2007/03/01 by Stephanie M. Garman, Matthew J. Eick, Michael Beck
Environmental Science · Energy · #Heavy metals in environment #Iron oxide chemistry and applications #Mine drainage and remediation techniques
paper · doi:10.1097/ss.0b013e31802ff8aa
In natural systems, the solution concentration and hence potential bioavailability of trace metals are primarily controlled by adsorption-desorption reactions at the mineral-water interface. Although many studies have been conducted to understand the adsorption of trace metals to soil minerals, less is known about long-term adsorption/desorption processes. In this study, we examined the influence of mixing and sorption period on the desorption of lead from goethite. Lead sorption was rapid and essentially complete in 1 h, with essentially no change in the quantity of lead adsorbed during the 6-month sorption period. Desorption of lead was slower than the adsorption reaction and was best modeled by two first-order equations. At all surface loadings, the desorption of lead followed the order short-term (24 h) > long-term nonstirred (6 months) > long-term stirred (6 months). Similarly, for most experiments, the desorption rate coefficients for the short-term experiments are greater than both the stirred and nonstirred long-term experiments. However, only the long-termed stirred experiment at the highest loading rate and a sample that was allowed to age for 5 years showed statistical significance at the α = 0.05 level. These results suggest that longer adsorption periods, perhaps a number of years, or high adsorbate surface coverages may be necessary to determine if residence time effects are an artifact of the experimental conditions or truly the length of the adsorption period.