5 Mobile beneficiation plants
5.1 IPCC Systems
Several manufacturers such as the global Finnish based company Metso are strong advocates of in-pit crushing and conveying (IPCC) systems, which are the main users of mobile crushers and screens. As such, the usage of mobile plant hinges very much on the success or failure of IPCC systems, and whether mining companies fully utilise them or not. IPCC systems are intended to supplement or even replace shovel and truck haulage systems, offering significant reductions in operating costs. The Australian Mining Journal states that “the bill for fuel, labour, tyres and carbon emissions can be reduced, markedly if a fully mobile system is introduced” .
An IPCC system typically involves crushers and screens close to the pit face, feeding conveyors that may lead to secondary or tertiary crushers, or direct to a heap leach pad. A fully mobile system uses tracked or wheeled crushers and screens, while a semi-mobile system is situated close to the pit but generally outside the blasting radius. The mobile type can eliminate dump trucks altogether, with the digging unit feeding the hopper of the crusher, but the semi-mobile type still needs trucks to operate between the face and the crusher. According to the Australian Mining Journal (AMJ), fully mobile units are limited to under 7000 t/h and could not deal effectively with hard rocks, while the semi-mobile systems have higher productivities on harder rock. Recent technological advances indicate that mobile systems are now able to perform just as well as semi-mobile units.
IPCC systems originated in German brown coal mines in the 1960s when bucket-wheel excavators fed into crushers (and still do). The European manufacturers have thus become world leaders in sales and development. This methodology has spread beyond coal and on to minerals although metalliferous miners have been slow to adapt the technology due to high capital costs, inflexibility and their comfort with shovel and truck systems. According to Sandvik, where it has been installed there have been mixed results due of poor mine planning. So far, the main use of IPCC systems in metalliferous mining is in overburden removal.
Technological advances mean that IPCC systems will become cheaper and more productive, this will result in their adoption in large regular ore bodies where the movement of conveyors is minimised and planning is simplified. Quarries will likely continue to use mobile crushers where a range of sized rock is required for the market.
As a consequence, truck manufacturers such as Caterpillar and Komatsu are fighting back. They are researching and developing automation whereby trucks will be driverless and operated by a central control room; hybrid electric-diesel motors are being refined, and other fuel economies are being mooted. Nonetheless, S.P. Angel on “Directors Talk” believes that truck and shovel technology is reaching its limit, and any further gains are likely to be small and incremental .
5.1.1 Advantages of the IPCC systems
Reduced operating cost
Noteworthy reductions in operating costs are the principal advantage of In-Pit Crushing and Conveyor (IPCC) systems over shovel and truck systems. The Australian Mining Journal states that an open-pit operation producing around 50 to 60 million tonnes per annum (Mta) would employ between 300 and 500 trucks (100 tonne capacity) which would require some 1200 drivers and mechanics . A fully mobile IPCC system could reduce operating costs by around 60 % and a semi-mobile system around 20 to 30 %. Metso indicate a cost saving of around US$ 0.20/t of ore by adopting fully mobile systems.
thyssenkrupp of Germany report that they are replacing a shovel and truck system in China. They detail that 26 dump trucks (350 tonne capacity) consume 190 l of diesel per operating hour. The use of an IPCC system will save 22 million l of diesel per year according to their calculations. thyssenkrupp also make a valid point that each large truck tyre can cost up to € 300 000 each. However, cheaper operating costs must be judged against higher capital costs, cited as being up to 25 % more than a shovel and truck operation.
IPCC are more environmentally friendly than the use of shovel and truck operations. As a result of the reduced diesel consumption stated above, Metso claim that an average IPCC set-up (around 30 to 50 Mta) will save around 10 000 to 15 000 tonnes of CO2 per annum.
thyssenkrupp claim a major motivator for developing their mobile crushers is to reduce greenhouse gas emissions by dispensing with the need for heavy trucks. Diesel is, of course, a fossil fuel and the move to electricity as a primary power source could result in IPCC systems having a notable reduction in the production of harmful greenhouse gases.
IPCC plant systems employ far fewer people than stationary plant which require support staff, mechanical staff and drivers. A fully mobile system, especially if automated, may employ no more than a handful of operators. Not only is this a huge cost saving, but it also reduces the frequency of accidents, incidents and near misses.
Life expectancy of equipment
The average life expectancy of a haul truck is approx. 60 000 hours (possibly even less in poor conditions), in comparison an IPCC system which can last up to 150 000 hours. This supports the assumption that IPCC systems, both fully and semi-mobile, are best suited to long life bulk deposits such as coal and iron ore.
5.1.2 Disadvantages of the IPCC systems
Fully mobile systems have to be relocated every time a new face is worked or moved for protection during blasting. To allow rapid relocation, crushers, screens and conveyors must be moved more or less simultaneously. According to Tom Armesy of thyssenkrupp this “requires a completely integrated approach and solution”. He goes on to say that there is a need to blend the mine’s conceptual vision with its planning functions, and integrate them into a working model. In other words, it entails a high degree of expert mine planning and mine design .
Phil Morris, an independent IPCC consultant, considers that irregular shaped ore-bodies and deep pits are unsuited to fully mobile systems . In addition, pit mine planning software is based on shovel and truck systems, and furthermore there is not enough expertise among mine planners and pit engineers to successfully implement mobile systems. He argues that IPCC is (wrongly) seen as niche speciality or curiosity at mining schools.
It is argued that IPCC systems work best in strip mines, large bulk deposits and during overburden removal. Semi-mobile systems have been used to overcome mobility issues when trucking is used to feed semi-mobile crushers just outside the pit, relocation periods can be between two and ten years.
Dennis Medina of FLSmidth argues that the works required for locating and stabilising semi-mobile plant can be as significant as that for fixed plant . Expensive retaining walls required to allow trucks to the required height to dump into a hopper, geotechnical investigations and site preparation can cost millions of dollars and the reluctance to further relocate may lead to unsuitably located crushing plants.
A semi-mobile system might reduce haul distances and require less trucks, but it is still a dual truck-conveyor system with the disadvantages of both. Operating cost advantages are less than a fully mobile system, but the capital costs could be similar if not higher.
IPCC systems require up-front installation from the start of production while trucks can be phased in as production ramps up. This can be a heavy capital cost to a small to medium sized mine. AMJ estimate that the average capital cost of a fully mobile IPCC system is about 25 % higher than for a shovel-truck system, although as discussed running costs could be far lower.
Planned or unplanned downtime on an IPCC will bring the entire operation to a halt. On the other hand, trucks are discrete units and breakdowns may cause problems but not a total shutdown.
Delays in relocating the mobile crushers and conveyors can become a serious issue for the mining cycle. Manufacturers go to great lengths to emphasise that their equipment is truly mobile and that conveyors are electronically locked on and will automatically follow the crushing plant when it is moved.
Mine operators generally understand the capabilities of trucks and loading units and are able to handle most production problems; it is a mature ‘tried and tested’ technology. By comparison IPCC is not as familiar and the downtime and mine planning issues weigh heavily with operators there is a reluctance to consider IPCC systems, and when installed, some resistance in making them work properly.
Resources Gold Technology
Resources Gold Technology, USA provide complete turnkey modular gold processing plant for design tonnages of between 500 to 2000 t/d. The plant is assembled in typically nine sea containers for ease of transportation and simple light civil foundations are required for site assembly. Fig. 22 shows the modular milling circuit housed within a sea container.
Installations typically include:
500 to 2000 t/d completed modular plant
Mobile crushing and screening plant
Variable speed ball mill
Concentrate filter process and
Process return tank
Sepro Minerals System Corp, Canada supply modular processing plant which they design for specific applications. The modular plants are designed so that it can shipped globally and to have minimal civil work requirements. The plants are also designed so that they can be easily assembled and commissioned. Some examples of process arrangements are shown in Fig. 23.
Sepro’s modular plant is used commercially: for example in 2014, Banks Island Gold Ltd. purchased two mobile plants from Sepro. The Sepro Mobile Mill Plant, which features one 1.8 x 3.6 m Sepro Tire Drive Ball Mill and one Sepro SB750 Falcon Concentrator is currently processing on average 200 t/day and has resulted in an estimated gold recovery of 92 % since processing began in August 2014.
Kappes, Cassiday and Associates
Kappes, Cassiday and Associates (KCA), has fabricated 37 portable or modular carbon adsorption plants and Merrill-Crowe plants. The modular plants can be constructed for gold operations treating up to 4000 t/d (above that size, KCA build the plants at site). Two examples, of the portable plants supplied by KCA is now given.
The Getchell, Nevada, Carbon ADR plant consists of a five-stage vertical tower adsorption column. Desorption and electrowinning take place inside the trailer. KCA has built several tower column plants, which offer portability and compact size. The plant was designed for a 1200 t/d heap leach operation. In 1988, the plant was repurchased by KCA and re-installed at the Atlas Gold Bar mine. The Tambor 200 t/d plant has a flotation circuit and is located in KCA’s Reno yard, US. The float cells and rear deck are mounted on standard shipping skids. Further installations in Nevada and in Ghana are shown in Fig. 24.
Gekko, Australia supply a system known as Python which is designed for low-energy processing in a narrow, portable plant. The Python shrinks a conventional processing plant to a size that can be operated underground and close to the deposit, or above ground with a marked reduction in equipment footprint. The objective is to enable the bulk of the ore to be processed underground so that waste transportation and treatment costs are reduced while only a pre-concentrate is transported to surface for additional processing.
The modular system is engineered for a low footprint and is 2.3 m wide and 5 m high, this allows vehicles to move freely pass the modular unit. The Python is also designed to save energy by crushing ore to a coarse particle size and separating the wanted minerals using InLine Pressure Jigs and/or flotation. The Python is suited to gold mining and is also adaptable to other minerals that can be separated by gravity and/or flotation, such as diamonds, tin and coal. The Python modules are compact enough to be transported worldwide in 40 ft shipping containers (Fig. 25).
The first prototype was completed in 2007 and was fitted with a jaw crusher and vertical shaft impactor (VSI) in a closed circuit to achieve a -5mm product suitable for the rougher gravity concentrator, an Inline Pressure Jig (IPJ). 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.
APT provide an alternative option for mineral processing plant that uses flexible and modular equipment (Fig. 26). Their modular equipment has been used in many applications including:
Alluvial gold and
Separation technologies including gravity, CIL and froth flotation (sulphide recovery).
The construction timeline of APT’s modular plants are relatively simplistic as shown in Fig. 27 One clear noticeable advantage is the fact that their systems can be initiated and installed within weeks as opposed to traditional, relatively expensive, methods of project development which can take several years. A further advantage, allows projects to be initiated with a relatively small investment with profits being used to allow further upscaling of the plant in subsequent years.
APT have also developed modular CIL/CIP (Tritank) and flotation (TriFloat) equipment which are compact units with the reported advantage of having fast kinetic response thus allowing smaller tank volumes to be used. These modular plants can be extended into elution and electrowinning using APT equipment. The Elu-X unit is a non-pressurised Zadra elution plant which can be supplied in conjunction with APT electrowinning cells for gold recovery from activated carbon.
APT are additionally developing a high-G centrifugal concentrator as an alternative to Knelson and Falcon concentrators. These units will process up to 10 t/h, and are aimed at the smaller-scale end of the market.
The Outotec cPlant is a low-capacity flotation plant equipped with Outotec FloatForce® mixing mechanism and Outotec TankCell® technologies. The plant has been developed for projects handling up to two million tons of ore per year, with cell capacities of 1.5, 3.6, or 11 m3. Its prefabricated modules are easy and cost-effective to transport and install, and can be quickly connected to your process. The flotation plant is based on pre-fabricated and functionally tested modules inside container-sized steel frames that can be easily transported and installed, and quickly connected to the process.
cPlant can be easily scaled up or down to meet the demands of any market situation. In addition, the plant’s modular steel frame construction makes it economical to move to a new site once ore deposits become depleted or unprofitable.
6 Sample preparation and analytic laboratory
Mines and processing plants require chemical analysis for control and audit purposes. This could be done either on site or at a commercial analytical laboratory. Whichever option is used the samples will need to be prepared. The sample preparation includes drying, crushing, fine grinding, and sampling. This could also could be done on site or at the same laboratory doing the analysis.
There are several companies which design and construct mobile sample preparation and analytical facilities which can easily be set up on site, including:
The sample preparation is relatively easy to operate with limited training and experience. However, the analysis requires a lot more experience and technical expertise. Also, for a relatively small throughput the cost of an on-site analysis laboratory is high. Hence it is better to utilise a commercial laboratory for the analysis, but do the sample preparation on site.
7 Conclusions and recommendations
The literature review has shown:
There is a strong technical resource in Europe
There are numerous equipment suppliers within Europe
Currently, mobile processing plants are predominately used today for the following applications:
• Crushing circuits within the minerals and quarry industry
• Gravity circuits for processing alluvial materials
Beneficiation and dewatering equipment are generally not marketed by equipment suppliers as being mobile
Equipment previously intended for stationary installations could be adapted for mobile applications, but this is likely to be dependent upon throughputs required and the material being processed. Items identified for potential conversion to mobile applications, although not limited to, include (subject to engineering):
• Ore sorting
• High intensity leaching
• Froth flotation
• Magnetic separation
• Dewatering technologies
Modular plants, such as those built by Sepro, could be adapted and incorporated into a mobile processing plant
Of interest to the FAME Project is that existing modular plants are designed with the benefits of:
• Pre-assembled modular units for fast and easy assembly
• Ideal for remote sites
• Units containerised, hence transportable worldwide
Europe has sufficient technical expertise and numerous equipment supplies to develop a flexible, modular and mobile processing plants for the purpose of unlocking European mineral resources. The key aspect in the development of these projects will be characterising their geology and mineralogy so that metallurgical testing can be progressed for the development of processing flowsheets and economic evaluations.
There is the opportunity to review mobile processing plant that have been manufactured by companies such as Metso and Gekko. This is recommended during the flowsheet development stage so engineering solutions, concepts and ideas can be incorporated into FAME’s engineering design of mobile plant. It is also recommended that processing technologies, be it conventional, modified or innovative, be pilot plant tested using targeted European mineralized samples. This will serve to demonstrate the feasibility of mobile extractive technology.
Literatur • Literature
 Foley, M.: In-pit crushing: The wave of the future? In: Australian Mining Journal, May/June 2012, pp. 46-53
 Disruptive technologies are going to transform mining costs. www.directorstalk.com, April 2015
 John Chadwick: New IPCC ideas. In: International Mining, 33/June 2010