Gypsum Precipitation Kinetics and Solubility in the NaCl–MgCl₂–CaSO₄–H₂O System

Abstract

Crystallization of calcium sulfate dihydrate (CaSO4·2H2O, gypsum) in sodium chloride solutions has been studied in the presence of magnesium ion. It was shown that Mg2+ has an inhibiting effect on the two stages of precipitation: nucleation and growth. Kinetic results were explained on the basis of the strong effect of magnesium ions on gypsum solubility. In the studied range of the ionic strength (IS), it was found that in the presence of NaCl the solubility increase stops beyond IS = 0.31 mol·L–1 whereas it continues to rise in the presence of MgCl2. X-ray diffraction analyses showed that magnesium ions act by substituting the calcium ones or by insertion in the defects of the gypsum crystal lattice.

Effect of Cu2+ on the nucleation kinetics and crystallization of rod-shaped CaSO4·2H2O in aqueous solution

“…The above phenomenon indicates that Cu atoms have been successfully incorporated into the lattice of CaSO 4 $2H 2 O. 33,35 Beyond that, the gradual decrease of peak intensity and the slight increase in the peak width with the introduction of Cu 2+ indicates the grain size is minimal and the crystallinity is decrease aer Cu is doped into CaSO 4 $2H 2 O. This indicates that the doping of Cu into CaSO 4 $2H 2 O lattice inhibit crystal growth, agreeing with the results of the length and width (Fig.…”

Effects of Impurities on CaSO4 Crystallization in the Ca(H2PO4)2–H2SO4–H3PO4–H2O System

“…It is attributed to the effects of impurities on ionic strength and supersaturation. 39,40 Meanwhile, Mg is likely to be present as ions or charged complexes and affects the activities of Ca 2+ and SO 4 2– . 14,41,42 As a result, the nucleation rate decreased from 1.10 × 10 17 to 4.40 × 10 16 with increasing Mg content.…”

The role of marine aerosol in the formation of (double) sulfate/nitrate salts in plasters

“…Chloride salts were also identified by using XRD and SEM-EDX measurements on the samples from gypsum plasters, suggesting that the input of sodium and magnesium, also present in the new crystals, can come from the chlorides transported by the marine aerosol (e.g. NaCl, MgCl 2 , KCl) [8].…”

“…Sometimes NaCl, MgCl 2 , CaCl 2 solutions can dehydrate gypsum as a result of the lower water vapour pressure of these solutions, modifying its solubility [8]. The later compounds, together with nitrates and sulfates, are present in marine aerosol [9], besides of fatty acids [10].…”