It’s no secret that pouring base metals matte in smelters built shortly after the turn of the century goes hand-in-hand with pumping acid rain-causing sulphur dioxide into the atmosphere. Ask any smelter worker in Flin Flon, Man. In this community, where 1,800 people are employed by Hudson Bay Mining & Smelting, in-plant environmental problems have reached serious proportions. And the company knows it. HudBay estimates it is going to cost $130 million just to make zinc and copper smelting physically feasible in Flin Flon in the 1990s. The installation of three autoclaves would cut sulphur dioxide emissions in this northern Manitoba mining community by 25%, and copper-smelting technology licenced by Noranda Inc. would cut fossil fuel consumption by 50%. But demand for Manitoba’s hydroelectricity would actually increase. This all adds up to good news for Manitoba, which is spending millions to develop hydroelectric capacity in the north and which has an interest in maintaining the long-term viability of the community of Flin Flon,–if, that is, Inspiration Resources, HudBay’s New York-based parent, can come up with the money to modernize its aged smelting complex.
HudBay has compiled detailed plans and preliminary engineering work to bring the 60-year-old zinc and copper metallurgical complex into the 21st century. It has made presentations to senior department heads in both the provincial and federal departments responsible for environmental regulations. Early this year Cominco Ltd. and Noranda Inc. both received government assistance to modernize their smelters in Trail, B.C., and Rouyn-Noranda, Que., after extensive lobbying. HudBay hopes to get support, in the form of long-term loans, for its plans as well, according to Area Manager Keith Callander. It has been lobbying the government for about one year now. (Inco Ltd. and Falconbridge Ltd., two other smelter operators in Canada, have until December, 1988, to submit their sulphur dioxide abatement plans to the Ontario government for their operations in Sudbury.)
The modernization plan at Flin Flon involves the introduction of new hydro- and pyro-metallurgical technology developed by two of Canada’s premiere base metals metallurgists — zinc pressure leaching technology developed by Sherritt Gordon and bath smelting of copper concentrates in a continuous converter developed by Noranda Inc. and Codelco (Corporacion Nacional Del Cobre de Chile). Highlights of the plan include:
* a slightly better copper recovery (95.3%-95.5%);
* a slightly lower overall zinc recovery (89.18% compared to 90.93%) due to zinc losses to the copper concentrate which are recovered under the present process but which will not be recovered under the proposed system;
* significantly lower production costs as a result of a 50% reduction in fossil fuel consumption and a reduction in the workforce in the metallurgical complex by about 200;
* higher electricity consumption (by about 9-10 mw) as a result of using the Noranda continuous converter;
* a significantly improved working environment because of improved containment; and
* the elimination of on-line maintenance in the smelter’s baghouse.
The existing plant is a conventional roast/leach/electrowinning plant, using 1930s technology. Ten multiple hearth roasters are used along with pachuca leaching, two stages of purification, solution cooling and electrowinning cells arranged in cascade. Copper and precious metals are removed from the ferrite residues in the reverberatory furnace matte while zinc follows the slag to the fuming furnaces.
The proposed system will require significant modifications to the Flin Flon smelter. Areas which will become redundant include the zinc and copper roasters, pachuca leaching section, the reverb furnace, the costly fuming plant, coal plant, baghouse and drying plant. New plant areas include a new oxygen plant, a stack dust leach complex, a feed preparation complex, a zinc pressure leach complex and a new electrical substation. Concentrates from Hud Bay’s mills will be prepared for further processing in a new feed preparation facility. A 600 hp ball mill will regrind about 500 tonnes of concentrates per day to 98% passing 45 microns. The slurry will be thickened to 70% solids and pumped to the zinc pressure leach plant.
In the pressure leaching circuit two horizontal autoclaves, each 20 m long and 3.3 m in diameter, will be needed. A third will be purchased as a spare in order to maintain year-round operation. Each autoclave will have five compartments and will operate at 150 C and 1,200 kpa. Discharges from the autoclaves will be depressurized in a 2-stage agitated flash tank after each autoclave. Discharges from the flash tanks will then be thickened in two brick-lined thickeners, 18.25 m in diameter.
By eliminating the roasting step, about 25% of the sulphur contained in the sphalerite concentrates will be recovered in its elemental form. Production of the yellow element could reach 40,000 tonnes per year. At a market value of $100 (US) per tonne, this could provide revenues if impurities, such as selenium, can be removed economically. Under the present operating system, about 96% of the sulphur is oxidized in the roasting step and sent up the stack in gaseous form. Using pressure leaching, only 68% of the sulphur contained in the ore would make it up the stack into the atmosphere.
There are two commercial zinc pressure leaching plants in operation in Canada — one at the Kidd Creek metallurgical complex in Timmins, Ont., and one at the Cominco’s smelter in Trail, B.C. The proposed HudBay operation would be unique, according to Chief Plant Engineer Brian Krysa, in that the total zinc plant concentrate feed plus a portion of stockpiled leach residues will be treated in a 2-stage counter-current leaching circuit.
Underflow from the second stage of thickening is filtered on conventional drum filters and sent to the sulphur flotation circuit. This circuit will consist of four roughers, three scavengers and two banks of three cleaners. All cells will have a capacity of 3 cu m. The flotation tails should contain 88% of the iron in the feed material plus most of the silver and about 1.6 g gold per tonne, according to Krysa. Recovery of these precious metals is being investigated. The flotation concentrate contains sulphur and most of the gold. This concentrate will be washed and filtered on a table filter, then melted in a Cominco- designed melting cyclone. The liquid is then pumped to a hot filter press to separate elemental sulphur liquid from the sulphide cake containing the precious metals. This will be treated in the smelter.
Separate circuits are planned for the removal of gypsum, copper and iron from the process. In addition, a leaching circuit to treat stack dust and a waste water treatment circuit will be constructed.
It’s no secret that pouring base metals matte in smelters built shortly after the turn of the century goes hand-in-hand with pumping acid rain-causing sulphur dioxide into the atmosphere. Ask any smelter worker in Flin Flon, Man. In this community, where 1,800 people are employed by Hudson Bay Mining & Smelting, in-plant environmental problems have reached serious proportions. And the company knows it. HudBay estimates it is going to cost $130 million just to make zinc and copper smelting physically feasible in Flin Flon in the 1990s. The installation of three autoclaves would cut sulphur dioxide emissions in this northern Manitoba mining community by 25%, and copper-smelting technology licenced by Noranda Inc. would cut fossil fuel consumption by 50%. But demand for Manitoba’s hydroelectricity would actually increase. This all adds up to good news for Manitoba, which is spending millions to develop hydroelectric capacity in the north and which has an interest in maintaining the long-term viability of the community of Flin Flon,–if, that is, Inspiration Resources, HudBay’s New York-based parent, can come up with the money to modernize its aged smelting complex.
HudBay has compiled detailed plans and preliminary engineering work to bring the 60-year-old zinc and copper metallurgical complex into the 21st century. It has made presentations to senior department heads in both the provincial and federal departments responsible for environmental regulations. Early this year Cominco Ltd. and Noranda Inc. both received government assistance to modernize their smelters in Trail, B.C., and Rouyn-Noranda, Que., after extensive lobbying. HudBay hopes to get support, in the form of long-term loans, for its plans as well, according to Area Manager Keith Callander. It has been lobbying the government for about one year now. (Inco Ltd. and Falconbridge Ltd., two other smelter operators in Canada, have until December, 1988, to submit their sulphur dioxide abatement plans to the Ontario government for their operations in Sudbury.)
The modernization plan at Flin Flon involves the introduction of new hydro- and pyro-metallurgical technology developed by two of Canada’s premiere base metals metallurgists — zinc pressure leaching technology developed by Sherritt Gordon and bath smelting of copper concentrates in a continuous converter developed by Noranda Inc. and Codelco (Corporacion Nacional Del Cobre de Chile). Highlights of the plan include:
* a slightly better copper recovery (95.3%-95.5%);
* a slightly lower overall zinc recovery (89.18% compared to 90.93%) due to zinc losses to the copper concentrate which are recovered under the present process but which will not be recovered under the proposed system;
* significantly lower production costs as a result of a 50% reduction in fossil fuel consumption and a reduction in the workforce in the metallurgical complex by about 200;
* higher electricity consumption (by about 9-10 mw) as a result of using the Noranda continuous converter;
* a significantly improved working environment because of improved containment; and
* the elimination of on-line maintenance in the smelter’s baghouse.
The existing plant is a conventional roast/leach/electrowinning plant, using 1930s technology. Ten multiple hearth roasters are used along with pachuca leaching, two stages of purification, solution cooling and electrowinning cells arranged in cascade. Copper and precious metals are removed from the ferrite residues in the reverberatory furnace matte while zinc follows the slag to the fuming furnaces.
The proposed system will require significant modifications to the Flin Flon smelter. Areas which will become redundant include the zinc and copper roasters, pachuca leaching section, the reverb furnace, the costly fuming plant, coal plant, baghouse and drying plant. New plant areas include a new oxygen plant, a stack dust leach complex, a feed preparation complex, a zinc pressure leach complex and a new electrical substation. Concentrates from Hud Bay’s mills will be prepared for further processing in a new feed preparation facility. A 600 hp ball mill will regrind about 500 tonnes of concentrates per day to 98% passing 45 microns. The slurry will be thickened to 70% solids and pumped to the zinc pressure leach plant.
In the pressure leaching circuit two horizontal autoclaves, each 20 m long and 3.3 m in diameter, will be needed. A third will be purchased as a spare in order to maintain year-round operation. Each autoclave will have five compartments and will operate at 150 C and 1,200 kpa. Discharges from the autoclaves will be depressurized in a 2-stage agitated flash tank after each autoclave. Discharges from the flash tanks will then be thickened in two brick-lined thickeners, 18.25 m in diameter.
By eliminating the roasting step, about 25% of the sulphur contained in the sphalerite concentrates will be recovered in its elemental form. Production of the yellow element could reach 40,000 tonnes per year. At a market value of $100 (US) per tonne, this could provide revenues if impurities, such as selenium, can be removed economically. Under the present operating system, about 96% of the sulphur is oxidized in the roasting step and sent up the stack in gaseous form. Using pressure leaching, only 68% of the sulphur contained in the ore would make it up the stack into the atmosphere.
There are two commercial zinc pressure leaching plants in operation in Canada — one at the Kidd Creek metallurgical complex in Timmins, Ont., and one at the Cominco’s smelter in Trail, B.C. The proposed HudBay operation would be unique, according to Chief Plant Engineer Brian Krysa, in that the total zinc plant concentrate feed plus a portion of stockpiled leach residues will be treated in a 2-stage counter-current leaching circuit.
Underflow from the second stage of thickening is filtered on conventional drum filters and sent to the sulphur flotation circuit. This circuit will consist of four roughers, three scavengers and two banks of three cleaners. All cells will have a capacity of 3 cu m. The flotation tails should contain 88% of the iron in the feed material plus most of the silver and about 1.6 g gold per tonne, according to Krysa. Recovery of these precious metals is being investigated. The flotation concentrate contains sulphur and most of the gold. This concentrate will be washed and filtered on a table filter, then melted in a Cominco- designed melting cyclone. The liquid is then pumped to a hot filter press to separate elemental sulphur liquid from the sulphide cake containing the precious metals. This will be treated in the smelter.
Separate circuits are planned for the removal of gypsum, copper and iron from the process. In addition, a leaching circuit to treat stack dust and a waste water treatment circuit will be constructed.
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