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Dealing with deeper drainage

16th October 2013


Diesel-drive Weir Minerals Multiflo pumps can be adapted to a range of aggressive water-handling duties in open-pit mines
Performing a vital duty, mine drainage pumps are often located in isolated, difficult-to-access positions and therefore have to be very reliable. Photo: Grundfos
A typical location and use for a small electric submersible drainage pump that can run dry. Photo: Grindex
A Weir Minerals centrifugal pump stripped down in the works to show interior of the impeller casing
Mitsubishi Mars slurry pumps are designed for heavy loads to clear mine sumps for example

Designs of modern drainage pumps and associated equipment are aimed at increasing life through robust drives, linings resistant to abrasion and corrosion, and seals resistant to chemical attack. Maurice Jones reports.

Water in mines has often been troublesome ever since the Romans discovered that drainage adits became ineffective for deeper mineral deposits and interfered with the business of mineral extraction, and mechanical means of lifting water was needed.

The size of the problem represent a major logistical challenge in many mine projects where the tonnage of water that has to be moved, and disposed of safely, can be greater than that of the mineral and waste rock being excavated.

Ideally a main mine pumping system would be an ‘install and forget’ operation, but such are the demands placed on pumps and associated equipment, this is usually an objective that will never be attained; only aspired to. In addition to the necessary location of pumping stations, factors such as acidic water, hard solids, and viscous sludge with clay can conspire to increase wear through erosion and corrosion. Chemical reactions can also produce incrustations in piping, screens and valves.

Thus the designs of modern drainage pumps and associated equipment are aimed at increasing life through robust drives, linings resistant to abrasion and corrosion, and seals resistant to chemical attack. Essentially these requirements are the same whether the mine is underground or open-pit, although there may be more need for underground pump stations to deal quickly with emergency situations such as inrushes.

Depending on the volume of water to be handled, a series of small, interlinked, pumping facilities may be adequate, but for deep mines with large water ‘makes’ it may be deemed necessary to invest in a custom-design solution such as those offered by Siemens Water Technologies. These solutions can be linked with facilities for mineral processing and the treatment and/or recycling of water before environmentally acceptable discharge. The Company’s Siminecis Services provided comprehensive life-cycle support covering acid mine rock drainage, containment and treatment.

Pump designs for handling mine water are usually of centrifugal design, perhaps with multiple stages, with adequate internal space to accommodate expected solids sizes.

Solids handling

The Weir Minerals centrifugal pump range covers a wide range of solids handling capabilities and resistance to corrosive, chemical-laden water. Its Multiflo self-priming chassis- or skid-mounted dewatering pumps can be adapted to work in the largest open pits with the harshest water conditions.

Models range from the MF-90V high-flow version to the MF210MV high-head unit with diesel drives. In addition to its wide range of pumps, Weir Minerals will custom-engineer pump flotation systems (or barges) for open pit sumps, lagoons, water intakes, etc to carry single or multiple pump units.

Sludge

Sludge, such as left in sumps and filters, requires a different approach to pumping or other clearance. Common designs employ positive displacement rotors and/or compressed air suction. Holywell Engineering produce sludge pumps as skid- or wheel-mounted units with no moving parts and therefore requiring low maintenance.

Mitsubishi Mars high-pressure slurry pumps for major needs with high lifts and high solids concentrations have a design that overcomes the limitations of both piston/cylinder pumps and diaphragm pumps. All parts, except valves, are free from contact with the abrasives slurry.

Submersible pumps, with electric or hydraulic drives, are the ubiquitous solution the drainage problems in harsh conditions and with rough handling. Different styles are designed for drainage water, sludge and slurry. Often intended to clear intermittent water makes, the pumps can be run dry without damage. Grindex drainage pumps will handle abrasive particles and have capacities up to 330 litre/s and a maximum of 110m pressure head.









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