Ruashi II is a big step for Metorex, a much larger project than Ruashi I, which produces 10,000 tonnes a year of copper in concentrate for processing by the company’s Sable facility at Kabwe in Zambia.
Ruashi, which has a total capital cost of US$250 million and is building up to a headcount of some 800 people, is an open pit oxide ore copper-cobalt project located near Lubumbashi. It will use solvent extraction electrowinning (SXEW) to produce copper cathode and will also produce cobalt hydroxide. The Ruashi II SXEW plant was scheduled to be commissioned towards the end of the July, which represents only a slight delay over the planned timing.
“The reason for the delay is that we wanted to have a dedicated fire fighting system in place for the SX plant, and in essence we took the delay to ensure we put in the emergency power supply for the fire fighting system,” Metorex project manager for Ruashi II, Trevor Faber says.
Ruashi II’s plant is not the first SXEW plant Metorex has operated and Faber says it has taken lessons from the Sable operation, which hosts Metorex’s first SXEW plant.
From July 2008 Ruashi II will start to feed run of mine (ROM) ore into the plant. The plant will build up to about 800 tonnes of copper in August, about 1,100 t in September and ramp up to 1,600 t in October.
The Ruashi ore body has a 34 million tonne oxide reserve, sufficient for a 20 year life of mine and the only drilling underway is infill drilling being done for short term grade control. “For now, our focus is on firming up the grades, which across the ore body range from 2% to 6% copper, for operational planning. However, we have identified sulphide deposits, which we will investigate in about two to three years time,” Faber says.
The Ruashi mine itself consists of three pits, two of which will merge, though only because of the scale of the operation. Ruashi does consist of three distinct copper ore bodies. The stripping ratio over the life of mine will be about 2.7:1 and mining will take place at a rate of 160,000 tonnes per month (tpm). The average copper grade is 3.2% while the cobalt grade is 0.3%. At Ruashi the copper mineralisation starts at 14 – 15 metres below the surface whilst cobalt mineralisation starts at some six metres below the surface.
Because Ruashi has been mining in an historical pit, Pit 1, it is already 25 metres below ground level. This mining is being undertaken by Mining Company of Katanga, a local mining contractor. The mining fleet includes three excavators, two 50 tonne machines and an 80 t unit, as well as nine Bell B40 articulated dump trucks. The fleet also includes four Hitachi 60 tonne rigid body trucks as well as the typical ancillary vehicles such as bulldozers and graders. Pre-stripping is underway for Pit 2, and some of the material from that is being stockpiled until Ruashi’s cobalt plant is completed. The third pit will only be mined from 2011.
“Grade control is important and the mine gives us the flexibility of high and low grade zones. Instead of direct tipping at the ROM pad, we blend the various ore material, which enables us to control the feed grade into the plant to ensure we efficiently manage our use of reagents.”
The mills will process 140,000 to 160,000 tpm. At many operations the mills represent the bottleneck, but that is not the case at Ruashi where the copper electrowinning cell-house represents the bottleneck. “The civil infrastructure has been designed for the cell-house to expand if needed,” Faber says.
Ruashi’s cobalt plant, to be completed in October, will produce some 3,500 tonnes of cobalt metal a year contained in hydroxide. “The reason we went for the cobalt hydroxide route as opposed to the conventional cobalt in carbonate route done by most other operations was due to an environmental issue.”
Copper is leached out of solution by sulphuric acid at a pH approaching 1, and then plated onto electrodes through electrowinning. However, the cobalt precipitates out of solution at a pH of 7.5 and to achieve this, the pH of the solution must be raised. Lime is added to the solution from which the copper has been leached, which raises its pH to 3 or 4 at which point metals such as iron and aluminium precipitate out. The cobalt remains in solution and the next stage requires raising the pH again. However, one cannot use lime to take the pH to 7.5 and the standard approach has been to use sodium carbonate (Na2CO3). This reacts with the cobalt to form cobalt carbonate (CoCO3) and the sodium, in other words brine, is left behind.
“It would be problematic should this brine, which is very osmotic and also forms a very visible crust, migrate to the water system. Particularly taking into account that fishing is an important industry in the Lubumbashi area, we could not take the risk of contaminating the water system. Instead, we will produce cobalt hydroxide. Our off-taker Jing Xuan is willing to accept this intermediate product.”
The Ruashi II plant will have a copper recovery rate of 80% – 85% and a more than 70% recovery of cobalt in cobalt hydroxide form. This is compared with the 75% copper in concentrate and 45% cobalt in concentrate that is taken to Sable from Ruashi I.
Ruashi is to be followed by one of three projects, Kinsenda, (the other two being Musoshi and Lubembe), which Metorex got operational control of as a result of it gaining a 51% controlling stake in Copper Resources Corporation (CRC). Camec also has a large shareholding in CRC, which owns 80% of Minière de Musoshi et Kinsenda (MMK) with the other 20% of MMK owned by state company SODIMICO.
The three projects are located some 120 km away from Ruashi, and are across the border from Zambia, not far from the town of Chingola. Kinsenda is a sulphide ore body with 4.0% to 4.5% copper content. Metorex is looking at a sulphide flotation plant similar to that at its well established Chibuluma mine in Zambia, and which will produce some 30,000 tonnes a year of copper.
MDM Engineering, the EPCM contractor for the Kinsenda concentrator project, has completed the front end engineering design, with the definitive and detailed engineering still to be done. The mills and flotation equipment have already been ordered and Metorex will undertake the mining itself. Kinsenda’s operating levels will be between 285 and 400 metres below the surface, accessed via two decline shafts, and a vertical shaft for personnel access. “We will add a conveyer belt in one of the declines and have to do the geotechnical and civil work, bring in drill rigs and loaders and do the shaft development work, as well as tidy up the old steelwork. We will install a milling circuit and float cells and then we need to open up the reserves. The idea is to run half the plant as we continue with reserve development.” Metorex has ordered six to eight Sandvik drill rigs and LHDs.
Kinsenda will require the pumping of 50 million litres of water a day, and Faber says it has installed a pump station with five pumps, three operational and two on standby. Overall the capital expenditure for the plant will be US$65 million with another US$120 million to be spent on re-establishing the mine. The aim is to produce the first concentrate by July 2009.
The refurbishment of the Musoshi operation is also being planned but much of that ore body has been depleted by past mining activities. However, Musoshi is producing 15 tpm of cobalt, which covers Metorex’s running costs of the CRC projects. Metorex employs some 500 people at Musoshi and a similar amount at Kinsenda.
Of a higher priority than Musoshi is the Lubembe deposit which holds good potential for an oxide ore open pit mine. There are two drill rigs on site and an 18,000 metre drill programme is going ahead.
Faber puts the expected sequence of projects after Ruashi, as Kinsenda which has been given the go-ahead, then the Lubembe project and finally Musoshi.
Thus taking Ruashi’s planned 55,000 tpa of copper, and Kinsenda’s likely 30,000 tpa it would only take Lubembe at 15,000 tpa for Metorex, as operator, to be producing 100,000 tpa of copper out of the DRC by about 2010.