Influence of ions-admixtures, typical for the carbonate rocks surface in the urban environment, upon morphology and solubility of gypsum crystals (experimental data)

Kuz'mina M. A., Frank-Kamenetskaya O. V., Vlasov D. Yu.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 4. P. 26-35

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Language: Russian

Abstract

Study was carried out on peculiarities in crystallization of gypsum Ca(SO4)2H2O from aqueous solutions under conditions of changing pH and concentration of ions-admixtures (Na⁺, K⁺, , Mg²⁺, Al³⁺, Fe²⁺, , C₂, C₆, C₄ and C₄)typical for the urban environment where the gypsum-rich patina is forming on the surface of marble and limestone monuments. It has been revealed that solubility of gypsum increases significantly with decreasing pH of solutions from 6.5 down to 2.0, as well as with elevated concentrations of K+ and Na+ cations (from 30 up to 700 mmol/l). The morphology of gypsum crystals is changing in dependence on the chemical composition of the medium. Thus, in presence of Na⁺, NH4⁺, Mg²⁺, Fe²⁺ and , ions gypsum crystallizes in long needles, flattened or prismatic crystals, whereas in presence of K⁺, Al³⁺ ions, citric, fumaric and succinic acids there are formed elongated plate-shaped S-curved gypsum crystals. It is shown that increase in the relative oversaturation of solution promotes the formation of spherulite-shaped intergrowths of gypsum crystals.

Key words: gypsum-rich patina, synthesis of crystals from solutions, solubility, morphology, ions-admixtures, carbonate rocks.