Purification of Liquid Radioactive Waste by Ultrafiltration
Development of the Method of Liquid Radioactive Waste Treatment with the Use of Micellary Enhanced Ultrafiltration
Tech Area / Field
- ENV-RWT/Radioactive Waste Treatment/Environment
8 Project completed
Senior Project Manager
Rudneva V Ya
Institute of Highly Pure Biopreparations, Russia, St Petersburg
- LLC Scientific Production Firm “Gella-Teco”, Russia, Moscow
- Emergencies Science and Technology Division Environment Canada, Canada, ON, Ottawa
Project summaryThe project is aimed at the development of the effective method for recovery of low-level liquid radioactive waste (LRW) with the use of micellary-enhanced ultrafiltration (MEUF).
A large body of LRW, which strongly need recovery, has been accumulated throughout the world over the whole period of atomic power engineering and atomic military-industrial complex development. LRW is usually a mixture of several types of contaminants with different chemical origin, among which are either the coarse-dispersed, or the low- and high-molecular water soluble compounds. As a rule radionuclides are present in all these components, that is why, any technology for recovery of LRW should provide the possibility of isolating each of the contaminants from water.
A large stock of different water-purifying devices for reduction of LRW body is used throughout the world. The most used processes are: evaporation, ion-exchange (sorption), and reagent coagulation. All these methods have several disadvantages, such as high specific energy consumption, high cost for burying of the large body of radioactive waste, and the need in large-sized equipment.
In the 90s of XXth century the baromembrane methods became of considerable practical importance for purification of LRW. These methods provide LRW purification to the required radiation safety and production of concentrates with salt content up to 200 g/l. But, to purify LRW from radionuclides, being in a form of low molecular compounds and ions, reverse osmosis is needed. Reverse osmosis separation is characterized by the use of high pressure (about 100 Bar) and of low-permeable (diffusion) membranes. This generates a need in the large-sized complex and rather expensive devices.
To eliminate the stage of reverse osmosis, it is proposed to use the method of micellary-enhanced (reagent) ultrafiltration. The proposed method combines both the high effectiveness of ultra- and microfiltration and the selectivity of sorption. The micellary-enhanced ultrafiltration is based on transfer of the dissolved low-molecular components to a new associated molecular or colloid state with further separation of the associated forms with microporous membrane. This is reached by addition of complexing agents (surfactants and water soluble polyelectrolytes) and adsorbent particles to the solution being purified, or by transfer of the solution to a sol by hydrolysis or by addition of chemical reagents. After that the low-molecular components of LRW can be easily separated and concentrated by ultra- or microfiltration.
Another limitation of membrane methods is the so-called concentration polarization (CP). CP is the formation of a cake or a gel layer on membrane surface. This strongly decreases the effectiveness of purification. Later on the CP layer is compacted and consolidated, causing a need in disassembling of the device or in the change of membrane.
To diminish or to eliminate the negative influence of CP on kinetics of the LRW purification, it is proposed to develop the high-effective process for turbulization of liquid in the over-membrane space by using special movable turbulators. To eliminate the influence of the intense liquid turbulization on the membrane, it is planned to use metal-ceramic membranes Trumem® designed by the project participants. These membranes are stable to mechanical stress, to radioactive, chemical and temperature action.
The scope of project activity will include:
- Analysis of composition of the atomic power plant LRW, using Smolensk APS, GYP MosNPO “Radon”, or Moscow Station for LRW Recovery as the examples. Formulation of a model mixture of low- and high-molecular water soluble components to develop the process of micellary-enhanced ultrafiltration as well as of a model suspension of coarse-dispersed components.
- Approbation with this model mixture of different methods of reagent ultrafiltration (UF). Selection of a concrete UF method or of combination of UF methods, which provide the most full complexing of dissolved substances.
- Based on characteristics of the model mixture after the reagent treatment, selection of the metal-ceramic membrane, which gives the highest capacity with the complete retaining of molecular complexes.
- Design of a membrane device with movable mechanical turbulators (DMMT) which give the increase of inter-regeneration period or fully eliminate membrane regeneration.
- Testing of the prototypes of DMMT with the model suspension of coarse-dispersed components as well as with solution (suspension) of molecular complexes after the reagent effect on the mixture of low- and high-molecular water soluble components.
- Design of a scale-model of the complex plant for purification and concentration of LRW which includes: unit for pre-microfiltration, unit for reagent modification of solution, and unit for ultrafiltration, in which the modified LRW flow is pided to two flows – the permeate one and the concentrate one. The latter accumulates all toxic contaminants and may be of 1-2% of the initial LRW flow and is sent directly for solidification.
- Testing of the plant with real LRW at one of the Russian atomic power plants.
Highly skilled personnel from Laboratory of Membrane Technologies, Institute of Highly Pure Biopreparations, which have a wide experience in membrane methods of separation of solutions and suspensions as well as in methods of characterization of ultra- and microfiltration membranes, will be involved in the project performance. Laboratory researchers were the participants of ISTC project #0918 “Chemically-modified nano- and ultrafilters”. For this project the asymmetric track-etched ultrafilters were first produced and characterized. The project participants also have an experience in inutilization of waste and the reagents of solution modification. The institute researchers developed the effective method of liquid radioactive waste from the nuclear submarines, together with CCB “Rubin” designed the microfiltration unit meant for the same purposes, and developed different processes for the reagent binding of solutions and suspensions.
The specialists of OOO NPF “Facilities for Ecology” have a wide experience in membrane technology and in recovery of LRW. They developed the fundamental basis for recovery of waste with the use of micellary-enhanced ultrafiltration with Trumem membranes and developed the new type of semi-permeable metal-ceramic membranes. Besides, the specialists of this enterprise have studied the properties of semi-permeable membranes under the influence of aggressive media, worked through the best conditions of ultrafiltration with rotating turbulators, optimized the hydrodynamic conditions for operation of semi-permeable membranes in separation of viscous and heterogeneous systems, and developed novel technologies for LRW recovery.