Dr Peter Kraal, Tenure Track Scientist:
From the harbour to the deep sea
“Building material can also be read as ‘raw materials’ for ecological engineering and building with nature”
Geochemist Dr Peter Kraal of the Ocean Systems department wandered quite far outside his natural habitat in 2020. “Together with a team at Utrecht University, we won a grant to look into and alter the chemical properties of dredged harbour sediment”, he explains enthusiastically.
“Every year, enormous amounts of sediment are dredged out of the port of Rotterdam. The dredged material is either moved to the North Sea, where lots of it came from in the first place, or, if it is contaminated by the industries along the rivers that end up in the Rotterdam harbour, stored under-water in a holding basin. The sediment itself and the process of dredging, which involves large ships scooping up and moving around sediment, are a source of CO₂. We want to find out if we can use natural CO₂-absorbing materials to turn the dredged sediment into a useful building material that is a sink for CO₂.” Raw materials ‘Building material’ does not mean that Kraal intends to actually bake bricks from the sediment that is taken out of the harbour. “Building material can also be read as ‘raw materials’ for ecological engineering and building with nature. In the Dollard region, for example, colleagues are experimenting to see if dredged sludge can be used to produce clay for dike reinforcement. And the newly built nature reserve Marker Wadden was also built with dredged sediment from the Markermeer. But before we can use sediments from the port of Rotterdam, we have to find out what is in it exactly, what can be released from the material under different environmental conditions and how we can potentially improve the chemical behaviour.”
During field work on board RV Pelagia
“We want to find out if we can use natural CO₂-absorbing materials to turn dredged sediment into a useful building material”
“We study the chemical processes that control the properties of sediments and water”
Binding CO₂ Now, ‘improve the chemical behaviour’ should be taken literally, Kraal says. “On land, there are already many experiments going on with the natural mineral olivine. This is a mineral that consumes CO₂ when it weathers. It is thought that by grinding the stones and speeding up this natural process, olivine could play a role in achieving negative carbon emissions to counteract atmospheric CO₂ accumulation and global warming. In our project, we will explore whether mixtures of harbour sediment and olivine can result in useful, CO₂-binding building material. Volcanic glass from the Eiffel mountains in Germany can play a similar role as olivine, or any non-hazardous CO₂-absorbing material for that matter. After testing these chemical processes in the lab, we will eventually test this in a natural setting too. That way, we may come up with a practical solution for the environmental impact of harbour dredging. Sediments that need to be stored now, while emitting CO₂, may become valuable raw material that binds CO₂!” Engineering fundamentalist Kraal admits that the Rotterdam project comes pretty close to engineering, as close as he has ever been before as a trained marine biogeochemist. “But at the end of the day, the processes are similar. Both in the meters-deep harbour of Rotterdam, as well as in the kilometers-deep open ocean, we study the chemical processes that control the properties of sediments and water.” In fact, in the same year that he was awarded the ‘Rotterdam-harbour-grant’, he also obtained a grant together with a colleague at Utrecht University to study chemical processes around hydrothermal vents in the deep sea: the I-NANO project. “Together with Dr Oliver Plümper at the Geosciences Faculty in Utrecht, we will look at nanometer-sized particles that are formed near these under-water volcanoes.”
Black smoker. Photo: MARUM – Center for Marine Environmental Sciences, University of Bremen (CC-BY 4.0)
“We may come up with a practical solution for the environmental impact of harbour dredging”
When dissolved minerals from under-water volcanoes hit the cold, oxygenated water of the ocean, they quickly precipitate into tiny nanoparticles. Kraal: “These particles form very rapidly and are therefore not very well-structured, with a lot of sites where they can bind molecules from seawater. This makes the nanoparticles potent catalysts, hosting and accelerating all sorts of chemical reactions. It is even hypothesized that the first complex molecules that generated life on earth, could have been formed in these thermal vents at the bottom of the oceans.” In unique experiments with X-ray microspectroscopy, Kraal and Plümper intend to study the nanoparticles as they react. “It is fair to say that this project revolves around many fundamental processes in the ocean. The vents ‘exhale iron’ into the deep ocean that, in turn, forms particles that scavenge phosphorus, among many other chemical processes. We are potentially looking at both a key to life on earth, billions of years ago, as well as to the stockkeeping of the most crucial elements that enable ocean life today. It is the nature of a fundamental research project like this that it may satisfy our curiosity. But it may just as well generate nature-based practical knowledge for industry, where nanomaterials play a huge role in technological advances in chemical catalysis.”
Active hydrothermal smokers at a depth of 2320 metres on the Mid-Atlantic Ridge near Horta, Azores (NICO expedition 2018)
“This project revolves around many fundamental processes in the ocean”