Early control strategies were simple "dilution is the solution to pollution" as exemplified by the government legislation driven installation of tall stacks at smelters across the United States and Canada. The tall stacks were designed to improve the local air quality via increasing the dispersion of SO2 emissions. While these installations improved the local air quality (Potvin,Negusanti 1993) they did nothing to reduce the regional, national, and even global impact of these emissions.
Most technologies developed and strategies implemented to date have tended to concentrate on end of pipe solutions to environmental problems (AWMA 1992). This is known as the 'react and cure' mode of developing environmental control technologies/strategies (Watson 1993). Using the old adage 'an ounce of prevention is worth a pound of cure', future direction must be towards a proactive approach or a reduction or prevention of environmental problems at source. The case study illustrates this concept in its infancy. The strategies need not be limited to the organisation’s own problems, but can take a proactive approach to resolve others' problems to its benefit. The case study includes such activity.
The Spawning and Development of Legislation
In the sixties and early seventies the deteriorating state of the environment led to a public outcry for action. The 1969 images of 'Spaceship Earth' taken by the lunar astronauts helped change public impressions of the limitless ability of the planet to absorb the waste products of our civilizations and view the planet as a finite closed ecosystem. The birth of vocal, radical environmental non-government organizations (ENGOs) such as Greenpeace circa 1969, raised public awareness of environmental issues. The sum of all this activity was to create pressure of the various levels of governments to act on environmental problems.
Governments around the globe began to develop, implement, modify and enforce new and broader environmental legislation (IUAPPA 1991). In 1967, the Ontario government introduced the Environmental Protection Act which provided the framework for directing specific legislation at corporations mandating emissions reduction. A prime example of this is the ongoing series of legislation, promulgated by the Ontario Ministry of the Environment and Energy, aimed specifically at INCO Ltd, once the world's largest single point source of SO2 emissions.
Sulphur Fixation - Pre 1993
The reverberatory furnace smelting technology used by the company until November 1993 consumed copious quantities of fossil fuel and produced large volumes of low strength waste gas unsuitable for past or current fixation technology. This gas was vented to atmosphere. Circa 1950, a 400 tonne per day sulphuric acid plant was installed at the smelter which had the economic benefit of supplying most of the company's internal H2SO4 requirements.
The mid-fifties introduction of flash furnace technology for copper smelting and the resultant high (~75%) SO2 concentration offgas allowed the construction of a 400 tonne per day liquid SO2 plant. The technology benefited the company in two ways. The flash smelting process is 'autogenous' which, in this application, means that the heat supplied by the combustion of S contained in the feed to SO2 replaces that provided by fossil fuels in the reverberatory process. The liquid SO2 product had and continues to have high market demand for the ~80 000 tonnes produced annually.
Legislation
The first emissions Control Order from the Ontario MOE for the INCO Copper Cliff smelter came in effect on July 1, 1970 and imposed a 5 200 ton per day SO2 restriction as well as mandating the construction of a 381 m 'Superstack'. This stack has become globally famous as a symbol of atmospheric air pollution. This first order was followed by a continuing series of Amendments with the following allowable SO2 limits. Dec. 31, 1974 - 4 400 tons per day Dec. 31, 1976 - 3 600 tons per day Dec. 31 1978 - limit of 750 tons per day(rescinded)
INCO balked at the last restriction. This limit was beyond the company's technical and financial resources at the time. Intense discussions between the company and the government resulted in the passing in 1980 of Regulation 301, an official act aimed specifically at INCO's Copper Cliff smelter. This legislation limited the SO2 emission to 2500 tons per day up to the end of 1982 and to 1950 tons per day thereafter.
The company and MOE reached an agreement to run a voluntary emissions reduction program. This program included a meteorological data gathering system, mobile SO2 monitoring, source modelling, and production reductions to meet ground level SO2 concentration limits no greater than 0.50 ppm from any combination of emission sources. In 1983 a Control Order amendment was issued which changed the voluntary program into an officially regulated program. In a globally unique situation, INCO had to supply the equipment and personnel to monitor ground level SO2 concentrations from April to October of each year. The Ministry of the Environment maintains a system of continuous SO2 monitoring stations which effectively ring the Copper Cliff operations.
In 1985 Regulation 660 under the Environmental Protection Act, came into force as part of the MOEE's Countdown Acid Rain program. This legislation imposed significantly reduced annual SO2 emission limits in 1985 of 685 kilotonnes to be reduced to 265 kilotonnes in 1994.
Developments in Technology
In order to comply with this regulation the company devised it's $Can 600 000 000 Sulphur Di-Oxide Abatement Program (SOAP). Based on suitability and economics, the prime technologies to be utilized were flash furnace technology with H2SO4 acid generation and increased pyrrhotite rejection.
The company developed a "bulk" smelting process for a combined nickel-copper concentrate in two flash furnaces. A portion of the offgas from the flash furnace is directly compressed into liquid SO2 while the remainder is air diluted to meet the requirements of sulphuric acid manufacture. The economic benefits to the company are lower energy costs and increased productivity, and the conversion of formerly waste gases into saleable products.
Increased pyrrhotite rejection at the mill reduces the S input to the smelter and hence SO2 emissions while boosting productivity as almost all the iron input to the smelter is rejected as slag in the furnaces. Improved milling practice, employing a semi-autogenous grinding mill and large volume flotation cells, has resulted in more of this pyrrhotite material reporting to tailings while retaining the valuable metals values. The rejected pyrrhotite is stored in a separate area of the company's tailings area as it is viewed as a future source of nickel. The economic benefits of this are obvious and illustrate the 'proactive prevention' principle in its infancy.
Recycling for Profit
The ever increasing costs of obtaining and milling ore and/or additional revenue generation have led the company to actively obtain other companies' waste material for recycling as feed. An example of this is the fact that the company has become the world's largest recycler of automobile catalytic converters for the platinum and palladium content. This diverts a potential environmental problem into a productive material and represents a dramatic departure from the old 'if it don't make nickel, don't do it.' company philosophy.
Discussion
Sulphur emission as sulphur dioxide gas via tall stacks merely serves to transport the sulphur problem to another location. However, the company's entire area facilities are based on a pyrometallugical process from which one can never have zero SO2 discharge. Conversion to a hydrometallurgical process and hence SO2 free process would create its own set of enviro-problems from a water standpoint and is an economic impossibility for the company.
While reducing the atmospheric problem, increased sulphur in ore disposal to tailings will add to the existing problems of acid drainage and additional industrially stressed land. However, the water discharging the tailings areas is routed to the company's Copper Cliff Creek Waste Water Treatment plant. The restoration of vegetation in tailings areas is an environmental control technology/strategy for which the company is world famous (Heale 1993).
The waste water treatment plant and reclamation program form part of the integrated environmental abatement, management, and restoration system in place at the company. Such integrated systems have become the norm in industrialised nations.
Sulphur fixation as liquid sulphur dioxide or sulphuric acid is merely an extended media transfer. The sulphur content of these chemicals eventually end up being discharged into the natural environment by the consumers. However, the opportunity for pollution prevention is much greater than possible for gaseous release.
The low SO2 concentration in the 381 m stack at 0.5 to 1.0 %(vol.) is not amenable to treatment by fixation as sulphuric acid. Most other treatment methods involve some form of 'scrubbing' which in turn generates solid and/or liquid wastes. The amount of the secondary wastes(s) that would be generated from a scrubbing approach to treating INCO's SO2 emissions creates a different set of pollution problems. The corrosive nature of the typical scrubbing exhaust gases puts the capital costs of this approach beyond the reach of the company. Disposal of the wastes , which would probably be a low quality high volume gypsum, would add to the present tailings problem and result in the need for additional expensive disposal area.
Summary
Driven by government legislation, the company devised a program of development of emission control technologies and strategies which have proved to be politically, socially, economically and environmentally advantageous. The emission situation now is a mirror of that which existed in the 1960s when 90% of the ore's sulphur content was emitted to atmosphere. Since the end of 1994 only 10% of the ore's sulphur content will be emitted to atmosphere; a reduction of 1 735 000 tonnes of SO2 input to the global balance.
The company had and is marketing its experience and technology on a global basis through a subsidiary. This is a small but real payback for implementing control technology.
The whole sulphur dioxide abatement process has been a rare WIN/WIN scenario for the enviroment and the company.