Effect of Clay Colloid Particles on Formaldehyde Transport in Unsaturated Porous Media

This study examines the effects of two representative colloid-sized clay particles (kaolinite, KGa-1b and montmorillonite, STx-1b) on the transport of formaldehyde (FA) in unsaturated porous media. The transport of FA was examined with and without the presence of clay particles under various flow rates and various levels of saturation in columns packed with quartz sand, under unsaturated conditions. The experimental results clearly suggested that the presence of clay particles retarded by up to ~23% the transport of FA in unsaturated packed columns. Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction energy calculations demonstrated that permanent retention of clay colloids at air-water interfaces (AWI) and solid-water interfaces (SWI) was negligible, except for the pair (STx-1b)–SWI. The experimental results of this study showed that significant clay colloid retention occurred in the unsaturated column, especially at low flow rates. This deviation from DLVO predictions may be explained by the existence of additional non-DLVO forces (hydrophobic and capillary forces) that could be much stronger than van der Waals and double layer forces. The present study shows the important role of colloids, which may act as carriers of contaminants.

Specification of the density of the mudflow mixture taking into account the clay-colloidal fraction

As a result of laboratory research, was obtained a formula for calculating the density of the mudflow mixture, taking into account the clay-colloidal fraction. The conditions for the formation of mudflows with different particle size distribution are determined. It was found that the formation and decay of the mudflow largely depend on certain ratios between the clay-colloid and rocky components of the mudflow, and not on the density of the mudflows and the percentage (weight) of water, as was presented in early scientific works. It is advisable to use the empirical formula, obtained in the work, to accurately calculate the density of mudflow mixtures for the prediction of mudflow phenomena in order to conduct effective and environmentally sound antimudflow measures.

Effect of the irrigation water type and other environmental parameters on CeO2 nanopesticide–clay colloid interactions

In this work, the stability and aggregation behaviour of CeO2 nanoparticles (NPs) was investigated to predict their fate in the agricultural environment.

COLLOID RELEASE FROM DIFFERENT SOIL DEPTH

Naturally occurring clay colloidal particles are heavily involved in sediment processes in the subsurface soil. Due to the importance of these processes in the subsurface environment, the transport of clay colloidal particles has been studied in several disciplines, including soil sciences, petrology, hydrology, etc. Specifically, in environmental engineering, clay colloid release and transport in the sediments have been extensively investigated, which are motivated by environmental concerns such as colloid-facilitated contaminant transport in groundwater and the subsurface soil. Clay colloid release is resulted from physical alteration of subsurface sediments. Despite the potential importance of clay colloid activities, the detailed mechanisms of release and transport of clay colloidal particles within natural sediments are poorly understood. Pore medium structure, properties and flow dynamics, etc. are factors that affect clay colloid generation, mobilization, and subsequent transport. Possible mechanisms of clay colloid generation in the sediments include precipitation, erosion and mobilization by changes in pore water chemistry and clay colloid release depends on a balance of applied hydrodynamic and resisting adhesive torques and forces. The coupled role of pore water chemistry and fluid hydrodynamics thus play key roles in controlling clay colloid release and transport in the sediments. This paper investigated clay colloidal particle release and transport, especially the colloidal particle release mechanisms as well as the process modeling in the sediments. In this research, colloidal particle release from intact sediment columns with variable length was examined and colloidal particle release curves were simulated using an implicit, finite-difference scheme. Colloidal particle release rate coefficient was found to be an exponential function of the sediment depth. The simulated results demonstrated that transport parameters were not consistent along the depth of the sediment profile.