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Sudbury Operations

Mill Process Description

Clarabelle Mill accepts nickel-copper ore from various sources and companies and produces a nickel-copper concentrate and copper concentrate for further processing.

The ore is delivered via rail or truck to the facility where it undergoes primary screening. The screened ore is then conveyed to the Crushing Plant. At the Crushing Plant, the ore is stored in silos and fed through a series of primary and secondary crushers. The ore is conveyed via covered, heated conveyors to the Mill Building. At the Mill Building, the size of the ore is further reduced in semi-autogenous (SAG) mills, rod mills and ball mills. All milling is done wet . A copper-nickel concentrate is extracted from the slurry via a series of magnetic separation, flotation and thickening steps. Several chemical flocculants, collectors, frothers and depressors are used in these steps. Specific conditioned slurry receives additional flotation and thickening to produce a copper only concentrate. The copper-nickel concentrate is piped to the Smelter’s Filter Plant for further processing. The copper concentrate is trucked to the Smelter for further processing. Clarabelle Mill also produces a pyrrhottite/rock tailings stream which is piped to the Central Tailings Area.

Smelter Process Description

At the Copper Cliff Smelter, the nickel-copper bulk concentrate from the mill is dried and processed through the Flash Furnaces and converters. This produces a bulk converter matte, sulphur dioxide and slag. The sulphur dioxide from the Flash Furnaces is fixed and sold as sulphuric acid and liquid sulphur dioxide, while the lower-strength gas stream from the converters is vented to the stack after being cleaned of particulate in electrostatic precipitators. The slag from the furnaces is a waste product that is sent to the slag dump.

The converter matte is slow-cooled to produce a coarse crystalline structure Bessemer matte. This is crushed, ground and separated into metallics, nickel sulphides and copper sulphides by magnetic separation and flotation in the Matte Separation Plant.

All of the precious metal bearing metallics and some of the nickel sulphide are sent to the Copper Cliff Refinery. The remaining nickel sulphide is roasted in fluid bed roasters. The resulting nickel oxide is processed in the Copper Cliff Refinery, the Clydach Refinery, or is marketed. Sulphur dioxide from the roasters is fixed as sulphuric acid.

Copper sulphide from Matte Separation is treated in a copper reactor where sulphur is removed as sulphur dioxide, which is then fixed as sulphuric acid. Additional impurities are removed from the molten metal in finishing converters, producing blister copper and a nickel oxide mush. The small amount of sulphur dioxide evolved in the finishing converters is vented to the stack after being cleaned of particulate in an electrostatic precipitator. The molten blister copper is further refined to remove the last of the impurities and then cast into anodes for customers. The nickel oxide mush is redigested with sulphide matte and sent to the Bulk Converters.

Nickel Refinery Process Description

The processes at Copper Cliff Nickel Refinery represents the final stage in the recovery of metallic products from mined ore before shipment to market. There are three main facilities at the Nickel Refinery – the Nickel Refinery Converter (NRC) Plant, the Inco Pressure Carbonyl (IPC) Plant and the Electrowinning Building.

At the NRC, feed input (nickel sulphide crudes, metallics, nickel oxides, precious metal baring intermediates and refinery intermediates) are charged into two Top Blown Rotary Converters (TBRCs), and melted using natural gas-oxygen lance burners. Once the temperature of the bath has reached approximately 1600ºC, petroleum coke is added to reduce the oxygen content of the bath (called reduction). High pressure oxygen is occasionally blown into the bath to desulphurize it if the sulphur content is too high. The melted product is transferred to a teeming ladle and poured through high velocity water jets (called granulation). The resultant granules are dewatered, dried in a gas-fired kiln and conveyed to the IPC.

At the IPC, the granules are batch-reacted with carbon monoxide at temperatures up to 180ºC and pressures up to 1000psi, in three 150-ton rotating reactors. Nickel and iron are extracted as carbonyl vapours, while copper, cobalt, precious metals and other impurities are retained in the residue. This residue is milled and pumped to the Electrowinning Plant. The carbonyl vapour is liquefied, purified in two parallel distillation columns and sent to decomposers. In the (eighteen) decomposers, nickel deposits from the carbonyl stream onto a stream of pre-heated nickel pellets. The remaining nickel carbonyl vapour is decomposed to produce pure nickel powder. The iron-nickel carbonyl is condensed, stored, re-vaporized and decomposed to ferronickel pellets.

At the Electrowinning Building, the IPC Residue is treated in an oxidative acid leach circuit to remove nickel, cobalt, iron, arsenic and other minor element contaminants. A second leaching circuit is used to dissolve copper, selenium and tellurium from the first leach solid residue. The slurry is filtered and the residue is sent to Port Colborne to extract the precious metals. The filtrate is pumped into tanks and an electrical current is applied through titanium cathodes and lead anodes. The copper plates onto the cathode over a two week period. The copper sheets are removed from the cathodes and sent to market. The first stage leach solution is fed to the iron/arsenic removal circuit and then through a copper clean-up circuit. The nickel and cobalt are precipitated from the solution with soda ash. The resultant carbonate stream is thickened and sent to Port Colborne.