Characteristics of fluorescence parameters of humic acids in water environment and their complexing constants with heavy metals

A laboratory study was conducted to investigate the influence of pH and ionic strength on the ratio of fluorescence peaks' intensity(r)and the fluorescence index(FI) of humic acids(HA), and to determine the complexing ability of the substance represented by HA fluorescence peaks with heavy metals by using three-dimensional excitation-emission matrix fluorescence spectroscopy(3DEEM). The results showed that the r of HA had a certain linear relationship with pH in a certain pH range. And the r was significantly dependent on the ionic strength. The FI was minimal at pH 10.0. The FI of commodity humic acid(CHA) and natural humic acid(NHA) were 1.14 ~ 1.30 and 1.55 ~ 1.87 respectively. The binding products of the humic-like acid represented by the CHA fluorescence peak located at (270~280)nm /(420~448)nm with Cu²⁺ or Cd²⁺had a stronger degree of stability than that of the humic-like acid represented by fluorescence peak located at (335~405)nm/(380~472)nm with Cu²⁺ or Cd²⁺.The complexing ability of the organic matters represented by fluorescence peaks with Cu²⁺ was stronger than that with Cd²⁺.There was a difference in the complexing ability of the organic matters represented by the fluorescence peaks of the different HAs with different heavy metals.