• pH2–5—carboxyl group
• pH5–9—carboxyl and phosphate group
• pH9–12—carboxyl, phosphate and hydroxyl (or
amine) group.
The equilibrium experiments (isotherms) were carried
out at pH7. Under these conditions carboxyl groups and
a part of phosphate groups were deprotonated and thus
available for metal ions. This corresponds to the value
qmax that is in some cases higher than calculated from
the concentration of carboxyl groups, itself.