French researchers may have solution to water-born arsenic
Millions of people in Bangladesh have suffered arsenic poisoning through drinking contaminated water from wells. Dangerously high levels of arsenic are present in other parts of the world too. While developed countries have access to sophisticated water treatments, poorer ones need cheap and sustainable alternatives. Two developments bode well for finding a solution to this lethal problem.
|Manganese oxide (MnO) is the best-known anti-ferromagnetic material, but calcite could prove cheaper for removing arsenic.|
The first piece of good news comes from European researchers whose successful experiments using calcite filters show promising results in reducing arsenic contamination in water. The new discovery by French scientists at the Institut Laue-Langevin (ILL), one of the world's leading facilities in neutron science and technology, could prove to be an inexpensive way of trapping the arsenic.
Tens of millions of people are exposed to dangerous levels of arsenic in their drinking water – up to 50 times the World Health Organisation thresholds – in countries such as India, Bangladesh, Vietnam, Taiwan and Argentina. Even in France, say the team of scientists, many sources of water, including mineral waters, may no longer satisfy new standards introduced in January 2004 – which limit the concentration of arsenic in drinking water to 10 μg L-1.
To decontaminate water supplies, cheap and efficient methods for containing arsenic are needed. ILL research into calcite filters could be the answer. Unlike current solutions, such as manganese sand, iron oxides or ettringite – which although more efficient tend to be rarer and, thus, more expensive – calcite is a very common mineral found in limestone which is ubiquitous.
The team carried out experiments to test the diffusion of arsenic into the bulk of a calcite sample. High-resolution neutron diffraction showed that up to 80mg of arsenic per gram of calcite can be captured by this material – because AsO33- replaces the carbonate (CO32-) in the calcite lattice, which expands to accommodate it. The higher the degree of substitution, the larger the lattice cell becomes, the researchers note.
This discovery is promising because calcite can be synthetically produced in water purification systems simply by allowing a milk of lime – used in water purification plants and power stations to neutralise effluent and separate pollutants – to react with the carbon dioxide in the air. Pure (synthetic) calcite could then be produced cheaply, and provide a simple solution for filtering water contaminated with arsenic.
In a related development, the US National Academy of Engineering has issued a million-dollar challenge to scientists worldwide: design or create a workable, sustainable, efficient point-of-use water treatment system for arsenic-contaminated groundwater in Bangladesh, India, Nepal, and other developing countries.
Individuals or organisations that come up with a cheap and sustainable way of removing the arsenic could qualify to win the Grainger Challenge Prize for Sustainability, which was set up by the academy this year to speed up the development of socially and environmentally sustainable technologies.
According to the Grainger Challenge Prize website, the winning system must "be technically robust, reliable, maintainable, socially acceptable and affordable”. Over the coming months the public are being asked to contribute to the competition's design. Detailed criteria for participating in the challenge will be made public in June 2005. Applicants will then have until June 2006 to submit their ideas, and the prize of around €770 000 will be awarded in February 2007.
SciDev and Grainger Challenger Prize
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