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

Migration of different mineral particles within columns of soild-sand mixtu res containing 10 or 20 mass % of soil was investigated by establishing dif ferences in the mineral suite between the "bulk clay" and the "mobile fine material" fractions. The "bulk clay" fractions of all soils contained smect ite, palygorskite, kaolinite, quartz, feldspar, and calcite. The soils were saturated with sodium by leaching with NaCl solution, and then leached wit h distilled water. Clay dispersion and particle migration occurred in the c olumns. Values of SAR (sodium adsorption ratio) of the effluent decreased w ith time due to carbonate dissolution. At a certain SAR value, the clays ap parently formed aggregates, and as a consequence particle migration stopped in the column. In addition to clay-sized particles (< 2 <mu>m), very-fine- silt-sized particles (2-5 mum) were able to migrate in the soil-sand mixtur es, too, and to some extent fine-silt-sized particles (5-10 mum) as well. A verage size of mobile particles decreases with increase of soil content in the soil-sand mixtures. The mineralogical composition of the "mobile fine m aterial" changed during the experiment. At the beginning of the experiment, the "mobile fine material" was enriched in the non-phyllosilicates (especi ally in calcite, and in some cases in quartz, feldspar and dolomite) and co ntained low concentrations of phyllosilicates (smectite, palygorskite and k aolinite). At the end of the experiment, the proportion of nonphyllosilicat es decreased, and as a consequence, the proportion of phyllosilicates incre ased. Among the non-phyllosilicates, calcite was the most mobile mineral. A mong the phyllosilicates, palygorskite was preferentially mobilized in tops oil horizons. In subsoil horizons, on the other hand, kaolinite was prefere ntially mobilized. This difference was explained by the different nature of carbonates in the topsoil and subsoil horizons. Palygorskite is preferenti ally 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 horizon s decreases the migration of mainly palygorskite.