Innovative method for more efficient conversion of gypsum into bassanite presented

29/02/2024

Gypsum and bassanite are among the most widely used building materials. A consortium led by BAM has now developed a more sustainable method of production.

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An international consortium led by the Federal Institute for Materials Research and Testing (BAM) and the Spanish Instituto Andaluz de Ciencias de la Tierra has presented a new sustainable method for converting gypsum into bassanite. The novel approach uses water solutions with a high salt content to achieve conversion at significantly lower temperatures than before.

Gypsum, scientifically known as calcium sulphate dihydrate, is a naturally occurring mineral. Bassanite or calcium sulphate hemihydrate, commonly referred to as "plaster of Paris", on the other hand, is obtained synthetically by dehydrating gypsum. This material is indispensable in the modern construction industry, as it serves as a fast-setting plaster and as a core component of various building materials.

However, the conversion of gypsum into bassanite requires high temperatures of up to 200 degrees Celsius, which leads to considerable energy consumption. At the same time, the current process is often limited to high-purity gypsum sources. Given the widespread use of bassanite and gypsum - the second most consumed building materials after Portland cement - the need for more sustainable production methods and a circular economy is obvious. This is all the more urgent given that the European Union expects gypsum to be classified as a critical raw material by 2030 and that natural deposits are dwindling. To date, gypsum waste has often been disposed of in landfill sites for fear of contamination.

For this reason, BAM and its Spanish partner have conducted a comprehensive study into how gypsum waste, which is produced in abundance in various industrial processes, can be used better and more efficiently.

As part of this, a new method was developed that significantly reduces the energy required to process gypsum into bassanite and thus makes a considerable contribution to avoiding greenhouse gas emissions. The new approach is therefore in line with broader environmental goals and the principles of a circular economy.

This was achieved through a novel low-temperature conversion process that uses a recoverable water medium instead of air. In order to observe the changes in gypsum during the conversion to bassanite in salt solutions in situ, the X-ray scattering at the BESSY-II synchrotron of the Helmholtz Center in Berlin (HZB) and Raman spectroscopy were used. The results indicate that bassanite persists in solutions with high ionic strength for extended periods of time - an important discovery that contradicts previous assumptions about its behavior in such environments.