Continuous Separation of Radionuclides from Contaminated Water by Shock Electrodialysis

Abstract

The increasing popularity of nuclear energy necessitates development of new methods to treat water that becomes contaminated with radioactive substances. Because this polluted water comprises several dissolved species (not all of which are radioactive), selective accumulation of the radionuclides is desirable to minimize the volume of nuclear waste and to facilitate its containment or disposal. In this article, we use shock electrodialysis to selectively, continuously, and efficiently remove cobalt and cesium from a feed of dissolved lithium, cobalt, cesium, and boric acid. This formulation models the contaminated water commonly found in light-water reactors and in other nuclear processes. In a three-pass process, a consistent trade-off is observed between the recovery of decontaminated water and the percentage of cobalt removed, which offers flexibility in operating the system. For example, 99.5% of cobalt can be removed with a water recovery of 43%, but up to 66% of the water can be recovered if deionization of cobalt is allowed to drop to 98.3%. In general, the energy consumed during this process (ranging between 1.76 and 4.8 kW h m–3) is low because only charged species are targeted and virtually no energy is expended removing boric acid, the most abundant species in solution.

Desalination Performance Assessment of Scalable, Multi-Stack Ready Shock Electrodialysis Unit Utilizing Anion-Exchange Membranes

“…As far as water recovery is concerned, the obtained data is again in conflict with the observations reported by [ 4 , 18 , 19 , 20 ], as described above. The water recovery stayed rather the same, moving in the range of 45% to 55%, occasionally dropping below 40% or rising above 60% without any apparent reason.…”

“…The theoretical and experimental work published previously suggests the usage of porous materials with close to 1 μm pore size to sustain deionization shocks in the OLC region [ 4 , 13 , 16 , 20 ]. Larger pores (approximately >10 μm) may lead to convective mixing that may interrupt the shock formation and produce instabilities inside the porous material.…”

“…As the purpose of this scale-up was to increase the production of freshwater, it was necessary to consider the usage of materials with higher solution throughput, possibly even with lower effectivity in the beginning. Therefore, two types of porous ceramics with different pore sizes that were both more than one order of magnitude larger compared to pores of the glass frit used in [ 4 , 16 , 17 , 18 , 19 , 20 ] (and different enough one from the other) were chosen for this study. The solution throughput was also related to the increased dimensions of the porous material, especially in the direction of the solution flow, which only added to the hydrodynamic resistivity of the material.…”

“…35 g/L TDS), is about 2.3 MPa, significantly drives up the energy requirements and/or lowers the water recovery of the systems [ 3 ]. On top of that, RO removes practically every non-water substance from the feed stream, which makes it unsuitable for selective decontamination [ 4 ].…”

“…Further works were published between 2015 and 2020 by prof. Bazant’s group demonstrating the functionalities of improved and scale friendly designs of a new shock electrodialysis unit that once again utilized a porous frit with negative surface charge sandwiched between a pair of cation-exchange membranes to induce the concentration polarization. The device was capable of reducing the ion concentration by four orders of magnitude [ 4 , 18 , 19 , 20 ].…”