Sulfuric acid is the most commonly used chemical. It is an essential reagent used in many industries, including paper, pharmaceuticals, and cosmetics, as well as batteries, detergents, and fertilizers.
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The fact that sulfuric acid frequently contains one of the most toxic substances, mercury, poses a global challenge. Chalmers University of Technology in Sweden has developed a method that can reduce mercury levels in sulfuric acid by more than 90%—even from low levels.
Until now, there has been no viable method for purifying finished sulphuric acid at all. With such a radical reduction in the mercury content, we come well below the current limit values. Such pure high quality sulfuric acid is in high demand in industrial applications and an important step in reducing environmental impact.
Björn Wickman, Associate Professor, Department of Physics, Chalmers University of Technology
Sulfuric acid is made from petroleum sulfur or a byproduct in mining industry smelters. In the latter case, naturally occurring mercury in the ore may end up in the finished products. Mercury can also be found in recycled streams from smelters.
Toxic Emissions That Affect All Life on Earth
Mercury dispersal is a worldwide issue because the substance is volatile and can be dispersed over large areas by air. When it rains, this toxic heavy metal is washed into streams and lakes. It accumulates in soil, water, and living organisms, affecting the entire food chain. It can harm both human and animal brains and central nervous systems.
According to a United Nations Environment Programme (UNEP) report, mercury emissions into the atmosphere accelerated by an estimated 20% between 2010 and 2015.
Human activities like cement manufacturing, small-scale gold mining, coal burning, metal production, and other manufacturing industries emitted approximately 2,200 tons of mercury into the atmosphere in 2015.
Furthermore, an expected 1,800 tons of mercury ended up in soil and water that same year. Mercury concentrations in the atmosphere may have increased by 450% over the last century, according to the report.
Any and all ways we can reduce mercury emissions are good because any mercury that is emitted accumulates in the environment and continues to pose a health threat for thousands of years.
Björn Wickman, Associate Professor, Department of Physics, Chalmers University of Technology
Captures the Metal Using Electrochemistry
Five years earlier, Björn Wickman’s research group at Chalmers introduced a pioneering method to remove mercury from water using electrochemical processes. The method works by a metal electrode absorbing the toxic metal and forming an alloy.
The mercury can be safely removed and the electrode reused. Scientists have now taken this technology a step further, demonstrating how mercury can be removed from concentrated sulfuric acid in a new study.
The sulfuric acid experiments were carried out in collaboration with the mining and metals refining company Boliden and the company Atium, a spin-off from the Chalmers School of Entrepreneurship with the goal of bringing mercury removal from water and chemicals to market.
The investigators now hope to move forward with their collaborators and create a type of reactor through which sulfuric acid can flow while being purified.
Potential to Reduce Costs and Environmental Impact
Mercury is largely removed earlier in the process, from concentrates and recycled streams at the smelter before sulfuric acid is produced. This is a well-established process, but it introduces trace amounts of mercury into the final products.
Purifying the sulfuric acid as well prevents additional mercury emissions while allowing industry to operate more cost-effectively and produce a high-purity, non-toxic product. The next step will be to scale up the method into a pilot process that is closer to real-world volumes of thousands of tons.
Vera Roth, Study First Author and Doctoral Student, Chalmers University of Technology
The study was published in the journal ACS ES&T Engineering.
Hoping for Lower Limit Values
According to the Statista database, the global market volume for sulfuric acid amounts to around 260 million tons per year. This figure is expected to increase to 314 million tons by 2029. The lower the sulfuric acid’s mercury content, the more valuable it is.
When the mercury content of sulfuric acid for commercial purposes is less than 0.30 milligrams per kilogram, it is considered acceptable quality. Sulfuric acid is considered high purity if the content is less than 0.08 milligrams per kilogram. In their pilot study, scientists used the new method to reduce the level of mercury to 0.02 milligrams per kilogram of sulfuric acid.
“The limit values for how much mercury sulfuric acid may contain are based on the technology available today. With the new method for purifying sulfuric acid, our hope is that the legislation around the limit values will be tightened in a global perspective where mercury levels are generally much higher,” concludes Wickman.
Journal Reference:
Roth, V., et al. (2023). Mercury Removal from Concentrated Sulfuric Acid by Electrochemical Alloy Formation on Platinum. ACS ES&T Engineering. doi.org/10.1021/acsestengg.2c00417.