Adsorption Ability for Cu(II), Pb(II) and Cd(II) Among Different Soils Under Different Systems

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 with the proportion of initial concentration of Cu(Ⅱ), Pb(Ⅱ) and Cd(Ⅱ) being 10∶10∶1 and 1∶1∶1, respectively. The results showed that when the proportion of the 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 was 1∶1∶1, the heavy metal selectivity sequence was PbCuCd for paddy soils at pH4.2 and pH5.2 and for red soil at pH4.2, while, the selectivity sequence was CuPbCd 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 that 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 played a dominate role in the adsorption of heavy metals and the composition of soil minerals and soil CEC exerted an important effect on the adsorption.