DUST CONTROL ISSUES DIFFERENT IN EAST
In the world of American mining, “East is East and West is West and never the twain shall meet,” is quite true, especially in environmental management. While Western mines work in drought like conditions, extreme temperatures, and high altitudes, Eastern mines have water, moderate temperatures, and low altitudes. The result is that issues like dust control and reclamation are seen in a different light.
Water makes a lot of difference. Mine scarring will revert to nature much more quickly than it will in the West thanks to rains. It also makes dust control different. In fact, in the East, a dust control problem one month can become a mud control problem the next.
For the Western miner, all that rain seems to make dust control a mute issue. They obviously haven’t seen a dry period when the topsoil turns into a flour-like dust. Nor do they realize that on haul roads, heavy rains will cost a mine thousands of dollars a year in additional gravel. When the roads are wet, the gravel is forced to the side of the road as the tires move through the mud. Then, when the road is dry, the gravel is thrown off the road and often into the windshields of other trucks and cars. As a result, vehicle repair costs are higher and the gravel must be replaced frequently.
Dust control product that work better in the east than the west are hygroscopic salts like calcium chloride (table salt) and magnesium chloride that draw water from the atmosphere and hold in the surface soil. Unfortunately, they can also corrode equipment over a long time.
A more environmentally friendly solution is organic sulfonates like lignosulfonate. They are byproducts of the lumber industry and control dust in the same manner as hygroscopic salts. The major difference is that the material, which looks like molasses is organic, non-toxic, and won’t corrode equipment.
The third group is emulsion products, which includes a wide range of natural and synthetic materials that bond the soil together like glue. They include latex, polymers, and petroleum products. They come as a concentrate, are mixed with water and sprayed on the road surface. Usually, the stronger the compound, the harder it is to penetrate the soil. Therefore, the dusty roads are treated with a weaker solution to bind all the soil within a few inches of the surface and then retreated later with a stronger solution that provides greater protection to the surface.
Another problem for Eastern mines is that conditions can change during the year, which necessitates differing treatments. For instance, if there are moderate rains, the haul road is a packed dirt road with little dust and a thick product that binds dirt will work very well. If the road is dusty from a prolonged dry season, the mine needs a lighter product that penetrates the dust and binds it. If the road handles heavy traffic during heavy rains, the issue isn’t dust control, but road maintenance.
In order to find the best dust control agent, the Department of Defense set up a test at Fort Sill and Fort Hood in the late 1990s. They looked at four agents and how they worked on dirt roads: polyvinyl acrylic polymer, soybean feedstock processing byproduct, calcium lignosulfonate, and a 38% calcium-chloride solution. They discovered that all four agents were equally effective during the first month by reducing dust by 50%. Generally the dust control agents continued to provide protect past 60 days. However, polyvinyl acrylic polymers tended to break down between the first and second month as heavy traffic tended to break down its surface sealing characteristics.
Another dirt road dust control study was done by California and focused on eliminating the fine dust that remains suspended in the air and is inhaled. They discovered that polyvinyl acrylic polymers reduced these fine dust particles by 90%. Lignosulfonates reduced dust by 20% and calcium chloride 10%.
When it comes down to it, there is no perfect dust control agent for haul roads. Mine managers have to consider several factors, including soil composition, local environmental regulations, and traffic.
Here’s an example. Lignosulfonates don’t last as long as chloride products, so they can cost more. However, they are more environmentally friendly. But if lignosulfonates get on heavy equipment, it’s like trying to get pine tar off. Usually warm, soapy water does the trick, but that increases water usage and pollution problems. There are also some minor downsides to the smell and color of lignosulfonate. When you first put it down, it smells like pine tar, but that dissipates quickly. The lignin also turns the road black because of the color of the product.
Whatever the dust control agent you choose, they all offer advantages. Just make sure your dust control program fits your climate, operation, local regulations, and soil conditions.