Analysis of critical water flow and solute transport parameters in different soils mixed with a synthetic zeolite

The addition of natural or synthetic zeolites alters a soil’s chemical, physical and biological properties. Due to the existence of a complex internal structure, zeolites have the potential to modify soil structure and texture with a direct impact on soil hydrological properties, introducing the possibility of controlling soil and groundwater pollution as well as irrigation management practices. In the present study, a series of laboratory tests were conducted on soil samples mixed with zeolite to investigate the possible changes in hydraulic and solute transport properties and related parameters. To determine the above properties, four soils of different textures were selected and two distinct groups of experiments were conducted on disturbed (i.e., repacked) soil samples by adding known amounts of zeolite (i.e., 1, 2, 5 and 10%; w/w). Solute transport properties were determined on one group of soil samples using the so-called Kachanoski approach to monitor miscible flow experiments. Soil hydraulic properties were determined on the second group of soil samples by measuring soil water retention curves (SWRCs) and saturated hydraulic conductivity (Ks). In general, we observed significant changes in the measured properties with zeolite percentages of 5% and 10%. However, some changes were also evident at 1% and 2% of zeolite addition. These observed differences may be mainly ascribed to changes in the soil’s pore size distribution due to the addition of a finer fraction (i.e., zeolite) to soils. This fraction reduces macropores (that are occluded in proportion to their amount) and thus enhances the formation of meso- and micropore regions.