Study On The Interaction Between Humic Substances And Metal Ions

Humic Substance?HS?is derived from biological and chemical decomposition of died animals and plants residues with the aid of air and water,which plays an important role on regulating the ecological effects of metal ions on the earth,such as chemical cycle,migration and transformation.HS can reduce the toxicity of heavy metals by its functional groups such as carboxy,hydroxyl,phenolic hydroxyl,sulfonic acid.Specifically,it can combine,exchange,adsorb and chelate with metal ions and influencing their migration and transport,fixation and accumulation process by physical and chemical interactions.In this work,the morphology and size of humic acid and fulvic acid from different places were investigated by different characterization methods,and the adsorption behaviors of fulvic acid to heavy metal ions were discussed.The main results are as following:?1?The elemental composition and surface functional groups of natural fulvic acid and humic acid from different places were compared by means of Fourier transform infrared spectroscopy?FTIR?,Elemental analyses.It was found that the content of C?H?O?N?S and atom ratio is only a little different.FTIR spectra indicated that they have similar structural and functional features,but had a little difference of the peak area and peak intensity in aliphatic C-H,aromatic and carboxyl groups.?2?Via direct dissolution method and alkaline soluble acid precipitation method,the size and morphology of fulvic acid solutions were compared at different conditions.We found that HA in aqueous solution form rod-like complexes at high pH value,and their size strongly depends on the pH of solution,i.e.the complexes formed at pH=2.3 and pH=12are significantly larger than that of other pH values.Further purifying the fulvic acid,the rod-like complexes can also be observed at pH=10?Buffer Solution?,but disappeared at both the acidic and neutral buffer solutions.?3?The effects of fulvic acid on the cadmium ion adsorption ability and solution stability were investigated by modulating the initial concentration of Cd²⁺ions and fulvic acid solution.Addition of CdCl₂ into fulvic acid solution leads to the formation of larger aggregates with increasing the concentration of Cd²⁺ions,above a critical metal ion concentration,the solutions loose its stability and the aggregates precipitate.Further changing the pH value,adsorption capacity of Cd²⁺to fulvic acid is weaker with lower the pH value.The maximum adsorption capacity was strongly dependent on pH value.