Study On The Formation Mechanism Of Humic Acid-Cd Complex

Heavy metal pollution in soil is environmental problems should be solved in China. Alongwith the development of the industry, heavy metal pollution has been gradually attention bypeople. Since people confirmed the bone pain and its kinds of harm caused by the Cd pollution,the researches on the law of migration and transformation of Cd in the soil are increasing.Humus is a kind of natural organic matter that widely distributed in the earth ecologicalenvironment. Humic acid is a major component of organic matter. Due to its complicatedstructure and contains a variety of functional groups, and thus has high reactivity. Humic acidbecomes the acceptance and provide source of the heavy metal in the environment, because of thestrong combining ability to various metal ions. It plays an important regulatory role on themigration, transformation and fixed of heavy metals in the environment.In this article, the grey desert soil of Mi Dong Area in Northern Xin jiang is mainly studiedas the research object. The different forms of Cd in the soil, the distribution regularity and formingmechanism of humus (humic acid and fulvic acid)-Cd complexes are systematically studied. Theresults are as follows:The results of different forms content of Cd in rural farmland soil of MiDong Area showed that,there is significant difference in different form content of Cd in some villages(P<0.05), and thereis extremely difference in that in others(P<0.01). In the soil of that Area, the variation range of thetotal content of Cd is0.740~2.986mg/kg, that of the Water-Soluble&Exchangeable form,Carbonate Bound form, Fe-Mn Oxide Bound form, Organic Matter Bound form, Residual formrespectively are0.216~0.641mg/kg，0.121~0.945mg/kg，0.121~0.731mg/kg，0.053~0.681mg/kg0.064~0.336mg/kg. The mainly content of Cd is Water-Soluble&Exchangeableform and the amount of Residual form is the least. The toxicity of the former is the biggest andthat of the latter is the minimum.There is significant difference in the content of humus-Cd, humic acid-Cd and fulvic acid-Cd complexes in rural farmland soil of MiDong Area (P<0.05), and there is extremely difference inthat in others (P<0.01)Under the condition of this study, pH value significantly effect the stability constant andcoordination number of humic acid-Cd and fulvic acid-Cd complexes. When the pH value is low,the stability constant and the coordination number is low. These two parameters will rise with theincrease of pH value, and when pH=7.5, they reache the highest value.Grasping the amount of Cd ion, effective content, the different form content of Cd and thecharectar of humus-Cd complexes under the condition that the influence of the natural andartificial factors on rural farmland soil of MiDong Area, will put forward scientific basis on theformation of complexes and the fixed mechanism of Cd at a drought conditions. This will providetheoretical and practical significance for rational utilization and improvement, and soilenvironmental restoration, food security, improving soil fertility, and the development of organicinorganic compound fertilizer of the typical gray desert soil in chemical industrial area.