The Canadian Mining Journal is Canada’s first mining publication.
This article was originally published – February/2008
Sherritt International is a resources company built from the bricks of a Canadian nickel miner, which recently celebrated its 80th anniversary, shown by the timeline in this article. Despite the intervening decades and corporate upheavals, Sherritt is still a nickel company grounded in the strength of its research, technical innovation and operational expertise. But it has become international, and is aggressively focusing on growth in all its business units–metals, coal, power generation, and oil and gas.
In a recent two-hour interview with the company’s president and CEO Jowdat Waheed at its uptown Toronto head office, I learned that Sherritt has decided to get its story in front of the public, which prompted Waheed to invite me to visit the company’s metals, technology and coal offices and facilities in western Canada followed by a trip to see its Cuban assets, all in four days in early February. It is from this brief immersion that I bring you a snapshot of Sherritt International, today.
This is by far the largest part of the company, bringing in 62% of Sherritt’s revenue and 80% of its operating earnings in the first nine months of 2007.
In fact, Sherritt International’s raison d’etre is pressure hydrometallurgical technology. Using ideas first put forward by Frank Forward of the University of British Columbia, the research group (called Sherritt Technologies) designed and built a plant in Fort Saskatchewan, Alta., to extract nickel and cobalt from concentrate from its mine in Lynn Lake, Manitoba, using a process that deviated markedly from pyrometallurgy (smelting) that was the then-current technology, and which continues to dominate the base metal extraction industry in Canada today.
Hydrometallurgy has one big environmental advantage over smelting: the former emits no SO2, the main cause of acid rain. The sulphur is captured and used to make elemental sulphur or combined with ammonia to make fertilizer.
Sherritt Technology went on to develop pressure hydrometallurgical processes for other metals including gold, zinc, copper and urani- um; so far it has licensed more than 35 commercial partners to use Sherritt technology. The Technologies group continues to be in the forefront of pressure hydrometallurgical technology, offering clients concept development and testing in their lab in Fort Saskatchewan, scaling up the design to commercial size, as well as help with construction, commissioning and ongoing help with operations.
From its half-century bank of experience as well as ongoing tweaking of the Fort Saskatchewan nickel hydrometallurgical plant, the Technology group can now forego the expensive and lengthy progression of bench test, mini pilot plant, pilot plant and demonstration plant. Now they go directly from the small scale pilot plant tests with 1-2-tonne (t) samples, and scale up to the commercial plant. “One of our great strengths is that we are not only technologists, we are also operators. We are actually selling our know-how,” says Robin Kalanchey, business development manager for Sherritt Technologies.
Fort Saskatchewan refinery
The SHERRITT PRESSURE HYDROMETALLURGICAL PLANT, also known as Corefco (“The Cobalt Refinery Co. Inc.”), began operation in 1954. It was located in Fort Saskatchewan, Alberta, for three reasons: a ready supply of natural gas (the main energy source), access to water, and the town’s location on the Canadian National Railroad line, just north of Edmonton. When Lynn Lake feed began to dwindle in the early 1970s, the plant started taking on additional feeds. It received its first mixed sulphide feed from the Pedro Sotto Alba plant in Moa, Cuba, in 1991; Moa today supplies about 95% of the plant’s nickel feed.
While the configuration of the leach stages and autoclaves has been altered many times over the last half century, the basic function and operation of the ammonia leach process has remained remarkably constant. A tour of Corefco by CMJ in early February revealed a 50-year-old chemical plant, with nearly a zillion pipes and valves leading to and from auto- claves, tanks and towers, showing the effects of generations of alterations and improvements.
In the three-stage leaching process, the nickel-cobalt suphide is fed into autoclaves, where it is mixed with ammonia and air, dissolving the nickel and cobalt. The remaining solids (mainly iron oxide) are filtered out, washed and stockpiled or sold.
Selective crystallization separates cobalt from nickel. The resulting cobalt salt is redissolved in the cobalt plant. In a continuous batch operation, hydrogen is injected into the reduction autoclaves causing cobalt to precipitate onto cobalt seed powder, which is kept in suspension by agitators. The depleted solution is drawn off and fresh solution is added until the cobalt particles reach the required size. The slurry is discharged to a flash tank, and the cobalt powder is filtered out and washed. The 99.8% pure cobalt powder is dried and packaged, or is compacted into briquettes and sintered to form a 99.9% Co product.
Meanwhile, the nickel-rich solution remaining after cobalt separation flows back to the leach plant where leached copper is removed by lowering the pH until the copper combines with sulphur. The solid copper sulphide is separated by a thickener and polish filters. This is sold as feed to a copper smelter.
An oxyhydrolysis tower treats the clarified nickel-rich solution at high temperature to eliminate unsaturated suphur compounds and sulphamate. Then the solution enters the nickel plant, where reduction autoclaves function in a similar way to the cobalt reduction autoclaves, in a continuous batch process. Hydrogen gas is added, the autoclave is agitated and nickel comes out of solution, depositing onto nickel seed powder. The depleted solution is drawn off, replaced by fresh solution and this continues until the nickel particles reach the required size. The slurry is discharged into the flash tank and transferred to a pan filter where the nickel particles are washed. The powder is dried and packaged (99.8% pure Ni), or compacted into 99.4% Ni briquettes that may be sintered to 99.8% Ni. The briquettes form 90% of the product, and are shipped in 2-t bags to customers in Europe and Asia. (With the metals originating in Cuba, these products may not be sold to the United States.)
Minor nickel and cobalt remaining in the depleted solution are precipitated as sulphides using H2S, and removed by a filter press. The filtered solution now contains mainly ammonium sulphate, which is recovered by evaporation in the ammonium suphate plant, and converted into fertilizer, which is sold in western Canada.
Pressure hydrometallurgy eliminates the emission of SO2 (most of white “smoke” coming out of the plant’s stacks is actually water vapour).Corefco has eliminated the impounding of new slurry (containing iron oxide solids from the leaching plant) through process innovations and filtering, as well as waterborne emissions that are processed at a regional treatment facility. Air emissions have remained below regulated limits.
There has never been a strike in the plant’s 54-year history. The current labour agreement will continue to 2010.
Corefco’s output has increased dramatically over the years. The eight autoclaves in the plant were originally designed to produce 7,700 t/y of combined nickel plus cobalt, but the same eight autoclaves today can make about 32,000 t/y of nickel and 3,500 t/y of cobalt.
Plans are in place for another large expansion to accommodate the increases in feed that will be coming from the Moa plant beginning in mid-2008.
Moa nickel-cobalt mine and plant
Feed for the Corefco plant comes mainly from the MOA MINE AND CONCENTRATOR in eastern Cuba. The operation was built by Moa Bay Mining Co., a subsidiary of Freeport Sulphur, using propriety Sherritt technology. The 25,000-t nameplate capacity plant began operation in 1959, the year of the Cuban Revolution. The Cuban government took over the operation and restarted it in 1961.With the collapse of the Soviet Union thirty years later, the Moa facility needed a new home for its feed, so it began to send its mixed sulphides to Sherritt’s Fort Saskatchewan facility in 1991.
Sherritt saw Moa as more than a steady source of feed for Corefco. It saw an opportunity to improve the performance at Moa, so Sherritt formed a 50/50 joint venture with Cuba’s General Nickel Co. S. A. (part of the country’s Ministry of Basic Industry) in 1994. The JV operating company, Metals Enterprise, consists of the Moa mine and processing facilities (Moa Nickel S. A.), the Corefco plant, and its marketing arm, International Cobalt Co. Today, all of Moa’s mixed sulphide is shipped to Fort Saskatchewan.
Moa operations have prospered under the joint venture. Production of contained nickel and cobalt was only 12,500 tonnes (t) in 1994, but, as a result of debottlenecking, has almost tripled and should be approximately 33,000 t in 2007, according to guidance provided by the company last fall. The cost of production dropped steadily by 2003,but has risen recently due to jumps in the price of acid, sulphur and oil. The operations employees at Moa include about a dozen expatriate Canadians.
CMJ was privileged to tour the Moa mine and plant site with the site manager, and provides this brief description of the operation.
After 54 years of operation, Moa’s West mine is nearly depleted; 75% of the limonite now comes from the East mine. Overburden is stripped to uncover the soft limonite (ore) layer. The underlying saprolite is being left exposed, available for future recovery for ferronickel operations at the request of the government, preventing reforestation of some land at this time. However, Moa Nickel has in place a fullfledged program that will ultimately address all reforestation requirements.
Nine excavators feed 10,000 t/d of limonite into the thirty-six 40-t articulated trucks and four rigid 60-t trucks, which haul it up to 6 km to the slurry plant. Expansion plans call for the development of a new slurry facility, which will reduce haulage distances for the mobile fleet. A 300,000-t stockpile is built up each year before the rainy season.
Limonite is slurried with water and screened to remove the coarse magnesiumbearing serpentine ore (about 15%), and then pumped 5 km to the plant. Thickeners there increase solids content to 47%, and return water to the slurry plant. The limonite slurry reports to the acid leach plant.
Five sulphuric acid leach trains, each consisting of four pachucas, leach 95% of the nickel and cobalt from the slurry with a retention time of about 75 minutes. Seven CCD tanks separate the solids from the metal-rich solution; the tails are treated and pumped to the tailings pond. H2S is then added to remove copper and reduce chrome and iron; and the addition of limestone excavated from nearby Moa Bay increases the pH to 2.5.
H2S is injected into the purified liquor in autoclaves to precipitate nickel and cobalt as mixed sulphides, which are thickened and dried to a concentrate containing about 55% Ni, 5.5% Co, 1% Fe, 1% Zn and 0.03% Cu. This is shipped from Moa Bay to Halifax, N. S., and railed to Fort Saskatchewan.
Substantial surge capacity allows for critical maintenance on the acid leach reactors and sulphide precipitation autoclaves while the rest of the plant continues to operate.
An expansion project launched in 2005 will take Moa’s production from 33,000 t/y to at least 46,000 t of combined nickel and cobalt. Hatch Associates is handling the construction management, with about 600 additional construction employees, mainly Cuban, currently involved. The Cuban partner will provide sufficient laterite concessions for an additional 25 years of operation.
Phase I of the expansion will be commissioned in the first half of this year, increasing the capacity to 37,000 t/y. The mining rate will increase, mainly from the East mine. An additional thickener will dewater the slurry. The CCD circuit is being extended by three tanks, and neutralization capacity is doubling. There will be another large autoclave for sulphide precipitation.
Phase II will increase annual output to 46,000 t and will include another leach reactor train. An additional sulphuric acid plant will make the processing facility virtually self-sufficient for acid supply.
Sherritt is the 40% owner and operator of the AMBATOVY NICKEL LATERITE PROJECT in Madagascar, with 27.5% partners Sumitomo Corp. of Japan and Korea Resources Corp. (a consortium of Korean companies), and 5% held by SNC Lavalin. Sherritt took over Ambatovy when it purchased Dynatec Corp. in June 2007.The most recent capital cost estimate for the project is US$3.3 billion.
Production is expected to begin in 2010, and the operation should reach full capacity of 65,600 t/year Ni + Co in 2012. Pressure hydrometallurgy will be used to make Class I nickel and cobalt in a plant at tidewater. Current reserves predict a 27-year life.
“Our philosophy in working in Madagascar is identical to Cuba,” says Waheed. “Ambatovy is a beautiful mine and a massive resource, amenable to the same type of processing that Sherritt designed for Moa and Fort Saskatchewan.”
The building of this project will help a country that is in need of basic infrastructure including power, coal oil and metals–all businesses in which Sherritt has expertise, according to Waheed. For example, Sherritt is well advanced in signing a memorandum of understanding to produce more than 100 MW of power, in addition to the power plant dedicated to Ambatovy. At the same time, cutting edge environmental management is helping to protect the very environmentally sensitive area.
See Part 2 in next posting.