SPECIATION OF FE(II) AND FE(III) IN CONTAMINATED AQUIFER SEDIMENTS USING CHEMICAL-EXTRACTION TECHNIQUES

The iron mineralogy of aquifer sediments was described by chemical extraction techniques. Single-step extractions including 1 M CaCl2, NaAc, oxalate, dithionite, Ti(III)EDTA- 0.5 M HCl, 5 M HCl, hot 6 M HCl, and a sequential extraction by Hf and Cr-II-HCl were tested on standard iron minerals and nine aquifer sediments from different redox environments sampled in a landfill leachate plume. Ion-exchangeable Fe(II) is easily quantified by anaerobic CaCl2 extraction. A rapid indication of the redox status of a sediment sample can be achieved by a 0.5 M HCl extraction. This extraction gives an indication of the content of amorphous Fe(III) and reduced Fe(II) species such as FeS and FeCO3, though the fractions are not quantified. A good estimate of the iron(III) oxide content contributing to the oxidation capacity (OXC) of the sediment is given by the Ti(III)-EDTA extraction. The iron(II) sulfide species are distinguished as AVS (acid volatile sulfide, hot 6 M HCl extraction) and pyrite (sequential HI and (CrHCl)-H-II extraction). By including a cold 5 M HCl extraction, the total distribution of the major reactive Fe(II) and Fe(III) fractions in aquifer sediments can be assessed.