Materials

Waste-derived synthetic gypsum could replace the real thing

Waste-derived synthetic gypsum...
Natural gypsum (pictured) has to ground into a powder before use
Natural gypsum (pictured) has to ground into a powder before use
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Natural gypsum (pictured) has to ground into a powder before use
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Natural gypsum (pictured) has to ground into a powder before use

Composed mainly of calcium sulfate dihydrate, gypsum is a naturally occurring mineral used in cement, drywall, plaster and other building materials. Scientists have now devised a method of creating synthetic gypsum, which should be more energy efficient than processing the genuine article.

Ordinarily, gypsum that's mined from the ground has to be crushed into a powder before it can be used. Doing so consumes a considerable amount of electricity. Additionally, not all countries have plentiful gypsum deposits to exploit.

Seeking a more sustainable alternative, an international consortium of research institutes instead looked to existing waste products as source materials. More specifically, they combined three key ingredients: sulfuric acid left over from the production of heat-resistant fibers, limestone powder produced as a byproduct in the processing of limestone, and water.

After these substances were mixed and processed, the result was a synthetic form of gypsum that was at least 95 percent calcium sulfate dihydrate by weight. In fact, three types of synthetic gypsum (or gypsum-like products) were created in three different ways.

By boiling the ingredients in a traditional gypsum boiler, the scientists were able to produce building gypsum – it is used mainly as a heat-resistant, moisture-holding, sound-absorbing and fireproofing material. When the materials were instead placed in an autoclave, a high-strength grade of gypsum was the result. And when the substances were fired and then cooled, a gypsum precursor known as anhydrite was produced – it is used along with gypsum in construction materials, plus it's utilized as a drying agent in plaster, paint and varnish.

In all cases, the synthetic gypsum was found to match or in some cases exceed the quality of the corresponding type of natural gypsum. Its production was less energy-intensive, however, plus it made use of waste products that might otherwise simply be discarded.

The research was conducted by scientists from Russia's National University of Science and Technology, Belarusian State Technological University, the National Academy of Sciences of Belarus, and Ireland's University of Limerick. It is described in a paper that was recently published in the Journal of Industrial and Engineering Chemistry.

Source: National University of Science and Technology

4 comments
4 comments
paul314
Can any of the stuff that's in demolished buildings be recovered and recycled?
Bill Fortune
paul314, yes. as i remember the gypsum plant in Newington, NH gets a lot of wall board & somehow they process it.
Worzel
@paul314 Yes, especially reinforced concrete which often ends up as road ballast. Also the reinforcing steel is recycled. Good quality used bricks can cost more than new ones, as they are in short supply for building extensions or new buildings to match original local styles. eg, 'London Stocks.' In the UK, scrap dry lining, (plasterboard,) is not as plentiful as in the USA, as a lot of old buildings that are demolished were built before it became popular, or even invented. In general buildings in the UK are not 'recycled as frequently as in the USA. so scrap P/board isn't so plentiful, and is usually just crushed with all the other 'hard-core' materials.


Expanded Viewpoint
Yes, Paul, most of a building can be recycled/reused! The father and brother of a guy I worked with in the 80s bought a building at a real estate auction. It was a four story commercial building with lots of windows. They removed all of the glazing and sold it to a glass shop. Cha-ching. The aluminum window frames were sold off too. The electrical system was removed and resold, the plumbing was removed intact and sold. When all of the good stuff had been removed, then came the wrecking ball and knocked the walls down. The smashed up concrete was sold to some plant for recycling. They made money on the sale of the building's parts, and then sold the lot it used to stand on for more than they paid for it! The profit wasn't a king's ransom, but it was a tidy sum, well worth their time and efforts. Then they bought a corner lot that had a big hill on it. Lindsay found a contractor who needed clean fill dirt, and the guy came over with his loaders and a dump truck to haul the dirt away, and he paid for the dirt! Then he resold the lot for MORE than he had paid for it, since it was now level ground and prime real estate to build on! Double cha-ching there!