SREL Reprint #2059




Nickel desorption kinetics from hydrous ferric oxide in the presence of EDTA

Amy L. Bryce, Sue B. Clark

Savannah River Ecology Laboratory, The University of Georgia,
P.O. Drawer E, Aiken, SC 29802, USA


Introducing 10 µM EDTA to a system of nickel adsorbed to hydrous ferric oxide (HFO) at pH 8 promoted esorption of Ni as well as dissolution of HFO. By monitoring changes in the solution concentrations of Ni and Fe after the introduction of EDTA, it was possible to discern the important processes controlling Ni desorption. This study focused on the effect of the Ni concentration while all other variables were held constant. Under these conditions, Ni desorption and HFO dissolution occurred over two time domains. The first time domain was short (<O.25 h), here desorption and dissolution were fast parallel processes. In the second time domain (>O.25 h), Ni desorption as slower and the solution Fe concentration did not increase measurably over an 8 h period. The rates of the observed processes were dependent on the Ni surface concentration, and were attributed to weakly bound surface species in the first time domain, and involved more strongly bound surface species in the second time domain. in the first time domain, increases in the surface concentration increased the Ni desorption rate and decreased the FO dissolution rate for all surface concentrations studied. The Ni desorption rate in the second time domains also increased linearly with Ni surface concentration, but at surface concentrations > 3.2 mmol Ni per mol Fe the Ni esorption rate began to approach a maximum value. At total Ni concentrations ->40µM, decreases in the solution concentration were observed in the second time domain, and was attributed to metal exchange. This process may become rate limiting at long equilibration times.

Keywords: Desorption; Dissolution; Iron; Nickel; Remediation

SREL Reprint #2059

Bryce, A.L. and S.B. Clark. 1996. Nickel desorption kinetics from hydrous ferric oxide in the presence of EDTA. Colloids and Surfaces A: Physicochemical and Engineering Aspects 107:123-130.

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