Adsorptionsisothermen als Regelgrößen beim Transport von Schwermetallen in Böden

Abstract

Adsorption isotherms as regulators controlling heavy metal transport in soils The adsorption and desorption of Pb2+ and Cd2+ from equilibrium solutions with heavy metal contents up to 5000 μg/1 were determined in bulk experiments for soil samples from an acid Braunerde developed in loess loam, taken from the humic surface layer of the mineral soil (0–10 cm) and from the subsoil fairly free from organic matter (30–40 cm). Pb and Cd in solutions were determined by flameless atomic absorption spectroscopy. Pb was more strongly retained in the solid phase than Cd, and higher amounts of heavy metals were retained in the humic surface soil than in the subsoil free of organic matter. In the case of Pb adsorption/desorption showed slight hysteresis in the subsoil. The quantity/intensity (Q/I) relationships found in the experiments could be described by the Freundlich equation. The Q/I‐relationships were substituted in the general transport equation. With a simulation model the transport of Pb and Cd through the soil with vertical water flow was calculated by the use of the Continuous Simulation Programming Language (CSMP). Two different cases were considered: a small, continuous increase in the heavy metal input of the soil surface, and a high, instantaneous peak input. Simulation of the transport and distribution mechanisms induced by the inputs over a period of 10 years showed strong retention of lead in the surface layer and consequently a strong damping of the concentration peak in the soil solution. In contrast, cadmium is distributed more quickly over the whole profile, yet the concentration peak in the solution phase is, too, damped considerably in the surface layer by temporary retention in the solid phase. The results of the simulation runs are in accordance with the situation in real soils where often strong accumulation of Pb is found in the top soil, while Cd is accumulated only slightly.

Solid Phase Cadmium and the Reactions of Aqueous Cadmium with Soil Surfaces

“…Long-term exposure for more than a year did not significantly change this desorption pattern. Mayer (1978) found no irreversibility for two acid German soils. Figure 4.11 shows desorption data for the same soils, but here the desorption takes place at different conditions with respect to pH and Ca concentration compared with the adsorption.…”

Heavy Metal Species, Mobility and Availability in Soils

“…Several authors have suggested methods for the fractionation of heavy metals in solid phases (Elsokkary and Lag, 1978;Fischer and Fechter, 1982;Kuo et aI., 1983;Shuman, 1982Shuman, , 1983Sposito et aI., 1982;see also Forstner, this volume). Also, successful computer programs have been developed for modeling the distribution of metal species in soil solutions (Jenne 1979;Sposito, 1981;Sposito and Bingham, 1981) and metal transport through the soil profile (Mayer, 1978;Poelstra et aI., 1979). Also, successful computer programs have been developed for modeling the distribution of metal species in soil solutions (Jenne 1979;Sposito, 1981;Sposito and Bingham, 1981) and metal transport through the soil profile (Mayer, 1978;Poelstra et aI., 1979).…”

Heavy metal species, mobility and availability in soils

“…For the determination of metal species in soil solutions methods are used which are based on more profound analytical background ( Gregson and Alloway, 1984;Jeffery and Uren, 1983;McBride and Bouldin, 1984;Tills and Allowuy, 1983). Also successful computer programs are developed for modelling metal speciation in soil solutions (Jenne, 1979;Sposifo and Bingham, 1981) and metal transport through the soil profile (Mayer, 1978;Poelstra et al, 1979).…”