Technetium(VII) transport across supported liquid membranes (SLMs) containing 2-nitrophenyl octyl ether (NPOE)

Abstract

Technetium is one of key issues in the treatment of radioactive liquid waste because of its long half-life in combination with high fission yield and its geochemical mobility. For the removal of Tc(VII) from water and concentrated alkaline solutions, 2-nitrophenyl octyl ether (NPOE) is a very effective extractant. In this paper we describe the application of supported liquid membranes (SLMs) impregnated with NPOE for the removal of Tc(VII) from these solutions by using 1.5 M HNO3 receiving phase solutions. Transport of Tc(VII) across a SLM was evaluated with a mechanistic model using a permeability coefficient P to describe the rate of transport. SLM transport of Tc(VII) with NPOE is completely membrane diffusion limited and that there are no aqueous resistances. The membrane diffusion coefficient D m was calculated to be D m =6.4×10-13 m2/s. Permeability is highest for transport from pure water source solution, with P = 3.2×10-4 cm/s. From NaOH solutions the permeability decreases slightly. For acidic source phase the permeability is even lower due to the poor extraction yields of Tc(VII) from acidic solutions into NPOE. Counter current transport of H+ does not affect the extraction and permeability. The Tc(VII)-NPOE system is very robust, only small quantities of NPOE are needed, and the membrane distribution and permeability coefficients are sufficiently large for practical applications.