Dispersion and migration of fine particles in two palygorskite-containing soils of the Jordan Valley

Migration of different mineral particles within columns of soil-sand mixtures containing 10 or 20 mass % of soil was investigated by establishing differences in the mineral suite between the "bulk clay" and the "mobile fine material" fractions. The "bulk clay" fractions of all soils contained smectite, palygorskite, kaolinite, quartz, feldspar, and calcite. The soils were saturated with sodium by leaching with NaCl solution, and then leached with distilled water. Clay dispersion and particle migration occurred in the columns. Values of SAR (sodium adsorption ratio) of the effluent decreased with time due to carbonate dissolution. At a certain SAR value, the clays apparently formed aggregates, and as a consequence particle migration stopped in the column. In addition to clay-sized particles (< 2 μm), very-fine-silt-sized particles (2-5 μm) were able to migrate in the soil-sand mixtures, too, and to some extent fine-silt-sized particles (5-10 μm) as well. Average size of mobile particles decreases with increase of soil content in the soil-sand mixtures. The mineralogical composition of the "mobile fine material" changed during the experiment. At the beginning of the experiment, the "mobile fine material" was enriched in the non-phyllosilicates (especially in calcite, and in some cases in quartz, feldspar and dolomite) and contained low concentrations of phyllosilicates (smectite, palygorskite and kaolinite). At the end of the experiment, the proportion of non-phyllosilicates decreased, and as a consequence, the proportion of phyllosilicates increased. Among the non-phyllosilicates, calcite was the most mobile mineral. Among the phyllosilicates, palygorskite was preferentially mobilized in topsoil horizons. In subsoil horizons, on the other hand, kaolinite was preferentially mobilized. This difference was explained by the different nature of carbonates in the topsoil and subsoil horizons. Palygorskite is preferentially occluded within the soil carbonates of lacustrine origin over smectite and kaolinite. These carbonates are present mainly in the subsoil horizons. As a consequence, the presence of these carbonates in the subsoil horizons decreases the migration of mainly palygorskite.