Colloid Transport in a Heterogeneous Partially Saturated Sand Column

详细信息    查看全文

• 作者：Mikhail Mishurov ; Alexander Yakirevich ; Noam Weisbrod
• 刊名：Environmental Science & Technology
• 出版年：2008
• 出版时间：February 15, 2008
• 年：2008
• 卷：42
• 期：4
• 页码：1066 - 1071
• 全文大小：658K
• 年卷期：v.42,no.4(February 15, 2008)
• ISSN：1520-5851

文摘

Colloid transport was studied in heterogeneous sand columns under unsaturated steady-state conditions, using two sizes of acid-cleaned sand to pack the column. Heterogeneity was created by placing three continuous tubes of fine sand (3.6% of the total volume) within a column of coarse sand (mean grain diameters 0.36 and 1.2 mm, respectively). Experiments were performed under three flow rates (0.1, 0.2, and 0.4 cm/min) applied by a rain simulator at the top of the column. Constant water-content profile in the coarse sand was achieved by applying corresponding suction at the column bottom. Three sizes of latex microspheres (1, 0.2, and 0.02 μm) and soluble tracers (LiBr), diluted in a weak base (pH 7.3, ionic strength 0.0023 M) solution, were used simultaneously. Introduction of preferential pathways reduced front-arrival time about 2-fold and increased colloid recovery which, at the 0.2 cm/min flow rate, was higher than at 0.4 and 0.1 cm/min. Maximum solution flux from coarse to fine sand (due to differences in matric pressure) at 0.2 cm/min, verified by hydrodynamic modeling, could explain this phenomenon. Results suggest that in heterogeneous soil, maximum colloid recovery does not necessarily occur at maximum water content. This has clear implications for colloid transport in natural soils, many of which are heterogeneous.