Insights into the formation of Mg(OH)2 particle size distributions in saltwork bitterns

Magnesium hydroxide (Mg(OH)2) is a key chemical for many different applications across industries from pharmaceuticals to wastewater treatment. As many magnesium sources are found in China, Russia, and the USA, efforts are ongoing in Europe to establish a local supply chain for magnesium. To do this, scientists are turning to novel raw material sources in the form of saltwater bitterns.

Magnesium is listed as a critical raw material in the EU1. One initiative that has emerged within Europe to bring the magnesium supply chain closer is the SEArcular MINE project, which explores the circular processing of seawater brines from saltworks for the recovery of valuable raw materials. This Horizon 2020 project has been granted a budget of almost €6 million and involves 12 partner institutions across 9 countries, with the aim of extracting magnesium, lithium, and other valuable trace elements from seawater bitterns.

One research paper produced by the SEArcular MINE project was, ‘Analysis of particle size distributions in Mg(OH)2 precipitation from highly concentrated MgCl2 solutions’, authored by Giuseppe Battaglia and his colleagues at the University of Palermo. This research was featured in the top 10 papers of Malvern Panalytical’s 2022 Scientific Award, and it explored a promising route for this research. As Guiseppe notes, “bitterns have a concentration of magnesium six times higher than seawater.”

The goal of the research project was to investigate how Mg(OH)2 particle size distributions (PSDs) changed under different mixing conditions when reactants of concentrated MgCl2 and NaOH were fed into two T-mixers. The research aimed to mimic the concentration of real bitterns found in saltworks. Working with different PSDs, Giuseppe et al. opted to use the Mastersizer 2000 to characterise the distribution range and used the Zetasizer Nano ZSP to determine particle stability.

Using the Mastersizer 2000 they found that, although mixing does not affect the PSD, if the solution is treated with ultrasound and anti-agglomeration agents, the PSD becomes narrower at higher mixing speeds and nanoparticles start to form. The Mastersizer results also found that the mixing results reached a plateau, with Giuseppe stating that, above Reynolds number 30000, the PSD will not change any more, and mixing no longer affected the precipitation process.”

“The Mastersizer 2000 allows you to study the real products of the precipitation process at high Reynold number mixing.” – Giuseppe Battaglia

The Zetasizer Nano ZSP was used to understand the influence of anti-agglomeration agents on the PSD, and it was found that the zeta potential of the particles was higher when these agents were present. With the addition of these agents, the Zetasizer showed that these dispersions went above a zeta-potential threshold of -30 mV, which is a critical value where dispersions above this value don’t aggregate.

“Since we were working with nanoparticles, we preferred to analyze them with the Malvern Panalytical Zetasizer Nano ZSP. ”
– Giuseppe Battaglia

The combination of the techniques enabled the researchers to confidently characterize the PSD and stability of Mg(OH)2 dispersions and provided valuable insights into the interaction between precipitation and mixing phenomena behind Mg(OH)2 formation.

Watch the recording of Giuseppe’s Ask an Expert webinar here!

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