Department of Environmental Engineering and Management, Chaoyang University of Technology, Wufong Township, Taichung County 41349, Taiwan, ROC.
J Hazard Mater. 2009 Dec 30;172(2-3):809-17. doi: 10.1016/j.jhazmat.2009.07.076. Epub 2009 Jul 25.
The binding between heavy metals and corresponding ligands affects their chemical behavior and toxicity in soil environments. The mechanisms of competitive complexation and/or chelation between Cd(2+) free cations and preferential concentrations of Cl(-), SO(4)(2-), and fulvate anions were investigated in simulated soil solutions at pH 4.00, 5.00 and 6.00. The Cd(2+) concentrations were calculated by a proposed equation, simulated by MINTEQ software, and directly determined by ion chromatography (IC). When Cl(-)/Cd or Cl(-)/Cd with SO(4)(2-)/Cd molar ratios of 3.18 and 4.05, the differences among Cd(2+) concentrations calculated by equation, simulated by MINTEQ software, and directly determined by IC were not significant, but their differences were pH independent for considering Cl(-)/Cd molar ratio and pH dependent for Cl(-)/Cd and SO(4)(2-)/Cd molar ratios. When Cl(-)/Cd, SO(4)(2-)/Cd, and additional FA/Cd molar ratios of 3.18 and 4.05, the Cd(2+) concentrations calculated by equation were significantly larger than those simulated by MINTEQ and determined by IC because in simulation and determination of Cd(2+) concentrations by IC, the complexation of Cd(2+) with ligands to form CdCl(+), CdSO(4), FACd(+) and FA(2)Cd had been considered, whereas in calculation this complexation aspect was ignored. Though IC can be used to determine Cd(2+) concentration in rhizosphere soil solutions ion chromatographic peak of Cd(2+) in 0.1M HCl saturation extract of slightly acidic soil and in deionized distilled water saturation extract of acidic soils still may be shielded by the vicinal chromatographic peaks of Mg(2+) and Mn(2+), respectively. The Cd(2+) concentrations in rhizosphere soil solutions of acidic or slightly acidic soils calculated by equation and/or simulated by Model may thus be used as potential alternatives for those determined by IC.
重金属与相应配体之间的结合会影响它们在土壤环境中的化学行为和毒性。本研究在 pH 值为 4.00、5.00 和 6.00 的模拟土壤溶液中，研究了 Cd(2+) 游离阳离子与 Cl(-)、SO(4)(2-)和富马酸根阴离子之间的优先浓度的竞争络合和/或螯合的机制。通过提出的方程计算 Cd(2+)浓度，通过 MINTEQ 软件模拟，并通过离子色谱 (IC) 直接测定。当 Cl(-)/Cd 或 Cl(-)/Cd 与 SO(4)(2-)/Cd 的摩尔比为 3.18 和 4.05 时，通过方程计算、MINTEQ 软件模拟和 IC 直接测定得到的 Cd(2+)浓度差异不显著，但考虑 Cl(-)/Cd 摩尔比时，其差异与 pH 无关，而 Cl(-)/Cd 和 SO(4)(2-)/Cd 摩尔比与 pH 有关。当 Cl(-)/Cd、SO(4)(2-)/Cd 和额外的 FA/Cd 摩尔比为 3.18 和 4.05 时，通过方程计算得到的 Cd(2+)浓度明显大于 MINTEQ 模拟和 IC 测定得到的 Cd(2+)浓度，因为在 Cd(2+)浓度的模拟和 IC 测定中，已经考虑了 Cd(2+)与配体形成 CdCl(+)、CdSO(4)、FACd(+)和 FA(2)Cd 的络合，但在计算中忽略了这种络合方面。尽管 IC 可用于测定根际土壤溶液中的 Cd(2+)浓度，但在 0.1M HCl 饱和提取的微酸性土壤和去离子蒸馏水饱和提取的酸性土壤的 0.1M HCl 饱和提取中，Cd(2+)的离子色谱峰仍可能分别被 Mg(2+)和 Mn(2+)的邻近色谱峰屏蔽。因此，通过方程计算和/或模型模拟得到的酸性或微酸性土壤根际土壤溶液中的 Cd(2+)浓度可以作为 IC 测定值的替代值。
