Phosphate Complexation of Gadolinium(III) in Aqueous Solution

Examination of the distribution of high specific activity Gd153 between tributyl phosphate and a 0.68 M aqueous phase at 25.0°C permits investigation of lanthanide phosphate complexation within rigorous solubility constraints. Our experiments provide the following formation constants with estimated standard errors: β′= [GdHPO4+] [Gd3+−1I[HPO42−]−1 = (8.05±0.7) x 103; β′2 = [Gd(HPO4)2−][Gd3+]−1 [HPO42−]− = (8.1± 1.9) x 106; β′H = [GdH2PO42+][Gd3+]−1[H2PO4−]−1 = 50.4 ± 6.8. Our results indicate that phosphate complexation of lanthanide ions and trivalent actinides is significant in natural systems, and that the use of phosphate salts as pH buffers in laboratory examinations of metal hydrolysis is generally inadvisable

Carbon dioxide along WOCE line A14: Water masses characterization and anthropogenic entry

16 páginas, 12 figuras, 2 tablasThe meridional WOCE line A14, just east of the South Atlantic Mid-Atlantic Ridge, was surveyed during the austral summer of 1995 from 4°N to 45°S. Full-depth profiles of pH, total alkalinity (TA), and total inorganic carbon (CT) were measured, allowing a test of the internal consistency of the CO2 system parameters. The correlation between CT measured and calculated from pH and TA was very good (r2 = 0.998), with an insignificant average difference of 0.1 ± 3.0 μmol kg−1 (n = 964 data). CO2 certified reference materials (CRMs) and a collection of selected samples subsequently analyzed at the Scripps Institution of Oceanography were used to assess the accuracy of our measurements at sea with satisfactory results. The three measured CO2 system variables were then used to identify the characteristic array of zonal flows throughout the South Atlantic intersected by A14. Equatorial, subequatorial, subtropical, and subantarctic domains were identified at the depth range of the surface water, South Atlantic Central Water (SACW), Antarctic Intermediate Water (AAIW), Upper Circumpolar Water (UCPW), North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW). The nonconservative CO2 system parameters (pH, TA, CT) have been useful in identifying the transition from aged subequatorial to ventilated subtropical surface, central and intermediate waters. They have been identified as good tracers of the zonal circulation of NADW, with marked flows at the equator, 13°S, and 22°S (the “Namib Col Current”) and the sharp transition from UNADW to UCPW at 23°S. The anthropogenic CO2 inventory (CANT) was estimated and compared with CFC-derived apparent ages for different water masses along A14. The anthropogenic entry reached maximum in the relatively young and ventilated subantarctic and subtropical domains where AAIW was the most efficient CO2 trap. The calculated annual rate of CANT entry by AAIW was 0.82 μmol kg−1 y−1, in agreement with the annual rate estimated from the equilibrium between the atmospheric pCO2 increase and the upper mixed layer.Special thanks to M. Arhan (coordinator of the WOCE-France program CITHER) and H. Mercier (chief scientist of cruise CITHER 3). This work was supported by the Spanish CICYT (grant ANT94-1168-E) and IFREMER (University contract 94 1430 087).Peer reviewe

Rare Earth Element Complexation by PO\u3csub\u3e4\u3c/sub\u3e\u3csup\u3e3−\u3c/sup\u3e Ions in Aqueous Solution

Complexation of trivalent rare earths by PO43− ions has been assessed at t = 25°C by examining the influence of aqueous phosphate concentrations on the distributions of 144Ce and 153Gd between 0.68 molar NaClO4 and tributyl phosphate (TBP). Estimated Ce3+ and Gd3+ phosphate complexation constants appropriate to zero ionic strength are Ce3+ + PO43− ↔ CePO40; logLβ10 ≤ 11.7Gd3+ + PO43− ↔ GdPO40; logLβ1o = 12.2. Our estimates of these formation constants at zero ionic strength are approximately seven to eight orders of magnitude lower than previously reported estimates for lanthanide and actinide PO43− complexation. Linear free energy relationships relating the complexation of Ca2+ and lanthanides (Ln3+) by a variety of organic ligands, in conjunction with previous direct observations of CaPO4− formation, are consistent with the experimentally derived CePO40 and GdPO40 formation constants reported in this work. Gadolinium speciation calculations indicate that the PO43− ion can effectively compete with the CO32− ion for free Gd3+ in model groundwater at pH 7–9. Rare earth element phosphate complexation is a significant process in natural freshwater systems which are neutral to mildly basic when the concentration ratio [HPO42−][HCO3−] \u3e[HPO42−][HCO3−] is greater than approximately 1 × 10−3

Rare Earth Element Uptake by the Marine Diatom

Rare earth distribution coefficients, DT = (moles cm-3, cells)/(moles cm-3, solution), obtained using seawater (S = 36.4, t = 25°C, pH ∼ 8.2, pCO2 ∼ 345 μatm) and the marine diatom, Skeletonema costatum, exhibited a strong tendency toward the order Ce \u3e Gd \u3e Yb. Observations of rapid initial uptake, with subsequent gradual uptake over time, are suggestive of initial adsorption onto cell surfaces followed by slow transport to interior cell sites. The average volume concentration factors (DT) obtained in our study are: DTCe = (3.33 ± 0.9) × 105; DTGd = (2.41 ± 0.7) × 105; DTYb = (1.64 ± 0.3) × 105. Distribution coefficient results, expressed as a competition between solution and solid-state complexation terms, indicate that rare earth element complexation, both in solution and on surfaces, strongly increases with atomic number. Relatively small differences in rare earth element distribution coefficients (DT) with atomic number are the result of small differences between large solution and solid-state complexation terms

Carbon dioxide, Hydrographic and chemical data obtained during the R/V Maurice Ewing cruise in the Atlantic Ocean (WOCE section A17, 4 January – 21 March 1994)

27 pages, 8 tables, 6 figuresThis documentation discusses the procedures and methods used to measure total carbon dioxide (TCO2), total alkalinity (TALK), and pH at hydrographic stations during the R/V Maurice Ewing cruise in the South Atlantic Ocean on the A17 WOCE section. Conducted as part of the World Ocean Circulation Experiment (WOCE), this cruise was also a part of the French WOCE program consisting of three expeditions (CITHER 1, 2, and 3) focused on the South Atlantic Ocean. The A17 section was occupied during the CITHER 2 expedition, which began in Montevideo, Uruguay, on January 4, 1994 and finished in Cayenne, French Guyana, on March 21, 1994. During this period the ship stopped in Salvador de Bahia and Recife, Brazil, to take on supplies and exchange personnel. Upon completion of the cruise the ship transited to Fort de France, Martinique. Instructions for accessing the data are provided. TCO2 was measured using a single-operator multiparameter metabolic analyzer (SOMMA) coupled to a coulometer for extracting and detecting CO2 from seawater samples. The overall precision and accuracy of the TCO2 analyses was ±1.6 μmol/kg. A second carbon system variable, TALK, was determined by potentiometric titration with an overall precision of ±1.7 μmol/kg. During the A17 cruise the carbon system was overdetermined because a third carbonate system variable, pH, was also measured potentiometrically with an overall precision of ±0.003. The underway partial pressure of CO2 (pCO2) in surface waters was also continuously measured along the cruise track. A comparison of A17 TALK with recent data in the South Atlantic Ocean confirms that A17 TALK data need a downward correction of 8 μmol/kg that was integrated in the CDIAC database. The internal consistency study carried out among the four carbon system variables led us to adjust the pH measurements by stations in order to eliminate the difference between TCO2 measured and TCO2 calculated from pH and TALK. The R/V Maurice Ewing A17 data set is available free of charge as a numeric data package (NDP) from the Carbon Dioxide Information Analysis Center. The NDP consists of three oceanographic data files, one FORTRAN 77 data retrieval routine file, and this printed documentation, which describes the contents and format of all files as well as the procedures and methods used to obtain the dataN