INCO R&D: Goro Laterite Development

New Caledonia is the site of Inco’s newest opportunity. The French island territory in the South Pacific is the home of the exciting Goro deposit. Not only is this the world’s highest grade laterite nickel deposit, but the project also represents Inco’s largest-ever investment in a new development.

Two-thirds of the Earth’s nickel reserves are found in laterite deposits. They are amenable to relatively cheap open pit mining, unlike sulphide reserves in Canada that are found at increasing depths. Laterites are red, orange, ochre or yellow, heavily weathered ultramafic formations found in the tropics. They were originally composed of iron and aluminum silicates, but these have been weathered, and leaching has removed the silica and many other elements. Laterites generally contain high ferric oxide.

The laterite nickel ore at Goro is composed of two layers–limonite and saprolite–between a cover of leached material and the bedrock below. The 10-20-m-thick cover has its own two layers: brittle iron oxide crust covers a high-hematite zone. Beneath these is the 10-m-thick limonite layer, which grades about 1.5% Ni. Then there is a cobalt- and manganese-enriched zone. Below all this lies the 5-m-thick saprolite zone, high in nickel (usually 2-3%) and magnesium. Within the saprolite layer are small boulders of unweathered bedrock that are unsuitable for recovery. The limonite-to-saprolite ratio at Goro is about 2-to-1, and the ore types will be blended for extraction.

Proven reserves in the initial mining zone at Goro are 42 million tonnes averaging 1.41% Ni and 0.13% Co. Probable reserves in the same zone are estimated at 12 million tonnes at 1.94% Ni and 0.08% Co.

Inco is confident that the US$1.4-billion investment will create an efficient, low-cost producer. First, Inco has a century of innovation in nickel mining and extraction. Second, the company spent US$50 million to build and operate a pilot plant to prove its pressure acid leaching technology at the Goro site.

“Professionally, it’s a very exciting project. It will be the largest single investment in a nickel project in the history of the world,” says Goro Nickel’s chief operating officer Ric Stratton-Crawley. “Arguably the future of nickel is in laterites, in the long term certainly. You feel that you’re part of history, and the scale and magnitude of the project is just exciting.”

Three Australian laterite developments in the last decade have run into problems, principally in processing. Their orebodies are slightly lower grade than Goro, but they are much closer to infrastructure. None of them built an integrated pilot plant to test their processes.

“The key thing that they were missing was a major partner with nickel experience,” Stratton-Crawley believes. “They had money, they had orebodies, but they didn’t have the technical experience. We’ve been working on the metallurgy of the Goro nickel project for over 10 years, so we haven’t come to it overnight. It doesn’t hurt to be in the second generation of projects if you can learn from the first generation. It at least tells you what not to do, even if it doesn’t give you too much information on what to do.

“History has, of course, demonstrated that cautiousness and prudence are the order of the day in new technologies. The investment we made in our pilot plant will pay off,” he adds. [continued on page 67]

Unique Extraction Process

The Goro metallurgical work began at Inco’s research centre near Toronto, where it was developed and tested at bench scale and in a miniplant. Part of the process was pilot-tested at 1/80,000 scale at Inco’s Port Colborne facility. Then the pilot plant was built to 1/1,000 scale in New Caledonia where it operated from October 1999 through April 2002. Locating it on site gave access to all ore types and exposure to local climate.

Inco’s patented new process for nickel and cobalt recovery is built around pressure acid leaching (PAL) and solvent extraction (SX). The commercial plant should have recoveries of 93% for nickel and 91% for cobalt. There are six steps to the nickel recovery process.

The limonite, a moist, clay-like material, is pulped. The hard saprolite must be crushed and ground to form a slurry, while rejecting barren oversize material. The two materials are blended to create leach feed.

PAL is carried out at very high temperature (270*C) with the advantage of shortening leach times and reducing the number of autoclaves needed.

The leach solution is passed through a counter-current decantation (CCD) circuit to separate the residue.

The nickel- and cobalt-laden solution is purified by raising the pH to precipitate impurities.

The solution passes through the primary SX circuit using a novel reagent to produce a pure nickel/cobalt/zinc chloride solution. The zinc is then removed by an ion exchange circuit, and the nickel and cobalt are finally separated from the resulting chloride solution in the secondary solvent extraction circuit. At the end of these processes, two pure chloride solutions of nickel and cobalt are obtained.

The pure nickel chloride SX solution is subjected to pyrohydrolysis at over 800*C, similar to fluid-bed roasting. This produces nickel oxide and also regenerates the hydrochloric acid used in the SX circuit for stripping.

“I have visited the pilot plant a few times and seen the ‘baby’ grow,” Inco’s director of process research, Eberhard Krause, told CMJ. “There have been no big surprises at all. Testing at the pilot plant has allowed us to make some changes in the equipment selection. For example, originally for the solvent extraction process we were thinking of using conventional mixer-settlers. But more recently, pulsed columns have been applied very successfully, particularly at Olympic Dam in Australia. That is a technology that is cheaper than the conventional mixer-separators.”

The pulsed columns solve another problem. Krause continues: “The solvent extraction reagent that we are using oxidizes if you don’t treat it property, so we have to exclude air as much as possible. Pulsed columns lend themselves better to exclude air than the conventional mixer-settlers. This was one of the things that could not be tested properly in the small mini-plant.”

For the pilot campaign, Inco has hired and trained many New Caledonians who will be the future commercial plant employees. One of the goals is to maximize employment for local people.

“I think that unless there’s a very specialized area that we can’t supply immediately there, the employees will come from New Caledonia and we will train them,” says Stratton-Crawley. “There’s no quotas or anything like that; it’s just the right thing to do.

“We’ll bring in some people with gray hair from our existing operations if they’re available, or from other operations to supplement and mentor the local employees. But the intent is that our work force will be New Caledonians.”

The local company created to build and operate the project is known as Goro Nickel S.A. (GNi). Inco holds 85% of GNi, and a French government agency, Bureau de Recherches Gologiques et Minires, holds the other 15%. Inco is currently seeking a partner to take over BRGM’s share and up to 30% of the total project.

The government of New Caledonia is fully onside in encouraging development of the Goro orebody. It has promised a 15-year, 100% tax holiday, followed by a five-year, 50% tax holiday. Inco has received preliminary approval from the French government covering financing of qualifying Goro project expenditures of US$350 million, under the country’s program of financial support for investments in French Overseas Territories.

What the Goro Project Involves

The Goro project is located on the southeastern tip of New Caledonia, about 1,500 km east of Australia. It is ideally situated to reach growing markets in Taiwan, Korea, China and other Asian countries. The major components are the open pit mine, adjacent feed preparation plant, processing plant, tailings impoundment, port facilities, and accommodations for the workers. The project team includes veteran Inco employees a
nd an engineering, construction and project management joint-venture group from Bechtel of the United States and Technip of France, in association with Hatch Associates of Canada.

Now that work has begun in earnest, plant start-up is anticipated in less than three years. Environmental, operating and construction permits are expected in the first quarter of this year. Construction has begun on infrastructure and the plants. Commissioning is set for the last half of 2004, and commercial production should begin before the end of that year.

The pit will be a conventional truck and shovel operation using 11-m3 excavators and 97-t trucks for overburden removal and limonite ore recovery. Smaller equipment–5.6-m3 excavators and 53-t trucks–will mine the saprolite ore and the irregular interface with the basement rocks.

The plan is to mine the pit in a series of benches from the west to the east, following the basement rock from low to high. This will facilitate pit drainage and allow in-pit storage of the overburden, and ultimately tailings. Roughly 12 million tonnes of material will be moved each year. Overburden will be segregated and stockpiled if it is suited for use during revegetation or for construction of haulage and other roads.

The feed plant is being built northwest of the mine. The two kinds of ore will be trucked from the pit to the plant. Limonite and saprolite will be stockpiled individually and pulped by crushing and ball milling in separate circuits. The slurries will be stored individually in agitated tanks but combined as they are pumped through a 700-mm diameter pipeline to the processing plant about 4 km to the southwest.

When the slurry reaches the processing plant it will be preheated and thickened to 32% solids. It will then be heated to 270*C and enter three parallel autoclave circuits where PAL will take place using sulphuric acid. This will be followed by five flash stages to let down the pressure and recover heat.

The leach residue will be washed in six sequential CCD thickeners. A process stabilization pond will provide surge capacity following the CCD circuit. This will allow the downstream circuits in the plant to operate continuously when varying numbers of autoclaves are in service.

Two stages of solution purification follow. Excess acid will be neutralized and the pH will be raised to precipitate impurities, which are then removed by thickening. The solution will be cooled and clarified, and fed into several sand filters to remove any residual solid. Five parallel ion exchange circuits remove the last trace amounts of copper contained in the solution.

The next stage is solvent extraction. Nickel and cobalt will be separated from impurities using Cyanex 301 as the reagent in several pulsed columns working together, seven for loading and eight for the stripping. Cyanex is a new reagent that is selective for Ni and Co over Mn, Mg and Ca, without the addition of a neutralizing agent. The reagent will be regenerated using a proprietary process using nickel powder. Two parallel ion exchange circuits, each comprising three columns, will remove trace amounts of unwanted zinc remaining after the primary SX step. The secondary SX step will selectively extract cobalt from solution, again using two pulsed columns, one for loading and one for stripping. The organic extractant will be treated to remove trace impurities.

Nickel will be recovered from solution using pyrohydrolysis. The solution will be first concentrated in a pre-evaporator. It will then go through three kerosene-fuelled modules to create a granular NiO product. Nickel oxide will be cooled and packed into bulk containers or 2-tonne bags for shipment.

Cobalt will be recovered from solution by precipitating CoCO3 with soda ash in a series of three agitated tanks. The precipitate will be thickened, filtered and washed on a belt filter before packing in 2-tonne bags for export.

The pH of the effluent and waste streams from the processing plant will be first raised to 4.0 using a limestone slurry in an effluent treatment circuit located at the plant site. The slurry effluent will then be sent via pipeline to a dedicated effluent plant located close to the tailings area. This plant will precipitate heavy metals as hydroxides by first neutralizing the incoming effluent at pH 7.8 using a lime slurry. The resulting slurry will then be thickened to produce a paste that will be piped to the tailings area. The supernatant solution from the thickening will be neutralized to a minimum pH of 8.3 and then thickened and clarified to produce a clear and environmentally safe effluent. The solids generated during this last neutralization will be recycled to the first stage.

The tailings management facility is located near the mine, on its southwest rim. Tailings will be pumped to it through a pipeline that parallels the one from the feed plant to the processing plant. They will be impounded behind a dam in an area of flat valley floors surrounded by steep hills. Over the initial 20-year life of the project, 117 million m3 of material will be contained in this location. The neutralized effluent from the effluent treatment plant will be piped out to sea and released through a diffuser.

As construction gets underway, closure plans are also proceeding. They will satisfy Inco’s high environmental health and safety standards and respect local laws and the public interest. In 1997, GNi established a greenhouse to test indigenous plant species for their suitability for revegetation. Use of local plants is now an integral part of Goro’s plans for revegetating mined areas.

The Goro project has much to recommend it besides being the only major nickel development underway at this time. It is close to markets, the orebody is very large, the grade is excellent, and Inco ingenuity makes economic metal recovery possible. The plant will produce 54,000 tonnes of nickel (contained in NiO) and 5,400 tonnes of cobalt (in CoCO3 filtercake) yearly. Based on prices of US$3/lb Ni and US$7/lb Co, cash production costs will be well under US$1/lb for nickel after byproduct credits.

Now, that’s exciting.

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