How mercury emissions from industry can be greatly reduced

Newswise — Sulphuric acid ranks as the most widely utilized compound globally. It serves as a vital agent across various sectors and plays a significant role in producing a wide range of items, including paper, drugs, beauty products, batteries, cleaning agents, and fertilizers. Consequently, the prevalence of mercury, one of the most hazardous elements, in sulphuric acid poses a significant global challenge. However, scientists from Chalmers University of Technology in Sweden have recently devised a technique capable of diminishing mercury concentrations in sulphuric acid by over 90 percent, even when present in minimal amounts.

"Previously, no feasible approach existed for purifying fully processed sulphuric acid. With this drastic decrease in mercury levels, we surpass the existing threshold values significantly. This pure and superior-grade sulphuric acid is greatly sought after in industrial sectors, representing a crucial stride towards minimizing environmental repercussions," states Björn Wickman, the lead researcher and Associate Professor in the Department of Physics at Chalmers University.

Sulphuric acid is generated through two primary processes: either from sulphur derived from the petroleum industry or as a by-product in the smelters of the mining industry. In the latter scenario, the presence of mercury in the final products can occur due to its natural occurrence in the ore. Additionally, mercury can be found in recycled streams within the smelters.

Toxic emissions that affect all life on Earth

The global distribution of mercury poses a widespread issue, as this volatile substance can be easily dispersed through the air, covering vast distances. When precipitation occurs, the toxic heavy metal is carried and deposited into streams and lakes. It accumulates within the soil, water, and living organisms, exerting its influence throughout the entire food chain. The detrimental effects of mercury include damage to the brains and central nervous systems of both humans and animals.

As per a report by the United Nations Environment Programme (UNEP), emissions of mercury into the atmosphere experienced a notable surge of approximately 20 percent between 2010 and 2015. In 2015 alone, human activities such as cement manufacturing, small-scale gold mining, coal burning, metal production, and other manufacturing industries resulted in the release of around 2,200 tonnes of mercury into the air. Furthermore, an estimated 1,800 tonnes of mercury found their way into the soil and water during that same year. According to the report, mercury concentrations in the atmosphere may have escalated by a staggering 450 percent over the past century.

Wickman emphasizes the importance of reducing mercury emissions, stating, "Every possible method to decrease mercury emissions is crucial, as any emitted mercury accumulates in the environment and remains a health hazard for thousands of years."

Captures the metal using electrochemistry

Half a decade ago, the research team at Chalmers University introduced an innovative technique utilizing electrochemical processes to eliminate mercury from water. This method involves a metal electrode that absorbs the toxic metal and forms an alloy, enabling safe removal of the mercury while allowing for reusability of the electrode. Building upon this breakthrough, the researchers have now progressed even further. In a recent study, they have demonstrated the successful removal of mercury from concentrated sulphuric acid, expanding the application of this technology to address the specific challenge of mercury contamination in sulphuric acid.

The research conducted on sulphuric acid involved a collaboration between Chalmers University, mining and metals refining company Boliden, and Atium, a spin-off company from Chalmers School of Entrepreneurship. Atium specializes in commercializing mercury removal technologies for water and chemicals. Together, the researchers and their industry partners aim to advance their work and develop a specialized reactor capable of purifying sulphuric acid while it flows through the system. This collaborative effort marks a significant step forward in bringing the practical application of mercury removal to the market.

Potential to reduce costs and environmental impact

Currently, the predominant practice involves removing mercury at an earlier stage, specifically from concentrates and recycled streams at the smelter, prior to the production of sulphuric acid. This established process effectively eliminates a significant portion of mercury. However, despite its effectiveness, trace amounts of mercury may still remain in the final products.

Vera Roth, a doctoral student at Chalmers University and the first author of the recently published article in the journal ACS ES&T Engineering, highlights the advantages of purifying sulphuric acid. By purifying the acid, it not only prevents additional mercury emissions but also enables industries to operate more efficiently and produce a high-purity, non-toxic product. The next crucial phase involves scaling up the method into a pilot process that reflects real-world volumes, reaching thousands of tonnes of sulphuric acid.

Hoping for lower limit values

According to the Statista database, the global market volume of sulphuric acid currently stands at approximately 260 million tonnes annually. It is projected to increase to 314 million tonnes by 2029. The value of sulphuric acid is directly linked to its mercury content, with lower levels enhancing its worth. Commercially acceptable sulphuric acid is considered to have a mercury content below 0.30 milligrams per kilogram. If the content is below 0.08 milligrams per kilogram, it is classified as highly pure sulphuric acid. In their pilot study, the researchers achieved a remarkable reduction in mercury levels, reaching 0.02 milligrams per kilogram of sulphuric acid using their new method.

Wickman emphasizes that the current limit values for mercury content in sulphuric acid are determined based on existing technologies. However, with the development of the new method for purifying sulphuric acid, the researchers anticipate that global legislation regarding these limit values will be revised and tightened. This is especially significant in a global context where mercury levels are generally higher, aiming to address the environmental and health risks associated with mercury contamination more effectively.

Researchers at Chalmers University of Technology, in collaboration with Atium and Boliden, have achieved a significant breakthrough in minimizing mercury contamination in sulphuric acid. Mercury, one of the most hazardous substances on the planet, often taints this vital industrial chemical, posing a threat to both air and water quality. The study demonstrates the successful reduction of mercury levels, even from initial low concentrations, by more than 90 percent.

More information about the method and the study:

• The cleansing technique eliminates mercury from the sulfuric acid by initially reducing the mercury ions to solid state and subsequently combining the solid mercury with platinum to form an alloy, which is coated onto the electrode area. It becomes feasible thereafter to extract the mercury and revive the electrode under controlled conditions. This implies the reuse of the electrode while ensuring safe disposal of the hazardous substance. The procedure is also remarkably energy-saving. In one episode of UR Samtiden, a show by the Swedish Educational Broadcasting Company (UR), Björn Wickman showcases the functionality of the approach in mercury removal from water.
• The scientific paper titled "Electrochemical Alloy Formation on Platinum for Mercury Removal from Concentrated Sulfuric Acid" is featured in the renowned journal ACS ES&T Engineering. The publication credits go to Vera Roth, Julia Järlebark, Alexander Ahrnens, Jens Nyberg, Justin Salminen, Teodora Retegan Vollmer, and Björn Wickman. These authors are affiliated with the Department of Physics and the Department of Chemistry and Chemical Engineering at Chalmers University of Technology, as well as Atium and Boliden.
• Sulfuric acid holds the distinction of being the most widely utilized chemical globally. It serves as a crucial reagent across numerous industries and plays a significant role in the production of a wide array of products, including chemicals, paper, pharmaceuticals, cosmetics, batteries, detergents, and fertilizers. Additionally, sulfuric acid serves as a vital ingredient in various recycling processes, contributing to the advancement of the circular economy and extractive metallurgy.
• The study conducted its experiments within a laboratory setting, utilizing a 50 milliliter beaker initially, and later transitioning to a larger 20-liter reactor. The subsequent phase involves scaling up the method to a pilot project, aiming to replicate volumes more commonly encountered in industrial applications. This step is crucial in bridging the gap between laboratory-scale testing and practical implementation in real-world scenarios.
• The research project received funding from Formas and the strategic innovation program Swedish Mining Innovation, which is a collaborative initiative involving Vinnova, Formas, and the Swedish Energy Agency. These funding sources provided support and resources for the study, highlighting their commitment to advancing scientific research and innovation in the field.

More about heavy metals in the environment:

• The presence of heavy metals in water and watercourses poses a significant environmental challenge with far-reaching consequences for the health of millions of people globally. Heavy metals exhibit toxicity to all forms of life and have the ability to accumulate in the food chain. Mercury, in particular, is recognized by the World Health Organization as one of the most hazardous substances to human health. Its detrimental effects include impacts on the nervous system and interference with brain development. Consequently, mercury poses a heightened risk, especially to children and developing foetuses, making it an exceptionally dangerous substance.
• In the present day, stringent regulations are in place to govern the handling of toxic heavy metals, aiming to prevent their dispersion into the natural environment. However, there are numerous locations that have already been contaminated or are experiencing the deposition of airborne heavy metals, potentially originating from other countries. Consequently, certain areas in our natural surroundings have accumulated toxic concentrations of heavy metals. One well-known environmental issue is the high levels of mercury found in freshwater fish, indicating the extent of heavy metal pollution. Even in Sweden, heavy metal pollution remains a significant problem, with a majority of lakes containing mercury levels exceeding the prescribed limit. Industries that employ heavy metals, as well as sectors involved in recycling, wastewater treatment, and decontamination, face a pressing need for improved and innovative methods to effectively remove toxic heavy metals from water.