Mercury removal made easy

Mercury pollution is a global problem in water, air and soil near goldmines, cement and some metal production, and other heavy industries burning fossil fuels – with removal too expensive or difficult in some of the poorest countries in the world.

Now Flinders University experts have expanded testing of a sustainable extraction material capable of absorbing almost all mercury in polluted water in minutes – itself made entirely from low-cost waste from the petroleum, citrus and agricultural production.

In fact, the tests showed almost total absorption of mercury within minutes in trial conditions, says senior author Professor Justin Chalker and fellow scientists in a new journal article published by the Royal Society of Chemistry.

“It is clear from the study that this mercury-binding material, invented at Flinders University, is ultra-fast in its ability to remove mercury from water. In some cases, more than 99% of the mercury is captured in just a few minutes,” says Professor Chalker.

Chalker Lab co-author Dr Max Worthington says testing was done on a new material created by coating silica with sulfur and limonene – a novel chemical combination already shown to effectively absorb waste mercury.

“This silica covered with an ultra-thin coating of poly(S-r-limonene), using sulfur left over in petroleum production and orange oil from orange peel discarded by the citrus industry, was extensively tested in various pH and salt concentrations,” he says.    

“Not only is this new mercury sorbent able to rapidly bind to mercury in water, but is also selective in taking up mercury but not other metal contaminants such as iron, copper, cadmium, lead, zinc and aluminium.”

Importantly this means that only mercury will bind to the orange-sulfur sorbent, which helps with safety after capturing the inorganic mercury, adds co-author Dr Max Mann from the Flinders University Chalker Lab.

“The particles contained in just 27g of this free-flowing orange powder has an approximate surface area of a soccer field, and it can be quickly produced in large enough volumes to suit contamination levels,” he says.

Chalker Lab PhD candidate Alfrets Tikoalu says silica sourced from agricultural waste, such as wheat or rice production, could also be used for the material to be made even more sustainable.

“This mercury remediation technology can be a circular economy solution for a more sustainable world because this value-added material is made entirely from waste,” he says.

To shore up the findings, mathematical modelling was used to qualitatively understand the rate of mercury uptake – data critical to measuring and optimising the new sorbent in real-world remediation.

“This is an exciting new development in producing renewable and accessible solutions to major environmental issues facing the world today,” says applied mathematician Dr Tony Miller, another co-author on the publication in Physical Chemistry Chemistry Physics.

The project is an “excellent example of collaboration across chemical and physical sciences and mathematics to understand the rate of mercury uptake by our new and innovative sorbent,” Professor Chalker says.

Images:  https://www.dropbox.com/sh/rqtu5mz1xmdvodl/AAAarhmU85ieMlhYo0CSnamWa?dl=0

Captions: Figure: Poly(S-r-limonene)-coated silica is a free-flowing orange powder and fast acting mercury sorbent. 300 grams produced in a single batch pictured.

Figure: Electron microscope (SEM) imaging and elemental surface (EDS) analysis. Silica is evenly covered with a nanometre-thin poly(S-r-limonene) coating in a fast process that can prepare hundreds of grams an hour.

Figure: Left: Hg²⁺ sorption at varying pH. Right: Hg²⁺ sorption at varying NaCl concentration. Mercury removal is rapid with over 90% captured in just one minute at neutral pH, and 99% within the first 5 minutes. Sodium chloride acts to inhibit mercury capture, limiting the sorbent’s effect in saltwater, but is overcome with the use of more sorbent.

The article, Modelling mercury sorption of a polysulfide coating made from sulfur and limonene’ (2022) by Max JH Worthington, Maximilian Mann, Ismi Yusrina Muhti, Alfrets D Tikoalu, Christopher T Gibson, Zhongfan Jia, Anthony D Miller and Justin M Chalker, has been published in Physical Chemistry Chemistry Physics DOI: 10.1039/D2CP01903E

See also: https://youtu.be/ubD-QMyLLsg (Innovation and Skills - South Australia)

Further information on mercury: https://www.unep.org/explore-topics/chemicals-waste/what-we-do/mercury/global-mercury-assessment

Acknowledgement: The project was funded by the Australian Research Council