Mercury purification from aqueous streams via electrochemical process

Water which has been contaminated with mercury and other toxic heavy metals is a major cause of environmental damage and health problems worldwide. Now, researchers present a totally new way to clean contaminated water, through an electrochemical process. The results are published in the scientific journal Nature Communications.

"Our results have really exceeded the expectations we had when we started with the technique," says the research leader. "Our new method makes it possible to reduce the mercury content in a liquid by more than 99%. This can bring the water well within the margins for safe human consumption."

According to the World Health Organisation (WHO), mercury is one the most harmful substances for human health. It can influence the nervous system, the development of the brain, and more. It is particularly harmful for children and can also be transmitted from a mother to a child during pregnancy. Furthermore, mercury spreads very easily through nature, and can enter the food chain. Freshwater fish, for example, often contain high levels of mercury.

In the last two years researchers have studied an electrochemical process for cleaning mercury from water. Their method works via extracting the heavy metal ions from water by encouraging them to form an alloy with another metal.

Their new method involves a metal plate - an electrode - that binds specific heavy metals to it. The electrode is made of the noble metal platinum, and through an electrochemical process it draws the toxic mercury out of the water to form an alloy of the two. In this way, the water is cleaned of the mercury contamination. The alloy formed by the two metals is very stable, so there is no risk of the mercury re-entering the water.

"An alloy of this type has been made before, but with a totally different purpose in mind. This is the first time the technique with electrochemical alloying has been used for decontamination purposes," says the author.

One strength of the new cleaning technique is that the electrode has a very high capacity. Each platinum atom can bond with four mercury atoms. Furthermore, the mercury atoms do not only bond on the surface, but also penetrate deeper into the material, creating thick layers. This means the electrode can be used for a long time. After use, it can be emptied in a controlled way. Thereby, the electrode can be recycled, and the mercury disposed of in a safe way. A further positive for this process is that it is very energy efficient.

"Another great thing with our technique is that it is very selective. Even though there may be many different types of substance in the water, it just removes the mercury. Therefore, the electrode doesn't waste capacity by unnecessarily taking away other substances from the water," says the author.

Patenting for the new method is being sought, and in order to commercialise the discovery, the new company Atium has been set up. The new innovation has already been bestowed with a number of prizes and awards, both in Sweden and internationally. The research and the colleagues in the company have also had a strong response from industry.

The technique could be used to reduce the amount of waste and increase the purity of waste and process water in the chemical and mining industries, and in metal production. It can contribute to better environmental cleaning of places with contaminated land and water sources.

It can even be used to clean drinking water in badly affected environments because, thanks to its low energy use, it can be powered totally by solar cells. Therefore, it can be developed into a mobile and reusable water cleaning technology.

https://www.chalmers.se/en/departments/physics/news/Pages/Removing-toxic-mercury-from-contaminated-water-.aspx