Year: 1957
Type: article
Abstract: The fundamental thermodynamic principles of the extraction equilibria for uranyl nitrate are examined. The equilibrium characteristics are associated with considerable nonideality of the aqueous phase — a strong electrolyte, and the organic phase -a practically undissociated nonelectrolyte. It is shown that, at ionic strengths of up to 10, ion association in the aqueous phase does not significantly influence the distribution of uranyl nitrate. It is noted that in most instances the solutions of uranyl nitrate in the organic phase are close to regular solutions, and therefore there is no need to postulate solvation in the organic phase for interpretation of the equilibria. The effect of a salting out agent on the activity coefficient γ at constant concentration x of the latter is examined. It is shown that the relationship between γ (x, m) and the concentration of the salting out agent m is determined by the ratio of the Harned coefficient δ for the salting out agent to a quantity δ e , characteristic for uranyl nitrate: log γ (x, m) /γ (x, o) = 2(δ U — δ s )J s , where δ (x,o) is the activity coefficient of uranyl nutrate in the absence of a salting out agent, and J s is the ionic strength of the salting out agent. If δ s < δ U , then addition of salting out agent raises γ, and conversely; when δ s = = δ U (ammonium nitrate), γ is practically independent of the concentration of salting out agent. The value of δ s decreases and the salting out agent becomes more effective with increasing number of molecules hydrating the cation. Equivalents of the salting out agents differ from chemical equivalents by activity coefficient corrections, and they can be only approximately constant. The variation of the distribution coefficient with the degree of dilution or saturation of tributyl phosphate in extraction by mixed solvents, and the conditions of mutual displacement of the substances being extracted from the organic phase are examined. The role of nonideality of tributyl phosphate — dilutent solutions in the extraction of uranyl nitrate is demonstrated. The parameters which determine the distribution of uranyl nitrate when different solvents and salting out agents are used are the distribution constant k , the nonideality constant of the solvent λ, and δ s . The most important parameter is the distribution constant k , which varies several 1000-fold for different solvents. It is shown that the distribution curves have three characteristic regions, the extents of which depend on the value of k and the nonideality constant of the solvent λ.
Source: Atomic Energy
DOI: 10.1007/bf01491003
Author: A. M. Rozen
Language: English
Subfield: Inorganic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W2015709482