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Focused on processing in Africa’s artisanal mining sector

4th November 2016

By: Robyn Wilkinson

Features Reporter

  

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While many large mining companies in Africa are processing size- able mineral deposits, there is also a vast small-scale and artisanal mining sector, requiring solutions tailored to their processing needs, such as those supplied by mining equipment supplier Appropriate Process Technology (APT).

APT CEO Kevin Peacocke notes that the artisanal sector cannot financially sustain a formal approach to mineral processing, which requires significant infrastructure and extensive technology. APT, thus, offers solutions that are tailored to the processing of smaller deposits, which require less capital investment and are easier to initiate, even in remote areas.

The company’s TriTank cyanidation carbon-in-leach (CIL) tank system for gold processing has proven especially popular in the African small-scale and artisanal mining market since its introduction in 2013, as, Peacocke notes, the engineering of the TriTank has been greatly simplified to make processing by small, less-sophisticated operations possible, catering to smaller operations processing up to 1.5 t/h.

The tanks come complete with interstage carbon screens and airlift pumps, making daily movement of carbon exceptionally easy and straightforward. The offering can also be expanded to include the necessary pre-ball milling to ensure the material is fine enough to accept into the tanks.

The TriTank range includes the TT20, with a solids throughput of 1.5 t/h; the TT80, with a capacity of 6 t/h; the TT200, which can handle 15 t/h; the TT300, with a 23 t/h capacity; and the TT500, which has a solids throughput of 40 t/h. These capacities are in relation to an eight-hour residence time.

Since its initial introduction, Peacocke says, the TriTank’s interstage screening and agitation mechanisms have been improved and a degree of automation is now possible in larger plants. “The screens are a wedge design, resulting in a self-compensating action where more screen area comes into play as needed. The agitators are now driven directly by geared motors, as in conventional CIL systems, rather than belt driven systems, resulting in less maintenance. Plants from 40 t/h upwards can have the daily carbon airlift function automated, not only relieving about five hours of labour, but also delivering a more accurate result.”

APT is the technology developer and the engineering, procurement and construction manager for CIL projects that are due to come on line in 2017 at new small-scale and artisanal gold mining operations in remote areas in Sudan, the Democratic Republic of Congo (DRC), Zimbabwe and India.

Peacocke highlights that such projects require a high level of efficiency at an affordable price, with minimal environmental impact.

The TriTank system has been “very well received”, says Peacocke, noting that APT has supplied the solution to small-scale and artisanal operations in Zimbabwe, Tanzania and Kenya with great success. “We have also had discussions with some large mining houses in South Africa, Zimbabwe and the DRC, as well as in the Middle East, which have seen a need in their operations for smaller-scale CIL plants.”

Peacocke explains that these plants enable larger companies to start projects with lower initial capital expenditure (capex) and with far shorter lead times. The smaller plant can, moreover, be specifically tailored for higher-grade zones of the orebody for an immediate return and, in a more intensive fashion, as dictated by the metallurgy.

How It Works
With the TriTank system, a cyanidation reaction is carried out in triangular-shaped tanks, rather than conventional circular tanks, to recover gold from fresh ore and tailings.

The triangular tanks are arranged in a hexagonal system comprising six small tanks. The hexagon configuration requires 27% less ground space than six traditional circular tanks of equivalent volume, also impacting posi- tively in terms of foundations, bunds, decking and cable and pipe runs, among other factors.

“This arrangement also enables far more efficient slurry movement and provides better reaction rates. The result is a better recovery rate and less residence time using a smaller plant, translating into a cost-efficient operation,” states Peacocke.

With the residence time being shorter, there is also less cyanide slurry in active use than in a conventional system, he notes, adding that APT can supply TriTanks with a nontoxic lixiviant, should the customer prefer. However, Peacocke points out that, should cyanide be used as a lixiviant, it is easy to surround the system with a protective bund wall to contain any spillages, as the TriTank is so compact.

Vigorous testing of the TriTank has shown that the design allows for better slurry mixing than traditional solutions, leading to superior solids suspension and gold dissolution, as well as higher dissolved oxygen levels. Peacocke points out that the well-sealed motor design also reduces slurry contamination, owing to oil leaks, further enhancing metallurgical performance. The mixing mechanism in the tank, which does not rely on baffles, also produces better leach kinetics for smaller plants.

The smaller systems are shipped in a 40' container and the larger tanks, up to 500 m3, are shipped in prerolled sections in 20' containers to allow for easy on-site erection. The TriTank requires less construction than other systems and can also be relocated to multiple sites, reducing mine-to-process costs.

While there are other cyanidation systems with six or more separate tanks available from other mining equipment suppliers, Peacocke notes that the TriTank system is modular and much easier to transport, erect and operate than competitor products.

“Build time of the TriTank system is significantly faster than other systems on the market. The smaller 1.5 t/h TT20 model can be operational within two days of delivery to site and the larger TT500 may take eight weeks, which is far less than conventional build times for these systems.”

Edited by Tracy Hancock
Creamer Media Contributing Editor

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