T
he solubility of CaSO
4·2H
2O was determined in aqueous NaCl solutions up to very
hig
h salinities and constantCaCl
2 concentrations at 35
![](/images/entities/deg.gif)
C. Addition of CaCl
2 into t
he aqueous NaCl system reduces t
he solubility of CaSO
4·2H
2O quite dramatically w
hile maintaining t
he basic pattern of t
he solubility curve. Mean ionic activity coefficients
hars/gamma.gif" BORDER=0 >± of CaSO
4·2H
2O derived using t
he extended Debye-H&
uuml;ckel law wit
h quadratic terms decrease wit
h an increasein ionic strengt
h. A comparison of t
he value of t
he t
hermodynamic solubility product constant,
Ksp(th) of CaSO
4·2H
2O to t
he solubility product
Ksp obtained from t
he observed solubility data indicate sizable differences. T
his
has been explained t
hroug
h a combination of t
he extended Debye-H&
uuml;ckel law and ion association t
heory. Wealso measured accurate densities for t
he quaternary system CaSO
4·2H
2O + NaCl + CaCl
2 + H
2O at 35
![](/images/entities/deg.gif)
C. T
hedensity of t
he solution increases linearly wit
h an increase in concentration. Solutions containing
hig
her amountsof CaCl
2 were found to be less dense w
hen compared at t
he same ionic strengt
hs. Solubility and density data asa function of concentration
have been correlated using polynomial and linear fits by t
he met
hod of least squares.T
hese studies are of relevance in t
he production of salt wit
h low impurities of Ca
2+ and SO
42- ions.