ZINC ADSORPTION BY STERILIZED AND NONSTERILIZED SOIL IN THE PRESENCE OF CITRATE AND CATECHOL

The effect of organic ligands on zinc (Zn) adsorption in the rhizosphere may be influenced by microbial activity depleting the concentration of the ligand over time. Zinc adsorption by sterile and non-sterile lateritic soil was measured by shaking the soils with Zn solutions at a soil-liquid ratio of 1:5 for five periods of time ranging from 17-480 h. The concentrations of Zn and the ligands were determined after the selected times. The speciation of Zn was then estimated. Changes in Zn adsorption with time in the presence of organic ligands were due to changes in pH and Zn complexation associated with the addition and breakdown of the organic ligands and with the technique of sterilization. Zinc adsorption was higher in non-sterile than in sterile soil. Adsorption in the presence of citrate was lower than in its absence except in non-sterile soil after 72 h. The adsorption in the presence of catechol was similar to that in its absence.