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| Influence of pH and ions on sorption of norfloxacin on humic acid |
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Abstract The influences of pH, concentrations of Ca2+, and ion types on sorption characteristics of norfloxacin (Nor) on humic acid (HA) were investigated by batch equilibrium studies according to OECD Guideline 106. Sorption coefficient (Kd) tended to increase with pH increasing in the range of 3.0~4.0, but to decrease as pH increase in the range of 6.0~7.0. The Kd values had two peaks at pH 4.0 and 6.0 than those at other tested pH values. The FTIR spectra of HA before and after hydrogen bonds were favorably formed at pH 3.0 between HA and Nor, while peptide bonds were likely formed between carboxyl group of HA and amino group of Nor at pH 6.0 and 7.0. The Kd values and sorption amounts of Nor gradually decreased with the increasing concentration of Ca2+, indicating that the cation exchange and completion sorption occurred between Nor and Ca2+. Addition of different cations and anions in solution led to different sorption characteristics of Nor. The valencies of different cations played the dominating role in affecting the sorption of Nor on HA. The higher valencies cations, the more strongly cations were adsorbed on surface sorption sites of HA, resulting in the following order of the maximum sorption amounts (Qm) for Nor: M+ (Na+、K+、NH4+) > M2+ (Mg2+、Ca2+、Zn2+). On the other hand, the radius and the hydrolysis of cations could also influence the sorption of Nor. The inhibition effect of anions on Nor sorption became pronounced when the hydrolytic anions were added in solution.
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Received: 04 June 2010
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