Kennecott Eagle Minerals has teamed up with Veolia to treat mine water to meet and exceed water quality standards set by its mining permits
Using the same water over and over again is one way mine’s conserve water and manage its emissions. However, Raymond Philippe, Chile Water Director and Hubert Fleming, Global Director Water at Hatch, writing recently in WaterWorld note one of the major disadvantages of recirculating and recycling water to be “the possible build-up of contaminants in the water balance. If less fresh water is used and instead more contaminated water is being reused, there will be a higher risk of contaminant retention in the system that may have various negative chemical effects, such as corrosion, scale formation, modification of metallurgical chemistry and so forth. As a result the mine may start suffering economic consequences due to less plant availability, higher maintenance requirements or even less metallurgical recovery and production.
“Although huge savings may be obtained in water supply requirements, this has to be offset against possible bleed stream requirements due to a build-up of contaminants in the process water circuit to avoid these downsides. This may especially be the case in mineral processing systems that consider the use of poor quality water such as direct seawater or brackish well water.”
They also note that desalinated water is proving a vital source but with mines in Chile and Peru, for example, up to 200 km from the coastline, water transport and networks are a major consideration. Most of the large number of Latin American projects will be executed in very challenging geographical settings, often high up in the Andes Mountains. It is the search for sustainable water sources to support both existing and new mineral processing needs that will prove even more challenging for these projects, and others in places like Western Australia, than electricity supply.
In many places, mines are competing for the same resources as other users, putting at risk any long-term project development depending on the same stretched hydrological resources. Conversely, and even in semi-arid regions, during part of the year mining operations may experience a surplus of water in their operations. In places like the Andes, wet seasons or snow and ice melt may enter the mining operations: mine pits, tailings ponds, waste dumps and leach pads. As a result, some of this water may have to be discharged temporarily to the environment. And, environmental discharge legislation is becoming more stringent for mining companies. “Peru and Chile, for example, have implemented some of the strictest environmental effluent discharge legislations worldwide, with some critical parameters required to meet standards even below potable water,” Philippe and Fleming explain.
Environment and community
“In most cases, the use of seawater requires significant investments of marine structures, desalination plants, energy supply systems and moreover very complex water conveyance systems.” They also note the “local political and economic challenges. These include local geography, community relations, environmental impacts, and energy requirements, for the implementation of large seawater treatment and conveyance systems. As such, there is a limit to alternative designs that can be considered for this type of coastal infrastructure projects. In order to achieve significant savings in investment and operational costs, the design of water supply projects must also involve the development of an accurate water balance. This is so that the seawater treatment plants, pipelines, and pumping stations, are not over (or under) designed. Project logistics must also reflect progressive change in the water demand and may need to consider a modular, expandable design.
“Although the majority of the seawater supply projects are being identified as seawater desalination projects, in reality they are a result of a complex integration of marine works, a desalination treatment system combined with a high pressure conveyance pipeline and an energy transmission project. In practice, mining companies consider the project as a whole, and require a complete supply solution. This may result in a disconnect with the actual market because of the limited size of the desalination plant compared to the overall project.
“Furthermore, it is not always logical that desalination OEM providers would manage the complete project, as they might in more conventional public sector desalination projects around the world. Other important aspects to consider for design and construction in a mining environment, besides a required heavy duty design, are the very demanding quality, health and safety demands that the mining industry imposes. These must be reflected both in design as well as in project execution.
“Consequences and costs are sometimes underestimated by process and equipment providers and construction companies, especially when their background experience is mostly in municipal potable and wastewater plants. The entire design, specification and procurement process is unique for the mining industry. The high energy demand required for conveying the water, due to the great distances and elevations involved, and the availability of an energy supply source represent a significant challenge. Hence, a strong focus on optimisation is crucial to delivering a successful seawater treatment and conveyance project in northern Chile, for example. Previous design experience is fundamental in developing and delivering successful water supply projects, considering the large number of issues, various aspects and interactions encountered during design that must be taken into account.”
They go on to explain that the use of untreated seawater rather than desalinated water “is generally a trade off between capital and operating costs. That operating cost must include the impact of seawater on operations of the mine as well, including effect on metallurgy of mine equipment, as well as efficiency of the mining or beneficiation or ore recovery processing plant. There is often a substantial difference in benefits associated with comparing parameters as metallurgical recovery and even effective production time due to plant availability between seawater and desalinated water.
Low-Energy treatment process
“Direct cost for desalinated seawater supply, depending on altitude and distance from the coast, and price of energy, will vary between $1 and $4/m3. This cost is evaluated against the benefits of water to mine production. In the case of copper mining, desalinated seawater supply cost may represent 3% to 20% of total direct operational costs. It’s clear to see how water becomes one of the most impacting consumables. In addition, with lower quality metal contents in available mineral resources, net higher water consumption per pound of metal produced is required, further driving up water costs as a percent of total cost of operations.”
South American mines are looking at strategies to improve water usage, especially focusing on better water recycling rates. Processes are being optimised to improve water return from tailings storage facilities (TSF), to avoid water losses due to evaporation and infiltration, and to avoid generation of effluents. A concentrator with a conventional TSF, for example, may retain up to 50% more water than newer developments such as thickened tailings or paste technology.
Philippe and Fleming stress the risks associated with water usage optimisation “that must be evaluated, which are not always understood or even considered when aiming at low make-up water supply. These risks can only be quantified through an analysis of both the quantitative water balance as well as a qualitative water balance.
“Mineral processing sites may use various feed water qualities, to which reagents are being added to the process streams, and may even suffer from geochemical processes like acid mine drainage generation. As a result, generally there is imbalance between the water quantity and quality distributions.
“One of the major disadvantages of recirculating and recycling water is the possible build-up of contaminants in the water balance. If less fresh water is used and instead more contaminated water is being reused, there will be a higher risk of contaminant retention in the system that may have various negative chemical effects, such as corrosion, scale formation, modification of metallurgical chemistry and so forth. As a result the mine site may start suffering economical consequences due to less plant availability, higher maintenance requirements or even less metallurgical recovery and production.
“Although huge savings may be obtained in water supply requirements, this has to be offset against possible bleed stream requirements due to a build-up of contaminants in the process water circuit to avoid these downsides. This may especially be the case in mineral processing systems that consider the use of poor quality water such as direct seawater or brackish well water.”
Last year Kennecott Eagle Minerals awarded Veolia Water Solutions & Technologies a contract for the wastewater treatment plant at its Eagle mine located in Michigan’s Upper Peninsula. This will be the only primary nickel mine operating in the USA and is expected to produce some 300 Mlb of nickel and 250 Mlb of copper over the life of the mine. Kennecott Eagle Minerals aims to protect the surrounding environment including groundwater, streams, rivers and lakes and has teamed up with Veolia Water to treat the mine water to meet and exceed water quality standards set by its mining permits. Veolia Water’s treatment solutions include the patented OPUS® high recovery membrane process and Liquid Evaporation and Distillation (LED) evaporators and crystallisers for brine management to achieve Zero Liquid Waste Discharge at the mine site.
The wastewater treatment process includes precipitation softening and clarification, filtration, ion exchange softening and a final two pass reverse osmosis (RO) polishing system. The discharge streams from this patented wastewater treatment process include treated effluent water, metals precipitation sludge, ion exchange regenerant and RO concentrate. The treated effluent water will be suitable for reuse in the mining process or to release back into the groundwater by a treated water infiltration system. The ion exchange regenerant and RO concentrate liquid wastes will then be sent to the evaporator and crystalliser system and converted to solids which will be disposed of off-site as a non-hazardous solid waste.
The system is designed to treat 100 to 500 gallons per minute (0.72 million gallons per day) of mine water and began operations late in 2011, started up and commissioned by Veolia Water.
Energy Resources Australia (ERA) has selected brine concentrator technology from Veolia Water to treat and reduce process water inventory from its Ranger uranium mine in Australia’s Northern Territory. This project is a critical part of ERA’s overall water management strategy and environmental protection initiatives.
The brine concentrator will be provided by subsidiary HPD and will treat approximately 1,830 mega litres of water annually (1.3 million gallons per day). ERA considers this technology a proven, long-term solution to minimise the environmental impact of operations and significantly reduce process water inventory at Ranger. The brine concentrator uses thermal energy to evaporate water, which produces clean distillate that will meet strict water quality requirements for release into ERA’s constructed wetlands system.
HPD was selected for this project because of its extensive experience in volume reduction applications, the ability to meet future needs of the mine, and testing capabilities. This includes shipment of a pilot-scale brine concentrator unit to Australia for demonstration of the process. Commissioning of the brine concentrator plant is expected to be completed in mid-2013.
The contract for the design and supply of a 1,000 m³/d effluent treatment plant to serve Trevali Mining’s Halfmile zinc-lead-silver-copper mine in New Brunswick has been awarded to Veolia Water Solutions & Technologies Canada. The new zinc-lead-silver-copper mine is situated 60 km south of Bathurst and commenced production in January 2012. The scope of this fast-track design/build project includes the entire treatment plant as well as the construction of the building. The treatment plant will provide precipitation, decantation and filtration plus pH correction to provide a treated mine effluent that meets the Canadian Council of Ministers of the Environment (CCME) Water Quality Guidelines for the Protection of Aquatic Life.
“Trevali is pleased to be working with Veolia in providing a compact turnkey water treatment solution for the Halfmile mining project,” said Paul Keller, Trevali’s Vice President of Operations. “Having the peace of mind of working with a major solution provider allows the company personnel to focus on mine development and production activities.” The plant incorporates metals precipitation using the ACTIFLO TURBO, a high-rate, small footprint clarification process. The ACTIFLO process uses sand-ballasted settling and a TURBOMIX draft tube reactor that allows for a very compact design with high overflow rates and short detention times. This design enables the unit to perform well under dynamically changing flow rates without impacting final effluent quality. By combining the proprietary Hydrex reagent to magnesium hydroxide, the solids produced in the ACTIFLO unit will be larger than sodium sulphide, which facilitates downstream filtration.
After clarification, the water undergoes sand filtration to remove any remaining solids, followed by pH correction. Also, the instrumentation and automation package permits remote monitoring of the entire water treatment plant, which is a major benefit for the operation of the plant. The building will be a 15 m x 22 m steel building with all ancillary services, including a 2 t overhead crane and water quality laboratory. The plant is currently in the final construction phase. Trevali has been constructing the Halfmile project civil works since March 2011, and commenced production of the water treatment plant in January 2012, with a planned production ramp-up to a rate of 2,000 t/d.
Low-energy treatment
MWH has developed a low-energy process to treat acidic, metalladen water at the Holden mine
Dan Dupon and his fellow engineers at MWH have developed a low-energy process for treating acidic, metal-laden water at the Holden mine in the remote reaches of the Northern Cascades of Washington State, USA. Conventional mine water treatment methods could not be seriously considered for the site because they require more energy than is available. A remote site, the inactive Holden mine is not reached by any utilities, roads or line power. Thus, the unique conditions presented required a more creative approach to water treatment.
Operated during the 1930s, 40s, and 50s, the underground operation left large tailing dumps located adjacent to Railroad Creek (the main drainage for the valley), a dilapidated mill site, waste piles, and a small village that housed the miners and their families. The mine is located in one of the many steep valleys along glacial Lake Chelan and the only access to the site is by boat. The small village is now an international summer retreat centre and is supported by a micro-hydropower plant located on a nearby creek. Power produced by the plant is limited by low river flows in the winter months, requiring the village to restrict its population seasonally.
The mine site is now undergoing remediation to address the waste and tailings piles as well as contaminated water issues. A major part of the remediation activities involve collecting and treating impacted waters to control the discharge of metals to Railroad Creek. The waters to be collected and treated include shallow ground water beneath the tailings piles, seeps, and drainage from the partially flooded underground mine workings. Metals concentrations in the treated effluent need to be very low, consistent with aquatic water quality criteria.
The treatment approach defined in the project feasibility study identified two treatment systems, one for the mine workings flow and another for the shallow ground water. The limited available power meant that each of these systems would need to operate by gravity and be located in separate areas of the site. The total amount of water requiring treatment is predicted to be between 63 and 95 litres/s (1,000 and 1,500 gpm).
Alkalinity would be added to a cascading stream to neutralise acidity and oxidise iron. The process of neutralisation would cause aluminium, copper, cadmium, iron, and zinc to precipitate as solids which would then accumulate in settling ponds. Overflow from the ponds would then be treated further, to remove suspended particles, through either a large sand filter system or a surface wetland. This approach was predicated on the assumption that gravity would be the only driver of flow.
MWH identified several potential problems with the proposed approach: (1) the method of alkalinity addition would be inefficient and unable to control solution pH, (2) the method of aeration would be insufficient for complete oxidation of ferrous iron, and (3) separate treatment of the two waters would not produce the most effective removal of the metals. MWH revised the approach to compensate for these potential problems.
The first change was to combine the flows into a single stream to take advantage of the high iron concentration in the shallow groundwater (dissolved iron was undetectable in the mine workings water). Combining the flows would allow copper and cadmium in the mine workings water to react with the elevated iron of the shallow ground water, yielding low dissolved concentrations. The second change took advantage of the elevation of the mine workings water, allowing it to be delivered to the plant location under pressure. This pressure was used to drive a jet eductor pump for efficient addition of alkalinity, thus conserving chemicals and providing adequate process control. Finally, MWH selected a low-profile, weir cascade system to aerate and oxidise the elevated ferrous iron (>200 mg/litre) present in the raw water. he cascade aerator system maximises oxygen transfer through increased water surface area and turbulent mixing in a relatively small unit.
This revised approach was then tested on-site in an MWH design pilot-scale system. A test plan was developed to appropriately size equipment, identify the best target pH for optimum removal of metals, and evaluate sand filtration methods. Results of the test work have been developed into full-scale design criteria. The performance of this low-energy process meets or exceeds that of conventional mechanical systems and is capable of meeting expected discharge criteria, MWH says. Design of the full-scale system is slated for 2012.
MWH was able to overcome the challenges and develop an effective treatment process capable of handling up to 95 litres/s of flow that is expected to consume less than 10 kW of power.
In other treatment news, speciality resins company Purolite has published an Iphone/Ipad App of useful resources related to water treatment, especially ion exchange. The free app can be downloaded from the App store, where it can be readily found by searching for “Purolite”. It has unit conversion calculators, a periodic table of elements, tables for screen size equivalents and regenerant strength plus other resources. “Our goal is to help our customers find the information they need as quickly and easily as possible. Much of the information in this App is on our website,” said Gary Thundercliffe, Global Marketing Manager for Purolite.
Purolite products are also used in the recovery of uranium, gold, molybdenum, rhenium, nickel, copper and other valuable metals. Purolite has a range of products tailored for all methods of industrial hydrometallurgy. Such methods include sulphuric acid and bicarbonate leaching of uranium, metals recovery from clarified solutions, either heap or in-situ leaching (ISL) operations; and uranium, gold and basic non-ferrous metals sorption from pulps at resin-in-pulp and resin-in-leach operations.
Arsenic removal
Piia Suvio, Product and Process Solution Specialist, and colleagues at Outotec are working on methods for removing arsenic from metallurgical process streams. They report that “being very abundant in the earth’s crust, arsenic is typically encountered in the processing of gold and copper ores and concentrates, where it is typically associated with minerals such as arsenopyrite and enargite.
“Depending on the metallurgical process in question and the state in which As occurs in the processed mineral, As can either be in trivalent (As3+) or pentavalent (As5+) form. In aqueous solutions within metallurgical applications arsenic is typically present in acidic form as either H3AsO3 or H3AsO4.”
Arsenic-rich liquids require treatment prior to discharge or reuse as process water. The most typical ways considered for removing As from mining and metallurgical effluents industry include:
■ Calcium arsenate precipitation (Ca3(AsO4)2)
■ Calcium arsenite precipitation (Ca3(AsO3)2)
■ Basic ferric arsenate precipitation (FeAsO4 *xFe(OH)3)
■ Scorodite precipitation (FeAsO4 2H2O)
■ Arsenic precipitation as sulfides (As2S3)
■ Adsorption
■ Coagulation
■ Ion exchange
■ Membrane separation
■ Biological precipitation.
Arsenic precipitation with lime is to date perhaps the most straightforward and costeffective means of removing arsenic from solution. However, the stability of the generated calcium arsenite or arsenate sludges is poor. An effective alternative to lime precipitation is provided by ferric precipitation (Fe2 (SO4)3), a chemical process that generates ferric arsenate sludges, out of which the crystalline scrorodite or ferric arsenate dihydrate (FeAsO4 2H2O) is the most stable form. Precipitation of scorodite requires, however, highly controlled process conditions.
Any precipitation-based process will benefit from advanced equipment technology and process design, but best results are achieved using customer and process-tailored equipment and process control, which allow stable, safe, reliable and cost efficient operation of the process.
With correct process design significant benefits are obtained, including:
■ Lower chemical consumption
■ Less scaling = less maintenance
■ Stable pH profile, allowing precipitation reactions to take place in the reactors and providing stable effluent
■ High quality sludge with uniform chemical composition = long term safe storing of As residues
■ High quality solid residue with minimum moisture = lower disposal costs and higher water retention
■ Process effluent with low, residual As concentrations and low solids carry over.
Lime can be used to precipitate arsenic out of solution in both, trivalent (arsenite) and pentavalent (arsenate) states, forming calcium arsenite or calcium arsenate, respectively. The precipitation of calcium arsenite Ca3(AsO3)2 is presented below.
2 H3AsO3 + 3 Ca(OH)2 – Ca3(AsO3)2 + 6 H2O
Depending very much on the way of operating the process, residual As concentration can reach levels between 1 mg/litre and 100 mg/litre when pH is raised above 10. The sludge so formed is typically a combination of gypsum, calcium arsenites/arsenates and heavy metal hydroxides.
Ferric iron can be used to precipitate As out of solution. Depending on the precipitation conditions, either basic ferric arsenates (FeAsO4*xFe(OH)3) or crystalline scorodite (FeAsO4·2H2O) are formed.
Typical iron dosing for basic ferric arsenate precipitation aims at Fe:As ratios between 4 and 10, whereas in scorodite precipitation the ratio is nearly stoichiometric (close to 1). High iron dosing typically allows lower residual As in effluent, but simultaneously increases the chemical costs and the amount of sludge produced.
Depending on the way of operating the process, residual As concentration after precipitation with ferric iron can reach levels below 1 mg/litre. The produced solid residues are more stable than the respective calcium arsenite and arsenate precipitates. Depending on the Fe:As-ratio and precipitation process, the ferric arsenate precipitates pass the EPA TCLP test limit of 5 mg As/litre1.
Atmospheric scorodite precipitation is carried out in three stages:
■ Oxidation of arsenic
■ Supersaturation controlled precipitation of scorodite
■ Polishing
Complete oxidation of trivalent arsenic (arsenous acid, H3AsO3) to pentavalent arsenic is completed prior to the precipitation stage, in order to ensure formation of arsenic acid (H3AsO4), which will further react with ferric ions. Oxidation of arsenic in the process is performed by means of hydrogen peroxide (H2O2). Scorodite precipitation takes place stepwise in a series of precipitation reactors with controlled pH. Slurry pH is adjusted by sodium hydroxide solution to ensure formation of pure crystalline scorodite. The reactions involved in the process are shown in these equations:
H3AsO3(aq) + H2O2 (aq) – H3AsO4(aq) + H2O
H3AsO4(aq) + Fe3+(aq) + 2H2O – FeAsO4(H2O)2(s) + 3H+(aq)
The process is complemented by a polishing stage by means of co-precipitation at elevated pH. Part of the sludge generated is recycled back to the process. Following the polishing stage, arsenic concentrations below 0.5 mg/litre are achieved.
Suvio and colleagues conclude that “Precipitation processes play a major role in As removal from metallurgical process streams. For relatively simple and straightforward As removal processes like calcium arsenite precipitation, advanced process and reactor technology can provide possibilities especially for decreasing reagent consumption and maximising water recovery through efficient solid dewatering. For more complex and sensitive processes, like the ambient scorodite precipitation process, sophisticated process control allows careful step wise processing that produces pure and stable crystalline scorodite.
Pump specification
Pioneer Prime PP64S17-75 kW mine dewatering pump operating on a remote VFD pumping 280 m3/h through a 1.2 km pipeline at 6.5 bar
Simon Ruffles, Managing Director of Pioneer Pump notes that “providing water to a mine is more than just about pump selection; it’s about understanding the design of the mine and its particular water requirements.”
Most mines around the world handle water in the process of either removing it from a mineral source or in the processing of minerals. “Quite often the mine usually finds it has either too much or too little water and most commonly one or the other at the wrong time.
In order to overcome the supply issues it is quite common for mines to use open storage lagoons (sometimes called ‘dams’) to store water for when needed, creating a buffer and allowing the mine to optimise its water resources. Some use old underground mines for storage and this has challenges in its own right.
“Quite often these lagoons will be man made,” Ruffles continues, by the mine as part of the original consultant designed layout and one of the key aspects would be to stop recirculation of the water from the storage point back into the working area of the mines. This is commonly done by lining the excavation but also by placing the lagoons far way from the mines, sometimes as far as 2 km and quite often over challenging topographical conditions.
“Any pump company should consider these points when specifying not only the pump but also the driver, whether it be an electric motor or a diesel engine driving the pump and from that, how best to utilise the equipment in order to minimise the costs of running the equipment and the environmental impact.
“Pump companies quite often offer fixed speed solutions dictated by frequency of electric motors for example 1,500 rpm on a fixed speed four-pole motor or by an engine which in most cases is flat out due to lack of operator training, which leads to excessive power requirements and fuel burn and in the worst cases equipment damage due to cavitation.”
Recent open-pit developments in Africa have however, he says, “used an alternative approach whereby mines are being offered electric driven pump sets which are often mounted on pontoons that are controlled by remote variable frequency drives (VFD) which are monitored and controlled by flow meters and pressure switches. This development has led to infinite control of the pumping application reducing power consumption thus reducing the lifetime costs of the projects particularly energy costs.
“One such project has been completed where a 250 kW electric pump set was specified for a project where the water had to be pumped out of a lagoon at a flow rate of 400 m3/h. This generally would have called for 200 mm diameter pipe however, the distance required to pump was almost 1,500 m so careful consideration had to be given to friction losses in the system and thus the diameter of the pipework.
“Pumping from the lagoon the water had to rise a static head of 150 m which was fine. However, after reaching the crest it fell away 110 m which meant once the system was primed the actual static head was only 40 m. On this basis therefore the pump experienced the following conditions in each cycle of operation:
1) Pump start, filling the line and rising 150 m of static head over a distance of 600 m in 300 m giving a total dynamic head of 165 m when one considers bends, entrance losses and an element of safety factor. To do this a self priming pump with a 525 mm impeller would have to run at 1,900 rpm or close to 65Hz through a VFD and would require 275 kW to complete the duty.
2) Once the pumpage reached the crest of the mine wall and began to fall away, the static head reduced and the total dynamic head fell as well causing the pump to experience less pressure resistance thus allowing the pump to generate more flow, possibly too much flow and leading to cavitation.
3) Once the pumping cycle is completed the pump would need to be shut down and this would now have to be undertaken in a controlled ramp down manner to ensure a minimum amount of water hammer which can destroy pipelines and pumps very quickly.
“The most cost effective way around these three challenges is to use a variable speed drive. In the first cycle of filling the pipe, because the flow is starting from a static head of zero, any pump operating at the 1,900 rpm, required at the top of the mine would lead to excessive flow rates causing possible cavitation. To control this, a flow meter in conjunction with a pressure switch would ramp the pump set up from a low speed of say 1,000 rpm through to 1,900 rpm over the entire cycle of the pipe filling on the rising leg.
“This would mean that the motor could be designed to optimise the process where in the initial stages flow may be at 400-500 m3/h to allow for fast filling. Then as it reaches the top and the static head is maximised, flow may momentarily be allowed to drop to say 300 m3/h at 160 m (lower friction losses at lower flow rate) to allow the priming duty to be completed by a 250 kW motor rather than a 275 or 300 kW motor were the 400 m3/h process flow rate developed.
“Once the pipe was full and flowing over the top of the mine wall and down the other side, static head would begin to be reduced and therefore the flow rate would naturally increase. At this point the signals from the flow meter and pressure switch would signal for the motor to slow down again and continue to slow until such time it generated a duty point of the required 400 m3/h at a total dynamic head sufficient to overcome the 40 m of static, the friction losses of the said flow rate through the entire length of the pipework and any subsequently introduced losses such as additional static head that may occur as the pontoon mounted pump set would experience as the level of the lagoon went down.
“The challenge of the application therefore is not necessarily selecting a pump set and system to achieve a duty point of 400 m3/h at say 65 m but to understand that in order to get to that point and being able to manage the safe delivery of water to the mine, the pump and systems including the driver control will experience a large range of conditions and if the equipment specifiers select equipment only for worst case scenarios (e.g. 400 m3/h at 165 m head) then the chances are they are over specifying the equipment causing increased capital and operational costs to the mine.
“If there is a moral to this story then it is twofold, firstly to carefully look at the management of the water as soon as possible in the design of the mine and secondly to make sure that the chosen suppliers have the technical capability or desire to offer the most efficient solution, because there is always a huge difference between the cost of [for example] a 300 kW slurry pump being used for such a duty with a 50% hydraulic efficiency and a valve at the end of a line to control the system, and an 75% efficient water pump requiring only a 250 kW motor and variable speed drive, that may cost the same in terms of capital expenditure but over five years may well save the mine $175,000 of electricity – or the price of the pump set and VFD in the first place.”
In another example of dewatering, Xylem has been working with Dannemora Mineral since May 2009 to pump water from the Swedish Dannemora mine, which is being re-opened, and ensure it remains water-free throughout the operation. Water had accumulated at a rate of 10 m/y in the main shaft and drifts since the mine was closed 20 years ago. The bottom of the main shaft is 620 m below ground; water had reached 323 m by 2007.
Xylem designed a customised dewatering system and in May 2009, when the water level was at 311 m below ground, four parallel Vogel pump systems, each with a capacity of some 60 litres/s, hanging in 180 m long steel pipes, at levels of -480 m and -300 m, were installed. Since then 3.4 million m3 of water have been drained from the mine.
As well as the initial dewatering and drainage work, Xylem has designed, and is in the process of installing, a permanent system that will ensure the mine stays dry and in operation. Lars Thoro, Consortium Manager with Xylem, said, “The permanent dewatering system consists of 12 Vogel and Flygt pumps which together remove 20 litres/s of water. The Flygt 2400 and Flygt 2630 pumps are ideal for this type of operation as they are specifically designed to withstand tough operating conditions. They are ideal for dewatering applications such as Dannemora, delivering highly consistent performances over a long period of time.”
According to Xylem, special features unique to the Flygt brand of dewatering pumps such as Dura-SpinTM, a hydraulic system which minimises impeller wear; Spin-OutTM a system designed to prevent clogging and protect the outer seal and the K-Impeller, a hard iron impeller specifically designed for high efficiency and wear resistance, make the company the experts in mine dewatering.
Thoro continued, “A great addition to the Dannemora dewatering operation is a Scada system which enables the operation to be monitored from above ground. A Flygt APP521 pump controller at each pump station manages operation of the pumps. This information is then communicated back to a computer system at ground level. This gives operators access to critical data from one location above ground allowing operators to monitor equipment, troubleshoot and identify trends, diagnose and resolve issues, quickly and easily. The end result is a pump station control system that provides ease of operation, flexibility and reliability, ensuring more uptime, greater energy savings and less operating and maintenance costs.”
Pump efficiency
John Schulkins, Business Development Director at TAS Online points out that “pumps are at the heart of industry and consume 15% of the world’s electricity output. If the other machinery in industrial plants which is directly affected by pump efficiency is taken into account, this proportion rises to approximately 30%.
“Due to neglect, poor design and, above all, lack of visibility of the efficiency of the system, much of this electricity is wasted – turned into heat, vibration and noise rather than producing throughput. Well managed and maintained pumps can drastically reduce overall energy consumption, but instead they continue to be overlooked.
■ International studies show that pumps typically operate at low efficiency levels – often between 15% and 40% away from optimum
■ Are very costly to run – electricity bills account for up to 90% of life cycle cost
■ Tie up scarce skilled manpower in time, travel and avoidable maintenance
■ Pump efficiency levels can be improved by an average of 20% when viewing the pump stand-alone
■ If viewed as part of the overall process, efficiency savings between 30%-50% are possible by optimising the entire pumping system.
The TAS PumpMonitor provides the technical and financial data required to cut excessive energy consumption from pumping systems. In addition to quantifying electricity wastage per unit pumped and analysing its causes, the data – fed from pump to desktop via the internet – identifies equipment failure before it manifests. This facilitates relevant, timeous maintenance and saves man hours and costly production losses.
Schulkins says “traditional condition monitoring is reactive – it only detects a problem once the pump has begun to destroy itself. One-off on-site pump testing is not a viable alternative to regular monitoring because it is costly, ties up manpower and only provides a snapshot of current operation, not a view of performance over time. TAS PumpMonitor is the only cost-effective, pro-active system enabling engineers and operators to accurately assess long-term pump performance from their office or control room.” It offers two options:
■ Manual input of data derived from readings taken on-site at regular intervals using portable instrumentation. This is appropriate for smaller pumps in stable, low-wear systems and for initial system assessment. It is an effective low-cost option as no permanent instrumentation is required
■ Real-time input of data from permanentlyinstalled instrumentation attached to each pump and transmitted off-site at frequent intervals. This is more expensive due to the cost of purchase and installation of instruments but amply justified where large pumps are consuming large amounts of electricity, where systems have fluctuating demand or where large pumps are pumping in parallel
The following data is required:
■ For clear water – suction and discharge pressure and power absorbed – flow can be derived by PumpMonitor
■ In addition, a flow meter is necessary for slurries, plus pump speed and specific gravity where these vary.
TAS PumpMonitor compares current operation against the optimum duty defined by the tested current Pump Performance Curve, the most reliable source outlining a pump’s potential performance. Data is then analysed in numerous ways and wastage quantified, per unit pumped, in both electrical and financial terms and results delivered to the required personnel.
It also classifies inefficiencies where savings can be made into three types – Wear, Duty and Volumetric. This distinction helps users identify the best corrective actions which, when implemented, result in savings throughout the system’s lifecycle.
Among the many benefits this technology offers is to provide an accurate understanding of pump requirements in future system designs, eliminating the need for redundant capacity frequently built into pumping applications to account for unit failure. TAS PumpMonitor also identifies surplus units that could be better used elsewhere.
TAS PumpMonitor integrates seamlessly into a plant’s existing communications infrastructure and to date applications have helped reduce short term operational pump electricity costs by between 10% and 15%. Long term savings are still being established and should be in the region of 15%-30%.
New pumps
Xylem says it “now boasts one of the most extensive portfolios of dewatering pumps on the market with the addition of three new sludge pumps to its flagship Flygt 2600 drainage range.” The company, which was spun off from ITT Corp in October 2011, specifically designed these versatile pumps (models 2620.280, 2630.280, and 2640.280) to meet customer demands for multi-purpose drainage pumps that can serve the evolving needs of mining and other markets. Available for rent or purchase the pumps have new features which are easy to install and service, reducing the total cost of ownership.
The portable Flygt sludge 2600 pumps have a range of 1.5 to 5.6 kW for 50 Hz countries and 2.4 – 8.9 hp for 60 Hz countries. Capable of flows up to 28 litres/s and heads to 38 m, these sludge pumps are ideal for open-pit and underground mine dewatering and emergency site drainage.
Wear-resistant, they handle solids up to 80 mm and sand concentrations of approximately 20% by weight, due to a larger inlet and pump volute, Hard-IronTM (60 HRC) vortex impeller, polyurethane-lined pump housing and side discharge design.
Peter Hansen, Product Manager says “because the hydraulics of the sludge pumps and drainage pumps are interchangeable, customers can adapt one 2600 pump to handle many applications.” The hydraulic ends share drive units and common parts, and are interchangeable with similar sized models of the 2600 drainage series. This interchange ability allows end users the flexibility to adapt to changing application requirements and reduce spare parts inventory.
Flygt customers already familiar with the easy-to-service 2600 design will find maintaining the sludge pumps just as simple and quick. The new sludge series features the patented Flygt Plug-InTM seal, which provides a double mechanical seal in a compact and easy to replace single cartridge. External oil and inspection plugs, allow for seal-condition check and oil change without dismantling the pumps, and the removable top gives quick access to all electrical components.
The three new models also incorporate the latest enhancement in Flygt pumps: the terminal board. By sealing off the junction box from the motor, the terminal board prevents any water from passing between compartments, thereby reducing repair costs. Plus the screwless springloaded terminal design assures reliable connections and simplified wiring.
Another recent addition to the Flygt drainage range is the two-stage Flygt pump 2660 SH. Twin impellers enable the 2660 SH to pump fluid higher. With 10 kW rated power the 2660 SH can be used in a broad range of applications in mining. A zero leakage ‘Active Seal’ increases the service life of the pump and contributes to longer intervals between oil changes and maintenance check-ups. A unique hydraulic system developed by Xylem, the ‘Dura-Spin’ effectively protects the impeller gap by transporting abrasive particles outwards. A Spin-Out system includes a special design of the seal chamber. Solid particles will be transported via a spiral groove in order to protect the seals and the bottom of the oil housing from sediments and wear. IM
Reference
1. Riveros P.A., Dutrizac J.E., Spencer P. 2001. Arsenic disposal practices in the metallurgical industry, Canadian Metallurgical Quarterly, Vol 40, No 4: 395 – 420.
