[Effect of Cu2+ on the water solubility enhancement of 4, 4'-dibromodiphenyl ethers by humic acid].

The effect of copper ions on the water solubility enhancement of 4,4'- dibromodiphenyl ethers (BDE-15) by a commercial humic acid (HA) has been studied using batch equilibrium technique at various pHs. The characteristics of HA-Cu complex were investigated with the aid of dynamic light scattering and Zeta potential measurements. The results showed that the interaction of BDE-15 with HA could be explained by partition according to the linear isotherms when HA were at lower level, while the non-linear isotherms were observed at higher level of HA. The capability of solubility enhancements was affected by the pH and the ratio of the concentration of copper ions and the concentration of HA. At low pH condition (pH 4.0), solubility enhancement of BDE-15 by HA was facilitated by Cu2+ at low concentration, but reduced by Cu2+ at high concentration. While the phenomenon was different at pH 6.0, and Cu2+ over all investigated concentration range promoted the capability of HA enhancing BDE-15 solubility and non-linear isotherms became more significant. The different effects of Cu2+ at pH 4.0 and 6.0 was mainly due to the dissociation of the HA functional groups as pH increased, thus affected the structure and size of HA-Cu complex.