sulfate-separation-selective-crystallization-with-bis

Sulfate Separation by Selective Crystallization with a Bis-iminoguanidinium Ligand

A simple and effective method for selective sulfate separation from aqueous solutions by crystallization with a bis-guanidinium ligand, ...

Oak Ridge National Laboratory

The University of Texas at Austin

An effective approach to sulfate separation from aqueous solutions is based on the crystallization of extended [SO4(H2O)5(2-)]n sulfate-water clusters with a bis(guanidinium) ligand. The ligand was generated in situ by hydrazone condensation in water, thereby bypassing the need for elaborate syntheses, tedious purifications, and organic solvents. Crystallization of sulfate-water clusters represents an alternative approach to the now established sulfate separation strategies that involve encapsulation of the "naked" anion.

Aqueous Sulfate Separation by Crystallization of Sulfate-Water Clusters.

Selective crystallization of sulfate with a simple bis-guanidinium ligand, self-assembled in situ from terephthalaldehyde and aminoguanidinium chloride, was employed as an effective way to separate the highly hydrophilic sulfate anion from aqueous solutions. The resulting bis-iminoguanidinium sulfate salt has exceptionally low aqueous solubility (Ksp =2.4×10(-10) ), comparable to that of BaSO4 . Single-crystal X-ray diffraction analysis showed the sulfate anions are sequestered as [(SO4 )2 (H2 O)4 ](4-) clusters within the crystals. Variable-temperature solubility measurements indicated the sulfate crystallization is slightly endothermic (ΔHcryst =3.7 kJ mol(-1) ), thus entropy driven. The real-world utility of this crystallization-based approach for sulfate separation was demonstrated by removing up to 99 % of sulfate from seawater in a single step.

Article	Year
Aqueous Sulfate Separation by Crystallization of Sulfate-Water Clusters. Angewandte Chemie (International ed. in English)\| PubMed ID: 26252802	2015
Aqueous Sulfate Separation by Sequestration of [(SO4 )2 (H2 O)4 ](4-) Clusters within Highly Insoluble Imine-Linked Bis-Guanidinium Crystals. Chemistry (Weinheim an der Bergstrasse, Germany)\| PubMed ID: 26643375	2016
Corrigendum: Aqueous Sulfate Separation by Crystallization of Sulfate-Water Clusters. Angewandte Chemie (International ed. in English)\| PubMed ID: 26836332	2016

Charles A. Seipp

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