Constants sulfate complexes, acid

The physical nature of the sulfate complexes formed by plutonium(III) and plutonium(IV) in 1 M acid 2 M ionic strength perchlorate media has been inferred from thermodynamic parameters for complexation reactions and acid dependence of stability constants. The stability constants of 1 1 and 1 2 complexes were determined by solvent extraction and ion-exchange techniques, and the thermodynamic parameters calculated from the temperature dependence of the stability constants. The data are consistent with the formation of complexes of the form PuSOi,(n-2)+ for the 1 1 complexes of both plutonium(III) and plutonium(IV). The second HSO4 ligand appears to be added without deprotonation in both systems to form complexes of the form PuSOifHSOit(n"3) +. ... 

It is necessary to consider a number of equilibrium reactions in an analysis of a hydrometallurgical process. These include complexing reactions that occur in solution as well as solubility reactions that define equilibria for the dissolution and precipitation of solid phases. As an example, in analyzing the precipitation of iron compounds from sulfuric acid leach solutions, McAndrew, et al. (11) consider up to 32 hydroxyl and sulfate complexing reactions and 13 precipitation reactions. Within a restricted pH range only a few of these equilibria are relevant and need to be considered. Nevertheless, equilibrium constants for the relevant reactions must be known. Furthermore, since most processes operate at elevated temperatures, it is essential that these parameters be known over a range of temperatures. The availability of this information is discussed below. 

These interactions were taken into account in our article [96]. As the adopted equilibrium constants were determined by different authors using different methods, it is not improbable that used fi values are somewhat self-inconsistent. Therefore, the results of simulations [96] could be treated as tentative, but they showed that the system under discussion is rather complicated. Three complex species may be present in comparable amounts. Sulfate complexes prevail in more acidic media and, as pH increases, they are replaced by SnLj. Finally, products of Sn(II) hydrolysis, Sn(OH), and Sn(OH)2, are thermodynamically stable at pH > 4. However, the formation of these species seems to be kinetically impeded, because we observed no precipitation of hydroxide. 

Bromine (128 g., 0.80 mole) is added dropwise to the well-stirred mixture over a period of 40 minutes (Note 4). After all the bromine has been added, the molten mixture is stirred at 80-85° on a steam bath for 1 hour, or until it solidifies if that happens first (Note 5). The complex is added in portions to a well-stirred mixture of 1.3 1. of cracked ice and 100 ml. of concentrated hydrochloric acid in a 2-1. beaker (Note 6). Part of the cold aqueous layer is added to the reaction flask to decompose whatever part of the reaction mixture remains there, and the resulting mixture is added to the beaker. The dark oil that settles out is extracted from the mixture with four 150-ml. portions of ether. The extracts are combined, washed consecutively with 100 ml. of water and 100 ml. of 5% aqueous sodium bicarbonate solution, dried with anhydrous sodium sulfate, and transferred to a short-necked distillation flask. The ether is removed by distillation at atmospheric pressure, and crude 3-bromo-acetophenone is stripped from a few grams of heavy dark residue by distillation at reduced pressure. The colorless distillate is carefully fractionated in a column 20 cm. long and 1.5 cm. in diameter that is filled with Carborundum or Heli-Pak filling. 4 hc combined middle fractions of constant refractive index are taken as 3-l)romoaccto])lu iu)nc weight, 94 -100 g. (70-75%) l).p. 75 76°/0.5 mm. tif 1.57,38 1.5742 m.]). 7 8° (Notes 7 and 8). 

The low TTA dependence at 35.0°C probably is attributable to dissolution of TTA in the aqueous phase. Observation of fourth-power dependence on acidity argues against any change in the extraction mechanism (e.g., Pu(IV) reduction or NO3 involvement). An aqueous Pu(TTA)3+ complex has been reported (14, 15) and this possibility has been considered in the error analysis of the Pu(IV)-sulfate stability constants. 

As was observed in the case of the extraction of zirconium and hafnium from nitrate media, it is probable that the different tendencies of the metals towards hydrolysis has some effect on the selectivity observed,298 313 expecially in view of the proved extraction of hydroxo complexes. The extraction of both metals decreases markedly in the presence of sulfate ions in the aqueous phase (a feature that is utilized in the stripping of the loaded hafnium with sulfuric acid), although the selectivity for hafnium over zirconium is simultaneously increased on account of the higher stability constants of the inextractable sulfato complexes of zirconium.298... 

Unlike V(II), both the V(III) and V(IV) oxidation states are stable in water. However, neither the V(III) nor the V(IV) oxidation states are easily maintained in the presence of oxygen if the pH is neutral or above, although, under acidic conditions, both these states are rather easily maintained. Somewhat surprisingly, the V(IV) species is more readily oxidized by 02 than is the V(III) species. In aqueous acidic solution, the vanadium(III) ion exists as a hexaqua octahedral complex that can deprotonate to form the 2+ and 1+ species, dependent on pH. Additionally, di, tri and tetra polymeric forms are known. Structures have been proposed and their formation constants determined [10], The occurrence of the various polymeric forms in the presence of sulfate has also been described and is particularly relevant to concentration of vanadium by bioaccumulators [10],... 

The way in which conditional stability constants are used to calculate the distribution of chemical species can be illustrated by consideration of the forms of dissolved Cu(II) in a dilute, acidic soil solution. Suppose that the pH of a soil solution is 6.0 and that the total concentration of Cu is 0.1 mmol m 3. The concentrations of the complex-forming ligands sulfate and fulvic acid have the values 50 and 10 mmol m 3, respectively. The important complexes between these ligands and Cu are CuS04 and CuL where L refers to fulvic acid ligands (see Section 2.3). These illustrative complexes are not the only ones formed among Cu, S04, or L, nor are the three ligands the only ones that form Cu complexes in soil solution.29 Under the conditions assumed, the equation of mole balance for Cu is (cf. Eqs. 2.11 and 2.30)... 

Previous investigations of the Pu(III)-sulfate system in 1 -2 M acid media have produced results in which the authors do not agree on either the nature of the complexes or the magnitude of the stability constants. Both Fardy and Buchanan W and... 

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