4ADSORPTION AND TRANSPORT OF Pb IN SOIL AS AFFECTED BY ORGANIC LIGANDS: BATCH AND COLUMN STUDY |
Y. He, A. P. Schwab, M. K. Banks, and S.R.. Burckhard, Kansas State University, Manhattan, KS 66506 |
The presence of soluble, metal-complexing organic ligands can have a strong impact on the fate and transport of metals. Some of the effects can be predicted using equilibrium speciation models and mathematical transport models, but kinetics and microbial interactions may alter the results.
The effects of citrate and salicylate on the adsorption and transport of Pb in soil were studied in a series of batch and column experiments. Batch experiments indicated that citrate enhanced Pb adsorption at lower citrate concentration (<500 mM) and reduced Pb adsorption when citrate concentration was beyond 1000 MM. Salicylate served as a bridge between Pb and soil; thus, Pb adsorption increased with increasing salicylate concentration. In the column study, solutions of 50mM Pb were continuously leached through soil columns in the presence of citrate or salicylate ranging from 0.5 to 5 mmol/L. The mathematical model predicated that first breakthrough should be observed within 30 to 40 days. However, for all the columns after running 70 days, effluent Pb was still less than the detection limit. The distribution of Pb in the columns demonstrated that the fastest Pb movement occurs in the columns with 50mM Pb but without the organic ligand. The results will be discussed with emphasis on the strong interaction between solution chemistry, solid phase reactions, organic complexation, and microbial activities. Key words: lead, citrate, salicylate, adsorption, transport.
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