GB830937A - Method of isotope concentration - Google Patents

Abstract

<PICT:0830937/III/1> The N15 isotope is concentrated by bringing gaseous nitric oxide into contact with an aqueous oxyacid or liquid oxide of nitrogen in which the atomic ratio of oxygen to nitrogen is greater than 1, so that the liquid is enriched by exchange of N15, wherein the gaseous nitric oxide is produced by reaction of the enriched liquid with a reducing agent, and recovering NO, or oxyacid, or liquid oxide enriched with N15. 6-12 molar aqueous nitric acid is passed from 34 into exchange column 10, which may have spaced perforated plates 12 and packing 14, or conventional bubble plates, and which may be operated at atmospheric pressure and room temperature, although a pressure of 2 atm. is also referred to. NO enters in countercurrent at 24. The HNO3 flows to reflux chamber 16, where it is reduced by gaseous SO2 from 40. The aqueous sulphuric acid may be withdrawn at 44, while the oxides of nitrogen. also formed, pass to condenser 18, maintained at say 3 DEG C., to condense less volatile components and allow the NO to pass into exchange column 10 to transfer N15 to the HNO3 therein. The liquid from condenser 18 flows back to reflux chamber 16. The NO gas depleted in N15 evolved from column 10 passes to reactor 26, which may be packed with raschig rings, and is converted therein, by air entering at 30 and water entering at 28, to aqueous nitric acid. N15 enriched HNO3 may be withdrawn at 52, or enriched NO at 54. It is stated that the reduction is controlled so that the composition of the gases passed to column 10 is about the same, as regards the various oxides of nitrogen, as that in equilibrium with the HNO3 in the column. NO2. in particular, is catalytic for the exchange, and the partial pressure thereof is maintained at that in equilibrium with the HNO3 by adding H2O to the reflux chamber, by controlling SO2 addition in response to a colour detector at the top of column 16 working on the intensity of NO2 coloration, or by the condenser temperature. Liquid dinitrogen tetroxide (N2O3), when the exchange column temperature is 3-5 DEG C., or liquid dinitrogen tetroxide (N2O4), when the exchange column temperature is below 21 DEG C., may be used in place of aqueous nitric acid. In Fig. 2 (not shown), a plurality of units, as in Fig. 1, each having a packed stainless steel exchange column, a packed glass lined steel reflux chamber and a condenser, are provided, through which HNO3 and NO pass in countercurrent in series. A portion of the HNO3 leaving each exchange column passes to the reflux chamber for reduction with SO2, and the NO formed passes back to the column, while the remaining HNO3 passes to the next exchange column in the series. The HNO3 formed from the N15 depleted NO from the first column is used in an additional tower to scrub the NO from the first column.