Overview of Mine Dust and Dust Controlling Agents

1.0 Background

A typical mine tailings site contains many millions of tons of tailings deposited during the operating life of the mine. The tailings impoundment usually covers a large area, sometimes hundreds of hectares, and is comprised of the embankment made of earth fill or tailings, a sandy beach grading to fine tailings adjacent to the tailings pond. Much of the tailings fines may be under water. Removal of water from the tailings, during periodic dry periods and on mine closure, results in the exposure of beaches which can dry out. Wind erosion can cause dusting from the embankment, sandy beaches or dried out fine slimes pond zones. In many instances this dust can be an annoyance or hazardous to the environment and needs to be controlled.

A wide range of control methodologies are available including the development of good vegetation cover, the placement of granular wind resistant materials and the spraying of bonding agents to form an erosion resistant crust. The practicality of use is dependent on the access that is required onto the tailings in order to place the dust control measure. Access onto embankments and sandy beaches is normally such that none of the above methods are precluded. Since the very soft nature of the tailings slimes often prevents access by heavy vehicles, the agent must be placed using extremely light equipment, possibly hand held sprays. This limits the agents that can be used to those agents that can be sprayed onto the tailings.

Since run-off from the tailings is into the tailings pond water, which may be discharged, it is often necessary that the spray agents be either insoluble or that they do not contain leachable constituents which would contaminate the pond water and result in unacceptable water quality.

2.0 Previous Studies

The US Nuclear regulatory Commission carried out an evaluation on various dust control techniques. (Elmore M.R. and Hartley J.N. (1985) - Evaluation of Field-Tested Fugitive Dust Control Techniques for Uranium Mill Tailings Piles.) They tested 17 chemical stabilizers by applying them to test plots on a Uranium tailings pile in Wyoming, USA. Windscreen systems were also evaluated. but are not considered here. In 1985, the cost/ha/year to chemically stabilize the tailings pond ranged from $1700 to $19000 for the tested stabilizers. The various chemicals were gene rally effective at reducing dust emissions over the short term (1 year) but their durability varied widely and was not proportional to their cost.

Soil-sement and Wallpol 40-133 were included in the 1984 study. Wallpol 40-133 gave good results and exhibited the highest durability in this study. Suppliers of both products have indicated that these agents have been modified since the study. This could mean that the previous results are not fully representative of the current products but they are useful for information regarding the minimum performance of these products. Wallpol 40-133 is now called Wallpol 40-143. We have investigated a number of available products which appear to be well suited for controlling tailings dust.

3.0 Product information

All products are supplied in liquid form in containers of various sizes. As an example, Enduraseal 100 and Soil-Sement are supplied in drum sizes up to 1200 litres and Wallpol 40-133 can be supplied in 5000 gallon containers. Product concentrations vary, therefore some products need to be diluted more than others to achieve similar results. All products have been used for various applications with good results. While we have not evaluated the chemical constituents in the various products it appears that t hey do not have negative environmental consequences.

4.0 Application Method

Most dust suppressant agents, including these, are water based and are supplied in a concentrated liquid form. They must be diluted with water and sprayed onto the dry tailings surface from hand held sprayers or from truck mounted spray canons.

5.0 Application Rates

All the investigated products must be diluted in a ratio of approximately 9 parts water to 1 part concentrate. They are applied at a rate of approximately 4 litres of dilution per sq. metre of covered surface. For all products an allowance must also be ma de for transporting to site, trucking on site and for the pumping and spraying equipment required.

6.0 Product Life

These products have a useful life which is dependent on the concentration applied and local weather conditions. It is estimated that, for the above concentrations, these products will have a useful life of approximately one year. It is possible to reduce the concentration of the mixture and spray the area more frequently. This will reduce costs for shorter control periods. In the study carried out in 1984 it was found that there were cheaper chemicals with a lower durability that could effectively control dust if the frequency of application was increased. The cost and difficulty of access and hand spraying will probably dictate the selection of application rates that minimize the need for repeated application.

7.0 Performance

All suppliers claimed that their products reduced dust emissions by up to 90%. Durability effectiveness will vary with time. The previous study indicated that some product effectiveness reduced by up to 50% after 30 days. References were obtained where possible and these were all favorable for whichever product was being queried.