European Commission, Environment DG

Metal sulfides could help clean up nuclear waste

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Source: European Commission, Environment DG

A number of materials and methods are available to dispose of harmful nuclear waste, but scientists continue to search for improved storage options. New research has identified materials, known as layered metal sulfides, that could help clean up liquid nuclear waste. These materials have unique properties, making them stable and useful over a wide range of conditions with considerable implications for the future of nuclear waste treatment.

Nuclear power is once again under consideration by many countries as an alternative energy to fossil fuel derived energy. However, despite the benefits of nuclear power, disposal methods for the associated radioactive waste must be improved if it is to be widely accepted. In particular, researchers have sought materials able to selectively capture strontium ions, one of the more dangerous waste materials from nuclear reactors.

The layered metal sulfides, known as KMS-1, were tested by US researchers who found it could effectively remove strontium from sodium solutions. Sodium solutions were used to mimic nuclear waste, as liquid radioactive waste contains high levels of sodium. The KMS-1 finds and captures the strontium inside, leaving the remaining liquid free of strontium. The strontium is concentrated by the KMS-1 into a solid, which the authors suggest could be handled, moved, stored or recycled.

The fact that KMS-1 can distinguish between strontium and sodium is unusual and important, because liquid radioactive waste contains higher levels of sodium than strontium, making the strontium harder to locate and remove. The material also works at extremes of the pH scale - in either very acidic or very alkaline conditions. These extremes are often found when dealing with nuclear waste and contaminated ground water. This property also gives KMS-1 an advantage because current materials available to clean nuclear waste usually work in only acidic or only alkaline conditions.

In the future, KMS-1 could be used as a filter for separating out radioactive strontium from large tanks storing nuclear waste. It is made from the common metals potassium, manganese and tin. Other metal sulfide materials may also have potential in nuclear waste remediation.

Looking forward, tests using actual waste solutions from a nuclear power station will be used to improve the metal sulfide and test its viability. To become commercially viable in the long term, the metal sulfide also needs to be made more affordable and readily available.

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