The Competitive Adsorption And Desorption Kinetics Of Cu(Ⅱ), Pb(Ⅱ) And Cd(Ⅱ) In Paddy Soils

In this research, the competitive adsorption and desorption kinetics of Cu(II), Pb( II) and Cd(II) in paddy soils were investigated and the effect of LMW (low-molecular-weight) organic acids on the adsorption and desorption was also studied. The results are shown as following:The investigation was conducted to compare the competitive adsorption and single adsorption of Cu( II), Pb( II) and Cd( II) by four kinds of paddy soils and one red soil from Changjiang Delta and Zhujiang Delta in the two systems in which the proportion of initial concentration of Cu(II), Pb(II) and Cd(II) is 10:10:1 and 1:1:1, respectively. The results showed that when the proportion of metals' initial concentration is 10:10:1, the amount of Pb( II) adsorbed by all paddy soils was bigger than that of Cu( II )both in single and in ternary metal systems. When the proportion is 1:1:1, the heavy metal selectivity sequence was Pb>Cu>Cd for paddy soils at pH4.2 and pH5.2 and for red soil at pH4.2, while the selectivity sequence was Cu > Pb >Cd for red soil at pH5.2 due to more increase in Cu( II) adsorption by red soil with increasing pH. The amount of heavy metals adsorbed in competitive condition was lower than in single metal system and the reduction in adsorption of Cu( II) and Pb( II) was larger under the initial heavy metals' proportion of 1:1:1 than that under the proportion of 10:10:1. The amount of heavy metals adsorbed by red soil at pH4.2 was much lower than that by paddy soils, while the increase in the adsorption of heavy metals in red soil from pH4.2 to pH5.2 was much larger than that in paddy soils. The inorganic minerals in these soils made a dominated role in the adsorption of heavy metals and the composition of soil minerals and soil CEC exerted an important effect on the adsorption.A red soil and a paddy soil were chosen to investigate the effect of low-molecular -weight organic acids on competitive adsorption of Cu(II), Pb(II) and Cd(II), and the results from multi-heavy metal system were compared with that from single metal system. The results showed that the presence of citric acid and tartaric acid induced an increase in...