Permeation of Am(III) from Water-Soluble, Organic Polyacids across Hollow-Fiber Renewable Liquid Membranes Facilitated with HDEHP/Dodecane: Contrivance of Chemical Dynamics and Mass Transfer Resistances

Abstract

An innovatory technique based on the process of selective permeation across the membrane for the treatment of solutions containing polycarboxylic acids strongly bonded with 241Am is formulated. The present article illustrates the parametric results of the process of optimization for the recovery or mitigation of 241Am activity from solutions containing diethylenetriaminepentaacetic acid and lactic acid, applying a methodology of the hollow-fiber renewable liquid membrane (HFRLM). In the liquid-membrane (LM) phase, a cation exchanger-type organic complexant, bis­(2-ethylhexyl)­hydrophosphoric acid (HDEHP), is incorporated as an ion transporter. The optimized process conditions are as follows: the LM phase containing 0.2 M (HDEHP)2/dodecane, pH of feed solution 1.2 ± 0.05, receiving solution with the LM phase, and 2 M HNO3 (1:4.5) in the form of emulsion. The flow rates of recirculation are maintained as 30 and 20 LPH for solutions of feed and receiving phases, respectively. With an overall mass transfer coefficient, 2.43 × 10–3 cm min–1, 99.9% recovery of Am with its concentration upgradation > 10 times is achieved. The separated product, Am­(NO3)3, is amenable for precipitation as Am-oxalate, a precursor to yield AmO2. After HFRLM treatment, the feed solution becomes nonalpha waste for its rightful disposal. For process modeling, the mass transfer coefficient of Am­(III) is attributed to the multiple mono- and biphasic chemical equilibria and a series of resistances for ionic diffusion across the HFRLM system. This process has been used successfully to alpha decontaminate, residual solution of the simulated trivalent actinide–lanthanide separation with phosphorus-reagent extraction from aqueous komplex process. In this, the alpha decontamination factor obtained for a single-step operation of 8 h is 836. In the two-step operation of HFRLM, the alpha activity in 5 L residual solution is reduced from 2.34 × 108 to 1.01 × 103 BqL–1.