Manipulating the crystallization kinetics and morphology of gypsum, CaSO4·2H2O via addition of citrate at high levels of supersaturation and the effect of high salinity

• Published in: Polyhedron 2021-08, Vol.204, p.115253, Article 115253
• Main Authors: Ziegenheim, Szilveszter, Szabados, Márton, Kónya, Zoltán, Kukovecz, Ákos, Pálinkó, István, Sipos, Pál
• Format: Article
• Language: English
• Subjects: Citrate; Complexation; Crystallization inhibition; Gypsum; Surface binding
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2021.115253

Citrate effects the kinetics of gypsum precipitation and the morphology of the solid forming both in pure water and in hypersaline solutions mimicking seawater. [Display omitted] Citrate ion possesses the right structure to be strongly bound on specific crystal faces of gypsum, CaSO4·2H2O, which results in an increase in the induction time of precipitation, and changes the structure and morphology of the solid. The inhibition of the precipitation kinetics of gypsum, in the stoichiometric reaction of Na2SO4 and CaCl2 was investigated in aqueous solutions with high supersaturation (0.1 M initial reactant concentrations). The induction time was found to be the longest when the inhibitor was present in fully deprotonated form in the solution (pH > 5). The inhibition effect levels off with the increasing inhibitor concentrations (ca. 3 mM). As a result of citrate binding, on the basis of SEM measurements, the morphology of the crystals change from rod-like to plate-like. Addition of high concentration of NaCl (mimicking seawater conditions) was found to facilitate the inhibition, but from the morphological studies, the inhibition mechanism of citrate appears to change under hypersaline conditions (relative to systems without added electrolyte.) From UV and IR spectroscopic measurements, it was found that the inhibitor ended up in the mother liquor after the completion of the precipitation reaction.