Global demand for gold and silver remains as high as ever. Precious metals are not only sought after by investors, but are indispensable materials in modern industry.
Look behind the scenes
The mixture must first be condensed and concentrated, therefore the water content of the gold slurry should ideally not exceed 40 percent. In the past, centrifugal pumps were typically used in the mining industry for this conveying step, although centrifugal pumps are in fact designed for fluids and therefore require a medium that contains at least 50 percent water. Additional water was hence injected to operate these pumps, accepting the drawback that the added water made subsequent extraction more difficult and costly.
In search of alternatives, a pump from another producer was installed in a mining region on a trial basis. However, the pump housing was completely destroyed within just two days. The high abrasiveness of the gold sludge was to blame. The stone particles in the sludge behave like sandpaper, particularly at high speeds, and wear away all surfaces extremely quickly – until the system fails completely.
This effect can only be reduced by particularly smooth pumping at an economically viable volume, as further tests with a NEMO® progressing cavity pump demonstrated. To achieve a system with as long a service life as possible, despite heavy wear, the designers at NETZSCH selected tungsten carbide for the rotor. Tungsten carbide, with a scratch hardness of 9.5 on the Mohs scale, is almost as hard as diamond and is therefore scarcely affected by the grinding of the crushed stone. SBE, a nitrile material, was used for the stator. It is similarly extremely wear resistant, but also soft enough to prevent the points of contact with the rotor from wearing out too quickly. The progressing cavity pumps are also low power consumers and are easy to clean and maintain, which in turn reduces operating and maintenance costs. However, it is the durability of the pumps which is decisive when it comes to conveying gold. In the first test, the pump ran for three months without damage to the stator or rotor. The mine operator has since installed further three NEMO® pumps with an average service life of approximately 3.5 months. The service life exceeds the life cycle of earlier centrifugal pumps, which were completely worn out after three months, despite the addition of water.