Harmony Gold – the largest gold producer in South Africa – is also a significant local operator of gold tailings retreatment facilities across the country. Managing mine tailings responsibly and sustainably to limit their impact on the health of people, animals and the environment and to maximise water re-use is a high priority.

Critical to the success of these important sustainability efforts is a filtration system that achieves the environmental objectives, uses water efficiently and reduces cost and downtime.

Mine tailings are one component of mine waste, which besides containing valuable gold also contains harmful material such as heavy metals, radioactive substances, sulphide minerals and reactants such as cyanide, which can pollute already-scarce water sources, as well as the soil, and therefore require responsible management.

To reduce the tailings footprint of its mining activities Harmony Gold operates waste reprocessing system works at four major tailings storage facilities around Klerksdorp, which not only reprocess tailings but also ensure precious water is reclaimed and reused.

Using slurry pumps, tailings are pumped from the four tailing dams to Mine Waste, where residual gold is removed. The waste from this plant is then pumped as slurry to Mega Dam, where it is stored for the long term, the slurry settles and the solids separate from the water – which is then pumped back at high pressure for use primarily as gland service water for the seals on the slurry pumps. 

These pumps are vulnerable to blockage and rapid erosion caused by excessive solids in the water.

If the gland service water becomes dirty or the supply is interrupted, the pump seals seize rapidly, causing damage to the shaft, stuffing box, gland packing and follower – and even to the bearing unit. The result is expensive downtime, additional labour requirements and part replacement at high cost.

An uninterrupted supply of clean gland service water is required.

The right filtration is crucial

The challenge is that the recycled process water that’s used as gland service water often contains high levels of suspended solids. And it is here where the crucial role of the correct filtration system becomes evident for profitable and responsible management of mine tailings and water recycling.

To overcome the challenge – and costly consequences – of dirty gland service water, Superior Filtration, working with Pump and Process Equipment, supplied five VA4 GraviFilters to Harmony’s tailings reprocessing plants – the first was installed at Harties 1 & 2 Plant, and is in full operation.

GraviFilters’ unique non-pressurised gravity filtration method eliminates permanent blockage or damage to the screens, and the unforced filtration process also prevents the breaking up of flocculated particles and organic matter. This ensures that the GraviFilter operates efficiently in process systems with higher solids loads and, thanks to its built-in continuous self-cleaning mechanism, it also offers extended long, uninterrupted filter runs with limited operator intervention.

As a result, the GraviFilter ensures optimal functioning of the downstream processes. This is critical in the mining industry, as the costs associated with ongoing maintenance and damaged gland arrangements are astronomical. The costs for part replacement alone can range from R25,000 to R200,000 per stoppage.

Even more costly is plant downtime resulting from a failed gland arrangement. The failure of a slurry pump can cause the entire plant to be idle, costing the mine hundreds of thousands or rands per day in lost production.

By removing all ‘large’ particles that would cause blockages and wear on the slurry pump glands, and by safeguarding sufficient water flow to the gland service storage tank and to the slurry pumps, the GraviFilters have eliminated all gland related issues since installation.

“The right filtration solution reduces risk, lifetime cost and downtime,” says Ndangi Mahangani, Business development manager of Superior Filtration, the South African company that designs and manufactures industrial filtration solutions used in 36 countries around the world. “Our mining filters play a vital role in managing water globally on many mines. As the imperative of ensuring water is re-used and that wastewater is disposed of in an environmentally responsible way, becomes ever-more pressing, efficient and effective filtration becomes more important. With more than 30 years’ experience in the mining industry we are well-positioned to provide crucial advice and filtration solutions.”

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