Investigation of Sorption and Diffusion Mechanisms, and Preliminary Economic Analysis

Abstract

This report describes the synthesis and evaluation of molecular sieve zeolite membranes to separate and concentrate tritiated water (HTO) from dilute HTO-bearing aqueous streams. Several monovalent and divalent cation exchanged silico alumino phosphate (SAPO-34) molecular sieve zeolite membranes were synthesized on disk supports and characterized with gas and vapor permeation measurements. The pervaporation process performance was evaluated for the separation and concentration of tritiated water.Experiments were performed using tritiated water feed solution containing tritium at the high end of the range (1 mCi/mL) anticipated in a nuclear fuel processing system that includes both acid and water streams recycling. The tritium concentration was about 0.1 ppm. The permeate was recovered under vacuum. The HTO/H2O selectivity and separation factor calculated from the measured tritium concentrations ranged from 0.99 to 1.23, and 0.83-0.98, respectively. Although the membrane performance for HTO separation was lower than expected, several encouraging observations including molecular sieving and high vapor permeance are reported. Additionally, several new approaches are proposed, such as tuning the sorption and diffusion properties offered by small pore LTA zeolite materials, and cation exchanged aluminosilicates with high metal loading. It is hypothesized that substantially improved preferential transport of tritium (HTO) resulting in a more concentrated permeate can be achieved. Preliminary economic analysis for the membrane-based process to concentrate tritiated water is also discussed.

Techno-economic Analysis of Advanced Zeolite Membranes for the Concentration of Tritiated Water

“…The X-Ray Diffraction (XRD) analysis and permeation measurement results showed that high quality membranes were synthesized which are well suited to evaluate the tritiated water vapor sorption and diffusion through the zeolite pores. 15 The characteristic peaks associated with LTA structure are detected in the XRD pattern and it is confirmed that no other competing phases are formed during synthesis. The bulk compositions of the as-synthesized NaA and cation-exchanged KA membranes were determined using EDX analysis of the Na, K, Si and Al content.…”

“…The rationale for the synthesis and evaluation of cation exchanged SAPO-34 is described by Bhave et al 15 Table 2 shows the results of pervaporation experiments with monovalent (K + , Li + , Na + ) cation exchanged SAPO-34 zeolite membranes. The separation factor (HTO/H 2 O) for the tritiated water separation with neutral SAPO-34 zeolite membrane was 0.83 which indicates that HTO did not preferentially permeate through zeolite pores over H 2 O.…”

“…For barium cation exchange, barium chloride dissolved in methanol was prepared. A more detailed description of the synthesis and separation performance on tritiated water samples was reported by Bhave, et al 15…”

“…In previous reports, the performance of silicoalumino phosphate (SAPO) zeolites and Linde Type A (LTA) zeolites for the separation and concentration of tritiated water was reported. 15,16 In this research ion exchanged SAPO-34 and LTA membranes prepared on alumina disk and tubular supports were evaluated to determine the feasibility of concentrating tritiated water from high volume dilute aqueous solutions.…”

“…As discussed in the earlier reports 15,16 , CECE is one of the available alternatives to the membrane process for the concentration of the tritiated water. Tritium removal from light and heavy water reactors is described with the application of combined electrolysis and catalyst exchange in U.S. and Canadian patent applications.…”