Fig. 9. Testing the sensitivity of Model A [through the distribution coefficient log₁₀(K_d)] to the value of proportionality factor F_W at various values of surface charge (Z). The free Cd ion concentration was 1.00 x 10^–8 M; pH = 5.50; ionic strength was 0.01 M (NaNO₃); total carboxyl group concentration (T_C) was 3.13 mol_c kg^–1. The values of constants and parameters used for Cd were: –log intrinsic stability constant for metal complexation to a monodentate carboxyl binding site = 0.290, –log intrinsic stability constant for metal complexation to a monodentate phenolic hydroxyl binding site = 4.76, proportion of carboxyl groups capable of forming bidentate chelates = 0.051, and proportion of monodentate binding carboxyl groups capable of forming bidentate chelates to a phenolic hydroxyl group = 0.951.