# Exchange isotherms, Rothmund-Kornfeld vs. active fraction
# Appelo and Postma, 2005, Example 6.6, p.259.
# Rothmund-Kornfeld...
EXCHANGE_SPECIES
 0.618Ca+2 + 2KX = CaX2 + 1.236K+; -log_k -0.281
 -no_check
 -mole_balance CaX2
 -gamma 5.0 0.165
SOLUTION 1
 K 100		# 100 mmol K/kg H2O
EXCHANGE 1
 KX 0.4         # 400 mmol KX, total K in the system = 500 mmol
END

PRINT; -reset false; -status false
USE solution 1; USE exchange 1
REACTION 1  	# Remove 500 mmol K+, replace with 250 mmol Ca+2
 K -1 Ca 0.5
 0 20*0.02499
INCREMENTAL_REACTIONS
SELECTED_OUTPUT; -file a_f.prn; -reset false
USER_PUNCH
 -head alpha_K beta_K
 10 punch tot("K") / 0.1
 20 punch mol("KX") / 0.4
USER_GRAPH      # Plot isotherm...
 -head alpha_K Rothmund-K
 -axis_titles "Solute K / (K + 2Ca)" "Exchangeable K / (K + 2Ca)"
 -axis_scale x_axis 0 1 0.2 0.1; -axis_scale y_axis 0 1 0.2 0.1
 -init false
 10 graph_x tot("K") / 0.1
 20 graph_y mol("KX") / 0.4
END
# active fraction...
EXCHANGE_SPECIES
  K+ + X- = KX; log_k 0.7; -gamma 3.5 0.015 0.7
  Ca+2 + 2X- = CaX2; log_k 0.8; -gamma 5.0 0.165 0.5
USER_GRAPH      # Plot isotherm...
 -head alpha_K active_fraction
USE solution 1; USE exchange 1; USE reaction 1
END