200 



COOKE 



2310 



2290 — 



O 2270 



O 



o 

 u 

 E 



200 400 



PRESSURE, atm 



Fig. 8 Dissolution behavior in artificial seawater without Mg 2 



It was further observed that, with the temperature and pressure fixed, the 

 system was able to reach steady state because the composition of the solid 

 solution of MgC0 3 and CaC0 3 in contact with seawater was a function of the 

 pressure. With seawater composition changed and the salinity less, less pressure 

 was needed to exceed the lysocline pressure. In another series of experiments, 

 with magnesium concentration 125% of normal in the artificial seawater, the 

 lysocline pressure was 366.3 atm. With the magnesium concentration 67% of 

 normal, the lysocline pressure was 273.0 atm. The chemical potential of an ion 

 in solution must be the same as the chemical potential of the same ion in the 

 solid if steady state is to be achieved. The phase rule of Gibbs was applied at this 

 point to systematize the observations. 



If the system is assumed to contain CaC0 3 and MgC0 3 and water as 

 components and these are distributed between two phases, solid and liquid, then 

 there are three independent variables in the system, the temperature, the 

 pressure, and the composition of either liquid (the seawater) or solid (the calcite 

 containing magnesium). With the pressure fixed, the temperature fixed, the 

 composition of the seawater the same throughout the calcite reactor and the 

 system in steady state, experimentation shows that the system has reached 



