Amorphous silica solubilities V. Predictions of solubility behavior in aqueous mixed electrolyte solutions to 300°C

Abstract

Solubilities of amorphous silica in several aqueous electrolyte solutions up to 300°C (Marshall, 1980a; Chen and Marshall, 1982) fitted the Setchénow equation, log( s 0 s ) = D·m as described earlier (Marshall, 1980b) where s 0 and s are molal solubilities of silica in pure water and salt solution, respectively, m is the molality of salt, and D is a proportionality constant related to the particular salt and temperature. It is now shown that, to a first approximation, the D parameters for various salts at the same temperature are additive. For instance, D( NaCl) − D( KCl) = D( NaNO 3) − D( KNO 3) or D( MgSO 4) = D( MgCl 2) + D( Na 2 S0 4) − 2 D( NaCl). It also follows that ( s 0 s ) = ∑ i (D im i) . This additivity principle was used to estimate amorphous silica solubilities in mixed NaCl-Na 2SO 4, NaCl-MgCl 2, NaCl-MgSO 4, Na 2SO 4-MgCl 2, Na 2SO 4-MgSO 4, and MgCl 2-MgSO 4 aqueous solutions up to 300°C. The method produces results that agree reasonably well with experimental values and would be useful for predicting silica solubilities, for example, in seawater and its hydrothermal concentrates and in geothermal energy applications.