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 CaC12, NaAc, oxalate, dithionite, Ti(II1)- EDTA, 0.5 M HC1,5 M HC1, hot 6 M HC1, and a sequential extraction by HI and CrIIHC1 were tested on standard iron minerals and nine aquifer sediments from different redox environments sampled in a landfill leachate plume. Ion-exchangeable Fe(I1) is easily quantified by anaerobic CaClz extraction. A rapid indication of the redox status of a sediment sample can be achieved by a 0.5 M HC1 extraction. This extraction gives an indication of the content of amorphous Fe(II1) and reduced Fe(I1) species such as FeS and FeC03, though the fractions are not quantified. A good estimate of the iron(II1) oxide content contributing to the oxidation capacity (OXC) of the sediment is given by the Ti(II1)-EDTA extraction. The iron(I1) sulfide species are distinguished as AVS (acid volatile sulfide, hot 6 M HC1 extraction) and pyrite (sequential HI and CrIIHC1 extraction). By including a cold 5 M HC1 extraction, the total distribution of the major reactive Fe(I1) and Fe(II1) fractions in aquifer sediments can be assessed.