geothermal resource potential of the safford-san simon basin, arizona

Equation (1)
Alumino-silicate + H 2
C0 3
(solid)
Cations + HC0 3
+ Si (OH)4 + kaolinite
(solid)
where H 2
C0 3
= CO (g) 2
+ H29
Si (HO)4 is dissolved silica
Comparisons of calculated dissolved carbon dioxide concentrations with silica
concentrations in all three types of ground water in the Cactus Flat-Artesia
area suggest that a steady-state disequilibrium with alumino-silicates and
quartz has a more important influence on silica concentration than does temperature-dependent
equilibrium with quartz (Figure 24).
Calculation of dissolved
carbon dioxide was accomplished using equation (2) from Paces (1972).
Equation (2)
-log pC0 2
= pH-log HC0 - 3
7.689 - (4.22 x lO-3T) - (3.54 x lO-5T2)
where T = Temperature
a
C
and concentration :
activity
Silica analyses were corrected for ionization at higher pH because analyses
report total silica.
Silica (Si(OH)4) derived from dissolution of quartz
or alumino-silicates dissociates to form SiO (OH);, which at higher pH becomes
an important form of dissolved silica.
The following equation is used to
correct for silica ionization:
Equation (3)
log Si (OH)4
corrected
log Si (OH)4
analyzed
log Si (OR);
dissociated
where log Si (OH);
equation (4)
and concentration ~
= - 720.15 - 7.3 + pH + log Si (OH)4
273.15 + TOC
analyzed
activity
Equation (4) is derl\Ted in Appendix 2.
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