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Appendix 6.10   Noranda Metallurgy Inc.,Horne Smelter, Rouyn-Noranda, Quebec

• Profile
• Process Description
• Releases
• Regulatory and Non-Regulatory Programs
• Monitoring and Research
• Programs and Plans
• Issues
• Technical Options to Achieve Further Release Reductions

Profile

Noranda Metallurgy Inc., Horne Smelter, operates a copper smelter in Rouyn-Noranda, Quebec. The plant started production in 1927 to process copper concentrates produced by an associated mine-mill complex. Prior to the 1970s, the smelter utilized conventional copper smelting technology including reverberatory furnaces and Peirce-Smith converters. Development and installation of Noranda's patented reactor for the treatment of copper concentrates permitted the gradual elimination of the reverberatory furnaces. The mine closed in 1976, and the smelter now processes custom and toll copper concentrates and secondary materials from a variety of sources world-wide. A sulphuric acid plant entered service in 1989. The smelter produces copper anodes and sulphuric acid. Selected production data for the period 1988 to 1995 are presented in Table A6.10.1, which includes projected levels for the year 2000.

Process Description

The process is outlined in Figure A6.10.1.

Figure A6.10.1   Noranda Horne Copper Smelter Process Flow Sheet

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Copper concentrates and fluxing materials (silica) are proportioned to form a low viscosity FeO-SiO₂ slag with low copper content. New feed is mixed with recycled slag concentrate and dust from the smelter and processed in a single Noranda Reactor. Most of the copper in the smelter feed are contained in sulphide minerals and reports to the molten sulphide matte phase, while the bulk of the non-sulphide gangue forms an oxide slag containing copper at low, but economically recoverable concentrations. The higher density matte separates from the slag, which is combined with converter slag and is slowly cooled, ground and processed by flotation to recover most of the contained copper. Off-gases from the Noranda Reactor are treated by a dry electrostatic precipitator to remove particulate matter. The clean reactor off-gases are then directed to a single absorption sulphuric acid plant for recovery of sulphur dioxide.

Dust is returned to the reactor for recovery of copper and is also bled from the circuit to control impurity levels and reduce emissions. The gas cleaning section of the acid plant includes a mercury tower to minimize mercury emissions and ensure acid quality. Weak acid solution from the acid plant is neutralized with lime and mixed to react with a ferric sulphate solution to precipitate metals in solution, combined with mill tailings from slag flotation and co-deposited in the tailings impoundment area.

Matte is processed on a batch basis in Peirce-Smith converters to oxidize sulphur to sulphur dioxide and reduce copper to the metallic state. Oxygen-enriched air is used to convert iron sulphide to iron oxide, which combines with added flux to form an oxide slag and separates from the copper sulphide matte phase. This slag contains relatively high copper levels and is processed together with the slag from the Noranda Reactor to produce a slag concentrate that is returned to the reactor. As the converter cycle continues, copper sulphide is converted to blister copper containing dissolved sulphur and oxygen. Conversion of iron and copper sulphides produces converter off-gases containing substantial quantities of sulphur dioxide at concentrations which vary over the course of the batch operation. Converter off-gases are treated by a dry electrostatic precipitator to remove particulate matter. Dust is returned to the reactor for the recovery of copper, and is also bled from the circuit to control impurity levels and reduce emissions. The cleaned converter off-gases are released to the atmosphere. A portion of the copper concentrate feed is dried and injected directly into the Peirce-Smith converters to supplement the matte feed and maintain production capacity since the shutdown of the reverberatory furnaces.

The dust bleed stream containing copper, lead, cadmium, arsenic and other impurities is processed to recover valuable metals and then stabilized at the site. Effluents from dust treatment are treated by lime neutralization and ferric sulphate at the weak acid treatment plant, combined with mill tailings from slag flotation, and codeposited in the tailings impoundment area.

Blister copper is processed in an anode refining furnace to remove most of the dissolved oxygen and sulphur. The product is then casted into copper anodes, which are shipped to Noranda Metallurgy Inc.'s CCR Refinery in Montreal-East for electrolytic refining of copper and precious metals.

Releases

Point sources of releases to air and water from the smelter are shown in Figure A6.10.1 and controlled as outlined above.

Dry process gases from the Noranda Reactor and converters are treated by dry electrostatic precipitators for particulate control. Process gases from the reactor are treated and cleaned through a single absorption acid plant. Process gases from the converters containing lower concentrations of sulphur dioxide are not strong enough or consistent enough in strength to be sent to an acid plant and are released to the atmosphere. These controls maintain vessels under negative pressure and reduce fugitive emissions from process equipment. All conveyors are fully enclosed to reduce fugitive emissions.

Major liquid effluents from the smelter site are collected and treated at the weak acid water treatment plant, combined with slag flotation concentrate tailings and are monitored. Other effluents are lime treated along with acid mine drainage from old sulphide mine tailings and are sent to polishing ponds and monitored.

Selected release data for the period 1988 to 1995 are presented in Table A6.10.2 and Figure A6.10.2 and projected levels for the year 2000 are included. Releases of CEPA substances decreased by over 60% from 1988 to 1995 and further release reductions are projected.

Figure A6.10.2   Noranda Horne Releases to Air and Water

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Some potential to form dioxins and furans exists at smelters with chlorinated plastics or other chlorinated substances in their feeds. Mechanical pretreatment can effectively separate metals and plastics contained in wire, but cannot separate copper from printed circuit boards or other electronic scrap. These particular materials constitute an important feed source for the Horne smelter.

This risk was anticipated by Noranda and Québec. Such materials are smelted only in the Noranda Reactor, and reactor off-gases are processed by an acid plant. Combustion parameters exceed design criteria established to minimize dioxin and furan releases from hazardous waste incinerators. Detailed and comprehensive sampling and analysis was conducted by or in the presence of provincial officials to verify performance over a wide range of operating conditions. Acid plant tail gas, weak acid and the intermediate and final effluents from the tailings pond were sampled and analysed for organic parameters selected by Québec, with the methodology based on methods published by the U.S. Environmental Protection Agency. An international toxic equivalent factor was used to express the results in terms of Toxic Equivalent 2, 3, 7, 8 PCDD/PCDF by calculation according to a method published by the North Atlantic Treaty Organisation. During the test periods, recyclable feed rates were as high as 64 t/h, exceeding the usual feed rate of 12 t/h by a factor of four to five. The results demonstrated that even at exceptionally high plastics feed rates, combined releases to air and water from the smelter would not exceed 0.1 g/y.

Regulatory and Non-Regulatory Programs

The copper smelter is regulated by the Quebec Ministry of Environment and Wildlife (MEF). An SO₂ emission standard of 276,000 tonnes/y (50% of the 1980 level) was implemented by regulation and came into force for 1990, triggering construction of an acid plant at the end of the 80's. Current emissions are around 165,000 tonnes/y SO₂. Québec has also established a particulate emission standard of 50 mg/m³ for ventilation sources associated with concentrate handling. Certificates of authorization are required for installation of controls on air emissions (such as baghouses, etc.). The air quality regulations are under review and may be amended to further limit SO₂ emissions to levels consistent with Noranda's public commitments. The smelter has committed to limit SO₂ emissions to 30% of the sulphur input and particulate emissions to 1.2 kg/t (feed basis) by 1998 and to reduce those emissions to 10% of input sulphur and 0.4 kg/t (feed basis), respectively, by 2002.

Québec has also established ambient SO₂ air quality standards for hourly, daily and annual averaging periods. The current standard for the hourly mean concentration is 0.50 ppm. The regulation under review would reduce the standard to 0.34 ppm but would allow for exceedances of not more than 0.20% of the total sampling hours provided that the concentration does not exceed 0.50 ppm.

The smelter effluent is subject to the general prohibition of deposits of deleterious substances in Subsection 36(3) of the Fisheries Act. Liquid effluents are controlled by the Quebec Ministry of Environment and Wildlife through Directive 019. A separate certificate of authorization covers the liquid effluent from the tailings pond, which receives treated water from the weak acid treatment plant.

Noranda accepted the ARET challenge in 1994 and submitted an action plan that detailed specific goals for each substance. Noranda's goals were reviewed and updated in mid-1996 and reported to ARET.

Monitoring and Research

The ambient air sampling network includes seven continuous SO₂ monitors, linked to the Intermittent Control System (I.C.S.). Introduced in 1971, the I.C.S. is operated by meteorologists and technicians for predictive control of sulphur dioxide concentrations in ambient air at ground level. Specialized scientific instruments are used to determine atmospheric conditions and stability, which affect gaseous distribution. These parameters are used to develop local meteorological forecasts and to predict future air quality. Weather conditions effectively determine the allowable SO₂ emission rate to the atmosphere and smelter production levels. An environmental policy clearly indicates the full commitment of smelter operations to comply with instructions from I.C.S. staff concerning smelter production levels and SO₂ emissions. Actual observations recorded at the SO₂ monitors confirm that the ambient air standards are not exceeded and can also be used to refine the predictive model. In the event of an exceedance, I.C.S. staff provide instructions to further reduce SO₂ emission rates.

The ICS was modernized and installed in a new building at the restored and revegetated Chadbourne mine site in 1990 at a cost of $1.3 million, where it provides staff with a clear view of operations, plume movement and direction in addition to continuous surveillance of ambient SO₂ concentrations.

Dust-falls and high volume samplers are operated for particulate monitoring.

During the period 1991 to 1993, the smelter participated in a pilot project with the Québec - MEF for evaluation of the Programme réduction des rejets industriels (P.R.R.I.) (Industrial Waste Reduction Program). In depth characterisation was performed for process emissions to air and water at a cost of approximately $250,000.

The Centre de technologie Noranda sampled water and sediment quality in various lakes around Rouyn-Noranda at the end of 1994. Comparison with the results of previous studies shows general improvements in water quality, while metal concentration in sediments stayed at the same level. Recent release reductions are not apparent in sediments due to the slow rate of deposition of new sediments.

Programs and Plans

1984
Constructed facilities to receive, sample and prepare recyclable materials for processing at a cost of $X million.

1987-89
Shut down last reverberatory furnace and commissioned sulphuric acid plant at a cost of $160 million, achieving reductions in particulate and SO₂ emissions in excess of 50% for 1990 compared to 1980.

1990
Commissioned systems for concentrate drying and injection to the converters to replace lost production capacity at a cost of $15 million.

1990-1996
Unused sections of the plant were demolished and a program of gradual revegetation with grasses and trees was implemented around the smelter. Demolition of Stack No. 3 was completed in 1993 at a cost of $750,000. Annual costs are approximately $500,000 for demolition and $200,000 for revegetation.

1991
Developed technical options for further reductions in SO₂ and particulate emissions.

Publicly committed to further reduce SO₂ emissions (aiming at 90% reduction compared to 1980).

1991-92
Worked in partnership with representatives of the community, ministére de l'Environnement et de la Faune, municipality and regional health services centre to initiate and complete a community program for removal of lead-contaminated soil from the Quartier Notre-Dame, a residential area adjacent to the smelter. Close to 650 lots were remedied by replacing top soil and lawns at a cost of $3.1 million.

1992-93
Developed, pilot tested and implemented Peirce-Smith converter modifications at a cost of $10 million.

1994
Constructed major in-door copper concentrate storage area at a cost of $6 million.

Commissioned mercury removal towers in the gas cleaning section of the acid plant at a cost of $2 million.

1994-95
Developed conceptual design of a new pyro-metallurgical vessel at a cost of $1.9 million to reduce Peirce-Smith converter SO₂ and particulate emissions by processing reactor matte and directing off-gases to the existing acid plant.

1996
Commenced Noranda Reactor building expansion and construction of a Noranda converter to replace existing Peirce-Smith converter technology at a cost of $53.3 million.

1997
Baghouse installation for particulate removal from secondary ventilation gases from the tapholes of the Noranda Reactor and future Noranda Converter at a cost of $2.9 million.

Noranda Environmental Awareness Training (NEAT) Program to be offered to all employees at the Horne smelter, focused on personal responsibility for environmental compliance and performance improvement.

1997-98
Commissioning of the Noranda Converter to initially process 40% of reactor matte, with the remainder being treated by the Peirce-Smith converter. One or two Peirce-Smith converters will be modified as refining furnaces to complete sulphur oxidation prior to the anode furnace. Sulphur fixation is expected to exceed 70%.

1998-2001
Adaptation of operations to the new process, with Noranda Converter throughput increasing to 100% of reactor matte. Expansion of some sections of the sulphuric acid plant to process all reactor and converter off-gases at a cost of $50 million. Sulphur fixation is expected to exceed 90% by 2002.

Issues

Commissioning of the Noranda Converter entails substantial technical and financial risks, since new metallurgical principles will be applied in this vessel. This proprietary technology was developed by Noranda and the Horne installation will be the first commercial application.

Custom smelting brings uncertainty in the long term supply of feed materials. A successful custom smelter must have the capability to efficiently process feeds of varying quality while maintaining consistent product quality and competitive operating costs and concentrate treatment charges.

Capital resources will be scarce within Noranda Metallurgy Inc. for the next several years as major investments are foreseen at the Horne, C.C.R. and C.E.Z. and for potential development of the Magnola project to recover magnesium from asbestos residues.

Technical Options to Achieve Further Release Reductions

An Environment Canada report for the Acidifying Emissions Task Group characterizes the Horne as a large size copper smelter with an acid plant. From a national perspective, SO₂ emissions remain major at this site in spite of substantial reductions to date. Noranda's current plans will increase the capture of SO₂ to 90% and will also achieve further reductions in metal emissions. When those plans have been implemented, the facility will employ current state-of-the-art process and pollution control technology and management practices and will have no significant uncontrolled sources of metal releases. Further incremental release reductions beyond the year 2002 could be achievable with continual improvement.