title: Aluminum speciation in natural waters: measurement using Donnan membrane technique and modeling using NICA-Donnan.
abstract: The study of Al speciation is of interest for the assessment of soil and water quality. For the measurement of "free" aluminum (Al3+), a recently developed Donnan membrane technique was tested by measuring Al3+ in aluminum-fluoride solutions and gibbsite suspensions. It shows that the Donnan membrane technique can measure free Al3+ reliably up to 10(-9) M and the equilibration takes 3-4 days. Next, Al binding to humic acid (HA) purified from a forest soil was measured using either the Donnan membrane technique or gibbsite suspension. Results were compared with those predicted with the non-ideal consistent competitive adsorption (NICA)-Donnan model. The predictions using the generic parameters without fitting were in reasonable agreement with the measured data. Finally, the Donnan membrane technique was used to determine Al binding to dissolved organic matter (DOM) in the solutions of 24 soil samples at pH interval of 3-7. Measurements agree well with the predictions using the NICA-Donnan model assuming 30% of DOM is HA and 30% is fulvic acid. With this model, the effects of pH and DOM changes on the concentration of Al in 81 soil solutions were predicted reasonably without adjustment of model parameters. The comparison between the results of analysis and the modeling provides a mutual validation for the two methods.
authors.affiliation: Environmental Science Department, Wageningen University and Research Center, Netherlands.
authors.forename: Liping
authors.initials: L
authors.lastname: Weng
authors.forename: Erwin J M
authors.initials: EJ
authors.lastname: Temminghoff
authors.forename: Willem H
authors.initials: WH
authors.lastname: Van Riemsdijk
mesh_terms: D000327:Adsorption; D000535:Aluminum / Q000032:analysis* / Q000737:chemistry; D006812:Humic Substances / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008567:Membranes, Artificial; D008956:Models, Chemical; D009930:Organic Chemicals / Q000737:chemistry; D015203:Reproducibility of Results; D012987:Soil / Q000032:analysis; D012989:Soil Pollutants / Q000032:analysis; D012996:Solutions / Q000737:chemistry; D013997:Time Factors; D014867:Water / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D006812:Humic Substances; D008567:Membranes, Artificial; D009930:Organic Chemicals; D012987:Soil; D012989:Soil Pollutants; D012996:Solutions; D014874:Water Pollutants, Chemical; D014867:Water; D000535:Aluminum