Schematic representation of the four stages of CaSO4 formation.
A new explanation of how gypsum forms may change the way we process this important building material, as well as allow us to interpret past water availability on other planets such as Mars. Gypsum (CaSO. 4· 2H2O) is an economically important mineral, extensively used as the commercial construction material Plaster of Paris, with a global production of ~100 billion kg per year. It is a ubiquitous mineral on the Earth’s surface, and is also found on the surface of Mars. Despite its importance, until now we have not understood how gypsum grows from ions in solutions.
The formation of gypsum, from concentrated aqueous solutions of calcium sulfate, was thought to be a simple, single-step process. However, a group of European geochemists has now shown that gypsum forms through a complex 4-step process: the understanding of this process opens the way to more energy efficient production of plaster.
The multinational team examined the process using in situ and time resolved synchrotron-based X-ray scattering at Diamond Light Source (Harwell, UK), and identified and quantified each of the 4 steps of the formation process, highlighting specially that the initial moments in the reaction chain are of particular importance, because they determine the final properties of gypsum. In this 1st step, tiny sub-3 nm elongated particles form the primary building blocks (bricks). In subsequent steps these bricks aggregate, self-assemble and rearrange themselves, and finally transform to gypsum crystals.
“Importantly, we envisage that it is possible to alter this pathway by specifically targeting individual stages. For example we could arrest the reaction at the first stage when only nano-bricks are formed, and thus directly synthesise a highly reactive precursor to Plaster of Paris” said Dr. Thomas Stawsky. Since plaster is normally produced by the energy-intensive heating of gypsum, such an approach would drastically reduce the cost of production, and significantly decrease the carbon footprint of the industry.
“We know that gypsum is naturally found on Mars, so applying our current finding will also help us understand and predict the hydrological conditions at the time of gypsum formation on other planets,” said Professor Liane G. Benning. http://www.eurekalert.org/pub_releases/2016-04/eaog-sdh032916.php
http://www.nature.com/ncomms/2016/160401/ncomms11177/full/ncomms11177.html#f5
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