EFFECT OF EDTA ON COMPETITIVE ADSORPTION AND DESORPTION OF Zn, Cd IN TEA PLANTATION SOIL MICRO-AGGREGATES

摘要

Batch culture and equilibrium adsorption-desorption test were used. The original soil and micro-aggregates arc taken as objects. The isothermal ad-sorption and desorption behavior of Zn (II), Cd (II) and EDTA ￠0.1,1,10 mmol/L) were studied. The results showed that:(1)the multilayer adsorption gradually saturated with the increase of the strength of Zn2+, Cd2+, and the optimal immobilization levels were (< 0.002 mm), 0.05-0.002 mm, followed by the original soil, 0.25-0.05 mm and 2-0.25 mm, with the lowest adsorption capacity and the opposite release capacity. The accumulation and migration of Cd were higher than that of Zn, and the overall competitive adsorption stability of Zn was stronger than that of Cd. Oil the contrary, the level of desorption Cd is higher. (2) Under the influence of EDTA. the maximum adsorption and desorption ranges of each structural unit show "positive peak" and ''inverted peak" dynamic changes with concentration of 1 mmol/'L as inflection point. The concentration of 10 mmol/L corresponds to the maximum or minimum opposite to the inflection point. (3) The fitting result of thermodynamic Freundlich equation is better than that of Langmiur equation. The correlation degree between the maximum adsorption and desorption amount and the content of each component is the best. (4) EDT A can promote and inhibit the adsorption and desorption of native soil and micro-aggregates. As a chelating agent, under the premise of good environmental compatibility, it can not only ensure the continuous supply of trace nutrients such as zinc to tea plants, but also alleviate the direct or indirect harm of excessive zinc and cadmium by strengthening the structural buffer inhibition or leaching of soil, so as to reduce the combined pollution of heavy metals in tea plantations.