Industrial activity like coal-burning and mining has greatly increased the amount of mercury in our environment, so much so that it now contaminates rivers, lakes and waterways as far away as the Arctic. Exposure to the harmful compound can not only damage wildlife, but humans in the early stages of development, too. Scientists have now developed a low-cost polymer that can soak up mercury in its most harmful forms, raising the prospect of a cheap and sustainable way to clean up the mess.
According to Dr. Justin Chalker, an organic chemist at Australia's Flinders University in Adelaide, the single biggest source of mercury pollution is artisanal gold-mining. Here, mercury metal is used to extract gold from the ore, and is then vaporized once the job is done, leaving behind mercury-rich fumes and tailings.
"This practice occurs in predominately poor nations and threatens the health of the 15 million miners that use mercury to extract gold," Chalker explains to New Atlas. "Because our polymer can be made entirely from waste, we believe that we can help solve this problem in a cost-effective manner."
The new polymer developed by Chalker and his team can be crafted using second-hand cooking oil and sulphur, a common by-product of petroleum production. It can apparently be used to trap the most harmful kinds of mercury pollution, both mercury metals and vapor, along with highly toxic organo-mercury compounds.
"The polymer is produced by the direct reaction of sulfur and canola oil," Chalker tells us. "The sulfur is first melted and then heated further to 180° C (356° F). This causes the sulfur to react with itself and form long stretch of sulfur atoms. Next, the cooking oil is added. The unsaturated oil contains carbon-carbon double bonds that react with the termini of the long sulfur chains.
"This results in cross-linking," he continues. "After about 20 to 30 minutes of heating, the reaction mixture solidifies to a rubber. The rubber can then be milled into desired particle sizes and then used to capture mercury. To make a high surface area porous version, we add salt (sodium chloride) to the reaction mixture. After the reaction mixture solidifies, it is soaked in water to dissolve the salt and leave channels and pores where mercury can be bound."
What's more, when the mercury binds to the rubbery polymer, it causes it to change color, offering an indication when it is saturated and needs to be replaced. Chalker says he and collaborating researchers from other universities have tested the polymer in a range of settings, where it was shown to clean mercury from water and soil, as well as from the air.
"Our collaborators at RMIT in Melbourne also tested the polymer and its ability to capture mercury vapor," he says. "Mercury vapor is very dangerous as it can enter and damage the nervous system if inhaled. We found that the polymer can trap mercury vapour very rapidly, in some cases less than one second of contact was required, provided the system was slightly heated. This discovery is important for situations where mercury gas is encountered: oil and gas refining, coal combustion, and artisanal gold mining."
US company Kerafast is already licensed to sell samples of Chalker's polymer to use for research purposes, but the chemist hopes that before too long it will be put to use beyond the lab.
"We currently run the key reaction on kilogram scale," he says. "We are working directly with engineers to increase our production capacity so that we can prepare a 1-ton inventory. We aim to build a pilot plant within two years in Adelaide, South Australia. The goal is to commercialize the polymer as a mercury sorbent for the oil, gas and coal industries. My personal goal is to use a portion of these profits to help end the mercury pollution crisis that results from artisanal and small scale gold mining."
A paper describing the research was published in Chemistry – A European Journal.
Source: Flinders University