“When I visited the website of my nephew, the artist Rob Thijssen, I was struck by how well his painting suited my PhD research,” says Hugo Hellebrand (37), who is with the hydrology group and will defend his dissertation on the 23 November.

“There’s a curve in the painting that reminded me of water flowing under the pier of a bridge. It also made me think about the horizons one makes of the soil. Lastly, I like that it’s called ‘Landscape’, because that plays an important role in my research.”

Hellebrand wrote his dissertation on the influence of precipitation. He focused on how rain water enters into rivers in hilly landscapes. “There are very complex models for these processes. They need a lot of parameters, but all the information isn’t always around. I therefore made simpler tools, which do not need a lot of parameters. With these tools one could use geological information, of land use, like how many trees there are in the neighbourhood, and soil property images, to predict the influence of precipitation.”

From potato starch producers to waste processing plants and mining companies, all kinds of industries that have to deal with waste and process streams with dissolved salts in them can clean up their production and recuperate valuable salts much more efficiently, says Professor Elif Genceli-Güner. If only they would use her ice machine, or, as she likes to call it, her recently scaled-up crystallization method.

Genceli-Güner (33) developed an Eutectic Freeze Crystallization (EFC) technique together with her departmental colleagues. She recently graduated cum laude for her work on this technique, which cools a liquid until it reaches the so-called eutectic point. At this point the water and the salts in the solution crystallize simultaneously. Scrapers that rub along cooling elements, like in a sorbet machine, create an emulsion of ice and crystallized salts. Gravity does the rest: the lighter ice floats and the salts sink, resulting in a perfectly layered separation.

Genceli-Güner’s main focus was the retrieval of magnesium sulfate from aqueous solutions, a process she devised for mining company Nedmag (her main research sponsor). Magnesium sulfate (MgSO4) is produced when flue gasses from power plants are ‘desulphurised’ to prevent sulpher dioxide (SO2) polluting the atmosphere. The SO2 is absorbed in a solution of magnesium hydroxide, resulting in a solution containing MgSO4. This chemical can be reused as a fertilizer, hence the interest of Nedmag.

But not only Nedmag is interested. Next year Genceli-Güner will also collaborate with researchers from South Africa, where water is scarce, and in the mining industry they need a lot of it. Many minerals are retrieved by pumping water under high pressure in the ground. When it resurfaces the water contains minerals and salts, such as all kinds of sulfates, carbonates and chlorides. After undergoing the Eutectic Freeze Crystallization technique, that same water could then be used over and over again.
Freezing techniques are already widely used in the industry, but then only to create solutions with a higher salt concentration. The higher the salt concentration gets, the harder it gets to freeze the water. At a certain point the process is stopped because of the high energy costs. Other techniques that are widely used in combination with freezing or separately are evaporative crystallization and anti-solvent crystallization, where chemicals are added to a solution to make the salts precipitate.

In her dissertation Genceli-Güner shows  that – contrary to what many researchers believe – Eutectic Freeze Crystallization is in fact very energy efficient. “The technique requires 90 percent less energy than conventional evaporation crystallization and theoretically results in 100 percent yield”, she says. “Once you reach the eutectic point nature takes over. When the salts crystallize, the solution becomes more diluted, so it can freeze more easily. Under sufficient cooling, the system directs itself to eutectic temperature and stays around that point; hence, you end up with almost 100 percent perfect salt and ice crystals.”

Last month Genceli-Güner received a Veni grant worth 250,000 euro from the Netherlands Organisation for Scientific Research (NWO) to conduct research on ‘Ice and Mineral Salt Formation below Zero Degrees’. She will now look for a way to calculate the eutectic points in solutions containing salt mixtures, amongst others.

But she will use her grant money for something completely different as well. In 2007, while studying the crystallization process of Magnesium sulfate, she discovered that this chemical, which is usually found in a hydrate form, was surrounded by 11 water molecules (MgSO4·11H2O) at sub-zero degree temperatures. Since 1837 to her discovery in 2007, it was thought that the hydrate contained 12 water molecules. Together with Japanese researchers, Genceli-Güner also discovered the hydrate existing in the wild (a prerequisite for the International Mineral Association to accept a molecule as a mineral), in Antarctic ice cores of several kilometers deep. The hydrate is now known as Meridianiite. With her Veni grant, Genceli-Güner will continue her hunt for new minerals.

Editor Redactie

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