Product has been added to the basket

Thinking outside the box

Macroscopic image of sepiolite from Norway (credit: ESRF)

The future of cat litter lies ‘outside the litterbox’, according to a new study by a team of European scientists to be published in American Mineralogist in October.  Sarah Day has the story.

Geoscientist Online, 19 July 2011

It might not look like much, but cat litter is composed of one of nature’s most useful and sought-after minerals – a clay known as sepiolite, or Meerschaum. At present, sepiolite is not particularly abundant in the Earth’s crust, and is only found in a few mines worldwide, most of which are clustered around Madrid – making Spain the world’s biggest exporter of the ‘wonder mineral’.

That could all change, thanks to the first ever atomic scale images of sepiolite, showing its crystalline structure in detail.

Well known for its lightweight porous structure, which is capable of absorbing two and a half times its own weight in water, sepiolite has been used since Roman times, when it was employed in the filtration and purification of wine. Since then its uses have been widespread, including industrial absorbents, an ingredient in drilling mud, odour removal in fridges and, of course, pet litter.

But until now, our understanding of how sepiolite’s tiny crystals are so good at absorbing liquids has been incomplete. As the crystals are only a few micrometres in length and a dozen or so atoms across, resolving their three dimensional structure has proved extremely difficult.

The team, including scientists from the Universities of Madrid and Salamanca in Spain, the Institut Laue-Langevin (ILL), the European Synchrotron Radiation Facility (ESRF) and the Spanish CRG Beamline at the ESRF, used single-crystal X-ray diffraction to obtain the images, using samples of sepiolite fibres from twenty different deposits around the world.

‘To study very small crystals’ explains Manuel Sanchez del Rio from the ESRF, ‘we use an X-ray beam with just 2 by 5 micrometres cross section. In the end, we collected X-ray diffraction data for two fibres’.

Even then, the results were hard to interpret. ‘We needed extensive computer simulations to confirm and refine the information gathered by electron diffraction experiments done in parallel at the University Complutense of Madrid’.
X-ray diffraction pattern produced by a few fibres of the sepiolite from Norway (credit: ESRF) This painstaking analysis has paid off, in producing the first ever atomic scale images of sepiolite crystals. It could pave the wave for synthesising the properties of sepiolite using other, more abundant clays.

‘Today, no synthetic clay surpasses natural sepiolite’ says Mercedes Suarez from the University of Salamanca. ‘This is about to change as our understanding of their atomic structure will guide...the design of completely new materials for use in catalysis and batteries.’

The images show needle shaped crystals, their elongated forms packed loosely together. The empty spaces between them, as well as tunnels within the crystals themselves, form a network of capillaries which allow liquid to flow deep within the mineral, where molecules can attach themselves to the surface of the crystals.

Armed with this knowledge, scientists are hoping they can not only recreate the properties of sepiolite using other minerals, but perhaps even improve them. This ‘out of the box’ thinking could produce a material with a whole new set of applications, such as binding food products and stablising drugs to extend their shelf life, and making sepiolite itself an edible product.

As Manuel Sanchez del Rio concludes; ‘the future of sepiolites in the household is outside the litterbox’.
  • Journal reference: Manuel de Sanchez del Rio, Emilia Garcia-Romero, Mercedes Suarez, Ivan da Silva, Luis Fuentes Montero, and Gema Martinez-Criado, 'Variability in sepiolite: Diffraction studies', American Mineralogist (in press)