# Calculate sorption isotherm for carbonate on Sherwood "Bunter" sandstone
#  ... needed for 14C retardation
SOLUTION 1
 pH 7 charge
 C 1
 Ca 1 Calcite 0
 Mg 1 Dolomite 0
EQUILIBRIUM_PHASES 1
 Calcite; Dolomite
END

PRINT; -reset false
SURFACE_SPECIES
 Hfo_wOH + CO3-2 + H+ = Hfo_wCO3- + H2O; log_k 12.56
 Hfo_wOH + CO3-2 + 2H+= Hfo_wHCO3 + H2O; log_k 20.62
SURFACE 1
 Hfo_w 8.4e-3 600 3.84 # estimated for the Sherwood sst
 -equil 1

USE solution 1
USE equilibrium_phases 1

REACTION 1
 CO2 1; 1.1e-2 in 20

USER_GRAPH
 -head c
 -axis_titles "solute Carbonate, mol/L" "sorbed Carbonate, mol/L"
 -start
 10 graph_x tot("C")
 20 graph_y mol("Hfo_wCO3-") + mol("Hfo_wHCO3")
 -end
END