With mining companies focused on reducing and recycling as much water as possible while recovering valuable minerals and metals, filter presses are becoming a much more common sight in the concentration process.

Weir Minerals Africa says these “mission-critical” filter presses demand a carefully selected pump to ensure optimal performance and uptime.

Marnus Koorts, Product Manager for Slurry Pumps at Weir Minerals Africa, says the high pressures associated with operating a filter press often lead the pump to underperform.

“The operation of a filter press involves a wide spectrum of pressure and flow conditions within each cycle,” Koorts says. “This ranges from high-flow, low-pressure conditions when slurry is initially being pumped into the press, to low-flow and high pressure when full.”

He emphasises it is not enough to simply specify a pump for the average of this range of conditions. Rather, it is vital to establish the minimum and maximum values on the spectrum, and to specify accordingly.

“Filter presses in the market can demand pressures of up to 45 bar,” he says. “In many cases, therefore, the application requires high-pressure pumps such as the Warman AHPP high pressure range.” These pumps offer multi-stage high pressure operation to 1,000 psi and are used in slurry transportation and tailings management operations.

Koorts continued: “Where lower pressure requirements are present, the newer technology of the Warman WBH could be used as it is generally a more efficient pump with longer wear life of spare parts.” The Warman WBH pumps, also used in slurry transportation and tailings management applications, come with a wide variety of impellers and shaft seals and maintains efficiency through ‘one point adjustment’ during the wear cycle, according to Weir.

Failure of pumps to deliver enough pressure to a filter press results in the solid-liquid separation process being inefficient, according to Weir, with the selection of the right pump an important starting point in ensuring optimal operation.

The next key aspect of the customer’s selection, Koorts says, is the choice of sealing arrangement. This aspect of the pump can often lead to issues in the plant, when valuable product is lost through leakage.

“An expeller seal is not usually recommended, as the pressure it generates to seal the pump is generally not sufficient in a filter press application,” he said.

Weir said: “The stuffing box option can be used under certain conditions. However, the pressure of the surface water needs to be higher than the pressure inside the pump. This means that it would usually be suitable on a low-pressure pump for a low-pressure filter press.”

Koorts added: “When the filter press requires a higher pressure, then the plant will have to provide a water line with a higher pressure to feed the gland, or it will not seal properly.”

The preferred sealing option is a mechanical seal for these applications. While this is more costly, it offers substantial savings by preventing product being lost and downtime being incurred, according to Weir.

A further consideration is the level of corrosive aspects of trace elements in the slurry. This can lead to rapid corrosion of mild steel pumps. This is why many applications require stainless steel options.

Comprehensive technical backup needs to underpin each step in this process, Koorts said. For Weir Minerals Africa, this begins with its local manufacturing process, which includes foundries for casting components, through to local componentry manufacture and assembly capability.

“This quality control and capacity feeds into our spares availability and service exchanges for refurbished pumps,” he says. “The result is quick supply through our strategically located branch network with 12 offices in South Africa and eight through the rest of Africa.”