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Greener, cleaner way to make plaster

U. LEEDS (UK) — The way gypsum crystals naturally form may offer clues on how to significantly reduce cost and energy in the production of plaster, widely used in building construction, fireproofing, and artwork.

Gypsum is a naturally occurring mineral which is often used in industrial processes and which in nature, if left alone for thousands of years, can grow into huge translucent crystals more than 10 meters tall, such as those in the Cave of Crystals in Mexico. Nevertheless, the formation of gypsum has until now been largely unexplored.

Researchers have discovered that gypsum starts off as tiny crystals of a mineral called bassanite, more commonly known as Plaster of Paris.

Currently bassanite plaster is manufactured at a rate of 100 million tons per year by dehydrating quarried gypsum at 150 deg C. Builders, artists, and medical specialists buy the bassanite powder and add water to create a malleable material that hardens once dried again.

By experimenting with supersaturated gypsum solutions, researchers were able to produce bassanite at room temperature. This then transforms to gypsum.

“This process has never been documented before. In nature gypsum grows as these fantastic large crystals, yet we show that in the lab gypsum actually grows through the assembly of many, tiny bassanite crystals,” says Liane Benning from the School of Earth and Environment at the University of Leeds.

“These link together like a string of pearls before they crystallize to gypsum. We studied hundreds of high-resolution images and caught the tiny bassanite crystals in the act of assembling into gypsum.”

Alexander van Driessche from the Laboratorio de Estudios Cristalográficos in Grenada says: “Our study shows a new, low cost and low temperature way of making bassanite, although so far we have only managed to keep it stable for up to one hour.”

Published in the journal Science, the findings may also be applicable for reducing the clogging of pipes and filters through the precipitation of gypsum during water desalination or oil production. It can cost millions of pounds to remove gypsum from a pipe—a serious economic problem specifically for countries supplying much needed drinking water.

“The study reveals how a natural mineral forming process can have important economic consequences for our daily lives,” says Juan Manuel Garcia Ruiz, the director of the Laboratorio de Estudios Cristalográficos in Granada, Spain.

“It also tells us how nature can make such beautiful and enormous crystals as seen in the caves at Naica or even the gypsum and bassanite, recently documented on Mars.”

“If we manage to produce and stabilize bassanite crystals at room temperature through a clean, green method for long periods, we don’t just learn something about a natural process but, compared to what is industry standard currently, our research could also lead to a massive cost and energy saving for the production of plaster,” says Benning.

The study was funded by the Marie Curie EU-FP6 Mineral Nucleation and Growth Kinetics (MIN-GRO) Research and Training Network, the School of Earth and Environment at the University of Leeds, and the Ministerio de Economia y Competitividad: Project Factoría de Cristalización.

More news from University of Leeds: www.leeds.ac.uk/news

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