TAILINGS PILE

FEED BIN

FIGURE 1—The agglomeration system ahead of the tailings pile.

tute of Safety and Health in the U.S., is now used throughout the asbestos industry. It involves passing two litres of air per minute through a filter membrane which entraps the fibre. The filter is then mounted on a microscopic slide and fibres are counted by using a 450 to 600X microscope and recorded as fibre per cubic centimeter (f/cc).

Cassiar’s new mill air building provides 480,000 cfm of pro- ~ cess and ventilating air.

FIGURE 2 — Diversion of Troutline Creek in 1976.

Since June 1973, with the introduction of the filter membrane technique of sampling, Cassiar has reduced its average fibre counts from approximately 16.0 to less than 5 f/cc by instituting concrete environmental programs along with education of the employees on the proper handling of asbestos fibre. It was not until the early 1970’s that engineers were able to develop the necessary improved technology to reduce dust emis- sions. In some instances, the technology is still to be attained.

Company Action Taken

By 1974, Cassiar had embarked on a program to meet government standards wherever possible by practical economics and existing technology. The fol- lowing are examples of action taken.

(a) Prior to 1973, wet collectors or cyclone collectors were known as providing the best suitable emission control techniques for hot gases from ore dryer stacks. However, with the development of filter fabrics for dry collection of high-particulate hot gases, bag filter units were adopted and proved to outperform conven- tional wet cyclone collectors. In 1973, Cassiar reduced emissions from its ore dryer stacks by removing its conventional cyclone collectors on three rotary dryers and installing bag filters; this reduced emissions from 300 lb/hr to less than 25 lb/hr per dryer stack.

(b) In 1974, Cassiar directed its attention to con- trolling dust emissions from the tailings pile. To reduce these emissions, an agglomeration system — or pug mill — was installed (Fig. 1). This reduced emis- sions to an acceptable level; there was no visible dust on discharge to the storage pile. It is now planned to install a second pug mill to wet other low-grade fines emanating from other product processing operations.

(ec) To avoid possible contamination of the town’s water supply, Cassiar re-routed Troutline Creek in 1976. This involved bulldozing a new creek bed and diverting the flow of water away from the low-grade storage pile (Fig. 2). The new water course has been seeded with suitable grasses and legumes to restore the beauty of the landscape.

(d) In 1977, Cassiar completed the construction of a changehouse (Fig. 3) for employees entering or leay- ing the plant. This facility is designed to prevent em- ployees from carrying free asbestos fibre into their homes.

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