Soil sorption of nickel in presence of citrate or arginine

摘要

The influence from 0.5 and 5 mmol L-1 citrate and arginine on nickel sorption in sandy loamy topsoil of a Mollic Hapludalf has been investigated in order to evaluate the effect of organic complexing agents on nickel retention in soils. Both ligands, which form strong complexes with nickel, represent common soil solutes but also serve as models for oxygen and nitrogen donor ligands in fulvic acids and other organic soil solutes. In the pH range 4.5-8, sorption edges showed a dramatic decrease in nickel sorption in presence of citrate, but not in the presence of arginine. These differences were further quantified at pH 6.0 through sorption isotherms covering initial nickel concentrations in the range 3.4-42.6 mu mol L-1. Again, the amounts of nickel sorbed without and in the presence of 0.5 and 5 mmol L-1 arginine were not significantly different, whereas 0.5 and 5 mmol L-1 citrate reduced sorption by 50 to 90. The ligand effects could be expressed through variation of the Freundlich affinity constant K. The results indicate that trivalent positively charged nickel-arginine complexes (NiH(3)arg(2)(3+)) are sorbed to cation exchange sites, while in the presence of citrate sites for the bonding of monovalent negatively charged nickel-citrate complexes (Nicit(-)) are sparse. References: 39