Humate phases

On the other hand, sorption/desorption experiments with copper and clay minerals have shown that true cation exchange (with BaCl2) is relatively insignificant and that the triethanolamine reagent (added to raise the pH of the solution) effects the release of additional metal compounds, which may be more appropriately designated as easily extractable phases (41). Extraction of humate phases was performed with O.IIV NaOH the same reagent was used for the determination of the concentrations of humic substances by comparison with standard humic acids (42). 

In the O.IN NaOH extractable fraction (which is assumed to reflect the humic acid phases) of the Rhine sediment, PCF values are particularly high for iron, copper, and lead, exhibiting a slight increase in the fine-grained particles compared with the silt-sized material. For the sample from Lake Constance, the concentration factors in the humate phase have been found to be 11 and 40 for copper, 9 and 12 for iron, and 5 and 9 for chromium, in the pelitic and silty sediment fractions, respectively. Similar concentration factors of trace metals in the NaOH-extractable matter have been observed by Chen et al. (14) for chromium, lead, copper, and zinc, whereas iron and manganese showed no significant association with this fraction. 

HUMIC Acid. Humic acid did not contribute detectable impurities to the eluates of blank parfait columns. This result was apparently due to the insolubility of humate in the organic solvents used to elute the Teflon and ion-exchange beds and the inability of the humate to volatilize in the GC. Humic acid did, however, distribute itself throughout the parfait column, as indicated by the observation of color entering the column effluent, F7. When 16 mg of humate in 8 L of synthetic hard water was passed through a parfait column having the Teflon bed divided into three sequential 50-mL beds, 8.9 , 5.0 , and 2.9 of the total humate were found in the aqueous phases that separated upon elution of these beds, as indicated by absorbance at 200 nm. The column effluent from this experiment contained 5.1 of the humate applied. The majority of the humate applied was found as color adsorbed to PTFE, and it did not elute into methylene chloride. Conditions to elute it from PTFE were not explored. 

The chemistry of actinide ions is generally determined by their oxidation states. The trivalent, tetravalent and hexavalent oxidation states are strongly complexed by numerous naturally occurring ligands (carbonates, humates, hydroxide) and man-made complexants (like EDTA), moderately complexed by sulfate and fluoride, and weakly complexed by chloride (7). Under environmental conditions, most uncomplexed metal ions are sorbed on surfaces (2), but the formation of soluble complexes can impede this process. With the exception of thorium, which exists exclusively in the tetravalent oxidation state under relevant conditions, the dominant solution phase species for the early actinides are the pentavalent and hexavalent oxidation states. The transplutonium actinides exist only in the trivalent state under environmentally relevant conditions. 

Little has been published in this area in relation to humic substances. Humates tend to have retention times close to, or before, the solvent front in most reverse-phase columns. In one report (Rodgers et al., 1981), a fulvic material was separated into seven fractions on a silanized BioSil column. The fractions were analyzed by infrared spectroscopy. One of the fractions was patently not a fulvic acid, although it co-precipitated with fulvic acid. 

The diversity of reactions which actinides can undergo in natural waters is pres ted schematically in Figure 22.9. Complexation by anions such as hydroxide, carbonate, phosphate, humates, etc. determine the species in solution. Sorption to colloids and suspended material increases the actinide concentration in the water while precipitation of hydroxides, phosphates, carbonates, and/or sorption to mineral and biological material limit the amount in the solution phase. 

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