On-site characterization of humic-rich hydrocolloids and their metal loading by means of mobile size-fractionation and exchange techniques.
Humic-rich hydrocolloids and their metal loading in selected German bog-waters have been characterized by a novel on-site approach. By use of an on-line multistage ultrafiltration (MST-UF) unit equipped with conventional polyethersulfone (PES)-based flat membranes (nominal cut-off 0.45, 0.22, and 0.1 microm, or 100, 50, 10, 5, 3 kDa) the hydrocolloids could be fractionated on-site in both sub-particulate and macromolecular size ranges. Characterization (dissolved organic carbon (DOC), metals) of the colloid fractions obtained this way was performed off-site by use of conventional instrumental methods (carbon analyzer, AAS, ICP-OES, and TXRF (total reflection X-ray fluorescence)). Major DOC fractions of the hydrocolloids studied were found to be in the size range <5 kDa. The assessed metals (Al, Cu, Fe, Mn, Pb, and Zn) were, however, predominantly enriched in the macromolecular and sub-particulate range, depending on the metal and the sample, respectively. In addition, metal species bound to these hydrocolloids were kinetically characterized on-site by use of competitive ligand (EDTA (ethylenediaminetetraacetate)) and metal (Cu(II)) exchange; the EDTA complexes formed and the metal ions exchanged were separated by means of a small time-controlled tangential-flow UF unit (cut-off 1 kDa). Bound metal fractions, in particular Al and Fe, reacted only slowly (500 to 1000 min) with EDTA; the conditional availability was 60-99%, depending on the hydrocolloid. In contrast, the Cu(II) exchange of colloid-bound metal species approached equilibrium within 5-10 min, with characteristic exchange constants, Kex, of the order of 0.01 to 90 for the metals (Fe<Al<Zn<Mn approximately/= Ca approximately/= Mg). The results were clearly dependent on the water investigated. Thus detailed information on the conditional kinetic and thermodynamic stability of colloid-bound metal species could be obtained from competitive EDTA and Cu(II) exchange under on-site conditions.
Burba
P
P
Institute of Spectrochemistry and Applied Spectroscopy, Dortmund, Germany. burba@isas-dortmund.de
Van den Bergh
J
J
Klockow
D
D
D002614:Chelating Agents / Q000737:chemistry; D003102:Colloids / Q000032:analysis* / Q000737:chemistry; D003300:Copper / Q000737:chemistry; D004492:Edetic Acid / Q000737:chemistry; D005618:Fresh Water / Q000737:chemistry; D005858:Germany; D006812:Humic Substances / Q000032:analysis* / Q000737:chemistry; D007700:Kinetics; D019216:Metals, Heavy / Q000032:analysis*; D013054:Spectrophotometry, Atomic; D013056:Spectrophotometry, Ultraviolet; D014462:Ultrafiltration; D014874:Water Pollutants, Chemical / Q000032:analysis*
D002614:Chelating Agents; D003102:Colloids; D006812:Humic Substances; D019216:Metals, Heavy; D014874:Water Pollutants, Chemical; D003300:Copper; D004492:Edetic Acid