As a result of a water chemistry survey at Whetstone Brook in western Massachusetts, during an acid mitigation study using a limestone doser, unusually high levels of aluminum were found in sediment pore waters with an overlying layer of limestone. Because of potential fish and biotic toxicity and the problems associated with commonly used speciation techniques for aluminum, a more comprehensive scheme was proposed including aluminum determination by optimized methods of GFAAS, cation exchange on a strong acid resin, and ultrafiltration at 0.5 kd, 1 kd, 3 kd and 10 kd MW cut-offs. The method of chemical extraction into MIBK following chelation by 8-HQ was also evaluated and all the experimental results were compared to a theoretical speciation using equilibrium calculations.
No experimental conditions were found that could extract a consistent fraction with all the model organic ligands for the 8-HQ extraction procedure. Recoveries ranged from 10% to 200% of the organically bound aluminum relative to inorganic standards. Cation-exchangeable aluminum, complexed with malonate, oxalate, phthalate and salicylate, matched a theoretical speciation to within 5%. Theoretical and experimental results for citrate complexed aluminum differed by 24%.
Ultrafiltrate experiments indicated that size fractionation may add more information about the aggregation of aluminum-organic monomers into higher MW oligomers and polymers. In all the synthetic systems studied there appears to be aggregation at lower MW values and the citrate, phthalate and salicylate complexes have fractions greater than 10 kd.
Experiments with fulvic acid showed that approximately 80% of the aluminum complexed species were noncationic. Greater than 90% of the aluminum-fulvate was recovered in the MW range above 10 kd.
Comparisons with stability constants in the literature showed that none of the available constants could predict the behavior of the citrate system and although constants were found that could predict the fulvate system, the majority could not.
