| Humic acids, a kind of widely spread natural organic chelating ligand, are essential for the structure and function of the whole ecosystem. In the latest two decades, the function and significance of humic acids in the eco-environment, especially the interaction of compositions of humic acids with various metal ions has become the focus of the research. Since 1970s researches on humic acids, especially on the characteristic of adsorption and stability constant of the interaction of metal ions with humic acid, have been widely carried out in foreign countries, many kinds of metal ions involved. From early 1980s domestic studies on the interaction of metal ions with humic acids, including Cu, Zn and Hg become jnore and more active with emphasis on the complexation constant.Previous domestic studies on humic acid-metal interaction focused less on FA than HA, and the results were with great discrepancy. Other than different source, purification and research methods, Ignoring the structural complexity of humic acids and the exact existing form in solution are important reasons, resulting stress has been laid on simulating experimental data with different mathematical models. Meanwhile, many studies obtained the characteristic parameters of the interaction before the reaction reached stady-state, ignoring humic acid solution's character of non-equilibrium system. So the interactive mechanism of humic acids with metal ions has not been truly revealed. The latest studies indicated that two-phase reaction is the main mechanism of the interaction of HA with calcium and copper ions, and the reaction included not only the chelation of the surface functional group of HA with the metal ions in the solution, but also that of the metal ions diffusing into the interior of HA with the interior chelating ligand. It is unknown whether two-phase reaction is interaction mechanism of FA with metal ions, because the molecular structure of FA is far different from that of HA.This experiment focuses on studies on the mechanism and characteristics of the interaction of FA with calcium, cadmium and lead, so as to reveal the mechanism of combination, adsorption characteristic, stability and affecting factors of the interaction, and provide theoretical basis for adjusting the metal ions activity in the environment andavoiding the environmental pollution.The experimental method was modified potentiometrictitration. Saturated calomel electrode was used as reference electrode. Lead electrode, glass electrode and ions selective electrode were used respectively to measure the redox potential, pH of the solution and the activity of metal ions. The steady state was controlled via redox and glass electrode. As the stable index, it is required .The contents of function groups and the basic components of HA and FA are measured by the method that Qixiao Wen recommended in "Study methods of soil organic matter" . The contents of the main function groups in HA were: total acidity 6.85mmol/g HA, carboxyl 2.92 mmol/g HA and phenolic group 3.93mmol/g HA, while those in FA were: total acidity 10.58mmol/g FA, carboxyl 6.87 mmol/g FA and phenolic group 3.71mmol/g FA. This showed FA had higher content of total acidity and carboxy than HA, while equal phenolic group with HA. The contents of C and N in HA were 46.38% and 3.98% respectively, and those in FA were 38.38% and 2.09% respectively. FA had higher content of C and N than HA.The acid-bask titration of FA was experimented in 0.lmol/L KC1 solution. The concentration of FA was 0.56g FA/L and 1.12g FA/L. After argon gas pumped into the solution continuously for 24hs, the titration began. The whole process was kept lightless at25+1 C on condition of anoxic by continuously pumped argon gas. The FA solution was titrated gradually from about pHl0.0 to 2.5 by adding 0.1 mol/L standard HC1 solution. From the curve of pH-Z, there were two inflexions at pH 8.7 and 2.7 respectively. By calculating, there was 5.64rnmol/g FA titratable H+ between these two points. So it could be concluded that a g...
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