Saturday, 15 July 2006
116-60

Determination of the Behavior and the Transport Parameters of Chromium in Soil-Water Systems.

Imre Czinkota1, Ibrahim Issa2, Gabriella Rétháti2, and Balázs Kovács3. (1) Szent Istvan Univ, Dept of Soil Science and Agricultural Chemistry, Páter K. 1., Gödöllő, Hungary, (2) Szent Istvan Univ, Páter K. 1., Gödöllő, Hungary, (3) Univ of Szeged, Dept of Mineralogy, Geochemistry and Petrology, Egyetem u. 2-6, Szeged, 6722, Hungary

A complex investigation was performed at a polluted area using both experimental and computer modeling methods. Among the experimental methods the adsorption and desorption isotherms were measured to estimate the concentration depending equilibrium in the soil – groundwater system. A new calculation method was worked out for determining the transport parameters from results of laboratory tests. Heavy metal solution was leached trough a soil column continuously. The effluent fluidum was collected, and the heavy metal concentration of the collected fractions was measured by atomic absorption spectrophotometer. As result of the analytic process breakthrough curve in the laboratory scale was measured. Due to the applied initial and boundary conditions the transport equation can be solved analytically. Using the OGATA-BANKS (1961) solution of the transport equation a new curve fitting method was introduced. After several transformations of the equation a theoretical function was fitted to the measured concentration vs. time and to the concentration vs. effluent volume data. The parameters of the fitted curve could be used as the dispersion and retardation parameters of a transport model. The water chemistry of the system controls the rate of adsorption and desorption of metals to and from sediment. Adsorption removes the metal from the water column and stores the metal in the substrate. Desorption returns the metal to the water column, where recirculation and bioassimilation may occur. Metals may be desorbed from the soil if the salt concentration of the water increases and in cases of some metals decreases with redox potential and with pH. Parallel to the determination the basic transport parameters of the system using the column study, the maximal equilibrium concentration of chromium-containing compounds with different oxidation states were calculated with MINTEQ model with two variable functions (pH and redox potential). As a result of the calculations a non-liner relation was determined since at specific points the maximal equilibrium concentration of chromium increases with high gradient. This means that there are combinations of pH and redox potential values where there is a high solubility of chromium. It is advisable to avoid this points in the pH eH field in case we want to stabilize the pollutant. But this state is to be reached when our goal is to mobilize the pollutant to make the soil cleaning process possible. With the introduced calculation method, there are areas on the pH-redox potential field (at high pH and eH values) found where the concentration of pollutants may reach a critical value. The introduced calculation method quick and gives enough accurate results for a pilot-test.


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