NUCLEAR TECHNOLOGIES AND METHODS 121

PROCESS ENGINEERING

CERAMIC MEMBRANES APPLIED FOR RADIOACTIVE WASTES PROCESSING Grażyna Zakrzewska-Trznadel, Marian Harasimowicz, Bogdan Tymiński, Andrzej G. Chmielewski Ceramic membranes (MEMBRALOX® and CeRAM use of different complexing agents are shown in INSIDE®) were used for filtration of liquid radio- Fig.1. Best removal of cobalt, europium and am- active wastes. The experimental runs with samples ericium was observed when chelating polymers of original radioactive wastes were carried out. The NaPAA or PEI were applied. Complexing with poly- waste was characterized by a relatively low salinity acrylic acid of molecular weight 1200 and 8000 did (<1 g/dm3), however, the specific radioactivity not result in sufficient increase of decontamina- was in the medium-level liquid waste range (~150 tion factor. For the membrane of 15 nm pore size, kBq/dm3). The main activity came from radioac- which was used in experiments, the proper molecu- tive cobalt and caesium, but also a significant lar weight of NaPAA was 15 000 or 30 000. In most amount of lanthanides and actinides was present. of experiments the removal of Eu-154 and Am-241 To enhance the separation, membrane filtration was complete (specific activity below the detection was combined with complexation (sole ultrafiltra- limit). Binding the caesium ions with all tested poly- tion gave decontamination factors in the range of mers gave rather poor results. The best complexing 1.1-1.7). Soluble polymers like polyacrylic acid agent for caesium was cobalt hexacyanoferrate, (PAA) derivatives of different average molecular which gave decontamination factors higher than weight, polyethylenimine (PEI) and cyanoferrates 100. of transition metals were used to enhance the re- Studying the results obtained in the experiment moval of radioactive ions [1]. Each polymer was when cobalt hexacynoferrate together with a sol- added separately to the feed solution. uble polymer (PEI) were employed one can ob- Decontamination factors calculated for the ra- serve a significant increase of Cs-137 removal, how- dioisotopes: Co-60, Cs-137, Eu-152, Eu-154, and ever the decontamination factors for other radio- Am-241 in ultrafiltration (UF)/complexation by the isotopes have decreased compared with experi-

Fig.1. Decontamination of a real liquid radioactive waste in a UF/complexation process with the use of different complexing agents. A 15 nm pore size membrane was used. 122 PROCESS ENGINEERING ments when only chelating polymers were applied the first stage, as was earlier observed during op- as complexing agents. The removal of isotopes by eration of an reverse osmosis (RO) plant [2]. UF/complexation is efficient when a mixture of the It was observed that the decontamination factors ligands binds the ions effectively under the same were higher for all the radioisotopes present in the conditions (the same pH, concentration of alkali- waste sample when the cyanoferrate and chelat- -metal salts, etc.). To avoid the DF’s decrease, the ing polymer were applied subsequently in a 2-stage process was arranged in two steps. At first, a CoCF process than those obtained when the complexing slurry was introduced into the feed solution to bind agents were added to the feed solution simulta- the caesium ions. After some hours, the feed was neously. All these decontamination factors were filtered with UF ceramic membranes up to 3-fold higher than those obtained for the single soluble volume reduction. Sodium polyacrylate, MW 30 000 polymer (NaPAA or PEI). was added to the permeate and after a wait and Ceramic membranes, made of aluminium, tita- pH adjustment the solution was ultrafiltered. The nium or zirconium oxides are expected to overcome DF’s for such a process arrangement are presented disadvantages of polymer membranes, like limited in Fig.2. In the first stage of filtration, a high re- resistance to strong chemical conditions, organic moval of Cs-137 was reached, while other radio- solvents or some kind of ionising radiation, as well. High temperature resistance allows the washing with warm streams and sterilisation by steam. Easy washing is very important when macromolecular complexing ligands are used to enhance the sepa- ration via ultrafiltration. Ultrafiltration combined with complexation ensured satisfactory decontamination factors and volume reduction to treat a wide range of contaminated streams. The process can be alternative to RO, and in some cases when recovery of some selected com- ponents of the solution is important, more benefi- cial than RO. Fig.2. Decontamination factors for a 2-stage process, The best conditions for UF/complexation re- CeRAM INSIDE® 15 nm. sulted in high decontamination factors were found in the multistage arrangement, especially when isotopes were rejected at a moderate rate. In the radioactive wastes contained one dominant com- second stage, where sodium polyacrylate was em- ponent. ployed, the decontamination factors were much higher for most of the radioisotopes present in the References waste. Only for Cs-137 ultrafiltration gave DF’s smaller than 1, which corresponds with a higher [1]. Zakrzewska-Trznadel G., Harasimowicz M.: Removal of radionuclides by membrane permeation combined specific activity in the permeate. Low DF<1 shows with complexation. Desalination, 144, 207-212 (2002). that Cs-137 is not bound by NaPAA and passes [2]. Chmielewski A.G., Harasimowicz M., Tymiński B., through the membrane. Additionally, the low de- Zakrzewska-Trznadel G.: Concentration of Low- and contamination for caesium is caused by the low Medium-Level Radioactive Wastes with 3-stage Re- concentration of this radioisotope and generally verse Osmosis Pilot Plant. Sep. Sci. Technol., 36, 5&6, low salinity of the effluent after the treatment in 1117-1129 (2001).

DETERMINATION OF SULFUR ISOTOPE RATIO IN COAL COMBUSTION PROCESS Andrzej G. Chmielewski, Małgorzata Derda Europe, including Poland, is a continent, where a Preliminary results show that sulfur in coal has great increase of social awareness for problems of a different isotopic composition (δ) and occurs in environmental protection is growing in the last two many different forms (pyrite sulfur, sulfate and or- decades. Production activity is usually connected ganic sulfur) [1]. The separation and determination with a consequence, to a certain degree, of waste of isotope composition may provide information production and pollutant emission. It has a visible concerning the area and mechanism of sulfur in- influence on wholesomeness of the population and corporation in organic-rich sediments. condition of the natural environment, which can The stable isotope composition of sulfur compounds be proved by such occurrences as acid rains, green- of industrial origin contained in the atmosphere, house effect, worsening conditions of forests, or biosphere, hydrosphere, groundwater, soil, etc., may destruction of ozone layer. differ from natural analogues. Analysis of stable Very important is the evaluation of economic re- isotopes of sulfur is the only method to distinguish sponsibility for emitted pollution. Therefore, scien- anthropogenic and natural sources of sulfur. tists look for a suitable marker which could be used The Bełchatów Power Plant Ltd consumes yearly as environmental tracer. about 35 million Mg of lignite. The lignite deposit