How can mercury emissions from industry be greatly reduced

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Sulfuric acid is the most widely used chemical in the world. It is an important reagent used in many industries and is used in the manufacture of everything from paper, pharmaceuticals and cosmetics to batteries, detergents and fertilizers. Therefore, it is a global challenge that sulfuric acid often contains one of the most toxic substances – mercury. Researchers at Chalmers University of Technology, Sweden, have now developed a method that can reduce the levels of mercury in sulfuric acid by more than 90 percent – even from low levels.

“Until now, there has been no feasible method to purify finished sulfuric acid at all. With such a radical reduction in the mercury content, we are well below the current limit values. Pure, high-quality sulfuric acid is in high demand in industrial applications and is an important step in reducing environmental impact,” said lead researcher Björn Wickman, Associate Professor in the Department of Physics at Chalmers.

Sulfuric acid is produced either from sulfur from the petroleum industry or as a by-product in the mining industry’s smelters. In the latter case, mercury, which is naturally present in the ore, can become the finished product. Also the recycling stream in the smelter can contain mercury.

Toxic emissions that affect all life on Earth

Mercury dispersion is a worldwide problem, as the substance is volatile and can be dispersed through the air over large areas. These toxic heavy metals then wash away into rivers and lakes when it rains. It is deposited in soil, water and living organisms, affecting the entire food chain. It can damage the brain and central nervous system of humans and animals.

According to a report from the United Nations Environment Program (UNEP), mercury emissions into the atmosphere increased by around 20 percent from 2010 to 2015. In 2015, around 2,200 tons of mercury were released into the air due to human activities. activities such as cement manufacturing, small-scale gold mining, coal burning, metal production and other manufacturing industries. Additionally, an estimated 1,800 tons of mercury ended up in soil and water that same year. According to the report, mercury concentrations in the atmosphere may have increased by 450 percent in the last century.

“Any and all ways we can reduce mercury emissions are good, because any mercury emitted accumulates in the environment and continues to pose a health threat for thousands of years,” said Wickman.

Capture metal using electrochemistry

Five years ago, his research team at Chalmers presented a pioneering method for removing mercury from water using an electrochemical process. This method is based on metal electrodes which pick up toxic metals and form an alloy. The mercury can then be safely removed, and the electrodes are reused. Now researchers have taken this technology one step further, and in a new study they have shown how mercury can be removed from concentrated sulfuric acid.

The experiments with sulfuric acid were carried out in collaboration with the metal mining and refining company Boliden and the company Atium, a spin-off of the Chalmers School of Entrepreneurship with the aim of bringing mercury removal from water and chemicals to market. The researchers now hope to move forward with their partners and develop a type of reactor where sulfuric acid can be flowing and being purified at the same time.

Potential to reduce costs and environmental impact

Currently, most of the mercury is removed at an early stage – from the concentrate and recycled stream in the smelter before sulfuric acid is produced. This is an established process, but leaves small amounts of mercury in the final product.

“Purifying sulfuric acid also prevents additional mercury emissions, while allowing the industry to operate more cost-effectively and produce high-purity, non-toxic products. The next step is to upgrade the method to a pilot process that approaches real-world volumes of thousands of tons,” said Vera Roth, doctoral student at Chalmers and first author of an article just published in the journal ACS ES&T Engineering.

Hoping for a lower bound value

According to the Statista database, the world market volume for sulfuric acid amounts to about 260 million tons per year. By 2029, this figure is expected to increase to 314 million tonnes. The lower the mercury content of sulfuric acid, the more valuable it is. Sulfuric acid for commercial purposes is considered to be of acceptable quality if the mercury content is below 0.30 milligrams per kilogram. If the content is below 0.08 milligrams per kilogram, then the sulfuric acid is considered to be of high purity. With the new method, the researchers have reduced the mercury level to 0.02 milligrams per kilogram of sulfuric acid in their pilot study.

“The limit values for mercury sulfuric acid content are based on currently available technology. With the new method for purifying sulfuric acid, our hope is that the laws around limit values will be tightened in a global perspective where mercury levels are generally much higher,” said Wickman.

Information: Sulfuric acid is an important industrial chemical, but it often contains one of the world’s most toxic substances: the volatile heavy metal mercury, which can pollute air and water. Researchers at Chalmers University of Technology have shown that levels of mercury in sulfuric acid can be reduced by more than 90 percent – even from low levels. The study was carried out in collaboration with spin-off company Atium and metal mining and refining company Boliden.
Picture: Boliden/Unsplash, Nazrin Babashova

More information on methods and studies:

This purification method removes mercury from sulfuric acid by ionizing the mercury and its ions to form alloys with other metals. Electrodes with platinum surfaces electrochemically bond the mercury to itself. Then it took toxic mercury and formed an alloy of the two metals. It was then possible to remove the mercury and regenerate the electrodes in a controlled manner. This means the electrodes can be reused, and toxic substances can be disposed of safely. This process is also very energy efficient. In an episode of the Swedish Educational Broadcasting Company (UR)’s UR Samtiden program, Björn Wickman demonstrates how the method works to remove mercury from water.
The article Mercury Removal from Concentrated Sulfuric Acid by Electrochemical Alloy Formation on Platinum is published in the scientific journal ACS ES&T Engineering and written by Vera Roth, Julia Järlebark, Alexander Ahrnens, Jens Nyberg, Justin Salminen, Teodora Retegan Vollmer and Björn Wickman. The author is active in the Department of Physics and the Department of Chemistry and Chemical Engineering at Chalmers University of Technology, at Atium, and at Boliden.
Sulfuric acid is the most widely used chemical in the world. It is an important reagent used in many industries and is used in the manufacture of everything from chemicals, paper, pharmaceuticals and cosmetics to batteries, detergents and fertilizers. It is also an ingredient for many recycling processes that contribute to circular economy and extractive metallurgy.
Experiments in this study were carried out in a laboratory environment, in a 50 milliliter beaker and then in a 20 liter reactor. The next step is to upgrade the method to a pilot project that is close to the actual volumes commonly used in industrial applications.
This research was funded by Formas and by the Swedish Mining Innovation strategic innovation program – a joint venture involving Vinnova, Formas and the Swedish Energy Agency.

More on heavy metals in the environment:

Heavy metals in water and waterways are a huge environmental problem that affects the health of millions of people around the world. Heavy metals are toxic to all living organisms and accumulate in the food chain. According to the World Health Organization, mercury is one of the most harmful substances to human health. Among other things, it affects our nervous system and brain development. Therefore, these substances are very dangerous for children and fetuses.
Currently, there are strict regulations governing the handling of toxic heavy metals to prevent their spread in the natural environment. However, there are many places that have been contaminated or affected by airborne mercury deposition which may have come from other countries. As a result, there are areas in our natural environment where the amount of heavy metals has reached toxic concentrations. For example, high levels of mercury in freshwater fish are a well-known environmental problem. Even in Sweden heavy metal pollution is a serious problem, and fish in most lakes contain more mercury than the limit value. In industries that use heavy metals, as well as in recycling, wastewater treatment and decontamination, there is a great need for new and better methods to remove toxic heavy metals from water.