-V control panel, which is boat-mounted and is driven by an external power pack generator of at least 17 kVA.

Imvubu was first tested on the project for regenerating the Boksburg lake. Conradie says that at the inlet of the lake, wetlands are affected by industries upstream, which produce large quantities of waste and sludge. The trial spanned over eight days and sludge was removed from the lake in a large stocking-like container which, when pumped with sludge, allows cleaner liquid to escape through the pores of the ‘stocking’, while a thicker concentration of sludge remains inside. This is cost effective says Conradie, as many companies charge for sludge removal by weight. When water is removed from the sludge, more sludge and waste can be collected.

Locally, SAME Water has also processed mine water at the Forzando coal mine, in Mpumalanga province. Water from underground coal oper-ations is processed by pumping the mine water into settling tanks. The pumped water is then filtered through sand filters, after which it is pumped through a reverse osmosis (RO) system. The two RO units process between 10 m3 and 15 m3 of water every hour .

Conradie says that owing to the corrosive environment at the coal mine, a number of water diseases and E coli bacteria have been discovered in the water. Chlorine has been introduced to the tanks to kill bacteria. The RO units have helped in reducing the total dissolved solids quantity from about 630 parts per million (ppm), to between 20 ppm and 60 ppm, which is an acceptable drinking water standard.

SAME Water, established in 1966, is mainly involved in sourcing technology from European markets by either buying it directly, or by buying it through royalties. About 90% of the equipment is manufactured locally at the company’s factory in Alberton, and some parts of the equipment manufactured are often re-engineered to suit African conditions.

SAME Water manufactures most water treatment equipment, including screening, waste washing, compaction and conveying equipment. Sluice gates, clarifiers, aerators, biofilters and thickeners also form part of the SAME supply.
The company also undertakes research and development, and supplies municipal industrial and mining water treatment equipment used in between 30 and 40 projects a year.