Extraction and separation of Th(IV) and U(VI) from nitric acid media using PIA-8 and HDEHP

Extraction behavior of Th(IV) and U(VI) has been investigated with bis(2-ethylhexyl) phosphinic acid (PIA-8) and bis(2-ethylhexyl) phosphoric acid (HDEHP) from nitric acid media in toluene. The optimum conditions for extraction of these metals have been established by studying various parameters like acid concentration, pH, reagent concentration, diluents and shaking time. The extraction of Th(IV) was found to be quantitative with 0.3-2.5M HNO3 by 2.5.10-2M HDEHP and in the pH range 0.1-2.5 with 2.3.10-2M PIA-8 in toluene. U(VI) was completely extracted in the acidic range of 0.1-2.0M HNO3 with 2.2.10-2M HDEHP and in the pH range of 1.0-3.0 with 2.0.10-2M PIA-8 in toluene. The probable extracted species have been ascertained by log D-log c plot as UO2 R2.2HR with both the reagents and Th (NO3)2R2.2HR with PIA-8 and Th (NO3)3R.3HR with HDEHP, respectively. Temperature dependence of the extraction equilibrium is examined by the temperature variation method. Separation of U(VI) and Th(IV) was also carried out from commonly associated metals.