水稻土壤组分去除有机质和游离氧化铁后对As5+吸附解吸特征的影响

采用平衡液吸附法、NaCl解吸剂解吸法研究了名山河流域水稻土原土及各粒径组分去除有机质和游离氧化铁后对砷(As~(5+))的吸附解吸特性,同时运用热力学和动力学方法,研究了去除有机质、游离氧化铁后的土壤微团聚体(0.25~2 mm、0.053~0.25 mm、0.002~0.053 mm、0.002 mm)对砷(As~(5+))的吸附解吸过程。结果表明:1)同时去除有机质和游离氧化铁后,水稻土原土及各粒径组分对砷(As~(5+))的吸附量有所减小,吸附量从大到小依次为(0.002 mm)、0.002~0.053 mm、原土、0.25~2 mm、0.053~0.25 mm。砷(As~(5+))的动力学吸附量随时间延长而逐渐降低,60 min内反应迅速,在600min达到吸附动态平衡,动力学吸附以Elovich方程拟合最佳;2)等温吸附量随砷(As~(5+))的初始质量浓度增加逐渐增加,初始质量浓度0~100 mg/L时反应快速,在砷(As~(5+))初始质量浓度达到160 mg/L时吸附趋于饱和,等温吸附以Freundlich方程拟合最佳;3)易解吸量随时间和浓度的增加而增加,易解吸率顺序与吸附量顺序相反,易解吸率也随着有机质、游离氧化铁含量的减少而增加;4)去除土壤中的有机质、游离氧化铁后,砷的吸附减少量随时间和浓度增加而增加,吸附减少量与有机质、游离氧化铁去除量呈正比。

Effects of organic matter and free iron oxide removal from the soil components on As5+ adsorption-desorption in the paddy fields

The paper is aimed at making an exploration of the isothermal adsorption and desorption equilibrium method via NaCl solution by investigating and determining the kinetic and thermodynamic features of arsenic (As5 +) adsorption-desorption by the soil and the particle-size fractions in the paddy fields in Mingshan River watershed as a case study sample.Besides,it has also made an exploration of the effect of the removing processes of the organic matters and free ferric oxide on the activities of adsorption-desorption of arsenic (As5 +) by the soil micro aggregates,which turn to be 0.25-2 mm,0.053-0.25 mm,0.002-0.053 mm,＜ 0.002 mm,respectively.The results of our investigation show that:(1) the adsorbed amount of arsenic (As5 +) by the paddy soil with different particle-sized fractions tends to decrease with the removing process of the organic matter and free ferric oxide going on.The order of the adsorbed amount of arsenic (As5 +),which can be illustrated from bigger to smaller,accounts for:0.002 mm ＞0.002-0.053 mm ＞ bulk soil ＞0.25-2 mm ＞ 0.053-0.25 mm,whereas the kinetics adsorption amount of arsenic (As5 +) tends to decrease with prolonging of the time of absorption.The said absorption reaction can be done quickly in a period of 60 minutes,going up to a stage of equilibrium in a period of 600 minutes.What is more,it is necessary to point it out that,Elovich equation should be the optimal equation for the kinetics adsorption.(2) With the increase of the initial concentration of arsenic (As5 +),the isothermal adsorption activity tends to increase,too.The strongest reaction can be found most clearly,when the initial mass concentration at 0 tends to get to 100 mg/L,and,then,the adsorption tendency may turn to be saturated on the condition when the initial mass concentration of arsenic (As5+) goes up to 160 mg/L.What is more,it can also be found that Freundlich equation may prove to be the best one for the isothermal adsorption.And,(3) the quantity of the likely-to-be appearing desorption may increase with the increase of time and the concentration of the said arsenic (As5 +).Nevertheless,the fastest desorption rate may turn to be opposite to the order of the adsorbed amount of arsenic,whose desorption rate tends to increase with the decrease of the organic matter and the free iron oxides in the reaction.(4) Once the organic matter and the free iron oxide have been removed,the reduced amount of the adsorption matter may tend to be increasing with the increase of concentration of the matter of the reaction as well as the reaction time.Thus,it can be found that the amount of the organic matter that can be removed may turn to be proportional to that of the adsorption and the removal of the free iron oxide.