Networking and crystallisation sometimes come together

Feb 23, 2015 No Comments by 1555 views

One of the first things I did when I started my job in the CO2-react network was to make crystallisation experiments in order to synthesize rare-earth (REE) bearing carbonates. I focused on hydroxylbastnasite (REECO3OH), a mineral of the bastnasite group (REE(CO3)(OH,F)) that is very common in carbonatite deposits and is an important source of light rare-earth elements (La, Ce or Nd). These were experiments that involved hydrothermal synthesis and were, at the beginning, difficult to reproduce. Soon, I found out that hydroxylbastnasite forms from poorly-ordered carbonate precursor and also that this mineral can develop very interesting –and really beautiful– morphologies depending on thermal treatment during synthesis (Fig. 1).


Fig. 1. SEM images of NdCO3(OH) produced via the four different hydrothermal treatments. The habits are changing as a function of the experimental conditions: (a, b) Triangular pyramids shapes obtained from batch A. (c, d) Cauliflower-type morphologies obtained from batch B. (e, f) Spine-shaped aggregates developed with batch C. (g, h) Fishbone (dendritic) morphologies obtained with a heating ramp from 21 to 220 ºC (Batch D). See details.

After a few weeks I was able to obtain nice data, so I started working on a manuscript for a MINSC and CO2-react special issue of Mineralogical Magazine  during a writing course at the network meeting in Fuerteventura. By coincidence I was approached by another CO2-react research fellow, Martin Voigt, who works at Université Paul Sabatier/CNRS (Toulouse) and is studying the mobility of rare-earth elements in aqueous solutions. In particular, he was working on determining the solubility of hydroxylbastnasite-Nd at different CO2 partial pressures and pH. He told me that he had a major problem: he needed to find some grams of pure bastnasite samples for his experiments. This was not easy because of two major issues: 1) Good bastnasite samples for sale are not abundant… and the bigger crystals can be really expensive (they are even used for jewellery); 2) Many of these samples, even the expensive ones, have a complex chemistry because they contains several light rare-earths and some traces of the heavier lanthanides (Dy, Eu, Gd, etc)… so this means that if you use them for your experiments, you may have too many variables to worry about.

Martin needed to use hydroxylbastnasite crystals with dimensions larger that 1 µm. Why? Well, this comes from the fact that solubility depends on particle size, so when the particles get smaller through the nanorange of sizes, their solubilities increase dramatically. Luckily, one of my synthesis methods allowed to make regular hydroxylbastnasite crystals with dimensions of several micrometers. So, after a chat with Martin, Eric, Liane and Juan Diego in Fuerteventura and we decided to collaborate together. In collaboration with Juan Diego –who also works on REE carbonate crystallisation– I produced pure La and Nd hydroxylbastnasite for Martin by using one of the synthesis methods I had developed, later characterising the crystals to make sure that they were suitable for his experiments. Several months later, at the Mid-term review in Seefeld (Austria) I was happy to see that my samples were useful and Martin was obtaining nice results that will be also very valuable for the interpretation of other crystallisation experiments I am working at present.

Overall, I would like to highlight two main things from this story: the first one is how useful networking can be. Our collaboration initiated just by coincidence because we had a chat during a CO2-react network meeting. Since then we maintain email contact from time to time because there are always questions we need to ask or discuss. The second idea is how cool some things we produce are. I really love the shapes and morphologies of the crystals we produce – they show that science and beauty are clearly interconnected.


beatriz_vallina About the author: Beatriz Vallina is a geologist working at the Cohen Labs (School of Earth and Environment, University of Leeds) who is specialized in crystallography and mineralogy. She has worked as a geologist in a large coal-mining company and also as a technician in different chemistry laboratories before focusing her work on solid characterization techniques.

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