Water: liquid assets

Louise Smyth

Rens Zwart explains how the mining industry is facing up to water management responsibilities

The 2015 Annual Review by ICMM, the Centre for Water in the Minerals Industry (CWiMi) suggested that water access, quality, use and environmental continue to impact directly affect the ability of the industry to operate worldwide. Indeed, it states: “Water usage and management is the most important concern among all stakeholder groups in Europe and Latin America.”

Yet despite these challenges, mine operators face ever-increasing obligations to reduce water consumption and operate within a framework that cuts overall environmental and water footprints.

The importance of water cannot be underestimated, and consequently all mines must carefully assess the impact of mining on local and regional water quantity and quality in order to retain a social licence to operate. Best practice water management is the new trend that defines credibility for the mining industry while negating the potential impact of additional costs.

Less water equals fewer costs

To increase production and, at the same time, minimise rising costs, companies need to adopt new approaches, which means optimising their mining procedures. The less time a mine requires to pump, add or remove water in the course of process usually translates into reduced operating costs. However, the taut relationship between maintaining a reliable supply of water to support mineral processing, and using as little as possible in order to have the smallest volume on hand at any time, means that mine water inventories must be managed carefully.

Here pumps have a vital role to play, and peristaltic pumps specifically can be considered water-saving devices, not simply because they can accommodate very high solids-content materials found commonly in mining operations, but because they do not require gland water, thus eliminating the requirements to either treat process wastewater or provide pump service water. Pumps such as these can play a key role in new management trends like water balance modelling. Water is obviously essential for mining operations, but when the quantity of water inventory at the mine is undesirable, it can be a considerable liability.

All peristaltic pumps supplied by Watson-Marlow Fluid Technology Group can be considered as inherent metering pumps offering repeatability of 99.5%. Furthermore, many models include integral digital drives with Profibus or SCADA control. Easy system integration with new or existing controls is coupled with operator friendly use. There is no need for separate VFDs or complex control devices, while a NEMA 4X corrosion resistant enclosure suits arduous mining environments.

Bredel hose pumps for instance, accommodate continuous flow rates up to 80m³/hr and are extremely durable (pressures up to 16 bar). There are no internal universal joints, valves, dead corners or glands to impede flow, and they are reversible for back-flushing.

Thicker flows

Although one main goal of mine operators is to use less water in the transportation process, doing so creates thicker, more paste-like slurries. Hence, the pump and hose (and other associated infrastructure) must be designed to handle thicker flows. Bredel high-pressure pumps can handle undiluted tailings and thickener underflow up to 80% solids. No seal water flush systems, strainers, dampeners, in-line check valves, run-dry protection devices or other ancillary equipment is needed. The entire family of pumps are self-priming to 9m, can run dry safely and can meter accurately to ±1%.

The upshot is that Bredel hose pumps have become first choice in mines throughout the world for a wide range of applications such as pumping shear sensitive polymers for flocculation, abrasive lime slurries for pH control, or corrosive chemicals like cyanide for gold recovery.

High solids content

Although pumping applications in the mining sector frequently involve abrasive, corrosive, shear sensitive and viscous liquid products, solids present the real challenge for pumps. Furthermore, solids such as rocks, sand and ore comprise different mineral contents and pump systems must be able to accommodate such variations.

Mining slurries often feature sub-micron solid contents in excess of 80% by weight, with specific gravity often greater than 2.0. These factors make correct pump specification vital. In addition to offering abrasion resistant slurry pumping performance in arduous conditions for extended periods, the selected pump must be capable of high operating pressures and flow rates to ensure a smooth liquid passage and deny the opportunity for the product to settle.

Other required features should include repeatable and reliable delivery performance, self-priming functionality, adaptability to process variations, and low and easy maintenance. However, with so many pump types available it is little wonder mines frequently end up employing pumps unsuitable for the task in hand. Ultimately this leads to inefficiency and increased costs, typically due to excessive wear and downtime.

Downtime is expensive

Although centrifugal and diaphragm pumps have traditionally dominated the mining sector, they are not without their shortcomings. In several applications, rotors or impellers on slurry pumps last only weeks and diaphragm pumps clog, leak or fail in a matter of months. Attempting to overcome these problems, some mine operators previously purchased special pumps constructed from acid-resistant materials rather than put up with frequent, costly pump maintenance or replacement. But this is an expensive alternative. For these reasons, the latest peristaltic (hose) pumps are today taking ever greater slices of market share. Among the many benefits of peristaltic pumps are: few moving parts; low and easy maintenance; can pump almost all materials, including slurries; zero contamination; and wear-free performance.

For the mining sector this last point is arguably the most advantageous. The wear-free performance of peristaltic pumps is an attribute that results from a unique operating principle. Unlike other pumps, the abrasive nature of the product has no bearing on pump life and the need for routine maintenance and spare parts is reduced greatly.

In a peristaltic pump nothing but the hose touches the fluid, eliminating the risk of the pump contaminating the fluid, or the fluid contaminating the pump. Fluid is drawn in and trapped between two shoes before being expelled. The complete closure of the hose, which is squeezed between a shoe and the track, gives the pump its positive displacement action. The result is a pump ideally suited for the transport of typical mining slurries including pyrite, copper, zinc, uranium, nickel, cobalt, silver, platinum, lime and gold concentrate.

Pumps such as the Bredel range are virtually maintenance-free as there are no impellers, liners or mechanical seals to replace, no check valves to clog and no rotors or stators to wear out. The only wear-part is the hose, which can be replaced in a matter of minutes with no special tools.

The hose is the secret at the centre of peristaltic technology. This is the part in direct contact with the slurry – so it needs to be both flexible and tough. At the heart of all Bredel pumps is a composite reinforced hose constructed from compounded rubbers reinforced with four individual layers of braided nylon, and finished by precision machining for enhanced suction, pressure and flow performance over the life of the hose.

Features such as these are important because over-occlusion of the hose stresses both the pump and hose, reduces hose life, and places unplanned loads on the pump bearings. Similarly, under-occlusion results in loss of pump efficiency and damaging back-flow, which also reduces hose life.

More and more mining industry customers are turning to peristaltic technology to solve solutions to specific problems. This is because peristaltic pumps can help mine operators face up to key challenges, which include: reducing downtime and operating costs; managing and reducing water inventories; reducing chemical usage; and lowering maintenance costs.

A good example can be seen at Jaguar Mining, which operates four gold mines in Brazil. The company first adopted Bredel pumps at its Turmalina mine when it was faced with pumping paste backfill comprising 4% cement and 69% solids. No centrifugal pump could handle the task.

To overcome the challenge presented by paste backfill, the mine operator installed a Bredel 2100 duplex pump on a trial basis and the results were so impressive that it subsequently purchased the pump, which is now transferring the mix at a rate of 50m³/hr over a distance of 420m.

Today, the Turmalina site has no less than five Bredel 2100 duplex pumps for backfill operations; six Bredel 2100mm duplex and two 100mm simplex models for floatation processes; eight 50mm, two 65mm and two 2100 pumps for leaching processes; two 2100 models for reject pumping; and ten 65mm models for working with reagents.

The story of success is similar at a large mine in New Brunswick, Canada, which has replaced centrifugal slurry pumps with Bredel hose pumps. Here, the 65% solids of the zinc and lead thickener underflow slurries was too high to allow the centrifugal pumps to deliver the desired flow rate, while abrasive wear was causing an unacceptable frequency of costly repair. Because the abrasives in the slurry do not affect Bredel pump life the mine is now able to minimise downtime and achieve reliability at the desired flow rate.

Keep chemical use in check

Another potential area of saving is by accurate chemical metering. The range of chemicals used in mining processes is vast and includes copper sulphate, xanthate, SIBX/MIBX, GUAR, cyanide, sulphuric acid, lime, flocculants, zinc sulphate, aerophine, sodium silicate, BIOX, surfactants and sulphides to name but a few. However, by using microprocessor-controlled brushless DC drive technology, Bredel pumps will properly maintain the flotation rates of ore extracts to ensure economical use of expensive chemicals and create significant process efficiencies.

Moving ores, concentrates and residues in a slurry form is such an essential part of industrial mining processes. In an effort to reduce water, energy and chemical consumption, and improve slurry transportation reliability, more and more mining operators are discovering the simplicity and benefits of peristaltic hose pumps. With thousands of Bredel pumps already at work around the world, there is little doubt that hose pumps are the future.

Saving water in the states

A recent beneficiary of peristaltic technology is a large copper and gold mining company in Arizona, USA, which had to frequently replace components on hard chrome iron centrifugal pumps used in a difficult tailings slurry application. The pump impellers were wearing out every two weeks, causing significant downtime and costly repairs. The mine considered several different pump technologies, finally selecting Bredel 100 hose pumps. In this application, the hose pumps transfer tailings slurry 670m to a separate plant. With no seals to flush and the ability to pump tailings with a high solids concentration (80%) the mine uses much less water with the hose pumps, providing considerable savings in both maintenance costs and water usage.

Rens Zwart is with Watson Marlow Fluid Technology Group

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