My pre-secondment at Eawag, distance made no difference

Hi, I’m Xingyu and in this blog I want to tell you about my preparation secondment at or better „with“ Eawag, because it was a virtual one. Between the constraints of the pandemic and the legal requisites in Switzerland for researchers, I couldn’t be physically present at Eawag. However, we made the most out of a remote collaboration to prepare another secondment at Eawag over hopefully a few months.

A glimpse into my experiment

There are many different types of iron minerals, each varying in their ability to absorb phosphorus (P). Under anoxic or suboxic conditions, ferrihydrite, a widely distributed iron mineral, can undergo transformations that is catalyzed by Fe²⁺, leading to more crystalline forms such as lepidocrocite and geothite. We have conducted an experiment to mimic this process in the presence of P and under static anoxic, oxic and cyclic redox conditions. Our main findings are: The presence of P limited this transformation, it seemed that cyclic redox condition retard the transformation, but more robust evidence was needed to support our finding.

Reactors of different P level and redox treatment. You can see that the colors of the suspensions were not the same!

From restrictions to data

As the pandemic gradually came to an end, plans for my secondment at Eawag began to solidify. The core question arose: We have concluded our experiment and analyzed the dissolved phase, but how do we dig deeper into the solid phase? How can we discern which mineral phases dominate a sample?

Andreas Voegelin from Eawag provided the solution: X-ray absorption spectroscopy (XAS). Exciting, right?

However, due to certain legal restrictions, my physical presence at Eawag was ruled out for now. But let me assure you, a virtual collaboration has its own set of advantages!

This is how i started to explore the world of XAFS	ESRF in Grenoble

The powerful X-ray beams needed for our work are in specialized locales called Synchrotron Radiation facilities. Gaining access to these facilities is a task in itself. Thanks to Andreas, our samples were expertly analyzed. Great!

After the measurements, we were presented with some spectra. Using linear combination fitting with reference spectra, we could gauge the relative contribution of iron minerals in a sample. It’s a complex procedure, demanding significant expertise. Thankfully, with Andreas at the helm, we derived meaningful results. Our findings made their way to the Goldschmidt 2023 in Lyon.

My supervisor Stefan Peiffer and me at Goldschmidt 2023.