The Global Boom in Modular Process Plants

Appropriate Process Technologies (APT), a South African-based modular process plant supplier, has a full order book, with many more orders in the wings. “Gold is the flavour of the day and with the boom having no foreseeable end in sight the emphasis is on simple implementation and operation parameters, along with maximum recovery in low-energy format,” says MD Kevin Woods. 

Plants are designed to arrive in simple modular units that can be combined in remote, inaccessible areas. Start-up is usually one to six days, depending on the size of the plant. Constant interaction with mining process operators on the ground is undertaken to ensure ongoing upgrades are implemented at all stages, Woods explains.

Three RG scrubbing plants, one in South America and the other two in Central Africa, have been commissioned recently. These plants are for processing gold: two being for alluvial plays and the other an alluvial/hard rock combination. 

“The South American plant was a logistical challenge as it was in a remote jungle site. Th is RG scrubber was implemented to rehabilitate existing riverbed material while simultaneously incorporating recovery. There was heavy rain – approximately 18 hours a day – and a new road had to be remade using an excavator to get the plant in place. Once there, it was a wet and sticky few days to get it up and running,” says Woods. 

An order has been received from West Africa for multiple RG scrubbing plants – both alluvial and hard rock alluvial combo plants. Woods notes that this is in fact the first phase of a three-part phased build for 11 plants in total, to be delivered over the next eight months, including two RG800s (80 t/h) and five RG200s (20 t/h). The configurations include pure hard rock, alluvial and hard rock/alluvial combination modules. All of these plants incorporate the latest RG designs and will include Knelson concentrators to recover the gold.

In addition, a South American miner has commissioned APT to build an SG200 plant. The all-new SG200 is a plant with a screen rather than a scrubbing drum to accept loose sand that does not require tumbling to pre-disintegrate the feed. The SG200 plant is equipped with a scavenger cyclone in closed circuit with a Knelson concentrator to target particularly fine gold that has escaped the traditional sluice processing methods used to date.

This simple new plant introduces an unprecedented low capex entry level in a simple, easy-to-operate package fed by a gravel pump. “What is really exciting is that the plant is also specifically designed to recover mercury and thus decontaminate polluted areas,” Woods enthuses. The Knelson concentrator used in this plant has a special feature to enable the capture of mercury to a separate container. The South American mining company has also opted for a traditional RG200 scrubber with the same mercury recovery system.

An IC30 hard rock plant has been built and is now in production in Central Africa. “This is a very neat impact crusher and screen arrangement in a space frame with an integral GoldKacha concentrator. The entire plant, including concentrates upgrade table and internal water pumps, runs off a 40 kVA generator. The IC30, at 3t/h feed (-150 mm), is the baby brother to the IC120, which handles 10t/h (the IC120 is combined with a Knelson concentrator). “The impact crusher up-front acts as a primary and secondary/tertiary crusher in one pass,” Woods elaborates. “The well-fragmented and fine product produced by the high-impact blow-bar enhanced crushing system within the crushers ensures that gold is released in what is termed as ‘early liberation’ for easy concentration by gravity downstream. The mining company using the IC30 in this instance has begun negotiations to swarm more of the same plants in high yielding areas and they are keen to get their hands on an IC120!” 

Closer to home, an order has been completed for the supply of a new-style MK2 RG200 Scrubber – a low-slung, wide-bellied scrubber rated at 20 t/h feed. “This machine will be installed in Mozambique shortly, along with a double-deck poly-screen to process bauxite. This is a repeat order for APT, with the bauxite mine already having run an RG200 on bauxite successfully for the last five years,” concludes Woods.

The mining sector, and the gold mining industry in particular, is booming, and so is the demand for modular process plants.

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Metallurgical Testwork and Mining: let the ore dictate the terms!

* Metallurgical testwork laboratory Peacocke & Simpson are experts in this field and if you are looking to get metallurgical testwork done in an efficient and thorough manner, we urge you to make use of their services based in their ISO9001:2008 certified metallurgical testwork laboratory in Southern Africa. During a visit to most hotels in Africa, you will invariably notice clumps of people huddled in close and concentrated meetings, all very deeply intent and focused. They are part of the mining fraternity (geologists, process engineers, exploration experts, metallurgists and mining engineers to name a few). The continent has attracted extreme interest from all corners of the earth and within because of its huge, and in many cases dormant, surface and underground resources. Africa is endowed with a huge array of minerals and to enter into that realm would take up a huge chunk of time. Suffice to say, the interest is there and many projects are being planned, implemented and commissioned.

Mining today is an applied art; the business model must be efficient & worthwhile, taking into account all aspects such as preliminary mineral and metallurgical testwork, resource targeting & evaluation, environmental and social impact, water and power needs & availability, return on expenditure etc. Old-time miners will easily take a seat and proclaim, “You need this and that,”, and in many cases would-be miners and active miners take advice from these revered men of yore, going ahead blindly and often boldly, only to find the recommended process equipment does not suit the actual ground conditions and feed material. White elephants in the form of abandoned plants can be found all over the African continent, rusting sentinels that have a tale to tell.

There is an up-to-date metallurgical testwork laboratory (www.peacockesimpson.com) situated on the continent where material can be submitted for actual amenability testwork to ensure that before a project is undertaken, the ‘ore does the talking’. A great mining cliché is: ‘Let the ore dictate the terms’. The metallurgical testwork laboratory boasts the latest state-of-the-art equipment, such as XRF/digital microscope technology, not to mention the Knelson Gravity testwork modules. The metallurgical testwork laboratory has recently commissioned a 2 litre DESWIK ultrafine grinding mill. This facility also includes a MALVERN mastersizer for determining ultrafine particle distributions and a cyclosizer for producing samples of ultra-fine classified products.

This metallurgical testwork laboratory is unique in Africa and represents a major advance in local testing capability. Combined with the other aspects of the lab, such as cyanidation and flotation, complex metallurgical problems can now be tested locally. This capability will be particularly important in investigating refractory gold ores and calcines as well as unlocking additional values from tailings stockpiles.

Using this world-leading technology hub, mining concerns can rest assured they will be given the red, orange or green light before proceeding to process specification.

A popular process that has evolved recently is scrubbing available resource to liberate minerals within the loose matrix which can be recovered by gravity, alleviating the use of chemical processing that takes up a lot of time, money and environmental issues. The Rubble Guzzler (RG) (a large-diameter scrubbing drum with integral trommel and screen) range of scrubbers represented by APT has taken not only Africa by storm but others to boot.

Advantages of the RG process are many. A few examples are:

• easy maintenance and easy operation
• easy installation
• quick return on capital expenditure
• low operating expenses
• chemical-free process
• high recovery efficiency
• low-energy requirement (usually below 2 kWh/t, as opposed to conventional mining process of milling and crushing that use in excess of 4 kWh/t
• low labour requirement

APT has recently offered the option of combining a unique fine-crushing module with the scrubbing plants. Consequently, if the washed oversize is carrying well it can be crushed and re-introduced to the scrubber feed system. This is proving a very popular addition to the range and by using up-to-date technology, APT has en-sured the energy required for these modules is kept to the absolute minimum.

Once a resource is ready and proven to be amenable, and there is enough raw water available onsite, the scrub/gravity or scrub/crush/gravity-recovery process plant can be implemented with the minimum of effort. Gone are the days of setting up mine administration centres, mine clinics and mine staff complexes that sprawl over the countryside as well as huge milling houses and engineering departments to perform just 20 t/h. The RG plants’ minimal footprint for 20 t/h is miniscule – only 100 cubic metres.

Startup is short and sweet, and mineral recovery is instant. What more could a miner want? The RG scrubbing plants cater for many different minerals, the most common being the big five: gold, chromite, tantalite, tin and silver.

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Low Energy Process Plants for use on Mines

*Low energy process plants have been developed further through rigorous research and development trials since this article was written many years ago. Browse our website for more the latest options available in the mining industry, some smaller options are available for purchase on our online store.  Process engineering company Appropriate Process Technologies (APT) has designed a simplified circuit for its low-energy processing plant that uses batch and continuous Knelson concentrators to capture elemental liberated gold, as well as sulphide carriers, reducing energy and space requirements. A number of process advantages were included in the design to improve the efficiency of the plant, with the emphasis on the reduction of energy use rather than solely on percentage recovery, says APT project coordinator Susan McMillan.

APT's low energy process plants include an efficient impact mill. This is used rather than a ball mill. It crushes the ore and, although the general particle size is much coarser, the initial degree of gold and sulphide liberation is high, owing to the fractures formed on grain boundaries.

“This early liberation can account for most of the value contained in some ores, but a small secondary mill is included to further reduce the coarse and dense portion in the primary tailings,” she says. "The elemental gold is recovered gravimetrically directly to the gold bar. The sulphides, being coarser, can be extracted using simple vat leaching," she adds.

The low energy process plants system operates at as little as 8 kWh/t as opposed to around 50 kWh/t used by a comparable conventional ball mill or carbon-in-pulp process.

"The small and compact system can be operated down a mine, with the tailings being pumped out rather than the ore being hoisted," McMillan explains, "again reducing the energy used by the whole process."

"Some ores are not suited to low-energy processing, but the system can supplement existing conventional processing by reducing the grinding energy, and also by recovering a portion of the gold before conventional processing,” she concludes.

APT designs low energy process plants that use early liberation techniques

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New Range of Scrubbers for African Market

With over 30 of its RG scrubber plants installed in Africa, modular mining plant manufacturer Appropriate Process Technologies (APT) is continuing to develop its RG range of rubble scrubbers. “We are consistently supplying complete modular process plants in the 6-t/h to 20-t/h feed rate range but market trends have shown that there is a gap available for 80-t/h plants of the same nature. With this in mind, we have developed the RG500 scrubbing plant, which is being put through its paces right now, at an undisclosed site, on a trial basis before its launch,” says APT consultant Kevin Woods.

Also eagerly awaited in the scrubber range is the arrival of the RG2500 in the near future. The RG2500 will be capable of processing 250 t/h of feed. APT has also been asked to develop RG scrubber plants with diamond pans and jigs.

The RG scrubbers are a process solution that increases the disintegration of placer and alluvial clays and releases bound minerals, normally for subsequent gravity concentration. The RG scrubbers range was developed specifically to confront and overcome the problem of African clays, which do not respond well to simple trommel scrubbers as used on loose glacial placers in the northern hemisphere.

The RG scrubber can be combined with a number of downstream processing options based on gravity separation that disintegrates the feed to release the valuable components, such as gold, chromite, tantalite, tin, diamonds and gemstones, as well as heavy sands, which are then recovered easily and economically. The combination of the RG60 scrubber with the Knelson MD12 is reported to disintegrate even the most stubborn clays by the autogenous scrubbing action in the drum section, proving suitable for the processing of eluvial and alluvial ores, particularly smaller high-value deposits.

APT recently delivered an RG60 gold plant, coupled with a Gemeni table and Knelson MD12 concentrator, to an Angolan gold project. The plant assisted exploration efforts with real-time visual assessment of gold production from target areas. An RG200 scrubbing plant operating at 20 t/h with a Knelson MD20 concentrator on board was later installed after initial results from the smaller plant proved promising.

“The RG200 plant, in Angola, was assembled and running on site within 24 hours and both machines are meeting the requirements on a daily basis,” adds Woods. The company also installed an RG200 scrubbing plant with a Knelson CD20 and Gemeni table at an alluvial platinum claim, in North Africa, in November 2008.

Other recent installations include RG200 chromite fines plants, on the Great Dyke, in Zimbabwe, feeding up to 20 t/h and recovering about 10% of feed as saleable 51% chromite fines. These particular plants cater for rich eluvial chromite fines found in hot-spot, outwashed plain areas below the Great Dyke ridge. These were supplied with water monitored sluice-feed systems.

Bauxite mine Minas Alumina, in Mozambique, was one of the earliest mines to install an RG200 scrubber with a small vibrating screen, which allows for the separation of clays from saleable material.

“The RG scrubber has revolutionised the mine,” says Minas Alumina mine owner John Meikle. He adds that Minas Alumina won the 2007 Exporter of the Year award, in Mozambique, largely as a result of the RG scrubber.

APT is currently installing an RG200 gold recovery plant at a large mining house, in the Democratic Republic of Congo. The company continues to build a number of scrubbing plants for various applications for the local, regional and global market.

“The RG plants have, in many instances, replaced conventional mining plants with their inherent baggage. The instant payback mining assists projects by ensuring the bottom line is achieved quickly and profitably,” says Woods.

An advantage of the RG scrubbing plant over conventional trommel scrubbers includes its mobility, alleviating the concern of fixed-foundation plants that diminish returns on return load transportation. The RG plant can be translocated once an area has been processed.

“This mobility, coupled with low power input, low carbon impact and a chemical-free process, ensures that miners can set up environmentally friendly production facilities on a same-day basis, as opposed to conventional plants that take weeks and, in most cases, months,” says Woods. He notes that the low energy allows for on-site power generation, freeing the operation from the grid.

The RG scrubbing plants, with multiple additions, can also cater for multifaceted mining approaches. The plants are easy to operate, require simple on-site erection and provide chemical-free recovery.

“Factors such as low capital expense costs, quick start-up, low energy requirements, low operating expenditure costs, a high productivity rate and easy translocation are factors paramount to the success of a venture, and each of these is encompassed within the RG scrubbing concept,” says Woods.

“We have now placed over 30 RG scrubber plants into Africa, and while APT is an African concern, it caters not only for African mining. We are spreading our wings further afield, with orders under way for plants in South America and Indonesia,” concludes Woods.

APT designs scrubber plants that can handle high clay contents and large rock-loads.

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Plant Manufacturer Expands into Africa

Mining plant manufacturer and engineer Appropriate Process Technologies (APT) has expanded its operations by installing several of its RG scrubber range plants in Angola, Ethiopia, Zimbabwe, the Democratic Republic of Congo (DRC) and Mozambique. APT is the designer, developer and supplier of the RG range of rubble scrubbers. The RG scrubber range was developed specifically to overcome the problem of tenacious African clays, which do not respond well to simple trommel scrubbers, like those used on loose glacial placers in the northern hemisphere. These mining plants are available at a variety of sizes.

The RG scrubber can be combined with various downstream processing options based on gravity separation. Minerals such as gold, chromite, tantalite, tin, diamonds, gemstones, and heavy sands are recovered easily and economically. Lead times are short.

The scrubber is, therefore, a process solution which increases the disintegration of placer and alluvial clays, and releases bound minerals. APT sold an RG60 gold plant, coupled with a Gemeni table and Knelson MD12 concentrator, to a mine in Angola, which assisted exploration efforts in the visual assessment of gold production from target areas.

In addition, an RG150 scrubbing plant, operating at 20 t/h with a Knelson MD20 concentrator on board, was duly installed upon good initial results. The manufacturer’s other installations include an RG150 chromite fines plant on the Great Dyke, in Zimbabwe, which feeds up to 20 t/h and recovers about 10% of feed as saleable chromite fines.

In addition, Minas Alumina, a bauxite mine in Mozambique, installed an RG150 scrubber with a small vibrating screen, which separates clays from saleable material. Minas Alumina mine owner John Meikle states that the RG scrubber has revolutionised the mine, after the mine won the prestigious Exporter of the Year award in Mozambique, in 2007.

APT's RG scrubber has a cutting-edge patented design for maximum mineral recovery.

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For more on mining plant manufacturer company APT, please visit our website where we now have a range of these scrubbers available for online purchase. You are also welcome to contact us regarding any questions you may have.