ZHOU DAI-HUA;DONG YUAN-YAN;LI XUE-YUAN;XU FENG-LIN

;Department of Soil Science, Huazhong Agricultural University, Wuhan 430070 (China)

cu~(2+) secondary adsorption;kinetics;soils;sorbed phosphate

The effects of sorbed phosphate on the kinetics of Cu~(2+) secondary adsorption on three major types of soils in southern and Central China were studied using the batch method and flow (or miscible displacement) techniques. Both of the methods showedthat diffusions were the ratedetermining steps in the Cu~(2+) adsorption by the soils. By the flow method, the course of Cu~(2+) adsorption kinetics consisted of two steps-sn initial rapid process and a later slow process of Cu~(2+) adsorption ; while bythe batch method, the 90% of Cu~(2+) adsorption reaction was found to finish within first 1 minute. The results obtained using the flow method also indicated that for red soil and yellow-brown soil, Cu~(2+) adsorptions during the initial reaction periods were restrained when the soils sorbed phosphate, whereas the adsorption reactions were stimulated at the final time. For grey Chao soil, sorbed phosphate retarded the Cu~(2+) adsorption in the whole reaction period. The results obtained using the batchmethod and flow techniques all implied that the different effects of sorbed phosphate would be attributed to its effects on Cu~(2+) ion diffusion in soil solution.