Analysis of Correlation between Amount of Chlorophenols adsorbed onto Humic Acid and pKa (Acid Dissociation Constant) of Chlorophenols

摘要

Chlorophenols are known as intermediate of dyestuff and insecticide. In spite of their usefulness, they are harmful to water organisms. Their toxicity depend on co-existing substances such as humic substances including fluvic acid (FA), humic acid (HA) and humus. Particularly HA has capability of adsorbing environmental pollutants like HOPs (Hydrophobic Organic Pollutants). In this study, the mechanism of adsorption between chlorophenols and HA was investigated. First, adsorption sites of HA were revealed by acid-base titration. Dominant adsorption sites were carboxyl group and phenolic hydroxyl group analyzed by using NICA (Non Ideal Competitive Adsorption) - Donnan model. Then, interaction between chlorophenols and HA were examined. The pKa value of three chlorophenols examined in this study were within the range of 6 to 10. Amount of 2,4,6-trichlorophenol (2,4,6-TCP) adsorbed onto HA was drastically decreased along with pH increase. Amount of 2,4-dichlorophenol (2,4-DCP) adsorbed onto HA was slightly decreased along with pH increase. No relationship between amount of p-chlorophenol (p-CP) adsorbed onto HA and pH of the solution was found. The 2,4,6-TCP is electronegatively charged because the proton dissociation generates repulsion between 2,4,6-TCP and HA. Moreover, a positive correlation between partition coefficient (log P) and amount of adsorption was suggested.