Computer Science
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58..553z&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 2, pp.553-566
Computer Science
7
Scientific paper
The sorption of Co 2+ (10 -6 mol/L) was measured on subsurface mineral materials in the absence and presence of a sorbed leonardite humic acid (LHA) to 1. (1) evaluate the sorptive role of mineral-bound humic substances, and 2. (2) establish approaches to model metal ion binding in composite materials. The subsurface materials were a < 2.0 m size fraction of an ultisol saprolite (CP) and this same material treated with dithionite-citrate-bicarbonate (DCB) to remove Fe-oxides (DCP). Comparable experiments (with and without LHA) were also performed with mineral sorbents representing dominant phases in the CP separate (gibbsite, Al-goethite, and kaolinite) to evaluate their potential contributions to Co sorption. The mineral-bound LHA ranged in concentration between 0.1-0.4 mg-C/m 2 , representing approximately 0.7% of the subsurface isolate by mass. The sorption-desorption of LHA on the mineral surfaces, and its affinity for Co as a aqueous phase complexant were also determined. Batch measurements were employed (sorbents at 20-90 m 2 /L; LHA-DOC at 11 mg-C/L) over a range in pH and ionic strength ( I ) at I = 0.01 and 0.1 in NaClO 4 . The LHA strongly sorbed to the subsurface mineral isolates (CP and DCP), and to all the specimen sorbents except kaolinite. Maximum sorption of LHA occurred at lower pH ( 4.5). In solid-free suspensions, the affinity of LHA for Co increased with pH and decreasing I ( K d ranging 20-450 L/g). Mineral-bound LHA increased Co sorption on all the sorbents by factors of 10-60 %, with the greatest augmentation noted at pH values (4.5-6.5) where 1. (1) maximum LHA sorption occurred, and 2. (2) Co sorption to the mineral phase was weak and dominated by ion exchange. The LHA appeared simply to augment, rather than to change the intrinsic adsorption behavior of the mineral sorbents. Accordingly, predictions of the K d for Co on the LHA-coated subsurface materials (DCP, CP) based on a linear additivity model agreed well with the experimental data, suggesting that the complex humic-mineral association acted as a noninteractive sorbent mixture at low aqueous Co concentrations.
Resch Charles T.
Smith Sean C.
Zachara John M.
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