New method to remove toxic mercury from water

Scientists have developed a method to efficiently clean water contaminated with toxic mercury -- one of the major causes of environmental damage and health problems worldwide.

Mercury spreads very easily through nature, and can enter the food chain. Freshwater fish, for example, often contain high levels of mercury.

According to the World Health Organization (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.

"Our new method makes it possible to reduce the mercury content in a liquid by more than 99 per cent. This can bring the water well within the margins for safe human consumption," said Bjorn Wickman, from Chalmers University of Technology in Sweden.

The method, described in the journal Nature Communications, works via extracting the heavy metal ions from water by encouraging them to form an alloy with another metal.

"Today, cleaning away the low, yet harmful, levels of mercury from large amounts of water is a major challenge. Industries need better methods to reduce the risk of mercury being released in nature," said Wickman.

The 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," said Cristian Tunsu, researcher at Chalmers.

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," said Wickman.