Water is the world’s most precious raw material, yet the global water crisis continues to grow in intensity.  Cheap desalination, if and when it comes, will make its inventors a huge amount of money. Meanwhile, trading water on exchanges, like other commodities, could help solve a shortage that is likely to hit long before oil runs dry. This is the opinion of the chairman of Nestle.  In May Peter Brabeck, chairman of the world’s largest food group, told Reuters the first place to consider it should be Canada’s Alberta province, due to the volume of water required in the extraction of oil sands.

“We are actively dealing with the government of Alberta to think about a water exchange,” Brabeck said. As a first step, he added, Alberta had separated land rights and water rights, so owning land did not automatically give rights to water that ran through it.

He also pointed to the ancient example of the Gulf state of Oman, which had a water exchange system dating back thousands of years, and noted how oil management helped bring the oil price back significantly in early May. “You see what happens when demand is growing. The market reacts and people start to use oil in a more efficient way,” he said. “One thing that does not move at all is the price of water.”

Speaking to a mainly academic audience in Geneva Brabeck addressed the challenges of providing water, energy and food for a world population, which is expected to head to 10 billion, according to a UN report in early May.

All operations must carefully assess impacts on local and regional water quantity and quality to retain a social licence to operate.  Best practice water management defines credibility for the mining industry while negating the potential impact of additional costs.

Using salt water 

In arid areas, the use of salt water for processing or the building of desalination plants are becoming more common. For instance, AREVA Resources Namibia operates the Trekkopje uranium mine, 70 km northeast of Swakopmund. Water to Trekkopje is provided by the Erongo desalination plant, thus negating the need for the mine to fulfil its water requirement by extracting water from the ground.

Trekkopje is an open-pit mine extracting a very large, shallow, high tonnage, low-grade uranium deposit hosted by calcretised palaeochannels with a main mineralisation that covers an area of approximately 14 x 3 km. Trekkopje processes 100,000 t/d of crushed ore, producing some 3,000 t/y of U3O8. It is a heap leach operation, commencing with a 40-day wash period using fresh water to remove chlorides, followed by an alkali leach. Yellowcake is recovered using the Nimsix IEX technology and two-stage precipitation. The leach pad facility will extend over 3 km in length and 810 m wide, making it one of the biggest heap leach operations in the world.

There is a severe water shortage in the Swakopmund and broader Erongo region. The Omdel aquifer (the groundwater source supplying water to the region) has reached its sustainable yield and potential permanent damage to the area exists if pumping is not rapidly reduced. In line with AREVA’s commitment to limit the footprint of Trekkopje on the environment, the Erongo desalination plant will enable the mine to operate free of any water pumped from the aquifer.

The seawater desalination plant and distribution infrastructure was commissioned at Wlotzkasbaken, some 30 km north of Swakopmund. This plant supplies sufficient water to support the mining operations in the Erongo region. The water is pumped to Trekkopje mine via a 48 km long, 800 mm diameter pipeline through the desert, supported by three pump stations.

The first and second phases of the process entail seawater passing through filtration membranes that remove coarse debris from the water. Reverse osmosis then separates the seawater into two streams -‘pure’ water and a brine stream, which is gravitationally forced back and dispersed into the ocean. The plant has the capacity to produce 20 million m3/y of potable water – a first for the region – and has a surplus of potable water available for domestic and industrial use in the Erongo Region. There are 55,000 m³ of treated water each day. On average, almost 40% of the seawater is converted into treated water, while the remaining 60% is returned to the sea.

Energy Recover, Inc (ERI), a global leader in ultra-high energy recovery products and technology for reverse osmosis was selected to ensure maximum power recovery from the brine discharge. ERI already had experience of mining projects. For example it supplied energy recovery devices for a SWRO desalination project in Australia. IDE Technologies awarded ERI the energy recovery contract for the 140,000 m³/d facility, supplying process and drinking water to a large operation in Australia.

IDE Technologies constructed the plant which uses ERI’s PX Pressure Exchanger(R) (PX(R)) technology as the energy recovery solution for the project. The ERI solution includes PX-220 devices which save an estimated 16 MW of power.

IDE says its technologies for optimised, highend thermal and membrane (Reverse Osmosis) desalination “are recognised as the most advanced in the world. The company designed, built and currently operates the largest SWRO desalination plants.” It has significant experience of plants for mines.

Also in Australia, CSIRO research is capturing the potential of saline water for mining and processing. CSIRO project leader Dr Hal Aral notes the “desperate measures” operators are using to secure their water requirements, specifically the use of saline water.

“Highly saline underground waters are often the only water available to miners in inland Australia,” Aral says. “And in northern Chile, seawater is pumped tens of kilometres to mine sites at higher altitudes.”

Aral says in Australia the mining industry’s use of water increased about 29% between 2000-01 and 2004-05, when it reached 2% of the total national water consumption. But mining is competing with other water users such as agriculture for the scarce resource, and is also facing other challenges such as climatic conditions and regulatory requirements. 

Using saline water is seen as a practical response that will also improve the sustainability of mineral processing generally, and CSIRO has been investigating this area since 2008. It is examining the use of saline water in physical processes, such as crushing, grinding, flotation, magnetic and gravity separation, and as a diluting agent in lixiviant preparation. The research concentrates on using seawater and saline underground water without any pretreatment, and recycling available water as much as possible.

While saline water can cause corrosion to pumps, pipes and other components at mine and mill sites, Aral says the advantages outweigh the disadvantages where fresh water is unavailable. “Use of seawater, with little or no desalination, could enhance the economic feasibility of mining operations.”

In one case study, process flowsheets have indicated that a South Australian copper producer could reduce its reliance on bore water by recycling saline water from processing. The research estimated the company could reduce its bore water consumption by about 260 t/h, also effectively reducing power costs and associated greenhouse gas emissions. Aral says this translates into a saving of about A$250,000 a year based on pumping 260 t/h from the borefield to the plant at a cost of A$0.10/kWh.  The only modifications required would be some additional pumps.

Toxic solutions 

Veolia Water Solutions and Technologies South Africa, a subsidiary of Veolia Water Solutions & Technologies (VWS), partnered with KV3 Civil Engineers in a R100 million project to make the Tubatse Ferrochrome smelter in Steelpoort a zero effluent plant aimed at conserving the water in the Steelpoort River by assisting the re-use of waste water without the risk of salinating process water. This was accomplished through the use of novel process designs and equipment supplied by Veolia.

The plant treats all water outflow on the smelter’s site, including industrial storm water, contaminated groundwater, treated sewage water and industrial effluent containing a high concentration of dissolved salts.

According to Frank Rosslee, Engineering Manager, Tubatse Ferrochrome, the true value of this plant lies in the fact that by treating the contaminated groundwater and other wastewater sources, a large volume of water is re-used, without releasing anything harmful into the surrounding environment. “The added environmental gain from the project is that the volume of water that the smelter needs to extract from the Steelpoort River is reduced, which translates into more fresh water for the residents in the fast developing rural areas downstream,” he says. He also notes that the smelter’s process water quality has improved considerably, which assists in enhancing the life expectancy of all its major process equipment. “Most components in the smelting process have to be water cooled and harsh water can cause damage due to corrosion, embrittlement, stress corrosion cracking, chemical deposition, fouling, organic growth and other negative effects of dirty and saline process water,” he explains.

The plant, modelled on the successful ZLD plant designed and constructed by the company for ArcelorMittal in 2006, has the capacity to treat 5,000 m3/d and was commissioned in November 2010. The basic processes that the waste water and groundwater are subjected to include adding ferrous chloride, removing silt and oil residue, clarification, ultra-filtration, reverse osmosis and a combination of thermal and solar evaporation.

The plant captures all industrial storm water on site and channels it via a silt-trap to an HDPE lined storm water dam capable of holding 35,000 m3 of storm water with a spill frequency of less than 1%. The storm water, considered contaminated due to having fallen within the industrial area, is stored and treated for use by the plant as process water. It is fed to the water treatment plant at a rate of 1,000 m3/d and assists in reducing river water extraction during the rainy season.

The plant process-effluent water is routed from the plant via an automated self-cleaning silt trap to the water treatment plant balancing dam, while the sewage water is piped to the plant’s own licensed sewage treatment works from where the treated effluent flows to the water treatment plant balancing dam. The contaminated groundwater is evenly extracted from eight boreholes situated over the spread of the aquifer, and is pumped directly into the water treatment plant balancing dam.

The four sources of water are fed from a balancing dam into VWS’s patented high-rate package plant Actiflo® clarifiers, which are configured to remove all suspended solids and some precipitated salts. A portion of the clarified water flows to the clean water dam for re-use by the smelter, while the remainder of the water flows to the desalination section of the plant.

The desalination stream is first filtered through MyCelx® bag-type oil filters, from USbased MyCelx, to remove oil slick before passing through a process of ultra-filtration, where all the ultra-fine suspended solids and most of the fouling potential in the water are removed for protection of the reverse osmosis membranes in the next process step.  Thereafter, the water is filtered through cartridge-type MyCelx® filters to remove any remaining traces of oil. The water is then desalinated through cellulose acetate reverse osmosis membranes. The high concentration brine remains in the plant, while the desalinated water flows to the clean water dam for re-use as process water in the smelter.  The reverse osmosis equipment was locally manufactured by VWS at its manufacturing facilities in the Western Cape.

Two mechanical vapour compression (MVR) evaporators, supplied by Veolia, concentrate the brine in order to reduce the volume of brine waste water and therefore the surface area of the final evaporation ponds, where the brine is stored. The MVR LED evaporators are standard modular package type plants manufactured by VWS in Italy.

The plant has high quality process water as product and generates three waste streams. The first waste stream is harmless silt from the silt traps that is stored on the smelter’s registered waste dumps. The second stream of waste is the sludge from the clarifier units, which is pressed to a stackable cake by two Dri-Belt® belt filter presses, supplied by VWS in the UK. This sludge contains no harmful chemical compounds and is also stored on the smelter’s registered waste dumps.

The third stream of waste is the hyperconcentrated brine that retains 1.5 t/d of salt. The brine is stored in triple skin HDPE lined dams with double leak detection where it is allowed to solidify through natural evaporation. None of the salts is poisonous and can be harvested as cattle-lick or raw material feed for other industries.

Rencken concludes that the Tubatse Ferrochrome water treatment plant will assist the client in minimising its impact on the environment, while still operating efficiently and cost-effectively, something that forms the core of Veolia Water Solutions & Technologies South Africa’s business philosophy.

Speaking on the Carte Blanche South African TV magazine show, Dr Anthony Turton, a scientist specialising in water resource management, likened the country’s acid mine drainage (AMD) problem to its “own Chernobyl.

“Let us not forget; the water we are dealing with, in the context of acid mine drainage, is toxic waste. It is hazardous waste – 57 million litres of toxic water will soon be looking for a place to surface every day.” AMD has been reported from a number of areas in South Africa, including the Witwatersrand gold fields, Mpumalanga and KwaZulu-Natal coal fields and the O’Kiep copper district.

Multotec has developed an environmentally friendly filter press believed to be a world first.  The result of a significant investment in time and funding, it was developed in response to the increasingly critical need to recycle waste water from mining operations in South Africa, specifically AMD.

Traditionally hydraulically operated filter presses are used in metallurgical processes and water reclamation plants, but these conventional products are associated with a high risk of contamination from oil and other lubricants during operation. It has become essential to overcome this challenge to protect the environment and assist mining companies to comply with the ever-tightening environmental legislation confronting the industry.

Multotec’s state-of-the-art fully automatic filter press, based on the successful Seprotech Rapid Filter (SRF) press, eliminates the risk of any contamination in this application.  This exciting new product has been developed using patented technology, with components sourced internationally to ensure long life and spares availability.

The hydraulic power pack has been replaced with a water pressure system which, while achieving the same clamping force, ensures optimum sealing of the plate pack while dramatically reducing noise pollution. The filter cloths have been further developed to ensure longer life, in turn achieving lower consumable consumption. Components have been designed to ensure safe operation, while finite element analysis has been applied to substantiate the integrity of the machine. The filter press is characterised by its energy efficient electric motors.

This filter press is ideal for use in a water reclamation plant where lime is used to neutralise AMD and the resulting gypsum slurry needs to be filtered out. The clean filtrate water is fed back into the plant for further processing and the filter cake produced can be sent for further processing to ultimately enable it to be recycled as a valuable product.

It can also be used in other liquid/solid separation applications, including copper concentrate, platinum concentrate and coal fines. Capacity is dependent on the application requirements.

Central Rand Gold ordered pumps from RITZ Pumps to help solve an AMD problem at its Main Reef operations, under the Johannesburg central business district. The pumps, which cost $4-million, are each able to pump 1.5- million litres/h from the shaft to the proposed neutralisation plant nearby. The pumps’ discharge pressure is in excess of 40 bar and they are driven by 2.4 MW submersible watercooled motors (IM, January 2011, pp18-32).

BPT says its Nano-Pro^TM and HMT are “revolutionary nanofiltration membranes for mining streams.” Nano-Pro are selective and chemically stable membranes with advantages claimed by BPT of high chemical stability in acids (longer life), high selectivity for separation of metals and acids, high separation ratios and high metals rejection High Flux.  They reduce overall costs (capital and operating).

Nano-Pro can be used to convert hazardous wastewater streams into purified, recyclable water and acids, or to purify and concentrate minerals for reclamation. The technology will handle all waste water types and is easy to install up- or downstream of biological waste water treatment plants., featuring full automation.

The HMT (Hybrid Membrane Technology) system is a multi-stage membrane-based system for treating highly aggressive and complex wastewater streams. BPT explains that, “based on Nano-Pro membranes, HMT enables customers to treat their waste water, recover water and other valuable materials and comply with environmental regulations at the lowest cost per m3.

HMT separates the wastewater stream into three separate streams – concentrated organic materials, concentrated minerals (Cu, Ni, Mo, for example), and clean water and acid for re-use (75-90%). BPT reports that “tested and approved by leading international companies, HMT can treats waste water at less than 25% of the cost of existing alternatives, such as incineration, evaporation and oxidation.”

In addition to enable compliance with regulatory authorities at an attractive price, HMT can eliminate or reduce sludge liability. It can also generates revenue from metals and byproducts, increase recovery of copper (a positive impact on the bottom line) and produces high quality treated water and acid.

GE has introduced a modular version of its pioneering ABMet® wastewater treatment system. ABMet is a patented biological water treatment system that uses naturally occurring microbes to reduce the amounts of selenium and other metals that can escape from coal mines, etc.

The process involves running wastewater through a biologically active filter, which is ‘seeded’ with naturally occurring microbes that target selenium and other potentially toxic metals. While selenium is typically difficult to remove from wastewater, ABMet enables the metal to be captured and converted into an easy-to-treat form.

Most of the initial ABMet systems that have been installed in the US feature customised designs that enable mining customers to meet their site-specific compliance requirements. However, in response to customers seeking a cost-effective system that could be installed quicker than custom-designed ABMet systems, GE now is offering its bioreactor water treatment product in a scalable, modular format that further reduces installation time and overall project costs.

The new modular ABMet system is particularly well-suited to meet the operational, regulatory and economic priorities of the coal mining industry.

“With coal mine operators and power companies facing increasingly stringent government limits on their emissions, we are offering ABMet to help these crucial industries continue to support our country with vital energy supplies and jobs while also meeting their regulatory obligations to protect freshwater supplies, fish and other wildlife,” said Jeff Connelly, VP, Engineered Systems.

The US Environmental Protection Agency first established a national water quality standard for selenium in 1987. In 2011, the agency is expected to propose a revised limit based on current selenium levels in fish and also is developing revised effluent limitation guidelines for the steam-electric power industry, which are expected to be released in draft form in 2012.

Management modelling 

Water and solute management at a mine are critical components for environmental permitting, mine facility design and operation, and mine facility closure. Knight Piésold Minder^TM, is a new, dynamic, internethosted model which uses site-specific daily and monthly climatological data and site-specific operational conditions, such as loading plans, filling curves, leaching curves, upset solute concentrations, financial targets, reclamation needs, and much much more.

The model provides the ability to enter actual operational and climatological information, automatically verifies input data, and provides interactive process schematics that allow the user to easily identify pipelines, ponds, plants, heaps, waste-rock piles, tailings storage facilities, and virtually anything else conceived.

The model can also be used for the initial sizing and design of the process components. The purposes of an operational water and solute management tool include: (1) to establish optimal and cost-effective pond storage and water treatment or make up (where applicable); (2) to identify flows to and from the heap/tailing facility allowing for appropriate sizing of process circuit pipelines; (3) to identify solute concentrations at various locations within the process circuit; (4) to identify potential fluctuations in the process circuit over time to aid in forecast planning; (5) to quantify potential flow and volume of treated and make up water in order to calculate associated costs; and (6) to meet continuing permit compliance.

The internet-hosted model is efficient, gives simulation results in seconds, and multiple scenarios can be quickly modelled. As a result, operational decisions based on actual values or probabilities can be made in real time.

Convenient, creative, and very descriptive model outputs include summary tables and graphs with colour coding, for example to indicate near- overtopping of a pond and other potential flaws requiring design modifications.  Spreadsheet-compatible exportable tables are available for each process component.

Tailings deposition modelling 

Joshua Rogers, a Senior Geotechnical Engineer and Ricardo Arnao, a Civil Engineer, at MWH recount how tailing deposition modelling was used to optimise the tailing deposition plan at a precious metal mine in Latin America Combining it with the water balance model improved the predictions of the tailing management facility (TMF) configuration throughout the life of the facility.

Space constraints required the optimisation of the tailing management strategy during operations. Combining the water balance model with the results of tailing deposition modelling provided a more rational and realistic method to forecast the configuration of the TMF throughout the facility life, thus providing solid data upon which to make decisions. The site challenges that the mine operators sought to confront included:

■ How to best maximise the storage capacity of the TMF

■ How to optimise the tailing deposition plan while maximising tailing storage capacity, managing the supernatant water pond location and size with time, and achieving sufficient subaerial beaches to support future dam construction

■ How to best manage excess water while ensuring sufficient water for processing needs during the dry season, considering the limited space available for tailing and water storage and the seasonal variations in precipitation at the site.

The tailing deposition software that was used allows user-specified tailing deposition point locations and deposition rates which can be varied over time. The resulting deposition surfaces are then further characterised based on input data related to the deposition slope. The model allowed for linear and non-linear beach profiles and variations for subaerial and subaqueous slopes. Based on the supernatant water pond input criteria, which can be based on either volume or elevation, deposition slopes are assigned within the model, based upon the calculated intersection of the subaerial beach with the pond. Finally, these model inputs and criteria are combined with the site-specific topography and facility geometry to produce predicted tailing deposition surfaces and pond locations.

Model development began with calibration to match existing conditions. As the facility had been in operation for several years, actual bathymetric data of the deposited tailing surface was available. Using tailing deposition locations which had been documented in the facility operation to date, multiple parametric model runs were performed by varying tailing deposition characteristics (deposition beach slopes) while incorporating historically measured pond locations and volumes. In performing the model calibration, it was determined that a more complex beach profile, with three beach slopes, was needed to develop a model that reflected the existing surface. Through calibration, the modelled tailing surface was found to nearly exactly replicate the measured tailing surface, providing confidence in the model inputs.  When it was clear that the model was correctly predicting existing conditions, it was used to predict the future tailing deposition surface and pond location throughout the life of the facility. This is an important step in the development of a representative tailing deposition model. As tailing deposition continues into the TMF, the model may be updated to reflect changes in the tailing deposition surface; this will increase accuracy of the estimates.

A variety of tailing deposition scenarios were evaluated, using the calibrated tailing surface as a starting point and continuing through the life of the facility. These scenarios considered varying spigot locations, deposition flow rates and deposition sequences, which are relatively easy to vary once the initial model setup is complete. The supernatant water pond volume for each of the runs was assumed to be the 50th percentile pond volume provided from the stochastic water balance.

The results of the modeling process were used to select a preferred tailing depositionconcept that was then incorporated into the site tailing deposition plan. The preferred scenario was selected based on the location of the supernatant pond, the length and continuity of the developed subaerial beaches, and the resulting tailing capacity.

To evaluate the effect on the facility of varying hydrologic conditions, the parameters for the selected tailing deposition scenario (beach slopes, deposition point locations, etc.) were maintained and additional model runs were performed using varying pond volumes representative of differing storm occurrence percentiles. These analyses allowed the mine operators to evaluate the sensitivity of facility characteristics such as beach length, pond elevation, and tailing capacity to changes in storm event intensity.

The combined outputs from the water balance and tailing deposition models made it clear that treatment and discharge of excess water was necessary. The combined modelling method helped forecast in what year a water treatment plant would be needed and the number of litres/d that would need treatment.  The model also provided a framework to assess risks, by predicting the effects of varying water inflows to the facility on the performance of the facility over time. 

In addition to evaluating water related concerns, the outputs from the combined modelling allowed for more accurate planning of construction and decommissioning of tailing deposition and water pumping infrastructure.  Finally, this approach, when combined with tailing consolidation data, provided an estimate of the available capacity of the TMF over time and the ultimate capacity of the TMF. Given the space limitations at the site, this data has a direct impact on the bottom line of the mine, providing an estimate of the total amount of ore that can be processed.

Steve Sedgwick, Product Manager at Weir Minerals highlights that managing the flowrate at each stage of the process cycle is critical to efficient operation. “A delicate balance must be maintained between water drawn from the tailings pond for use in the process and the cleaned water returned from the processing plant and there are a wide range of variables that make this equilibrium challenging to achieve.

“Of course, water management at mining operations of any scale will be underpinned by models specifying the ideal flow-rates at each stage of the process. However, putting this theory into practice at any given site is a significant technical challenge. 

“This can be the case on smaller sites, where the storage ponds are not large enough to be kept at a steady level by rainfall entering the system. Increasingly, variable speed pumps are being deployed to compensate for these changes. This eliminates the need to constantly start and stop fixed speed pumps.

“These systems are particularly useful for more complex applications where significant changes in water levels – and therefore static head requirement – are expected throughout the course of the project.

“Today, with the range and scale of hardware offered by leading pump manufacturers – and the capacity for innovative coupling of control systems – means that a solution can be provided for almost any on-site configuration, however complex.

“For example, Weir recently encountered a project where the water level in the source pond was expected to fall by around 100 m as water was extracted and removed from the site.

“We calculated that delivering the required flow rate for the duration of the extraction process would still be possible, but only by gradually increasing the speed of one of the pumps in a three-stage process. The whole system would need to consist of six pumps – two separate streams, each with two pumps and a booster station.

“A significant frequency range was required to meet the exacting demands of the client, which not only involved the huge change in head, but also the ability to change the flow rate.

“For this to be achieved, pumps would need to be specified that could handle the appropriate head range – in this case the Warman. Then, flow-rate monitors at the outlets would be electronically coupled to frequency converters to intelligently control the electric motors driving the pumps, ensuring exactly the right speed at every stage as the water level changed. This arrangement would also allow accurate changes to be made to the flow rate as required. This system could be connected to, and controlled by, remote stations giving the client full and instant control from the most convenient location.

“A further concern when pumping water from a source with a varying surface level is the position of the pump inlet, which must remain fully submerged at all times. Because of the dramatic change in level for this project, a pontoon-mounted pump was used. This had the dual advantages of keeping the pump located at the surface of the water and also allowing a self-priming arrangement whereby the pump was set at an incline and semi submersed. This allowed impeller to sit sufficiently below the water level to quickly self-prime on start-up while the drive gear and all electronics were kept above the surface.”

Carlos Vernet, Marketing & Global Business Development Manager at Weir Minerals Multiflo, said: “A reliable and structured water delivery system is critical to the economic operation of every mining project. The pump that delivers water from the tailings pond to the beginning of the process is critical and efficiency and reliability are paramount. Because no two projects are exactly the same, it is crucial to specify the right system for the particular job in question. As these pumps can be in operation for a decade or more, installing a sub-optimal system can lead to inefficient use of fuel and have a significant impact on the bottom line.

“There is constant development and innovation in the construction of pumps both in terms of the materials used and in designing flow testing procedures to ensure performance always matches specification. Equally important, however, is the project-by-project innovation of ensuring the right system is delivered for any given job and this will always be dependent on the specific head and flowrate required for the process – as well as on the project budget.

“For less demanding head and flow requirements, fully submersible units are often the best solution as they are self-contained, ready-primed units that can simply be installed and switched on. The latest generation of submersibles – for example Weir’s Warman SJ range – can handle heads of more than 80 m for lower flow rates. Alternatively, at lower heads, they can deliver flow rates of up to 1,000 m3/h. For more demanding applications, shore or pontoon-mounted pumps – such as Weir’s Multiflo units – can handle heads of up to 200 m or capacities of up to 1200 m3/h.

“The ease of use of these largerscale units has also increased in recent years with the development of innovative automatic priming systems, using advanced combinations of vacuum systems and electronics to ensure pumps are quick, easy and efficient to prime and start up.

“For the most demanding applications, with very large heads or flow rates of up to 8,000 m3/h, vertical turbine pumps such as Weir’s Floway – which use a series of impellers in a vertical arrangement – offer high levels of efficiency and resistance to abrasives.

“It is crucial to work closely with the project team to ensure that every element of the installation meets their requirements. This includes practical concerns such as building in the weight of operational personnel to pontoon designs to ensure stability in the water and providing appropriate walkways and handrails to maximise on-site safety”.

Tailings management 

In the tailings field, Coeur Manquiri, a wholly owned subsidiary of US-based Coeur d’Alene Mines, recently purchased three MC Press filter presses from Siemens Water Technologies for its San Bartolome mine in Potosi, Bolivia. These dewatering filter presses will allow improved dry stacked tailings management on site. The MC Press units are expected to become operational later this year.

Dewatering tailings to higher degrees than paste produces a dry cake. These unsaturated tailings are usually hauled by truck or via conveyor to a tailings management facility (TMF), where they are spread and compacted. Dry stacking is a stable form of storage that requires a smaller footprint than tailings ponds, is ideal for sloped terrain, and generally allows for easier reclamation at the end of mine life.

Coeur Manquiri also uses J-Press filter presses from Siemens at the silver recovery plant. They were installed as part of the Merrill-Crowe process – a zinc dust precipitation method used to separate silver from a cyanide solution.

Located at the base of the Cerro Rico Mountain (Andes Mountains), San Bartolome is one of the world’s newest and largest pure silver mines. With a projected 14-year mine life, it has Proven and Probable reserves of 120 Moz of silver within gravel deposits at the base of the mountain. The mine produced 7.5 Moz of silver in 2009, its first year of production. Its mountaintop location and limited available land for dewatered material made dry stacking the most viable tailings management option.  Apart from the MC Press filter presses for dewatering, Siemens also supplies some aftermarket parts to help Coeur Manquiri ensure uninterrupted mining operations.

Deep disposal wells 

Cameco Resources will rely exclusively on deep well injection to dispose reject water from mill processing at the in-situ Smith Ranch Highlands Uranium Project (SRHUP). To determine the water injection requirements of the mine, Cameco hired contractors and established the well locations, well design, required permitting, and forecast injection rates and volumes. To meet the injection rates and volumes for the project, three new injection wells were required, and each required a permit for Class I Underground Injection Control (UIC) non hazardous water disposal. The permits were to be achieved under supervision by the Wyoming Department of Environmental Quality as defined by the US EPA. As part of a turnkey deep injection disposal well project, Schlumberger Water Services (SWS) was selected to provide technical and business services.

Climate, subsurface conditions, and other uncertainties such as contractor negligence have the potential to produce future atypical events that harm multiple parties. To account for liabilities prior to their potential occurrence, SWS negotiated negligence-based contracts with Cameco and the sub-contractors. The shared liability addressed future atypical events, produced ownership of the applicable risks, and reinforced productive relationships between all parties.

A former oil well and an incomplete disposal well were planned for conversion to Class I UIC non hazardous injectors. Due to their ages, that they were not designed for water disposal, and that completing Class I UIC wells in multiple formations is logistically challenging, both wells required technically challenging maintenance and remedial treatments. This involved plugging the 3,050-m deep wells at the required depths then inserting cement between the existing casings and formations.

For one well, the challenge was further intensified as the casing was not of standard size, making the required tools difficult to obtain. This placed setbacks in the aggressive schedule and required on-the-fly decision making to keep the dynamic project on schedule and within budgetary constraints.  After the cement bond survey demonstrated that sources of drinking water were protected, the wells were recompleted at several sandstone formations to allow for the disposal of water.

Essential to this project was the determination of the injection rates, bottom hole pressures, and the life of the injection wells. Through the complete analysis, testing, and interpretation of the well and formations, the new injection well was identified as underperforming.

To achieve Cameco’s required injection rates, SWS went beyond the original scope of work to provided additional production logging to determine quantitative volume flux out. Based on the production log interpretation, additional swabbing was performed to clean predicted frac proppant and fluids prior to additional injection testing and disposal. The result was an increased injection rates during long-term testing.

Cameco received a successful turnkey solution that resulted in the production of three injection disposal wells that exceeded the required injection rates and volumes. Though the schedule was aggressive, the project was completed ahead of schedule and within the budget approved by Cameco. SWS fulfilled the rigid guidelines for Class I UIC non hazardous disposal wells through its construction methods and through establishing systems for operation, monitoring, testing, reporting, and recordkeeping for continual compliance and protection of the underground sources of drinking water.

Pump news 

Pioneer Pump has launched its new 220-440 kW mine dewatering sets complete with the Rock & Rain^TM weather protection system for use in mines that experience extreme weather conditions. They are powered by Caterpillar C9-C18 (225-475 kW) engines enabling the common designed pump sets to offer maximum flows in excess of 1,000 m3/h (275 litres/s) and pressures in excess of 23 bar (230 m) making them the highest performing dry prime engine driven pump sets on the market, Pioneer says.

High on the list of the industry’s current requirements to keep the pumps operating and with minimum down time was greater weather protection to handle the heavy rainfalls seen in mines like those in West Africa and parts of Asia where rainfall of 50 mm can be seen in a matter of hours. In addition to this, Pioneer was asked by the mines to increase protection from rocks that fall during blasting, which can occasionally cause catastrophic damage to the engines if not protected.

The solution Pioneer developed was to use heavy duty 3 mm sheet roofing formed to offer maximum protection for the engine whilst directing torrential rains away from the key engine parts such as air filters and electronics. In addition to the roofing, Pioneer developed a deep housing for its standard CAT controller unit to restrict weather ingress seen in the heaviest downpours.

In addition to the Rock & Rain system, Pioneer made further designs additions including the ability to convert the pump sets from skid to trailer in less than an hour depending on customer requirements. Through the use of an integrated skid, the axles can be mounted on a complete A frame tow hitch directly to the skid to allow these sets to be pulled behind wheel loaders or a mine dozer.

Pioneer also decided to make the sets less than 4 m long, which enables it to ship up to three complete pump sets anywhere in the world inside a standard 40′ Hi-Cube container, dramatically reducing shipping costs to the mines.

Other options include the availability of the suction hose crane allowing for up to 6 m reach in front of the pump set to ensure good submergence and safety during operation and safety cages for operator protection in areas such as the engine.

The less time a mine requires to pump, add or remove water in the course of processing usually translates into reduced operating costs.  However, mine water inventories must be managed carefully to balance maintaining a reliable supply of water to support mineral processing while using as little water as possible.

Here pumps have a vital role to play, and peristaltic pumps specifically can be considered water-saving devices, according to Watson-Marlow Pumps, not simply because they can accommodate very high solids-content slurries, 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.

All peristaltic pumps supplied by Watson-Marlow Pumps 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 suitsarduous environments.

The Bredel SPX pumps, for instance, accommodate continuous flow rates up to 80 m³/h 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.

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

One common task is pumping paste backfill.  The goal for the high density paste formulations is to produce a pumpable material that does not segregate when placed – the fines content should be a minimum of 15% by weight of the paste. Naturally, choosing the right pump technology for the task is vital. While pumping applications 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 necessary features are repeatable and reliable delivery performance, self-priming ability, 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.

While centrifugal and diaphragm pumps have traditionally dominated, 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.

The latest peristaltic (hose) pumps are 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

■ Prevent backflow and siphoning without valves

■ Wear-free performance.

In mining, the last point is arguably the most advantageous. Peristaltic pumps’ wear-free performance 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 such a pump as a Bredel high pressure hose 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.

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.

A recent beneficiary of peristaltic technology is a large copper and gold mining company in Arizona 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 SPX100 hose pumps. In this application, the hose pumps transfer tailings slurry 670 m 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 SPX pumps, providing considerable savings in both maintenance costs and water usage.

Other examples can be seen at Jaguar Mining’s four gold mines in Brazil. It first adopted Bredel SPX 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 installed a Bredel SPX100D 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 50 m³/h over a distance of 420 m.  Today, Turmalina has no less than five SPX100D pumps for backfill operations; six Bredel SPX100D and two SPX100 models for flotation processes; eight SPX50, two SPX65 and two SPX100D pumps for leaching; two SPX100D for reject pumping and 10 SPX65 models working with reagents.

A large mine in New Brunswick, Canada, replaced centrifugal slurry pumps with SPX hose pumps. Here, the 65% solids of the zinc and lead thickener underflow slurry was too high for 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.

Another well-known manufacturer of peristaltic pumps, Larox Flowsys (now changing its name to Flowrox) notes that users of wastewater systems are moving more towards sourcing complete pumping systems rather than having contractors purchase the individual components and then assemble and design the systems. “Outsourcing complete systems creates a more reliable, more costeffective system. Also the pump system supplier is responsible for the promised performance, up-time and service to the owner for the system’s lifetime.

“Contractors also benefit with predesigned systems in which they do not have to understand the complete system to install and startup the system. A good system is designed that is factory tested and delivered to the site.  [In most cases] the contractor only need connect the input and output piping and electrical connections to the system. When needed factory personnel can be on hand to assist in start-up and training of system operability.” Service agreements for complete packaged pumping systems can also be purchased.

In waste water typical systems provided would be for flocculants, sodium hypochlorite, sodium bisulphite, ferric chloride and other chemicals. Ideally the pumps used in these systems should have safety devices to ensure that if a hose or tube breaks then the pumps affected would be shut down automatically.  For instance Flowrox can incorporate hastelloy C probes in the pump heads which will sense liquid from a tube leak within a few seconds.

It is important to select the correct pump for pumping chemicals such as flocculants. For instance gear pumps have a tendency to shear valuable flocculants and cause them to become less effective. This can lead to using twice as much of the required flocculants to perform the required task. A peristaltic pump is ideal for flocculants because it is a low shear device. So it is very gentle and does not damage costly flocculants. Thus flocculant consumption can be optimised.

Many hose pump manufacturers use two rubbing shoes or two rollers to compress the hose twice every 360° revolution. Newer designs use an eccentric shaft and roller that compress the tube or hose only once per 360° revolution. Single compression per revolution devices will produce at the very minimum twice the hose life than shoe designs and two or more rollers, says Flowrox. Because the single roller design creates less friction and heat, the life of its hose or tube is often four to five times longer than two or more shoe or multiple roller designs. The savings in maintenance and operational costs of a single roller design compared to two or more shoe or roller designs is often just as much as the cost of new pump every year.

In general the maintenance on peristaltic pumps is extremely easy. In 99% of instances the maintenance required is simply replacing a failed tube or hose. This process usually takes less than one hour to complete and in some designs only minutes.

The latest pump offering from Weir Minerals, the Warman Mill Circuit (MC) slurry pump, has been trialled at a number of mines in West and Central Africa and has recorded considerable success both in terms of increasing mill throughput capacity and doubling the lifespan of pump wear parts.

Rui Gomes, Product Manager – Slurry Pumps at Weir Minerals Africa, explains that the pump was first trialled at First Quantum Minerals’ now-closed Frontier copper mine (mill throughput of up to 1,200 t/h) in the DRC.

“The Warman 550 MCR slurry pump was installed and commissioned at Frontier in March 2010. It achieved a target of 2,000 hours of operation without failure; the impeller lasted approximately 2,926 hours before requiring replacement; and the rubber liners continued without requiring replacement,” he says.

The improved performance and longer life expectancy of the pump, which is due to the increased wear life of the Warman MC slurry pump wet-end parts, resulted in substantial savings on replacement parts. The pump has been engineered for arduous operating conditions and manages the large particle sizes of the raw product as well as the scats and foreign material so often found in the dense abrasive slurries in a mill discharge application.

It has been equipped with a larger impeller, which allows the unit to be run slower, resulting in reduced wear. The expeller vanes on the pump have also been engineered to reduce recirculation and this further minimises wear while at the same time improves pump efficiency.

The adjustable throat bush and back liner is a significant feature of the pump. By adjusting the front and back liner, the gap between the liner and impeller is kept to a minimum reducing recirculation and this further improves the wear life of the components.

The pump has also been successfully trialled at Gold Fields’ Damang mine in Ghana – “to increase the throughput tonnage with the benefit of increasing the wear life of the mill discharge pumps and reducing the operational costs. The pump was installed in June last year and was trialled for three months,” Gomes elaborates.

During the trial period the pump recorded significant operational results: the mill tonnage of 2,100 t/h was successfully milled and pumped; the target of 1,000 hours of operation without failure was achieved; the impeller lasted approximately 1,900 hours before requiring replacement and the rubber liners continued without requiring replacement. Again, substantial savings on replacement parts was achieved.

Gold Fields deemed this trial a success and ordered two 350 MCRs, one to be installed on the primary circuit and the additional pump to be installed as a standby unit. In addition, both the smaller Warman 12/10-AH metal pumps in the secondary mill application were replaced by the new generation mill circuit pump, the 250 MCR. The installation of the pumps was completed in September last year and, to date; Gomes reports that no replacements have been required on either pump.

“A paradigm shift of understanding of the mill circuit has significantly improved the operations at Gold Fields Damang mine,” Gomes says.

“We are in discussions with a number of local mines to install Warman MC pumps on a trial basis. Two of these negotiations have been successful and we have just installed pumps at two platinum mines in the Rustenburg area on a trial basis. The trial offer that we present to clients and potential clients, which is a standard Weir Minerals policy, is quite attractive because there is no capital outlay to begin with and mines can assess the benefits of the equipment first hand before being required to purchase a unit,” Gomes concludes.

Brubin Pumps manufactures the Magflo Plastic Magnet Drive pump series, which the company supplies to various mines. Tracy Rochat, a sales executive at Brubin Pumps, says the most important feature of the Magflo pump is that it is immune to corrosive and toxic liquids. “The impeller and internal magnet are integrated, making the pump more compact, and there are no seals so the pump cannot leak; they are the most popular of our company’s products,” she adds.

Water delivery 

Increased energy costs in combination with massive pumps for water transport are a problem for many underground mines. The construction of new pump stations at the LKAB’s Kiruna mine in Sweden embraced a difference approach. Optimising the inside diameter of the pipe makes it possible to reduce the output of the pump, or even downsize the pump itself. In other words, optimised inside pipe translates to savings in energy costs. It is common to compare the outside diameter of different pipe systems but it is the inside diameter that determines the maximum flow. Alvenius has developed the new FlowMax steel pipe to meet the needs of LKAB and many other mines – pipes that allow maximum flow per dimension.

A core of thin walled high quality steel with one of two anti-corrosive surface treatments means a lightweight pipe with maximum flow and long service life.  In combination with quick connected coupling s it also allows easy and cost-effective installation. The FlowMax pipe is available with one of two anti-corrosive surface treatments, standard hot dip galvanized or thermoplastic (TP) coated. The TP-coated pipes have shown great durability in very tough environments such as low pH, salty or acidic water.

Disaster recovery 

In Queensland floods brought Australia’s $50-billion coal industry to its knees as flooding began in late December 2010. Only eight of Queensland’s 57 coal mines were operational the following month. With estimated coal industry losses of $2.3 billion, the Queensland floods underscore the need for solid disaster recovery strategies as well as emergency services for pumping floodwater from open pits.

Mining companies and contractors contacted ITT Water & Wastewater Australia and Godwin Pumps to provide additional pumping resources for disaster recovery efforts. ITT’s recent acquisition of Godwin was fortuitous in this situation, enhancing Flygt’s submersible dewatering product portfolio with Godwin’s surface-mounted Dri-Prime® pumps.

One Queensland mining contractor company acted quickly to ensure that its clients operating in the Bowen Basin coal district, Australia’s largest coal reserve, had fast access to disaster recovery equipment. As Queensland prepared for a record wet summer with torrential rains, flash flooding, saturated ground, and major rivers and dams peaking, this mining services company was preparing for the worst -dewatering the flooded mines to make them operational again.

On December 22, 2010, it contacted the ITT Townsville office to enquire about rental and purchase of large centrifugal pumps capable of handling flow rates between 600 and 1,000 litres/s with a total dynamic head between 20 and 30 m. Within 24 hours, ITT scoured its 14 locations across Australia and presented the company with Flygt rental and purchase options for consideration as well as options to match the pipe work with the pump’s capacity.

“We had one Flygt C3400 250 kW pump in stock that was a perfect match, and then we identified two Flygt NS3312/705 55 kW submersible pumps that were able to achieve flow rates of approximately 500 litres/s when pumping in parallel,” says Cameron Gilchrist, Branch Manager for ITT Townsville. “That enabled us to offer the mining service company yet another alternative to augment its recovery efforts. Eight Flygt PFM1150 pump floatation modules are also a critical part of the solution, suspending the pumps just below the surface of the water.”

Two weeks later, as flood levels began to subside, the mining services company confirmed a five-month rental agreement with ITT for the Flygt pumps and accessories to assist with pit recovery at one of its clients’ sites, with the option to extend the agreement to 12 months. Within four working days, equipment had been gathered from five ITT branch offices in Western Australia and New South Wales, all three pumps had been fitted with new cables and dispatched to Townsville. IM