Strontium complexation in aqueous solutions and silicate glasses: Insights from high energy-resolution fluorescence detection X-ray spectroscopy and ab-initio modeling

Analysis of the spectra of the silicate-rich fluids shows that both melt and fluid composition strongly influence Sr complexation. For the silicate-rich fluids, formation of Sr-Cl complexes occurs at low (Na + K)/Cl and (Si + Al)/(Na + K) ratios in the fluid, whereas Sr hydroxide and possibly silicate complexes (similar to those in the silicate glass) are favored at higher ratios. Our X-ray spectroscopic results offer an explanation for the dependence of fluid-melt partitioning of Sr on melt composition measured in previous ex situ studies, and highlight the importance of components other than chloride (silicate and aluminosilicate) in controlling metal speciation in fluid-melt systems at high temperatures and pressures.