1 3 5 7

CO3

a

2

HCO3 -

CaCO3 (s)

(Ca2+)max

H2CO3

PCO2 Fixed

Log C-pH diagram for Ca2+ and carbonate at equilibrium with PCO2 = 10-3.5 atm

and CaCO3hatched area of the graph is supersaturated with respect to CaCO3(calcite); at equilibrium the free calcium concentration and the pH must yield a point on the

the condition [HCO3 -] = 2[Ca2+

from the intersection of the corresponding vertical line the graphs of the various species.

*

pH 9 13

-9

-7

-5

-3

Log

C

-1

+1 1o of freedom if aqueous fluid, CO2 (q) at fixed PCO2, and CaCO3(s)

T)

-11

P, T, and

(s). A system whose calcium concentration and pH yield a point in the

saturation line of the diagram. The solution is given by point a, which satisfies ]. The composition of the system is then obtained

11

are in eq at fixed P, T (so if no P, T, no [Ca]

Figure by MIT OCW.