老冲积黄壤各粒径组分对镉与硒竞争吸附特性的研究

为了研究区域土壤中硒的环境改良及镉-硒复合污染的治理效果,采用批量吸附法进行了黄壤原土和去除土壤组分(有机质、游离氧化铁)原土的各粒径微团聚体,以及Cd2+-SeO_3~(2-)共存下黄壤原土及去除组分(有机质、游离氧化铁)原土吸附SeO_3~(2-)的热力学试验。结果表明:1)黄壤原土及各粒径的微团聚与黄壤去除各组分(有机质、游离氧化铁)原土及各粒径微团聚体的SeO_3~(2-)吸附量具有相同的分布趋势,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,土壤在去除有机质、游离氧化铁后吸附量减小,吸附量从大到小依次为原土、去除有机质土、去游离氧化铁土,其结果用Langmuir方程拟合最好;2)镉的存在明显抑制了原土对SeO_3~(2-)的吸附,在不同添加顺序下SeO_3~(2-)吸附量从大到小为共同加入、先镉后硒,土壤组分对不同添加顺序下SeO_3~(2-)的吸附没有明显影响,在SeO_3~(2-)初始质量浓度为200μg/L时,随Cd2+质量浓度增加,SeO_3~(2-)吸附量先下降,后略有上升,Freundlich方程对以上结果拟合效果较好;3)土壤吸附SeO_3~(2-)反应是自发放热反应,SeO_3~(2-)在Cd2+的影响下从溶液聚集到土壤表面过程中生成的分子种类和数量减少,Cd2+通过影响土壤表面性质进而影响SeO_3~(2-)的吸附,且土壤游离氧化铁比有机质对SeO_3~(2-)有更强的亲和力。

Competitive adsorption characteristics of Cd and Se on the micro-aggregates and components from the old alluvial yellow soil

The paper intends to make an exploration of the characteristic features of the competitive adsorption of Cd and Se to the micro-aggregates and components from the age-long alluvial brown soil by taking the general raw soil and the raw soil without organic matter (the free iron oxide) from Mingshan River as the study sample. In the paper,we have made an analysis of the adsorption capacity of SeO2-3 on the micro-aggregates of differentgrain particles (0. 25-2 mm,0. 053-0. 25 mm,0. 002-0. 053 mm,＜ 0. 002 mm),and the effects of Cd2 + on the adsorptive features of the concurrent solution of SeO2-3 in Cd2 +-SeO2-3,with the isothermal adsorption method of equilibrium liquid through batch thermodynamic experiments. The results of our investigation show that: (1) The general raw soil and the raw soil free from organic substance and free iron oxide have the similar distribution trend to the adsorption amount of SeO2-3,as well as the adsorption amount order: (＜ 0. 002 mm) ＞ (0. 002-0. 053 mm) ＞ bulk soil ＞ (0. 25-2 mm) ＞ (0. 053-0. 25 mm). It has been found that the relation between the reduced volume of the adsorption after removing the organic components and free iron oxide and the volume of adsorption can be stated in the following way: the raw soil without organic components ＞ the raw soil without free iron oxide ＞ the raw soil. The results of our batch experiment gained through Langmuir equation fitting prove optimistic; (2) The adsorption of the raw soil to SeO2-3 proves significantly inhibited by the presence of cadmium. The amount of SeO2-3 adsorbed by the raw soil by way of different addition sequential orders shows that simultaneous processing tends to be more effective than the ordinary sequential one,with no significant effect of soil composition on the adsorption of SeO2-3 in different adding sequences. For example, when the initial concentration of selenium is 200 μg /L,the adsorption capacity of SeO2-3 turns to be decreased first and then slightly increased for the raw soil and the raw soil without composition (organic matter and free iron oxide). In addition,Freundlich equation proves more suitable than that of Langmuir for the above results. (3 ) The adsorption of SeO2-3 to the soil surface tends to be spontaneous and exothermic. Under the impact of Cd2 +,the kinds and amount of SeO2-3 molecules turn to be generated from the solution to the surface of the soil,whereas Cd2 + influence the adsorption of SeO2-3 due to the different features of the soil surface. Furthermore,the soil free iron oxide has been found enjoying a stronger affinity for SeO2-3 than the organic substance. Thus,it can be concluded that the above findings are in a position to provide some valuable reference data for improving the selenium-containing soil and the reducing the cadmium and selenium contamination from the farm land.