两种有机酸对茶园土微团聚体等温吸附锌的影响

Influence of the two organic acids on the zinc isothermal adsorption from the tea micro-aggregate garden soil

为了明确茶园紫色土Zn容量及潜在污染状况,利用虹吸沉降和离心冻融法进行批量培养,研究区域土壤及不同粒径微团聚体等温吸附Zn^(2+)的水平,以及去除有机质和外源添加柠檬酸、乙二胺四乙酸(EDTA)对吸附的影响。结果表明:1)以专性吸附为主的多层吸附随Zn^(2+)质量浓度增至200 mg/L总体接近饱和,吸附量从大到小依次为<0.002 mm、0.002~0.05 mm、原土、0.25~2 mm、0.05~0.25 mm,游离Zn^(2+)向较小粒径富集趋势明显,去除有机质弱化了微团聚体的吸附能力;2)吸附过程为自发吸热反应,热力学Freundlich方程(R2=0.9722~0.9995)整体拟合水平优于Langmiur方程(R2=0.9505~0.9987),土壤吸附能力与有机质、游离氧化铁、CEC呈正相关;3)两种有机酸均以0.1 mmol/L为阈值,随浓度增加均表现为低浓度增强Zn^(2+)积累、高浓度加快迁移,最大吸附量呈"峰形"变化,有机酸浓度"峰值"在去除有机质后增大到1 mmol/L;在未去除有机质土壤及结构单元中,EDTA对Zn^(2+)的释放能力更优,柠檬酸能更好地吸持,大粒径微团聚体0.25~2 mm及原土随有机酸浓度变化吸附量差异明显;去除有机质使两种有机酸促进及抑制功能削弱明显。

The paper is aimed at making a sample case study of the isothermal adsorption characteristic features of zinc（ Zn-（2＋）） of the micro-aggregates in different size fractions as well as the effects of citric acid and ethylene diamine tetraacetic acid（ EDTA） on the isothermal adsorption features of zinc（ Zn-（2＋）） by using the methods of siphon sedimentation and centrifugal frozen thawing acid on the purple raw soil and that without organic matter from Mengshan tea plantation. The results of our study show that：（ 1） It would be possible for the multilayer adsorption dominated by the specific adsorption to get saturated slowly in an adsorption rate order of 〈0. 002 mm 〉 0. 002-0. 05 mm 〉 bulk soil〉 0. 25-2mm 〉 0. 05-0. 25 mm. Zn-（2＋）with the free state being enriched remarkably towards the smaller micro-aggregates and decrease of the adsorption capacity of the said micro-aggregates as a result of organic component removal,so that the concentration of the Zn-（2＋）tends to reach 200 mg/L gradually;（ 2） The adsorption of zinc（ Zn-（2＋）） to the soil surface has been going on spontaneously with the exothermic Freundlich equation being better than that of Langmuir on the monolithic fitting level. At the same time,it can be found that the adsorption capacity of the raw soil and the soil＇s micro-aggregation tend to be positively correlated with the content concentration rate of the organic substance,the free iron oxide and that of CEC. And,（ 3） it has been found that both of the citric acid and ethylene diamine tetraacetic acid（ EDTA） can be taken as the threshold of the tea content concentration rate at an amount of 0. 1 mmol/L with the increase of the low concentration of the organic acid with the accumulation of Zn-（2＋）,whereas the high concentration organic acid can help to accelerate the migration of Zn-（2＋）,so as to make the maximum adsorption capacity its＂peak＂value. Furthermore,when the organic matter is removed,the＂peak value＂of the organic acidic concentration may tend to increase gradually till 1 mmol/L. Thus,it can be found that,before removing the organic matter in the soil and the structural unit,the releasing ability of EDTA to Zn-（2＋）was better while its retention of citric acid proved more stable. The adsorption amount of the micro-aggregates（ 0. 25-2 mm） and the bulk soil was to change significantly with the increase of the organic acid concentration. On the contrary,after the organic matter was removed,the function of the two kinds of organic acids might have been obviously weakened. Thus,the aforementioned findings of this paper can be expected qualified to provide some reference data for improving the Zn-（2＋）function in the given soil evaluation.