Coprecipitation of microamounts of Cs with ferrocyanides of various metals, exhibiting a high sorption activity with respect to Cs ions, was studied. The distribution coefficients of 117 Cs were determined in coprecipitation with the ferrocyanides in 0.1 M NaNO 3 . The precipitated ferrocyanide was separated from solution by filtration through a Trumem metal!ceramic membrane. Cesium is recovered most efficiently with ferrocyanides of bivalent transition metals (Ni, Co, Cu, Fe, Cd).Utilization of liquid radioactive waste (LRW) of various activity levels implies selective isolation of long-lived radionuclides, in particular, 137 Cs having a long half-life of ;30 years and a high radiotoxicity.Cesium is isolated from multicomponent solutions by sorption, precipitation, extraction, membrane filtration, and other methods [1].Among these methods, precipitation is distinguished by easy procedure and simple implementation. A drawback of precipitation in LRW treatment is formation of abundant secondary waste, precipitates and pulps, whose utilization presents a fairly complex task. This drawback can be eliminated by precipitation or coprecipitation of LPW either on earlier formed precipitates or on precipitates freshly prepared in the solutions being treated, followed by filtration of the suspension through porous membranes with different pore sizes (micro, ultra-, and nanofiltration).In this work, we precipitated microamounts of Cs with ferrocyanides of various metals, which, according to published data, have a high sorption activity with respect to Cs ions [2, 3]. The resulting precipitates were separated from solution on a Trumem metal3ceramic membrane [4] with a pore size of 0.2 mm. EXPERIMENTAL Coprecipitation of microamounts of Cs with ferrocyanides of various metals was performed as follows. Into a model solution containing 0.1 M NaNO 3 (pH 6.0) and microamounts of 137 Cs (;100 Bq cm 33 ), solutions of potassium ferrocyanide and of a salt of the appropriate metal were introduced successively so that their final concentrations in solution were 2.86 0 10 35 and 3.81 0 10 35 M, respectively, at the Me n+ /Fe(CN) 6 43 molar ratio of 1.33 and the content of the resulting ferrocyanide precipitate of 8.5317.8 mg dm 33 . The resulting mixture was continuously stirred for 33 4 h and was then filtered in a vacuum through a Trumem metal3ceramic membrane with a pore size of 0.2 mm. In the resulting filtrate, we measured the specific activity of 137 Cs using an NRG-603 (Czech Republic) g-ray analyzer. Based on the measured activities, we calculated the distribution coefficients K d of 137 Cs and the purification coefficients K pur of the solution by the formulas K d = [(a 0 ! a eq )/a eq ](V/m),where a 0 and a eq are the initial and equilibrium specific activities of 137 Cs in solution, Bq cm 33 ; V, volume of solution, cm 3 ; and m, mass of the precipitated ferrocyanide, g.When calculating the mass of the metal ferrocyanide precipitated, we assumed formation of compounds with the composition K 1.33 Me II 1.33 Fe(CN) 6 in the c...
A method for evaluating the serviceability of an iodine filter is proposed. For the projected apparatus, the minimum volume and height of the sorbent layer is calculated using the sorption power index and the contact time between the gas flow and the sorbent layer. For the iodine filters in use at nuclear power plants, to attain the required efficiency of removal of radioactive iodine from gas flows it is recommended that the sorbent be based on the total volume and operating conditions of the apparatus.To eliminate iodine compounds from gaseous radioactive wastes produced at nuclear power plants, it is necessary to determine the minimum volume of the sorbent that will be used to attain the required degree of purification and thereby reliably and effectively protect the atmosphere and the environment. This is also important from the standpoint of energy conservation, since the energy consumption on the operation of iodine filters depends directly on the thickness of the sorbent layer in them.The concentration distribution of the radioactive iodine along the sorbent layer is exponential [1][2][3][4]. For any sorbent, the amount of the sorbed material, including radioactive iodine, is determined by the contact time between the gas flow and the sorbent. There parameters are related with one another as follows [5]:where A and A x are the total activity of the radioactive iodine and the same quantity at a distance x from the entrance into the column with the sorbent, respectively, Bq; α the sorption power index; χ is the fraction of the free volume V free with respect to the sorbent-occupied volume V sorb , which takes account of the effect of the size and shape of granules of the sorbent being tested on the sorption power index; L is the total thickness the total thickness of the sorbent layer, cm; x ≤ L is the running value of the coordinate, cm; U is the linear velocity of the gas in the total cross section of the column, cm/sec. The term χL/U in Eq. (1) reflects the actual contact time between the gas-flow-volume and the sorbent volume, i.e., τ c = χL/U. Then Eq. (1) becomes ln[A/(A -A x )] = ατ c . The contact time is determined by the ratio τ c = V free /Q col , where Q col os the volume velocity of the gas flow.
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