ADSORPTION OF CATIONS ON HYDROUS OXIDES OF IRON .3. ADSORPTION OF MN, CO, NI, AND ZN ON BETA-FEOOH FROM SIMPLE ELECTROLYTE-SOLUTIONS AS WELL AS FROM A COMPLEX ELECTROLYTE SOLUTION RESEMBLING SEAWATER IN MAJOR ION CONTENT

The adsorption behavior of Mn, Co, Ni, and Zn onto a synthetic akageneite (β-FeOOH) sample from different background electrolyte solutions, such as KNO3, NaCl, and major ion seawater, has been studied. Constant pH adsorption isotherms indicate the heterogeneous nature of the adsorbent surface, and Langmuirian behavior is followed only for concentrations below 10-5M of the metal ions. The effect of pH shows that the adsorption edge shifts to the alkaline side not only with increasing concentration of the electrolyte solution but also in major ion seawater. The extent of metal ion uptake calculated from different surface complexation models is found to predict 50-90% of the adsorption depending upon the trace metal as well as on the supporting electrolyte medium. This also suggests more than one adsorption site on akaganeite. A critical appraisal of the adsorption behavior of hydrous iron oxides is presented. © 1994 Academic Press, Inc.