腐殖酸在黑云母表面的吸附动态和分布特征研究

采用原位原子力显微镜智能模式初步观察了弱酸性土壤腐殖酸分子在层状硅酸盐含钾矿物黑云母表面的吸附动态和形貌变化。采用纯化、干燥后的腐殖酸固体样品配制p H 6.0,浓度分别为0 mg L-1、100 mg L-1和1000 mg L-1的腐殖酸溶液。原位观察所用的矿物薄片为土壤中常见的2∶1型含钾矿物—黑云母,其化学结构式为K(Mg2.46Fe0.45Ti0.09)Al Si3O10](OH)2。结果表明,时间尺度是影响界面上腐殖酸形貌结构的一个重要因素。在通入p H 6.0的腐殖酸溶液作用下,原位反应0~180min内,腐殖酸分子与黑云母(001)面的相互作用以吸附为主并伴随脱附现象,吸附的腐殖酸呈球状,为单个或多个腐殖酸分子的聚集体,高度介于1~5 nm之间;原位反应180~300 min内,黑云母(001)面上吸附的腐殖酸仍以颗粒态为主,高度介于3~5 nm之间,平均为4 nm;而黑云母(001)面上的台阶和边缘位置则分布有较多的片状结构以及黑云母线型边缘诱导产生的链状结构腐殖酸聚集体,其高度介于6~8 nm,较颗粒态腐殖酸的聚集体平均高出约2.5 nm。此外,腐殖酸分子不仅能够在黑云母表面进行吸附和脱附作用,还能够溶解黑云母的表面结构,促进层间K及结构单元内Al和Si的释放。因此,腐殖酸与云母类矿物的界面反应是一个溶解—吸附—聚集并伴随着脱附和离子释放的过程。

Adsorption Dynamics and Distribution Characteristics of Humic Acid on Surface of Biotite

Objective]An in-situ atomic force microscopy(ScanAsyst)was used to study adsorption dynamic and morphological variation of humic acid on the surface of K-bearing biotite.Method]Humic acid is a principal component of humic substances,which are the major organic constituents of soil,peat, coal,eutrophied lakes,and ocean water. Humic acid solutions,the same in pH(6.0),but different in concentration(0 mg L-1,100 mg L-1 and 1 000 mg L-1)were prepared out of dried humic acid solid. The mineral sheet used in the in-situ observation was biotite,a kind of phyllosilicate mineral belonging in the mica group(2∶1 type structure),commonly found in soil. The chemical formula of biotite is K (Mg2.46Fe0.45Ti0.09)AlSi3O10](OH)2. In order to observe how humic acid is adsorbed onto biotite and changed temporally in structure,an experiment was carried out treating the biotite sheet with slightly acidic humic acid solutions,6.0 in pH.Result] Results show that time was an important factor affecting morphological structure of humic acid on the surface of the sheet. Under the effect of the humic acid solution, 6.0 in pH,the interaction between humic acid molecules and the surface of biotite(001)was dominated with adsorption and and accompanied with some desorption phenomena. The humic acid adsorbed on the surface of the biotite(001)sheet appeared to be in the shape of bulbs,which were congeries of a single or several humic acid molecules,varying in the range of about 1 ~ 5 nm in height within the first 180 min after the treatment;humic acid bulbs remained in dominancy,being about 3 ~ 5 nm in height,or 4 nm on average, during the following period till 300 min,while,sheets of humic acid congeries were found on benches and edges of the biotite sheet and chains of humic aid congeries,too,along the linear edges of the biotite(001) sheet,about 6 ~ 8 nm in height,or 2.5 nm higher than the humic acid bulbs. In addition,humic acid molecules were not just adsorbed or desorbed on the surface of the biotite(001)sheet,and they could also disintegrate the surface structure of the biotite,thus promoting the release of K trapped in the interlayers and Al and Si in the structural lattices.Conclusion] Therefore,it could be concluded that the reaction in the interface between humic acid and biotite is a process of dissolution-adsorption-aggregation accompanied with desorption and ion release.