Toxicologie environnementale et analytique

Adsorption and Desorption of Lead (Pb) in Sandy Soil Treated by Various Amendments

Abstract

Loissi Kalakodio, Odey Emmanuel Alepu and Abraham Amenay Zewde

The ability of sandy soil to adsorb lead (Pb) to limit its dispersion in environmental compartments and its adverse effects on humans and ecological receptors depends on certain reaction parameters. The sandy soil has a low Pb retention capacity, but treatment of this soil with amendments such as bentonite, crabmeal and eggshells could significantly improve its ability to adsorb the Pb. To this end, various sorbent tests of Pb by sandy soils, soil amendments and soil+amendments have been carried out in a static mode in the laboratory. The adsorption parameters tested are: reaction time, volume/mass ratio, temperature, increasing Pb (II) concentrations, nature and type of amendment. Furthermore, it was under thermodynamic control and was endothermic in the case of an increase in adsorbed and exothermic Pb levels as they decreased. Moreover, the adsorption of Pb obeys the Langmuir model for the soil (R2=0.986), bentonite (R2=0.915) and crab meal (R2=0.790) and Freundlich for eggshells (R2=0.936). The adsorption of Pb as a function of the types and doses of amendment showed that the retention effect of Pb was very significant (p<0.0001) and that 2.5% of crab meal, compared to the minimum intakes of 10% bentonite and 20% eggshells were sufficient to adsorb the maximum Pb for soil treated with a single amendment. The application of two soil amendments showed that the amended soil adsorbed more Pb with the minimum Fe content compared to other amendments. These results show that crabmeal is an excellent biosolid for the retention of anthropogenic Pb. The desorption test demonstrates that Diethylene Triamine Pentacetic Acid (DTPA) extracted much higher amounts of freshly adsorbed Pb than those extracted with ammonium acetate. The amounts of Pb adsorbed were significantly correlated with the amounts of desorbed Pb. Adsorption and desorption are therefore important phenomena controlling the bioavailability of Pb in sandy soils.