Antimony(III) binding to humic substances: influence of pH and type of humic acid.
Conditional distribution coefficients (Dom) for Sb(III) binding to three commercial humic acids (terrestrial, coal, and aquatic) were measured at environmentally relevant Sb(III)/DOC ratios and as a function of pH using an equilibrium dialysis method. Maximum binding of Sb(III) was observed around pH 6 for two of the humic acids. The third humic acid showed constant Dom values up to pH 6 and decreasing Dom values for pH > 6. Sb(III)/DOC ratio was found to be important for Dom (20 times higher Dom for 60 times lower Sb(III)/DOC ratio). Moreover, Dom depends on the individual humic acid, suggesting that different functional groups are involved and/or different degrees of stabilization by chelation or H-bridges. Chemical modeling of Sb(III)-humics binding at different pH values is consistent with two binding sites involving (i) a phenolic entity forming a neutral complex and (ii) a carboxylic entity forming a negatively charged complex. Under environmentally relevant conditions, over 30% of total Sb(III) may be bound to natural organic matter.
EAWAG, Swiss Federal Institute for Environmental Science and Technology, P.O. Box 611, CH-8600 Dübendorf, Switzerland. johanna.buschmann@eawag.ch
Johanna
J
Buschmann
Laura
L
Sigg
D000327:Adsorption; D000965:Antimony / Q000032:analysis / Q000737:chemistry*; D002244:Carbon / Q000032:analysis; D003956:Dialysis / Q000379:methods; D006812:Humic Substances / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D008956:Models, Chemical; D010084:Oxidation-Reduction; D012987:Soil; D014874:Water Pollutants, Chemical / Q000032:analysis*
D006812:Humic Substances; D012987:Soil; D014874:Water Pollutants, Chemical; D002244:Carbon; D000965:Antimony