suggested that the ammonium group in the zwitterionic form could
still contribute to the adsorption via cation exchange mechanism. As
the pH increased, the amount of CIP adsorbed decreased sharply to
210 mg/g at pH 11. The sharp decrease in CIP adsorption when
solution pH was approaching or above its pKa2 confirmed that cation
exchange was no long dominating. One the other hand, significant
amounts (more than 200 mg/g) of CIP was removed from solution.
Tests using an initial CIP concentration of 1500 mg/L at pH 11 did not
show any precipitation. Thus, the removal of CIP from solution due to
CIP precipitation was excluded and other mechanisms, such as nonelectrostatic
interaction should be considered to account for CIP
removal at high pH.