The stability constants for trivalent Eu and Am complexes with a humic acid (extracted from sediment from Lake Bradford, near Tallahassee, Florida) were measured at trace level using a solvent extraction system. The organic extractant was di(2-ethylhexyl) phosphoric acid (HDEHP) in toluene; aqueous phases were humic acid solutions at a constant ionic strength of 0.1M (NaClO(,4)). / The humic acid carboxylate capacity (3.86 (+OR-) 0.03 meg/g) was determined by direct potentiometric titration. The humic acid displayed the typical characteristics of a polyelectrolyte--its apparent pK increased as the degree of ionization ((alpha)) increased. The Eu and Am stability constants also increased as (alpha) increased. / For Eu: log (beta)(,1) = 8.86(alpha) + 4.39; log (beta)(,2) = 3.55(alpha) + 11.06For Am: log (beta)(,1) = 9.32(alpha) + 3.83; log (beta)(,2) = 4.07(alpha) + 10.4 / Calculations show that with hydroxide, carbonate, and humate as competing ligands, under conditions present in natural waters, only the M(humate)(,1) complex is important for many trivalent lanthanides and actinides. / Humic acid precipitated to varying degrees when contacted with toluene in the solvent-extraction system. UV-visible absorption spectroscopy was used to monitor humic acid concentrations (GREATERTHEQ) 0.005 g/l. The radioactive mass balance of the solution phases is not constant due to the activity bound to the precipitated humic acid, therefore radioactivity in both phases must be assayed. / Solvent-extraction and cation-exchange resin systems were used to measure Pu-humate binding. Experiments were done with Pu(IV) and Pu(VI) at pCH('(TURN)) 3.7. Pu(VI) was never stable in the experiments, irrespective of the presence of humic acid. The stability constants for Pu(IV)-humate binding at (alpha) = 0.29 are estimated as log (beta)(,1) = 12.4 and log (beta)(,2) = 17.2. Because humic acid adsorbs to cation-exchange resin, the resin technique is not suitable for stability constant measurements, since it is not possible to monitor the radioactivity in the solid resin phase. / Source: Dissertation Abstracts International, Volume: 43-09, Section: B, page: 2901. / Thesis (Ph.D.)--The Florida State University, 1982.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_74939 |
| Contributors | TORRES, RICHARD ALAN., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 138 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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