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MEI Online: Plant Operation News: Africa: February 16th 2005


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:: SENET to Commission Wet Gold Plant in Africa

The CIP gold plant at Siguiri Gold Mine in Guinea, Africa, to be commissioned by leading project management company, SENET, has a design throughput of 11.5 million tons per year.

SENET was responsible for the design, engineering, procurement, construction and commissioning of the CIP (carbon in pulp) plant at Siguiri, which will replace part of the heap leach operation at the mine. Anglogold Ashanti decided to install a CIP plant and reduce operating costs.

Within the CIP plant itself, one of the biggest challenges was posed by the size of the interstage screens, which are almost double the size of the biggest built to date. The ore treated is low grade and in order to make it viable, the plant needs to treat a high tonnage of ore per month. As a result, all the equipment is larger than usual.

The CIP plant at Siguiri has 15 Anglo Mineral Process Separating (MPS) pumping (P) interstage screens complete with stainless steel wedgewire baskets.

The MPS(P) interstage screen is equipped with an impeller that pumps pulp to the next adsorption tank. This pumping feature allows the adsorption tanks to be located on the same horizontal elevation, resulting in the adsorption circuit being placed on a flat platform.

Kemix supplied the MPS(P) interstage screens, and Multotec supplied the wedgewire baskets for these screens.

Gavin Veale, managing director of Kemix, explains that the wedgewire basket is at the MPS(P) interstage screen as this is the medium through which the carbon and pulp is separated.

"The mechanically driven screen has pulse blades moving around the stationary basket, causing a pulsing action that facilitates the flow of pulp through the basket. The pump impeller lifts the pulp, while the pitch blade turbine keeps the pulp in suspension within the basket," he continues.

"The most important element is getting the pulp through the screen as efficiently as possible, explaining the fact that the wedgewire basket is critical. Also important is the profiling of the wedgewire and the robustness of the screen. The screen is the interface and the largest wearing item on the interstage screen, " Veale says.

The stainless wedgewire basket is manufactured in South Africa by Multotec at its facility in Spartan, and a wide range of apertures and profiles is available.

"Stainless steel ensures long life even in abrasive and corrosive applications and the wedgewire cylinders supplied for the interstage screens at Siguiri were designed with high release angles to ensure minimal pegging, " Roy Roche, of Multotec explains.

"The type and size of profile as well as the slot width and materials were chosen to suit the mechanical and process requirements at Siguiri. The close tolerances on the aperture sizes ensure an accurate cut point and minimal blinding," he says.

Kemix is regarded as the world leader in adsorption design technology while Multotec is regarded as a leader in the manufacture wedgewire screen cloth. It is significant then that the interstage screens ≠ at 20 m≤ - are the largest ever made by Kemix and similarly the wedgewire baskets the biggest ever manufactured by Multotec.

Kemix also supplied a carbon regeneration kiln to the Siguiri Gold Mine. This 750 kg per hour diesel fired kiln will be used to reactivate or clean the carbon before it is re-used in the CIP plant.

Also included in Multotecís scope of supply are a hammer cross-belt sampler, a leach feed launder cross-stream sampler including a primary launder sampler as well as a secondary vezin sampler, an in-line tailings sampler which is a cross cut pipe gravity-fed sampler with a secondary vezin sampler, a ball mill trommel for screening and vibrating screens with polyurethane panels.

The Multotec hammer sampler is used to sample R.O.M. product with a top size of 300 mm from a feed conveyor with an average throughput of 2000 tph, giving a sample increment of 173 kg.

"The CIL leach feed launder sampler is used to sample the gold slurry after milling. The feed launder to this sampler is two metres wide handling a flow rate of 1200 m3/hr. The primary sampler takes a cross cut sample at the launder discharge. This sampler, with an increment of 12 litres of gold slurry then goes through a secondary vezin sampler with multiple cutters, where the sample increment is reduced to .36 litres to make it an ergonomically-sized final sample per shift of approximately 20 litres," says Rolf Steinhaus of Multotec Process Equipment.

The large tailings sampler is a 900 mm nominal bore two-in-one pipe sampler. Use of a two-in-one sampler ensures that there is no separate rejects handling from the secondary sampler, as the rejects report back in to the main pipeline. The flow rate is 1200 m3/hr of gold slurry, giving a final sample of 20 litres per shift once again. This is the largest pipe sampler manufactured by Multotec to date and will enable accurate sampling of the CIL tails.

Warman slurry pumps, supplied by CH Warman Pump Group, are also operating within the plant, with support coming from this Groupís representative in Ghana.

The pumps are driven by WEG electric motors, well known and well respected for their efficiency. Ninety-five percent of the motors in the plant were shipped directly from WEGís manufacturing facility in Brazil; the interface on the mine was facilitated by the sole WEG distributor in sub-Saharan Africa, Zest Electric Motors and Drives.

The project posed a number of challenges for Senet in terms of logistics. With the site located some 800 km from the capital of Guinea, Conakry. Most of the equipment was shipped via Richards Bay to Conakry in chartered vessels since normal shipping lines go via Europe to Guinea. The decision to use chartered vessels saved considerable time, which made up for the increased transport costs.

Commissioning of the CIP plant will commence in the first quarter of 2005 with all suppliers involved in the process. Multotecís branch in Ghana will provide optimum levels of support with spares, technical assistance and servicing on an ongoing basis.

"As South African companies move into Africa, we are able to take our skills and transfer our technology to countries such as Guinea, helping them develop and grow their economies," Roche concluded.




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