广西富硒土壤中氧化铁对Se(Ⅳ)吸附解吸的影响机制

Effects of Iron Oxide on the Adsorption and Desorption of Se(Ⅳ)in Selenium-Rich Soils of Guangxi

为探究游离氧化铁对富硒土壤吸附解吸Se(Ⅳ)的影响机理,以广西富硒赤红壤、红壤为研究对象,通过等温吸附解吸实验,比较去除游离氧化铁前后土壤对Se(Ⅳ)的吸附解吸特征,同时运用Zeta电位、扫描电镜-能谱分析和傅里叶红外光谱技术分析其机理。结果表明:Langmuir和Freundlich等温吸附方程均能较好地拟合供试土壤吸附Se(Ⅳ)过程,相关系数在0.920~0.995之间。供试土壤最大吸附量由高到低依次为:赤红壤(1399 mg·kg^(-1))、红壤(1336 mg·kg^(-1))、去氧化铁赤红壤(444 mg·kg^(-1))、去氧化铁红壤(352 mg·kg^(-1))。去除游离氧化铁后,红壤、赤红壤的Zeta电位分别由-24.42、-18.06 mV变为-33.06和-26.43 mV,且比表面积减小。红壤、赤红壤及其去氧化铁土对Se(Ⅳ)的解吸率在2%~7%之间,去氧化铁土的解吸率高于红壤、赤红壤。红外光谱分峰拟合分析可知,土壤主要通过-OH、Fe-O、C=O等含氧基团与硒发生反应,土壤去除氧化铁后,Fe-O在吸附中的作用减弱或消失。综上,游离氧化铁可通过自身理化特性及表面基团提高土壤对Se(Ⅳ)的吸附容量和强度,减少土壤对Se(Ⅳ)的释放。

【Objective】The influence of free iron oxide on the adsorption and desorption of Se(Ⅳ)in a lateritic red soil and red soil in the selenium-rich area of Guangxi was studied.【Method】The adsorption and desorption characteristics of Se(Ⅳ)in the soil before and after removing free iron oxide were compared by isothermal adsorption and desorption experiments.Zeta potential,scanning electron microscopy and energy spectrum analysis and Fourier transform infrared spectroscopy was used to explore the influencing mechanism.【Result】The results showed that the adsorption process for Se(Ⅳ)fitted the Langmuir and Freundlich models,with correlation coefficients ranging between 0.920-0.995.After removing free iron oxide of red soil and lateritic red soil,the zeta potential became more negative and changed from-24.42 and-18.06 mV to-33.06 and-26.43 mV.Also,the specific surface area was decreased.This observation correlated with the lower adsorption capacities of the soils after the removal of free iron oxide.Hence,the order of maximum adsorption capacity was:lateritic red soil(1399 mg·kg^(-1))>red soil(1336 mg·kg^(-1))>DCB-treated lateritic red soil(444 mg·kg^(-1))>DCB-treated red soil(352 mg·kg^(-1)).The desorption rates of the tested soils were between 2%and 7%,while that of DCB-treated soils were higher than that of the original soils.The FTIR peak fitting analysis showed that the soils reacted with selenium mainly through the oxygen-containing groups such as-OH,Fe-O and C=O.After the removal of iron oxide,the effect of Fe-O in the adsorption was weakened or disappeared.【Conclusion】Free iron oxide can significantly increase the adsorption capacity and strength of soil for Se(Ⅳ)and reduce the release of Se(Ⅳ)by its physical and chemical properties and surface groups.