Engineering & Mining Journal

DEC 2015

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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DECEMBER 2015 • E&MJ; 81 www.e-mj.com O P E R AT I N G S T R AT E G I E S ing in the harsh conditions typical of mining environment fare even worse, with one leading pump manufacturer estimating that, of the 2,700 pumps they have examined since the 1980s, more than a third were running at less than 40% efficiency. These high operat- ing costs can, in some cases, be avoid- ed by designing a gravity flow solution in preference to a pumped system. Plastic pipe supplier Polypipe can assess a mine's water management sys- tem design to determine if a pumped system is required, and identify areas where gravity flow is appropriate. In designing an efficient and safe tail- ings management facility, for example, establishing a stable water balance will prevent future problems such as over- flow. This can be achieved by taking into account not only the daily inflow and out- flow expected of the facility, but also allowing for storm surges. Using a series of gravity pipes to drain into the tailings pond itself can help maintain a manage- able, steady flow, while at the other end of the system, gravity pipes can be used to decant water from the dam walls to water treatment facilities. Heap leaching converts the desired minerals into a chemical compound, which, at the bottom of the leach pile, drains into perforated pipe and is carried by gravity to the final extraction process, usually via a pregnant solution pond. With no pumping required, heap leaching is gaining in popularity—offering a mini- mal level of capital expenditure com- pared with other more intensive meth- ods—though it does require a greater time investment over other methods such as tank leaching. Bypassing pumped systems at the recovery and wastewater stages can pro- vide tangible cost benefits, but must be carefully planned to ensure the chosen pipes perform at their optimum level. At the specification stage, the American Water Works Association (AWWA) offers the following guidance in its Standard for PE Pressure Pipe and Fittings (1990): "The working pressure of the system plus recurrent surge pressure associated with a specific piping arrangement or opera- tion should not exceed 150% of the pipe pressure rating." For gravity-flow or low-head pipeline applications, HDPE is an effective solu- tion due to its smooth bore and low resistance to flow. If large volumes of liq- uid are being transported, there is also very low friction within HDPE pipes, meaning less drag or turbulence at high flow rates and greater resistance to scal- ing than traditional materials. Used for non-pressurized surface and subsurface drainage as well as sanitary sewers, leachate collection and storm drainage, HDPE solutions are easy to install and maintain while providing the robust dura- bility required of mining environments. Importantly, HDPE has the capability to transfer its load to the surrounding soil and substrate under stress, resulting in long-term structural stability and assist- ing in the longevity of the pipeline. Regardless of the PN rating, all HDPE pipes possess the key characteristics that make them suitable for mining applica- tions. Highly resistant to abrasion from both minerals and substrate carried in slurry, they are also resistant to many of the chemicals commonly used in mining and mineral extraction, including acetat- ic acid, ammonium hydroxide, hydrogen peroxide and calcium hydroxide. Utilizing a gravity flow system will not only deliver cost savings in terms of avoid- ing expensive pumps, ongoing mainte- nance and high-pressure pipes; HDPE pipes are lighter than traditional materials and are therefore cheaper, easier and safer to transport and install. They can be supplied in longer lengths than more expensive concrete or ductile iron solu- tions, meaning fewer joints are needed, which further reduces the possibility of leakage. Ideally suited to harsh operating environments, HDPE water management solutions can withstand temperatures in the range of -40°C to +60°C. Polypipe's PE100 solution is an effec- tive intermediate pipe solution with all the benefits of PE, capable of handling up to 25 bars (~350 psi) of pressure depending on the temperature. Ridgidrain, mean- while, is an HDPE twin-wall pipe solution for non-pressurized drainage applications, which is up to 94% lighter than concrete and features a structured wall design for high ring stiffness and strength. For addi- tional storm surge water storage, Poly- storm is a crate-based, modular water stor- age system, which can be integrated with either PE100 or Ridgidrain to provide emergency storage for excessive rainwater or for attenuation and soakaway systems. Correct specification of pipes for min- ing applications can help save money in several ways; from the initial purchase cost, to the added expense of running an unnecessary pump system when gravity could be exploited within tailings man- agement and heap-leach applications amongst others. Working closely with a water management specialist such as Polypipe can help optimize a mine's pipeline design without compromising on quality of materials. When a pipeline points downhill, Polypipe's recommenda- tion is to use the power of gravity—it is as free as the air we breathe. Phillip Wood is international business de- velopment manager at Polypipe. For further information, visit www.polypipe.com/mining . According to Polypipe, HDPE pipe products for mine applications can be supplied in longer lengths than other tra- ditional pipe fabrication materials, offering reductions in installation labor and leakage problems.

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