Adsorption and desorption of iodine by various Chinese soils: II. Iodide and iodate

It is important to understand iodine availability in various soils in China to efficiently manage and control environmental iodine. A series of batch experiments was conducted on a variety of Chinese soils in order to determine the adsorption characteristics of iodide and iodate. For five soils, the sorption isotherms of iodide were determined, while for all 17 soils, iodide adsorption was studied under one initial concentration to evaluate its sorption capacity. Furthermore, iodate sorption isotherms on two soils at five different initial concentrations were determined in this study, to complement the earlier work of Dai et al. (2004a). From the sorption isotherm results, five Chinese soils were ranked in terms of their capacity for iodate adsorption: Perudic Ferrisols soil, HN > Orthic Aridisols soil, XJ1 > Udic Ferrisols soil, JX2 > Usdic Luvisols soil, BJ > Udic Isohumisols soil, JL. As a comparison, iodide adsorption was ranked as follows: Udic Ferrisols soil, JX2 > Perudic Ferrisols soil, HN > Udic Isohumisols soil, JL > Usdic Luvisols soil, BJ > Orthic Aridisols soil, XJ2. It was also found that the desorbed amounts demonstrated a significant positive correlation with the adsorption of the XJ1 and BJ soils for iodate, and also did the HN and JX2 soils for iodide. At an initial iodide concentration of 4 mg L− 1, the values of the sorption distribution coefficient, Kd, ranged between 0.78 and 6.59 mg kg− 1 soil in 17 soils from China, and iodide adsorption was significantly correlated with soil organic matter and cation exchange capacity. Kd exhibited a linear relationship with soil organic matter, a polynomial relationship with free iron oxide content and a logarithmic relationship with cation exchange capacity. Furthermore, results from iodate and iodide adsorption from 17 Chinese soils, except for Fimic Anthrosols soil (GX) showed that the adsorption capacities of iodate were greater than those of iodide, and organic matter in soil environments plays an important role in controlling iodine geochemistry.