1999 GSA Annual Meeting -- Denver, Colorado
1999 GSA Annual Meeting -- Denver, Colorado
Author(s): SMITH, Kathleen S., U.S. Geological Survey, M.S. 973 Federal Center, Denver, CO 80225-0046, ksmith@usgs.gov; RANVILLE, James F., and MACALADY, Donald L., Chemistry and Geochemistry Dept., Colorado School of Mines, Golden, CO 80401; and GEBHARD, Steven C., TDA Research Inc., 12345 W. 52nd Ave., Wheat Ridge, CO 80033.
Keywords: trace metals, sorption
Batch studies of Cu, Zn, Pb, and Al sorption onto ferric oxyhydroxysulfate (FOHS) coated with natural organic matter (NOM) were performed with both natural and synthetic materials. The natural iron-rich sediment originated from a stream that receives acid-mine drainage and the sediment contained about 4 wt.% organic carbon. X-ray photoelectron spectroscopic analysis confirmed that the surface/near surface of the sediment particles was enriched in organic carbon (C-C and C-O bonded moieties) relative to iron compared to the bulk composition. The synthetic material was precipitated from a mixture of ferric nitrate and calcium sulfate, and then coated with Suwannee River fulvic acid (SRFA), a well-characterized natural fulvic acid. In both systems, the initial pH was about 3.5, the Fe:C mole ratio was about 5, and metal sorption was examined over a pH range of about 3.5 to 6.5. Results from the mixed FOHS-NOM systems were compared with metal-sorption results using pure FOHS. This comparison shows that FOHS dominated metal sorption in both the natural and synthetic systems, with the influence of NOM being minor to insignificant. The probable explanation for the relatively insignificant contribution of NOM is preferential binding of ferric iron and aluminum to organic functional groups on the NOM. At the initial pH 3.5 of the natural system from which the iron-rich sediment was collected, enough dissolved ferric iron and aluminum was present to preferentially bind to available sites on the NOM. In the synthetic experiments, enough ferric iron was solubilized by SRFA from the substrate to tie up the NOM metal-binding sites. This work demonstrates that NOM does not appear to play a significant role in the transport and fate of trace metals in acidic iron-rich environments.
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