Is bitumen still a safe option for dust control?
In this article, we examine why it’s so widely used and suggest some cleaner options that have the same performance.
“The reason bitumen has traditionally been used for haul road stabilisation is that it lasts so long,” says Luitpold Fried, Chief Technical Officer at Bind-X. “It’s flexible, so you can drive huge loads along it and it won’t break — it’s like chewing gum in the soil.”
Bitumen may be effective at stabilising roads — which is particularly important on heavy use haul routes — but changing attitudes and regulations around the environment mean it’s worth looking at what else is out there.
The ugly side of bitumen emulsion
Even on its own, bitumen is “ugly stuff”, Luitpold says. It’s difficult to handle and almost impossible to clean up. Splash it on your clothes and it will never come out. As a crude oil-based product its production generates high levels of CO₂. Industry attempts to make it easy to transport and liquified have led to the emulsion being diluted with toxic chemicals.
“For the mining industry, bitumen emulsion is commonly blended with other waste streams,” Luitpold says. “Mostly they’ll add a polymer, a biopolymer or sugar to mix it down. Pure bitumen emulsion is better, but the cheaper version will do the job.” These additives mean bitumen might still be used because that’s what has always been done, but it’s not necessarily safe. “The bitumen blends always have at least three to six different hazardous symbols on the packaging, so you know there are a lot of poisonous chemicals in there. You’re looking at toxins and acids that are being brought into the environment.”
The impact can be disastrous, effectively sterilising the soil by killing essential bacteria and organisms. If the chemicals aren’t seeping into the dirt, they risk evaporating into the air, from where they can easily end up contaminating groundwater. Chemicals, crude oil products and increasingly scarce water supplies don’t go well together. That staying power can make clean-up jobs an expensive and complicated prospect when mines close — and can get in the way of future mining if there’s a need to dig up the ground where bitumen roads have been laid.
“If the water is close by, this is a serious issue,” Luitpold says. “Lots of communities are unhappy having bitumen works nearby, because you don’t want to have poisonous stuff in your drinking water.”
Water pollution can be an expensive business. There are examples from overseas of mines having to be closed down, Luitpold says, after drinking water has been contaminated by their activities. Nearer to home, Alcoa has had to commit $15 million towards researching the impact of its mining upon West Australian water catchments, after the government found nine out of 15 major drinking water catchments had been affected by toxic run off. A fix was priced in the order of $2.6 billion.
Less messy alternatives
Given that high price tag, it’s understandable that large mining companies across the globe are looking for a less toxic solution to dust suppression.
Biological dust control methods offer a proven and increasingly popular alternative that removes the risk of contamination. The natural process uses micro-organisms to react with dust and dirt to create a solid layer as hard as cement. It’s easier to ship and store than bitumen and far less messy to apply. It also means less water wasted, fewer applications and a reduced risk to the local flora and fauna.
“The ingredients in these biological binders are bio-based and also biodegradable, meaning that organisms within the soil can consume it,” Luitpold says.
These claims of biodegradability aren’t made lightly, he insists. While some plastic bags are touted as degrading naturally, they tend to require the sort of temperatures unlikely to be found in ordinary or even compost conditions — sometimes as high as 70 degrees centigrade.
Of course, it’s that very strength that is also one of bitumen’s shortcomings. Once bitumen emulsion has been sprayed on the ground, it’s almost impossible to get out again. Being biodegradable, biological dust control doesn’t need the same exhaustive cleaning regime. It can be safely broken up when needed, but while in use has the added bonus of getting stronger with each application. The big question, of course, is whether biological dust control methods can deliver the same stability that has made bitumen so reliable.
“It has similar performance to bitumen in the strength parameters and wet stability — and does slightly better than bitumen blends,” Luitpold says. “For maintenance, a small amount of product is sufficient to capture fugitive dust, which then produces another stable layer, closing any cracks that might have developed.”
Importantly, biological dust control doesn’t come with a high upfront cost, being cheap to source and easy to apply with equipment you probably already have on site.
Phasing out bitumen emulsions
“There are already lots of reasons to stop using bitumen emulsion, but we know it will be more expensive in future,” Luitpold says. “Prices will increase due to CO₂ taxes, the high energy need and the reduced availability of fossil fuel sources.”
Chemical companies are already researching how to cut back on the amount of bitumen in their products, substituting chemicals that might not yet be regulated. Some companies are even investigating biologically based bitumen, made out of renewable organic sources such as cashew nuts. As environmental regulations toughen in different parts of the world, Luitpold says it isn’t hard to imagine a near future in which the use of bitumen is banned entirely.
“It’s ugly stuff and it might very soon be coming off the market.”
Sticking with bitumen for dust suppression on haul roads is anything but a safe bet. In the short term, it’s difficult to handle, messy to apply and brings the risk of a costly clean-up bill. But in the longer term, it means investing in a product that — after a strong and steady run — might soon be reaching the end of the road.