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The extraction of Np(Ⅳ) from nitric acid medium by using di(1-methyl-heptyl) methyl phosphonate diluted in kerosene was investigated. The influences were studied in this research including the contact time, the concentration of DMHMP, HNO3 as well as nitrate and the temperature. Slope analyses indicate that Np(Ⅳ) is coordinated mainly in the form of neutral molecules and the extractant complex is Np(NO3)4·2DMHMP. The value of enthalpy change for the reaction is negative which means that the extraction of Np(Ⅳ) is an exothermic process.

The extraction behaviors of Np(VI) from nitric acid medium by di(1-methyl-heptyl) methyl phosphonate (DMHMP) diluted in kerosene has been investigated. The effective factors studied in this research included the contact time, the concentration of DMHMP, HNO3 as well as nitrate and the temperature. Slope analyses indicated that Np(VI) was coordinated in the form of neutral molecules and the extractant complex was NpO2(NO3)2·2DMHMP. Distribution coefficients increased with the increase of HNO3 concentration until up to 4.0 mol/L and then decreased. The value of enthalpy change for the reaction was negative which means that the extraction of Np(VI) was an exothermic process. [ABSTRACT FROM AUTHOR]

The extraction behaviors of U(VI) and Th(IV), as well as the extraction of HNO 3 were investigated by using di(1-methyl-heptyl) methyl phosphonate (DMHMP) as an extractant and kerosene as a diluent. Effects of contact time, acidity, concentration of extractant and temperature on the distribution ratios of U(VI) and Th(IV) were evaluated. HNO 3 was extracted as mono-solvated species. In the investigation of acidity range from 0.01 to 6.0 mol/L, the distribution ratios of U(VI) and Th(IV) increased at first with the rise of HNO 3 concentration up to 3.0 mol/L and then decreased. DMHMP exhibited higher selectivity for U(VI) than for Th(IV) with the separation factor SF U/Th values of 25–120, whereas under the same conditions, tri-n-butyl-phosphate (TBP) only had SF U/Th values of 1.4–26. Slope analyses showed that U(VI) and Th(IV) were extracted as di-solvated and tri-solvated species respectively. The thermodynamic parameters (Δ H , Δ S and Δ G ) were presented and revealed that the extraction was exothermic. For the extraction of Th(VI) from various HNO 3 by 30 vol.% DMHMP or TBP, the limiting organic concentration (LOC) was also given. FT-IR spectra indicated that it was P O bond, not P O bond that took part in the coordination with U(VI) and Th(IV). In addition, the solubility of DMHMP and TBP in various concentration HNO 3 was determined using ICP-AES, and their thermal stability in air was also examined through TGA. DMHMP has much lower water solubility and higher thermal stability than TBP. [ABSTRACT FROM AUTHOR]