Operations: Sudbury Saturday Night
More than a century of experience and innovation grace Inco’s Sudbury operations, which make up the largest part of Inco’s Canadian and UK Operations. The determination and sweat of Canadians throughout the Twentieth Century polished the world’s finest nickel-producing company. Today’s men and women contribute their foresight and technical expertise to keep it shining brightly far into the future. CMJ visited the Sudbury operations on the eve of Inco’s centenary.
The Sudbury area is synonymous with rich nickel-copper deposits. But it takes more than geology to create a global nickel giant. Inco’s success lies as much with its ability to create new markets for its output as it does with its resource base. New ore sources are still being found, albeit at increasing depths. To recover ore efficiently and safely, Inco researches and applies technologies that go far beyond the definition of mining. Computers, automation, remote control and robotics are as much a part of modern mineral production as the jackleg was 100 years ago.
Inco’s Sudbury operation includes all phases of exploration, mining, mineral processing, smelting and refining. Seven underground mines supply ore to a central milling facility, which produces bulk concentrate feed for the smelter. Copper and nickel are refined in separate plants.
The active mines in the Sudbury area benefited from the switch in the 1980s to bulk mining methods, which significantly reduced costs, and they remain very cost-competitive. Besides the production mines, Inco operates a research mine near Sudbury, allowing the company to test and adjust its technologies in a true underground setting.
All of Inco’s operating mines near Sudbury–Coleman/McCreedy East, Copper Cliff North, Copper Cliff South, Crean Hill, Creighton, Garson, and Stobie–have long histories. Each year they meet higher standards of safety and efficiency than ever before, regardless of age. Creighton is a perfect example.
Breathe Deeply to Reach Bottom of Creighton Mine
Inco’s oldest mine is also the target of a major deepening project. Now in its 101st year, Creighton has spent $88.6 million to reach ore between the 7,400-ft and 7,660-ft levels. The lowest working level will be 8,180 feet below surface when the $88.5-million second phase of the project is completed in 2019. That’s deep enough to bury Toronto’s CN Tower 4.5 times.
Mining began at Creighton in 1901 from an open pit. The No.1 shaft project was started the same year, leading to underground production in 1907. Other shafts were sunk, most notably the No.9 production shaft from surface to 7,137 feet between 1965 and 1969. The No.11 ventilation shaft was collared in 1977; three years later it was complete to 5,840 feet.
Likewise, mining methods evolved and now include vertical retreat mining (VRM), slot/slash, and underhand cut and fill. Wherever possible, drilling, mucking and hauling are automated. There are five Cubex tracked drills with compressors in use. They are mobile and remotely operated. Four Elphinstone R1700 and R1600 vehicles make up the LHD fleet in the deepest levels.
Creighton is fondly referred to as three different mines. They are the near-surface stopes from 4,000 to 5,000 feet; the mid-level from 5,400 to 6,800 feet where remnant recovery is underway; and the deep stopes from 6,900 to 7,530 feet. Each of the three sectors contributes roughly the same proportion of ore daily. Grades increase in the deepest portion where combined copper-nickel grades are about 4%, compared to 2% Cu-Ni in the two shallower mining areas. Reserves between 7,400 and 7,660 feet are estimated at 2.8 million tonnes grading 2.97% Cu and 3.45% Ni. From 7,660 to 8,180 feet they are 3.1 million tonnes grading 3.25% Cu and 3.62% Ni. The first stope recovered on the 7500 level graded 3% Cu and 5% Ni. No wonder deepening became an attractive option.
The Creighton mine has two mucking circuits. One circuit directs muck through a crusher on the 5000 level and it is delivered via conveyor to the shaft on the 5200 level where it is hoisted to the surface. The second handles ore from deeper portions of the mine through a pair of crushers, one located on the 6600 level and the other (a 42-inch Allis-Chalmers crusher) on the 7000 level. Ore is delivered by inclined conveyor from both crushers to a loading pocket at the 6680 level. Ore is crushed to -6-inches and hoisted up the No.9 shaft using an automated system and a pair of 16.5-ton, bottom-dump skips.
Ore from the deepest working level, 7530 feet, is hauled up to the orepass on the 6920 level in a 50-ton Kiruna electric trolley truck. This awesome vehicle fills the drift to within inches of the walls. Experienced drivers make all their turns and dump with precision. The electric truck is admittedly more expensive to operate than a diesel-powered unit, but the savings in ventilation makes up much of the difference. A new maintenance garage is being built on the 7,400-ft level to service the Kiruna truck.
To deepen a mine requires that planners juggle three issues. First there are the logistics of development while maintaining production. As the 17-ft-high by 18-ft-wide ramp wound down toward the 7,600-ft level, it was the only way to move men and equipment around. Scheduling required some thought to keep haulage going at the same time foot traffic and other machinery used the same travelway. “We worked around the old workings. It was like building a new mine around the old,” said mine manager Steve Wood. Eventually the ramp will reach the mine bottom at 8,180 feet below surface.
The second issue is dealing with increased seismicity at depth. One line of defence is thorough rockbolting and screening and to shotcrete all permanent openings. Another is careful monitoring. The mine is outfitted with 80-channel monitors, 59 uniaxial and seven triaxial sensors. Together they detect up to eight seismic waves used to calculate events. Recorders register about 115 microseismic events per day. All this information is used to model ground behaviour, and this in turn helps when planning the stope sequence. The next step will be to use the models as a predictive tool for rockbursts.
The third, and very important, issue is to deal with elevated rock temperatures (about 130*F) and provide the necessary volumes of fresh air. “Deepening a mine like Creighton is mainly a ventilation problem,” said Don Gibson, who was project manager during the deepening and is now at the Garson mine. Without adequate fresh air, the heat, humidity and dust at 8,000 feet below the surface would rise to impossible levels.
Of the $88.6 million spent so far on deepening the Creighton mine, about $47 million was spent to expand the ventilation system. It has twice before been expanded, and the system has several features of note. AMEC was awarded the engineering contract for the mechanical and electrical engineering, and the EPCM contract for the fans went to Hatch Associates. When complete to the 8100 level, the ventilation system will move 1.75 million cubic feet of air per minute.
The most visible part of the new ventilation system is the triad of 20-ft by 20-ft square Robinson exhaust fans at the collar of the No.11 shaft. These are double-width, double-inlet variable speed centrifugal fans with 3,250-hp motors. Not only are these the first centrifugal fans Inco has installed in a mining operation, they are the largest mine ventilation fans in Canada. They are capable of moving 50 tonnes of air per minute. They are secured to massive concrete foundations with tensioned bolts to avert vibration problems.
Creating a well-engineered ventilation system goes far beyond installing new fans. The fresh air portion of the project involved a new raise between the 800 and 1900 levels; a fresh air transfer ramp from the 1900 level to the 2500 level with a booster fan station on the 2300 level; new raises between the 2500 and 4000 levels and between the 4000 and 5400 levels where another fan station is established; two more raises between the 5400 and 6600 levels and between the 6600 and 7200 levels; and the stripping
and extension of the No.8 internal shaft, which runs from the 5000 level and 7200 level. The new portion of the return air system includes a return air raise from the 7400 level to 6400 level and a return air transfer drift to the No.11 shaft on the 5400 level.
The raises above the 6600 level were difficult. As long as 1,550-ft and in some cases running through poor ground, they necessitated that the Alimak raise climbers be in perfect condition and the crews be very experienced. The team overcame rockbursts, delays, and rock removal problems. The raises were either ring-drilled and slashed out to 20 ft in diameter, or benched out to 24 ft, and in some areas finished with as complete ground support technology as a production shaft would have. Below the 6600 level the Alimak could not be used for safety reasons. These raises were reamed with a 4-ft diameter head and blasted to the finished 20-ft diameter. The escape raise between the 7400 and 7530 level presented a unique ground support problem that was resolved using a corrugated metal culvert dropped down the raise to provide ground support.
The temperature of the fresh air going into the mine is controlled to provide a constant temperature year round at the 800 level. Drawing the air down through the original open pit, where broken rock acts as a heat exchanger, makes this system virtually free to operate. Air passes through the pit to the fresh air transfer drift on the 800 level. There are temperature monitors on each slusher trench, and the flow is controlled by opening or closing doors on boxholes at the pit bottom. When Inco devised this natural heat exchange system in the mid-1960s, it was the first in the world and remained unique until a few years ago. It was expanded in 1981 and again last year. The rock field has the capacity to cool intake air until the mine reaches 8,400 feet deep without the construction of an expensive refrigeration system.
The new Creighton ventilation system will be complete in May 2002, six months ahead of schedule. It will be extended 100-ft at a time to eventually reach the 8,180-ft level.
Clarabelle Mill Updated
Inco’s Clarabelle mill in Copper Cliff, Ontario, has just received a $15-million redesign.
Lower tonnages of higher-grade ores have allowed some primary grinding mills to be switched to regrind service in order to improve metal recoveries. Other changes include adding a new flotation cleaning circuit, building facilities to store and add new reagents (acid and copper sulphate) to improve sulphide recoveries in the scavenger circuit, and the construction of an in-ground receiving system to handle up to 5,000 tons/day of waste refractories to process through a reverts circuit.
The commissioning earlier this year of the first components of the “Mill Redesign Project” went very smoothly, according to acting mill superintendent Jim Truskowski, and the investment is expected to return $100 million over the next four years.
Originally there were four mills in the Sudbury operations: Copper Cliff, Frood Stobie, Levack and Clarabelle mill (built in 1971). All milling had been consolidated into a single, expanded Clarabelle mill by the early 1990s when the two new flash furnaces at the smelter became operational. At that time, capacity at the Clarabelle mill was expanded to 40,000 tons/day with the addition of a SAG mill and 1,350-cu.ft. flotation cells. Instead of feeding separate copper nickel concentrates to the smelter, Clarabelle produced a single, bulk Ni-Cu concentrate for the new flash furnaces.
Ore arrives at the Clarabelle mill either by rail or truck, depending on the distance from the mine. In 2001, eight new 2,000-hp diesel-electric locomotives were leased by Inco to replace the aging fleet of 22 electric locomotives previously used to haul ore from the mines to the Clarabelle mill. Minus 8-inch ore is unloaded into a 23,000-ton receiving bin and then conveyed to a 2,500-ton coarse ore bin that feeds two grinding circuits.
The semi-autogenous grinding (SAG) circuit includes a 900-tph, 32-ft diameter by 13.5-ft Boliden-Allis mill with double 5,500-hp variable speed, DC motors. It is steel-lined with integrated lifters. The charge includes 8-10% 5-inch steel balls. The SAG discharge passes over a rubber-lined trommel with 2-inch by 5/8-inch slots. Trommel oversize is returned to the SAG mill, and the undersize material is rescreened on two 8-ft by 24-ft vibrating screens. Oversize from the vibrating screen returns to the SAG mill and the 1/8-inch undersize is pumped to the ball mill circuit. Depending on throughput rates, 60% to 100% of the mill feed is treated in the SAG circuit.
The conventional circuit includes four parallel crushing plants and rod milling. Each crushing line has a 6-ft by 14-ft Tyler double deck scalping screen, a 7-ft Symons standard cone crusher, a 5-ft by 12-ft Tyler double deck secondary screen, and a 7-ft Symons shorthead cone crusher. The crushers are powered by 300-hp motors. The crushed ore, nominally 15% + 3/4-inch, is conveyed to a pair of 13.5-ft diameter by 18-ft long Dominion rod mills. Discharge is cycloned to -65 mesh and is pumped to the ball mill circuit.
One of the features of the Mill Redesign project is to screen the rod mill discharge on the two SAG screens. This gives a finer feed to the ball mill circuit and improves grinding efficiency. Feed for the ball mill circuit includes the rod mill and SAG mill discharge, undersize from the SAG vibrating screens and the fines from the crushing plant. The circuit has five 13.5-ft by 18-ft Dominion ball mills, each of which operates in closed circuit with 26-inch cyclones (four or five per mill). An on-stream, particle-size analyzer ensures that that an overflow density of 48% solids and solids of 90% passing 65 mesh is achieved.
Five years ago an expert system was installed on all crushing and grinding circuits. It was developed by Inco and Eimco Minerals. The strategy is to maximize the feed rate using the smallest number of ball mills while maintaining cyclone overflow density and grind size targets. The system advises operators to start or stop rod and ball mills subject to ore availability, pumping capacity, circulating loads, and potential mill overloads.
The focus of the separation circuits is to maximize the recovery of the valuable metals while rejecting as much as possible of the rock and iron sulphide mineral, pyrrhotite. The pyrrhotite contains 70% of the sulphur in the ore. Maximizing its rejection is the key to reducing SO2 environmental emissions.
The pyrrhotite occurs as two mineralogical forms: monoclinic pyrrhotite is magnetic and hexagonal pyrrhotite is not. After ball milling and cycloning, the next step is to remove magnetic pyrrhotite from the ore, which makes up 30-80% of the total pyrrhotite in the ore, depending on the ore source. Fifty-four 3-ft diameter by 6-ft long wet permanent magnetic drum separators are used to recover the magnetic pyrrhotite, which is then reground into 13.5-ft by 18-ft ball mills operating in sequence. This two-stage milling circuit was another feature of the Mill Redesign project.
The finely ground product from the regrind circuit reports to a two-stage cleaner flotation circuit. The first stage consists of 10 banks of 100-ft3 Denver DR cells with 10 or 12 cells per bank. The second stage has four banks of 100-ft3 Denver cells. A combination of TETA (triethylene tetramine) and sulphite are used to reject pyrrhotite to tails with minimal loss of nickel. The unique use of TETA in this application was developed and patented by Inco in the late 1980s. “It’s had a tremendous effect on improving grades,” said Truskowski.
The non-magnetic fraction of the ore is pumped to six lines of eight, Dorr Oliver/Outokumpu 1,350-ft3 flotation cells. The first four cells have traditionally produced the rougher AB concentrate, and the last four in each bank–the “CD” cells–operate as scavengers. The roughers operate under grade control and the scavengers under recovery control. However, with only four cells in a line operating under recovery control, recoveries were sometimes compro
mised in the past when high-grade ores or ores containing large quantities of non-magnetic pyrrhotite were processed. As a result, a key feature of the Mill Redesign was to install a regrind and cleaning circuit to upgrade the B rougher concentrate. An existing regrind mill was equipped with five high-efficiency, 10-inch Warman Cavex cyclones. Two banks of seven Dorr Oliver 300-cu.ft. cells were also installed.
“The new circuit has exceeded our expectations and has increased the concentrate grade capability,” said Truskowski. “The transformation of the B roughers to a scavenging mode has raised the number of cells operating in a recovery mode by 50%. As a result, the improved concentrate grade capability has been achieved without loss in recovery.”
The concentrate from the CD scavenger banks is thickened and reground in a 13.5-ft by 18-ft ball mill equipped with high-efficiency Warman Cavex cyclones. The slurry then passes through a scavenger cleaner circuit of six bands of 100-ft3 Denver DR cells with 10 or 12 cells per bank and finally four identical recleaner banks. TETA and sulphite are also used in this circuit.
Besides TETA and sulphite, other reagents used in the mill are potassium amyl xanthate, frother and lime. Two Courier-30 x-ray fluorescence on-stream analysers sample and provide assays used for process control for 14 streams.
The bulk concentrate grading 20-21% Cu+Ni is pumped to four 110-ft diameter Dorr thickeners located outside the smelter. It is thickened to 65% solids and either stored or pumped directly to the filtration plant, where four 8-ft-10-inch diameter, 12-disc Eimco filters further reduce the moisture content to about 11%. The filter cake is sent to bins in the smelter.
Clarabelle mill produces two distinct tailings streams. Rock tails come from the CD scavengers and can be either returned to the mines as backfill or impounded in the 5,500-acre tailings area three miles west of the mill. Pyrrhotite tails are produced from the magnetic Cu-Ni flotation circuit and have an acid-generating potential due to their high sulphur content. They are deposited under a layer of water in the centre of the tailings area to reduce their oxidation and acid-generating potential.
Although all components have not yet been commissioned, the Mill Redesign project has already met performance expectations. “It has been an incredible success story,” said Truskowski.
A Cleaner Copper Cliff Smelter
Sulphur is a “four letter word” around Sudbury. That’s why Inco has spent $830 million over the last 15 years to contain it. The battle has been waged with improved pyrrhotite rejection during milling, innovative smelting practice, and extraordinary efforts to capture and clean off-gases.
The Copper Cliff smelter operates under strict sulphur dioxide (SO2) emission limits set by the Ontario government. The current limit is 265 kilotonnes (kt) annually, and the smelter has no problem staying below this level–less than a tenth of what went up the stack in the mid-1960s. In other words, 90% of the sulphur associated with the ore is contained during processing.
The quantum leap that allowed the smelter to stay below its SO2 emission levels is the pair of flash furnaces installed between 1990 and 1993 to treat bulk concentrate. They replaced the old roasters, reverberatory furnaces and Bessemer matte technology for treating nickel concentrate and the separate flash furnace for smelting copper concentrates. Gone is the old fossil fuel-burning technology, replaced with flash smelting that makes good use of the exothermic characteristics of sulphide ores.
Bulk concentrate feed enters the smelter and is passed through a pair of natural gas-fired fluid bed dryers (one for each furnace) to drive off all the moisture. The feed is collected in a bag house and conveyed to bins ahead of the flash furnaces, which have two burners at each end. Dry concentrate is top-fed via drag chains and screw conveyors, and 95% oxygen is injected through the burners to melt the feed. Slag temperature is maintained at 1,260*C by the addition of coke when necessary.
The slag floats to the top of the bath and collects the majority of the iron in the ore. It is skimmed from one end of the furnace into slag pots and railed to the slag dump.
The 1,200*C matte, which contains 45% combined Cu, Ni and Co plus sulphur and iron, is tapped from the sides of the furnace into ladles that are transported through a tunnel to the converter aisle.
Furnace off-gases, which can contain up to 80% SO2, are cooled, cleaned and sent to the sulphur products plant. Most of the gases are passed through a Monsanto-designed acid plant to make sulphuric acid. Liquid SO2 can also be produced in a separate facility.
Inco takes a proactive approach to emissions control from the smelter. In 2001 there were only two incidents of exceeding the 0.5 ppm SO2 ground level concentration, the best year ever. Weather data collected from the Internet are used to produce local forecasts. From the forecasts, predictions of ground level concentrations are made. The upper limit for average hourly ground SO2 concentration is set at 0.34 ppm this year, down from last year’s 0.5 ppm target. The company maintains 16 monitoring stations in the community to record smelter emissions. There is also a mobile monitor operating from April to October to measure the effect of the stack plume on the region. Complaints are followed up, incidents are investigated, and all results are documented.
The converter aisle operates with three Pierce-Smith units, but it is a very busy area. Quartz flux is added to the converters and they are blown with oxygenated air. The three converters are now run from a single control room rather than by three separate operators. Slag is skimmed and returned to the furnaces. The finished matte assays 75% combined Cu, Ni and Co, 0.8% Fe, and 21.5% S. It is poured into 30-tonne in-ground moulds where it is allowed to cool for five days. Then it is pulled from the moulds and crushed.
The crushed matte goes to the matte separation plant. Here it is reduced to 35% passing 325 mesh by rod/ball milling. The slurry is passed through wet magnetic separators, and the magnetic portion is sent to the nickel refinery. The non-magnetic portion is pumped to the flotation circuit where copper sulphide is separated from nickel sulphide in 300-ft3 Denver cells and flotation columns.
The nickel sulphide passes through a fluid bed roaster to create nickel oxide, which is refined either in Copper Cliff or in Clydach, Wales.
The copper concentrate is smelted at 1,250*C in the MK reactor to remove sulphur by Inco’s top-blow bottom-stir process. A 14% SO2 gas stream is captured from the reactor and sent with the furnace off-gas for treatment. Semi-blister copper from the MK reactors contains less than 3% S. It is poured into multipurpose vessels and finished to create blister copper. The blister copper is then reduced in the anode furnaces to lower the oxygen content to 1,200 ppm O2 from 10,000 ppm O2 before casting.
Clean, Efficient Anode Plant on Line
A cleaner, more efficient copper anode casting plant is up and running in the Copper Cliff smelter. It was commissioned in 2001 to address concerns about emissions and the inherent risks of moving molten metal. In fact, everything about the new casting plant is an improvement over the original one.
The old anode casting facility was located at the copper refinery, which dates from the 1920s. Blister copper was moved in heated rail cars from the smelter to the refinery. The time was right for a serious overhaul of that practice. Now solid metal moves between the two sites, eliminating the potential for a spill and the energy used to keep the rail cars hot.
The old anode plant employed “poling” as part of the blister copper reduction process. That meant inserting 15-inch tree trunks into the anode furnace with the inevitable clouds of smoke and ash. To make room for the two new anode furnaces, an old converter at the smelter was removed. Each 320-tonne furnace is injected with natural gas and steam to remove oxygen from
the molten copper. The bath is agitated by injecting nitrogen gas through porous plugs in the furnace shell. Air quality and metallurgical quality are improved.
The Outokumpu casting system is new and is coupled with a refurbished wheel. The wheel has 26 moulds from which 130 anodes are removed hourly. The casting ladles are equipped with load cells to ensure accurate anode weight; 98.7% of the anodes are within 1% of the 307-kg target weight. The anodes are first cooled by a water spray and then pass by a reject machine that makes its determination based on information from the casting ladle load cell. The anodes then move back to the Bosch tank where they are further cooled, stacked and removed with a forklift. The moulds are prepared for the next casting with an automated barite spray. The man-machine interface is accomplished with a Foxboro distributed control system, WonderWare software and user-friendly touch screens.
Each casting crew consists of seven people, compared to the 17 required at the old facility. They work in a brightly lit, spacious environment. Four roof exhaust fans remove what few fumes there are, and a ventilation hood is installed over the area where the dry barite is slurried. Crew members rotate stations during their shift and are qualified on all jobs. The union was involved when planning began for the new copper casting plant to address human resources issues, intensive training, and the general effects of such a major change.
The total cost of the new anode casting plant was $31.9 million. The target production rate of 472 tonnes/day was reached only six months after commissioning. Start-up was delayed five months and the budget slightly overrun because mechanical failure caused one of the anode furnaces to over-rotate and spill several hundred tonnes of molten metal. No one was hurt. Even with the delay and extra work, the plant will pay for itself in 4.5 years, all the while providing the highest quality anodes with less labour, equipment and energy and without the movement of molten metal between plant sites.
Copper Cliff Nickel Refinery
The carbonylation nickel refining process was developed in 1889 and commercialized 100 years ago with the building of the Clydach refinery in Wales. Pressure carbonylation was introduced when the Copper Cliff nickel refinery went into service in 1973 in Sudbury.
The Copper Cliff nickel refinery treats three feed stocks: Ni-oxides, magnetics from Inco’s Matte Separation Plant and a concentrate from Inco’s Clydach refinery. All are melted in Top Blown Rotary Converters and then granulated to prepare the material for the carbonylation process.
The granules are fed in 150-tonne charges into three horizontal 3.7-m diameter by 13-m long, high pressure reactors. Carbon monoxide (CO) is injected to bring the pressure up to 70 kg/cm3. Nickel and iron in the granules react with the CO to produce nickel-carbonyl (Ni(CO)4) and iron-carbonyl (Fe(CO)5). Off-gas is drawn from the reactor, and filtered to remove particulates; carbonyls are condensed to liquid and carbon monoxide is returned to the reactor.
Carbonylation residue is treated for the recovery of metals in the electrowinning process. The residue is leached in two stages. The first stage dissolves nickel and cobalt, which are then recovered from solution as carbonates. The second stage dissolves copper, selenium, and tellurium and the residue from this leach is sent to Inco’s Port Colborne refinery for further processing to recover precious metals. The solution from the second stage leach is heated and passed through a column containing copper to create Cu-selenides and Cu-tellurides, and then aged in four towers. Solids recovered from the ageing towers are treated at Inco’s silver refinery. The aged solution is fed to the EW tankhouse, which has 49 cells, each of which contains 66 titanium cathode blanks and 67 antimonial lead anodes. After seven days the blanks are pulled and the cathodes are washed, stripped and bundled for shipment.
The condensed carbonyl liquid from the carbonylation process includes both nickel-carbonyl and iron-carbonyl. They are separated by fractional distillation in two 50-ft tall columns. The column bottoms yield a liquid carbonyl containing the iron-carbonyl and some nickel-carbonyl. This liquid is decomposed to form ferro-nickel pellets. The column off-gas carries high-purity nickel carbonyl, a consistent feed gas for the nickel-carbonyl decomposition process, which is registered to the ISO 9002 Quality Standard. Finished nickel products (pellets, discs and powders) are remarkable for their purity.
Copper Cliff Copper Refinery
The Copper Cliff copper refinery produces 99.99% Cu cathodes. Anodes are treated in an electrorefining (ER) circuit, and cathode handling is performed with a high degree of automation.
Each ER cell is loaded with 33 anodes sandwiched between 34 copper starter sheets grown on titanium blanks. The electrolyte is composed of 40 g/L Cu and 150 g/L H2SO4. Over the course of two weeks, cathodes grow to about 120 kg before being pulled, washed and stacked. The electrolyte is purified at the acid plant and returned to the tankhouse.
Slimes from the ER tanks are treated in the silver refining process to recover silver, selenium and tellurium. The remaining concentrate is shipped to Inco’s Port Colborne refinery for further recovery of precious metals.Constant updating and automation keeps the copper refinery efficient, even after more than 70 years of operation. It continues to produce the highest quality ORC cathodes that command a premium price in the marketplace.Active Mines at the Sudbury OperationColeman/McCreedy EastStart-up: 1970Shaft depths: 3,440-ft production; 4,100-ft ventilationNominal annual mining rate: 1.2 million tons (approx.)Current working levels: 3,500-ft to 2,810-ftMining methods: VR blasthole; post pillar cut & fill; narrow vein cut & fillBackfill: Cemented sandHighlights: Lower Coleman was mined out in 2002. The mine is being deepened to 4,090-ft at a cost of $45.8 million.Copper Cliff NorthStart-up: 1886 (operation not continuous)Shaft depth: 4,160-ft productionNominal annual mining rate: 0.9 million tons (approx.)Current working levels: 1,200-ft to 1,400-ftMining methods: Vertical retreat; blastholeBackfill: Cemented slagHighlights: The shaft crew has worked 13 years without a disabling injury.Copper Cliff SouthStart-up: 1896, No.1 shaft (now closed)Depth of shafts: 4,245-ft production; 2,320-ft ventilationNominal annual mining rate: 1.0 million tons (approx.)Current working levels: 690-ft to 4,130-ftMining methods: VR blasthole; uppers retreatBackfill: Cemented mill tailsCrean HillStart-up: 1905Depth of shaft: 4,180-ft productionNominal annual mining rate: 0.2 million tons (approx.)Current working levels: 1,000-ft to 4,240-ftMining methods: Bulk VCRBackfill: Cemented sandCreightonStart-up: 1901 (mined continuously for 101 years)Depth of shaft: 7,127-ft, No.9 shaftCurrent working levels: 7,200-ft to 7,630-ft; ramp reaches 7,660 ftNominal annual mining rate: 1.1 million tons (approx.)Mining methods: Vertical retreat; slot & slash; underhand cut & fillBackfill: Cemented mill tailsHighlights: The current mine deepening and ventilation project carries a price tag of $160 million. The underground greenhouse has been growing trees for over 17 years. This is the home of the Sudbury Neutrino Observatory.GarsonStart-up: 1907, No.1 shaftDepth of shaft: 4,241-ft productionNominal annual mining rate: 0.7 million tons (approx.)Current working levels: 2,440-ft to 4,400-ftMining methods: Blasthole; bulk VCRBackfill: Paste fillHighlights: Won the John T. Ryan safety trophy in 2001.StobieStart-up: 1941Depth of shafts: 4,120-ft No.7, 2,624-ft No.8, 2,774-ft No.9Nominal annual mining rate: 3.5 million tons (approx.)Current working levels: 1,900-ft to 3,600-ftMining methods: Vertical retreat; sublevel cavingBackfill: Cemented mill tails; caving