Studies On The Chelation Relationship Between Cu～(2+),Cd～(2+),Pb～〔2+),Zn～(2+) And Dissolved Organic Matter Of Peat

Complexiation of heavy-metal ions by naturally occurring dissolved-organic-matter(DOM) is widely studied because this complexiationcan chang the transport pathways and toxicity of metal ions.The group characteristics, molecular weight of the DOM extracted from a peat,humic acid(HA),fulvic acid(FA) and water-soluble-organic-matter (WSOM),and the complexiation relationship between HA. FM WSOM and Cu2~~ Zn2~~ Pb2~~ Cd2~ were studied. The oxgen- containing functional group of HA FA WSOM was identified by direct chemical analytical methods .A solid state ?C-NMR was done to describe the structure of the DOMs.An aqueous gel chromatography was developed for determination of molecular and molecular weight distribution of the DQMs.The results of the studies showed that HA was of higher molecular weight and contained a large amount of alkly carbons in its structure,while FA was of lower molecular weight and contained a large amount of polysaccharide carbons.Although the molecular weight of WSOM was a little lower than that of FA ,the structure of WSOM was similar to that of FA.The contents of total acid group and carboxyl group in fulvic acid were far higher than that of l-IA,while that of total acid group and carboxyl group of WSOM was olower thanthat of HA. An infrared spectroscopic investigation of the complexes of four metal ions with DOMs demonstrated the participation of 桹H and C0 groups in addition to 桟OOK in binding of heavy- metal cations.However the nature of the metal-carboxylate linkages cannot be accurately determined from the positions of antisymmetric and symmetric carboxylate stretching vibrations .The complexiation tendency of the four divalent cations with HA and FA, revealed by the infrared spectroscopic spectrum, decreased in the order of Cu2~>Pb2~>Cd2~>Zn2~,while the tendency of the ions with WSOM was not clearly revealed by the IR method. Ion-exchange equilibrium method was used to determine the stability constants of the ion- DOM complexes formed by four different ions under two PH conditions.The results were as follows: at 10.l,PH=3.5,the orders of the coordination numbers x were: M-HA: Cu2~ (1.21) >Zn2~ (0.90) >Pb2~ (0.85) >Cd2~ (0.42): M-FA Cu2~ (0.99) >Pb2~ (0.93) >Cd2~ (0.59) >Zn2~ (0.46); M-WSOM: Cu2~ (0.92) >Pb2~ (0.59) >Zn2~ (0.33) >Cd2~ (0.18). the orders of stability constants were: M-HA Cu2~ (4.81) >Pb2~ (3.76) >Zn24 (3.72) >Cd2~ (1.91); M-FA: Cu2~ (3.16) >Pb2~ (2.96) >Zn2~ (1.72) >Cd2~ (1.46); M-WSOM Cu2~ (3.31) >Pb2~ (1.57) >Zn2~ (0.73) >Cd2~ (0.37). At 10.1,PH=5.0, the orders of the coordination numbers x were: M-HA: Cu2~ (1.76) >Zn2~ (1.28) >Pb2~ (1.01) >Cd2~ (0.64); 47 M-FA: Cu24 (0.98) >Pb24 (0.90) >Cd24 (0.80) >Zn2~ (0 .48): M-WSOM: Cu24 (1.42) >Pb24 (0.65) >Cd24 (0.53) >Zn24 (0.34)~ the orders of stability constants were: M-HA Cu2~ (6.48) >Pb24 (4.45) >Zn24 (4.29) >Cd24 (2.36); M-FA: Cu24 (4.26) >Pb24 (3.12) >Cd24 (2.49) >Zn24 (1.75): M-WSOM Cu24 (4.71) >Pb24 (1.26) >Zn24 (0.79) >Cd24 (0.47)~ Metal ions and DOM usually formed mixed or plynuclear complexes.Under high PH condition,there was a marked increase in coordination numbers and stability constants.The stability constants Of ion-DOM under the same PH condition were: M-HA>M-FA>M-WSOM.