EXPERIMENTAL ZN (II) RETENTION IN A SANDY LOAM SOIL BY VERY SMALL COLUMNS

The use of column experiments, usually performed to better aproximate field conditions, may provide information that is not available from batch experiments. In such experiments heavy metals are often adsorbed until saturation followed by desorption experiments. When the affinity of the metal to soil is high, the retention factor (R) could be greater than thousands and the duration of experiments can become impractically long. In order to use reasonable laboratory time, the flow rate should be increased or the column size decreased. The increase in flow rate produces undesirable kinetic and dispersion effects, so we used very small soil columns (pore volume = 0.31 - 0.70 mL) and relatively high flow rates (0.03 - 0.12 mL min-1) in studies of Zn (II) adsorption and retention in soils. Conservative tracer flow column experiments under saturation conditions were carried out to determine flow parameters for different flow rates. Column pore volume (Vp), Peclet numbers (Pe) and longitudinal dispersion coefficients (DL) were determined from breakthrough curves. The effect of type of electrolyte and ionic strength on the Zn (II) retention onto soil was determined. The influence of flow rate and bed height on the retention coefficient and on the mass transfer zone was also studied. The effect of different influent Zn (II) concentrations on the R values obtained was analyzed. Freundlich parameters from column experiments were compared with batch ones. The leaching efficiency of different electrolytes, salts of weak organic acids and EDTA was also studied.