Single-source convenience, quicker delivery and efficient use of space and materials
attract growing interest from project owners
By Russell A. Carter, Managing Editor
The precise definition of the term “modular” mineral recovery plant is somewhat elusive, with examples ranging from small, skid-mounted units that perform specialized tasks to much larger, prefabricated component systems that, when installed and commissioned, serve as a principal processing facility. What is much more easily definable, however, is the continued level of industry interest in modular plant technology to solve project-design challenges posed by increasingly remote mine locations; rising transportation, energy and materials costs; and scarcity of skilled tradespeople in less-developed regions of the world.
And, although the concept that usually comes to mind when “modular plant” is mentioned is gravity separation systems for gold and other precious metals, the scope of modular applications is actually much wider, encompassing recovery of diamonds, coal, copper, and other mineral commodities. Bateman Engineering, for example, originally designed modular plants used mostly for diamond recovery, but has expanded its range to applications for coal, graphite, magnesite, andalusite, chromite, platinum, tantalite, copper and cobalt oxide. The pool of modular plant suppliers ranges from full-range providers such as Metso, Telsmith, and FLSmidth—which late in 2009 acquired modular plant specialist Summit Valley Equipment & Engineering—to more specialized vendors such as Gekko, Consep, DRA, ADP and others.
It’s an industry segment that regularly spawns innovations. Recent technological developments in modular plant design range from simple—such as an ingenious fastening system for tank construction that eliminates conventional bolting or welding—to complex, involving completely modular pre-concentration plants that can be towed down an incline or lowered down a shaft to carry out crushing, screening and gravity/flotation processing underground.
In a modular world, “less” is a key concept—less infrastructure needed, less equipment and parts, and less need for specialized installation skills. Moving in that direction, Xstrata Technology, developers of ISASMELT and ISACONVERT smelting processes, IsaMill grinding mills, the Jameson Cell flotation machine, and other mineral processing systems, recently introduced an innovative, modular storage tank system for slurry applications, called ZipaTank. According to the company, ZipaTank uses a novel locking mechanism to provide watertight sealing of pre-fabricated vertical panels, eliminating the need for welding to assemble the tank panel walls.
Mike Hourn, business manager-hydrometallurgy at Xstrata Technology, said the ZipaTank system was designed to overcome the limitations of current slurry tank design, in particular the high capital cost and lengthy installation times currently associated with slurry tanks. “The ZipaTank system can reduce the capital cost of conventional welded slurry tanks by up to 35%, with installation of large ZipaTanks being one to two weeks compared with upwards of six weeks for welded tanks. The system is also very simple to use; a 100 m3 tank will only require six vertical panels to put together. No welding is needed in the construction of the tank, so minimal skilled labor is required,” Hourn said.
The ZipaTank consists of vertical panels locked together to form the tank shell using a compression joint. The cylinder is then bolted to the base, eliminating any welding at heights and the need for scaffolding. Each vertical panel is manufactured from a single cold-rolled section of mild or alloy steel to the total height of the tank. The width of the panel is rolled to match the tank diameter, with all panels designed to fit in a standard shipping container, reducing the transport costs to site.
The key to joining the panels together is the proprietary Joinlox joining system. The Joinlox system is an innovative mechanical method of joining rigid or semi-rigid components together. The joint consists of two interlocking sinusoidal sections fabricated on each edge of the tank panel, which are brought together and then locked with a tensioning key, resulting in a spring-loaded joint. As the tensioning key is pushed into place, it wedges the two panels together and locks the joint. The mating surfaces of the joint are rubber lined, providing a watertight seal between the panels. No bolts are used for the panel connections, significantly decreasing the installation time. This joining system also allows the panels to be taken apart if required, so at the end of the project’s life, the tanks can be disassembled and used again at another operation.
A major advantage of this type of tank construction, according to Xstrata Technology, is it enables all components of the ZipaTank to be fabricated and lined off site, under controlled conditions, so high quality lining can be achieved.
Hourn said that one of the issues facing tank installation is the failure of site-applied linings due to variable local weather conditions during installation. The ZipaTank panels, however, employ lining systems that are applied under controlled factory conditions. This reduces the cost of the lining, and allows lower-cost lined panels to be used in the place of more expensive alloy steels. A large range of rubber and GRP/FRP lining systems can be used.
The ZipaTank can be used for a wide range of applications, such as storing concentrates, reagents, repulping and conditioning duties, flotation tanks, thickeners and clarifiers as well as all types of leaching applications in mining and non-mining operations.
Xstrata Technology said it designs and supplies the tanks specifically to suit a client’s application, providing loading details as well as foundation design if required. Fully modular ancillaries can also be designed into the tanks, such as baffles, slurry risers/downers, nozzle and sparger inlets, lids, launders, surrounding structural steel work and stairways, platforms etc outside the tank. All equipment is designed to be containerized for ease of transport. Xstrata Technology can also provide the tanks as a complete package inclusive of the agitator, impellers and agitator support beams.
“We have only really scratched the surface as to what we can provide with the ZipaTank technology,” said Hourn. “It is such a simple system, but has the potential to provide substantial savings in both cost and installation times for our clients. While most mining equipment has undergone continual advancement, slurry tanks have not advanced significantly over the last century. With the ZipaTank, we are planning to improve tank quality and modernize the fabrication techniques for large slurry tanks, resulting in a step change in tank technology.”
Original inventor of the Joinlox concept, Dean Cameron, reportedly got his inspiration for the technology from the way clams attach themselves to rocks via hooks on the end of hundreds of silk-like filaments. Joinlox, too, uses a series of interlocking hooks, which are joined together by a “key” that slides between the hooks. The hooks on Joinlox convert shear forces into tensile and flexural forces, dramatically increasing the strength and pressure rating of the joint.
The patented technology does not use traditional fasteners, welding or adhesives, all of which Joinlox said are expensive, time-consuming, irreversible or lead to weaknesses in the joints. The system is claimed to be adaptable to suit almost any linear or complex joint, providing rapid, strong and pressure sealed joints across a broad range of materials and combinations without need of costly equipment or skilled labor.
Joinlox said the system can be used for a wide range of applications, from the construction of storage tanks and structures to returnable containers and crates, electrical enclosures, large diameter pipes, rapid formwork and bridge piles, and a range of building materials and construction methods.
“Before commencing any new project, we carry out an initial engineering and cost analysis that involves comparing Joinlox with all other available methods, designs, costs and processes,” said Joinlox CEO John Pettigrew. “From this we are able to provide a clear indication of the savings and benefits our clients may expect to realize by implementing the Joinlox system for their products or applications.”
Pettigrew said Joinlox is continuing discussions with other international manufacturers across a wide range of industries, exploring ways of using its technology to overcome joining problems.
Less Distance to Haul
Victoria, Australia-based Gekko Systems, which opened for business in 1996 and began designing modular plants in 2003, offers an array of mineral processing systems with a primary focus on gravity separation. Gekko has pursued a design direction away from conventional CIP or CIL gold recovery plants, with emphasis on treatment of free and complex gold ores as well as pre-concentration of various ores.
Gekko builds modular components fitted with its own equipment, as well as with equipment sourced externally. The skid-mounted modules are pre-commissioned at the factory, then broken down into container-based components ready for shipment and reassembly on-site. Gekko said it has supplied more than 200 systems designed around its Inline Pressure Jig (IPJ) and more than 80 of its Inline Pressure Reactors (IPR).
Most recently, Gekko installed a pre-concentration module consisting of six IPJ2400s to increase the throughput of the milling and flotation circuit at the Pirquitas mine in Peru, operated by Silver Standard. Pirquitas began producing silver concentrate in July 2009, and reached full production in December; 2010 output is estimated at 7 million oz of silver. Mining is by conventional open-pit methods using 100-mt trucks and 12-m3 loaders.
Gekko says its InLine Pressure Jigs at Pirquitas pre-concentrate the ore, allowing a substantial increase in the plant feed rate prior to the ball mills. This is achieved by passing plus 2- to 12-mm crushed material through the jigging circuit, where the lighter (barren) material reports directly to tails. The total feed is reduced by 50% after the IPJ treatment, recovering over 90% of the values in the concentrate stream. This allows an increase in the plant feed rate without economically compromising recovery.
Interested in taking its pre-concentration concepts underground, in 2004 Gekko applied for and received a $1.2-million research grant to develop an underground mineral processing system. In a paper presented at the 2008 Narrow Vein Mining Conference, Gekko representatives decribed the key objective of the project: to fine crush and pre-concentrate ore underground as near to the working face as possible with a combination of gravity and flotation methods. The pre-concentrated, valuable material can then be transported the surface while the non-valuable tailings remain underground for backfilling.
A prototype underground processing system, named Python, was completed in 2007, fitted with a jaw crusher and vertical shaft impactor (VSI) in a closed circuit to achieve a -5 mm product suitable for the rougher gravity concentrator, an Inline Pressure Jig. Tails from the IPJ are screened to return oversize to the VSI with undersize product reporting to flash flotation. The rougher IPJ concentrate is cleaned using an IPJ1000 with the cleaner concentrate and flotation concentrates transported to the surface for final treatment. The cleaner tail is recirculated back to the rougher IPJ and the flash flotation tails are available for backfill. Although the VSI is suitable for use with soft ores, the Python can be fitted with high pressure grinding rolls for harder materials.
Central Rand Gold, a South African gold producer developing an underground project near Johannesburg, subsequently installed the first unit—the Python 200, rated at 20 mt/h—in October 2008. That system is currently working on the surface, operated under contract by Gekko’s South African office; plans are for it to be eventually moved underground. Interestingly, CRG also ordered a similar, 30-mt/h modular plant from Bateman Engineering in 2008.
When assembled, the Python 200 measures 2.4 m wide × 5 m high × 67 m long. The plant can be split in two equally wide and high sections 35 m and 32 m long, respectively, and can be installed on two mining levels with piping and power cables running between them. According to Gekko, only two operators are required: one to drive an LHD feeding the plant and operate the plant ‘front end,’ and a concentrator circuit operator.
CRG’s experience with the Python 200 prompted the gold producer to order two larger Python units designed to operate at a throughput rate of 50 mt/h. Plans are to have at least one Python 500 operating underground at CRG before the end of 2010.
Gekko believes the new Python 500 design is a stepping stone to a broad range of throughput options. Modular expansions can also be included, such as milling or flotation, as dictated by the variability of the ore. “We view the Python system more in line with the purchasing of earthmoving equipment where you have the available range of throughput options that can be customized for ore variability,” said Gekko’s Technical Director, Sandy Gray.
Less Environmental Risk
Consep, another Australian supplier of specialized processing equipment, has had significant success with its Acacia system, a packaged processing plant for treating high-grade gravity gold concentrates, such as those generated from a Knelson Concentrator. The Consep approach involves production of a concentrate from ore that undergoes intensive cyanide leaching in a closed-circuit system. The plant is built around an upflow fluidized reactor for leaching, designed to produce proper solid-liquid interaction for maximized gold leaching reaction kinetics without mechanical agitation.
Garrison International Ltd. recently selected Consep to build and install a turnkey processing plant relying on Acacia technology at Garrison’s Tovshiir gold project in southeastern Mongolia. Consep will provide an automated screening plant and a 20-mt/d Acacia Intensive Leach Unit with associated electrowinning, solution recharge and detoxification units. All plant components will be automated and can be monitored from a main control room, requiring only one skilled person to operate the process.
According to the company, test work conducted to date using the Consep system on test ore from its Tovshiir project produced overall gold recovery of 86%, and Garrison’s management said it is optimistic that similar recovery rates will be achieved when full-scale production commences at Tovshiir.
Consep claims that, compared with other competing technologies, its patented closed cyanide-electrowinning circuit requires a lower volume of chemicals, yet can often achieve recoveries in the 95% range.
The basic version of the Acacia system is offered in various sizes to treat 50 kg to 24 mt per cycle of concentrate, and in manual or automated configurations.
Garrison’s management believes using the Consep technology will allow the Tovshiir operation to recover gold from ore with less environmental risk than from a conventional carbon in pulp cyanide plant. Because the Consep system does not use a leach pond and does not expose cyanide to the open environment, the risk of environmental contamination is reduced.
Garrison expects the Consep plan to arrive for installation at the Tovshiir site during the third quarter of the company’s 2010 fiscal year.