Sepiolite is a lightweight porous mineral used in cat litter and other applications. The extraordinary properties of this clay make it a highly sought after mineral, despite its scarcity in the Earth's crust: only a few mines worldwide extract it, several of them clustered near Madrid in Spain, the world's biggest exporter of this material.
Sepiolite has been known since Roman times when it was used to filter and purify wine, but our understanding at the atomic scale of how these tiny crystals absorb enormous amounts of liquid has remained elusive until now. A team of scientists from Spain and France has obtained for the first time single-crystal X-ray diffraction images of sepiolite, opening the path to industrial synthesis and further improvement of its properties. The results will be published in the October 2011 issue of the journal American Mineralogist.
The team included scientists from the Universities of Madrid and Salamanca in Spain, of the Institut Laue-Langevin (ILL), the European Synchrotron Radiation Facility (ESRF), and the Spanish CRG Beamline at the ESRF (SpLine), all in Grenoble (France).
No other mineral is known to absorb more water or other liquids as efficiently as sepiolites. The reasons are its structural nanoporosity due to tunnels in the crystals, and the fact that the elongated, needle-shaped sepiolite crystals pack very loosely into a lightweight porous material. The surface area ranges between 75 and 400 m2/g, meaning that 20g of mineral have an internal surface equivalent to that of a football court. This is why sepiolite can absorb 2.5 times its weight in water. The tunnels in the crystal structure along with the empty space between the needles form a capillary network through which liquids can easily flow deep inside the bulk where the molecules attach to the surface of the crystals.
The tiny size of these crystalsthey measure a few micrometres in length and as little as some dozen
|Contact: Claus Habfast|
European Synchrotron Radiation Facility