Thermodynamics of Solvent Extraction of Rhenium(VII) with N1923
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Basic and Applied Research: Section I
Thermodynamics of Solvent Extraction of Rhenium(VII) with N1923 Da-wei Fang, Xue-jun Gu, Ying Xiong, Shuang Yue, and Shu-liang Zang
(Submitted August 21, 2009; in revised form December 14, 2009) At temperatures from 278.15 to 303.15 K, equilibrium molalities of ReO42 were measured in the aqueous phase containing NH4Cl as supporting electrolyte at ionic strength from 0.1 to 2.0 mol Æ kg21 and at constant initial molality of extractant. The standard extraction constants K0 at various temperatures were obtained by methods of Pitzer’s theory. Thermodynamic properties for the extraction process were calculated.
Keywords
extraction, N1923, rhenium
List of Symbols
a, c, i, j, n M, X
1. Introduction Rhenium is one of the rarest elements in nature. Moreover, it occurs in a scattered form, and methods for its separation in a form of metal or compounds are complicated and costly. These facts result in a high price of rhenium and its compounds, and also in limited practical applications of this element.[1] Solvent extraction is one of the main methods of separation and enrichment of rhenium from nonferrous metals mine tailings. Thermodynamic extraction equilibrium constant and thermodynamic parameters are the basis of research on extraction process techniques and best design.[2] In this paper, we measured concentration of rheniumate in aqueous phase at different ionic strength in hydrochloric acid system. The standard extraction constants K0 are obtained by methods of extrapolation and polynomial approximation.[3] Thermodynamic properties for the extraction process are calculated. In the presence of excessive extractant N1923 (one kind of primary amine), the structure is given in Fig. 1. The extraction reaction is[4]: RNH2 ðorgÞ þ Hþ ðaqÞ þ ReO4 ðaqÞ ¼ RNH3 ReO4 ðorgÞ ðEq 1Þ where (aq) and (org) refer to the aqueous and organic phase, respectively, RNH2 is the extractant N1923, and RNH3ReO4
Da-wei Fang, Xue-jun Gu, Ying Xiong, Shuang Yue, and Shu-liang Zang, and S. Zang, Research Institute of Rare and Scattered Elements, College of Chemistry, Liaoning University, Shenyang 110036, China. Contact e-mail: davidfi[email protected].
AP Ai M
parameter in Pitzer’s equation cation and anion in a multicomponent electrolyte solution Debye-Hu¨ckel coefficient of the osmotic function parameter in Eq 19 molality
is the extraction complex. The standard equilibrium constant K0 is given by logK 0 ¼ log½mfRNH3 ReO4 g log½mfHþ g mfReO4 g mfRNH2 g þ log½cfRNH3 ReO4 g log½cfHþ g cfReO4 g cfRNH2 g
ðEq 2Þ
where c is the activity coefficient in the molality scale, and m is the molality.
2. Experimental The water used was doubly deionized and its conductivity was 1.59104X1 m1 (X is ohm). The ammonium chloride was of AR grade. The n-C7H16 used as diluent was of AR grade. All initial solutions to be measured were freshly prepared. The aqueous phase was prepared by dissolving NH4ReO4 in an aqueous solution of HCl of constant molality. The initial molality of the NH4ReO4 was r = 0.001 mol Æ
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