Saturday, 15 July 2006

Adsorption of Cadmium on Three Soils with Different pH Values as Influenced by Dissolvable Organic Matter.

Hongqing Hu, Jing Liu, Suwan Chen, and Yongguan Zhu. Huazhong Agricultural Univ, Shizishan Mountain, Wuhan, 430070, China

Soil pollution by heavy metals, such as cadmium (Cd) was more and more popular with the development of industry and waste water irrigation. Dissolvable Organic Matters (DOM) are one of the carriers of soil pollutants and the organic ligands to complex heavy metals; therefore, DOM played an important role to heavy metals adsorption by soils. DOM has significant influence to chemical behaviors of heavy metals, dissolubility, adsorption-desorption, uptake, transport and bio-toxicity of ions in the soils. It could either increase or decrease adsorption amount of heavy metals, or did not change significantly to the adsorption, depending on the organic matter, heavy metals, and adsorbents and their interactions. Various organic compounds may have completely different influence to heavy metals adsorption. Thus, to study the interaction between DOM and adsorption of heavy metal is very important for both theoretical and practice. In this study, the isothermal adsorption experiment was employed to investigate the effects of three kinds of DOM on the adsorption behaviors of Cd by three soils with different pH values of Wuhan Zoo under 20, 30 and 40 C. The results showed that the adsorption of Cd was affected by the soil pH, DOM sources and concentrations of Cd solution, and they interacted. There existed a significant antagonism of Cd adsorption under DOM addition for alkaline and neutral soils, and there were smaller variations based on the concrete situation. In the same soil (taking neutral soil for example), DOM of cabbage could mostly enhance the adsorption of Cd, the enhancement function of DOM of sewage sludge was smaller, and that of DOM of rice straw was the smallest in acidic soil, with a magnitude sequence of rice straw-DOM (61.83%) > sewage sludge-DOM (12.58%) > cabbage-DOM (0.74%). The same DOM had various functions in different soils. Taking sewage sludge as example, the sorption increased most in acidic soil, and less in alkaline and neutral soils, with the rate of 22.16%, 1.36% and -0.74%. The temperature played a role to the Cd sorption in some scope. It showed that the effect of DOM on Cd sorption at higher temperature (30CA40C) was bigger than that at 20C, with the rate of 46.75% and 43.93%, taking rice straw-DOM in neutral soil as example. These suggested that for Cd uptake by plants, both soil pH and DOM source should be considered. Heavy metal pollution could be controlled by different DOM addition, and temperature had some distinct impact as well.

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