Uranium anion exchange

Uranium ores are leached with dilute sulfuric acid or an alkaline carbonate [3812-32-6] solution. Hexavalent uranium forms anionic complexes, such as uranyl sulfate [56959-61-6], U02(S0 3, which are more selectively adsorbed by strong base anion exchangers than are other anions in the leach Hquors. Sulfate complexes are eluted with an acidified NaCl or ammonium nitrate [6484-52-2], NH NO, solution. Carbonate complexes are eluted with a neutral brine solution. Uranium is precipitated from the eluent and shipped to other locations for enrichment. Columnar recovery systems were popular in South Africa and Canada. Continuous resin-in-pulp (RIP) systems gained popularity in the United States since they eliminated a difficult and cosdy ore particle/leach hquor separation step. 

Ion Excha.nge, The recovery of uranium from leach solutions using ion exchange is a very important process (42). The uranium(VI) is selectively adsorbed to an anion-exchange resin as either the anionic sulfato or carbonato complexes. In carbonate solutions, the uranyl species is thought to be the tris carbonato complex, U02(C03) 3 [24646-13-7] and from sulfate solutions the anion is likely to be U02(S0 , where nis ) [56959-61-6] or 2 [27190-85-8], The uranium is eluted from the resin with a salt or acid solution of 1 AfMCl or MNO (M = H", Na", The sulfate solution is... 

The separation of basic precipitates of hydrous Th02 from the lanthanides in monazite sands has been outlined in Fig. 30.1 (p. 1230). These precipitates may then be dissolved in nitric acid and the thorium extracted into tributyl phosphate, (Bu"0)3PO, diluted with kerosene. In the case of Canadian production, the uranium ores are leached with sulfuric acid and the anionic sulfato complex of U preferentially absorbed onto an anion exchange resin. The Th is separated from Fe, A1 and other metals in the liquor by solvent extraction. 

Chloroform extraction of uranium quinoline complex Uranium adsorbed as azide on basic ion exchange column, uranium desorbed with 1 M hydrochloric acid Uranium adsorbed on bismuthol(II) modified anion exchange resin, desorbed with 0.1 M cysteine Uranium, by square wave adsorptive stripping voltammetry... 

Radioactivity of uranium can be measured by alpha counters. The metal is digested in nitric acid. Alpha activity is measured by a counting instrument, such as an alpha scintillation counter or gas-flow proportional counter. Uranium may be separated from the other radioactive substances by radiochemical methods. The metal or its compound(s) is first dissolved. Uranium is coprecipitated with ferric hydroxide. Precipitate is dissolved in an acid and the solution passed through an anion exchange column. Uranium is eluted with dilute hydrochloric acid. The solution is evaporated to near dryness. Uranium is converted to its nitrate and alpha activity is counted. Alternatively, uranium is separated and electrodeposited onto a stainless steel disk and alpha particles counted by alpha pulse height analysis using a silicon surface barrier detector, a semiconductor particle-type detector. 

After leaching, a concentration/pmification is done to get rid of other materials leached from the ore. This can be done by ion exchange or solvent extraction. In the ion exchange method, three steps are employed (a) the absorption of uranium from the leach liquor onto the resin, (b) the selective elution of uranium from the resin, and (c) the regeneration of the resin. Anion exchange is the preferred method of ion exchange with the relevant chemical reactions for acid leach being... 

Amine salts represent the only commercially important class of extractants of the anion-exchange type. Their most widespread use is in the extraction of uranium from sulfate leach liquors, but they have found application in the recovery of cobalt, zinc and copper from chloride solutions, as well as in the extraction of metals that readily form oxyanions, such as vanadium, molybdenum and tungsten. 

There are several uranium ore-bodies in the world that cannot be leached economically with sulfuric acid because of the high limestone content of the ore. Such ore-bodies are generally leached with an alkaline solution of sodium carbonate and bicarbonate. Carbonate also forms anionic complexes with the uranyl ion the predominant species being UC fCC 4- — and may therefore also be treated with anion-exchange resins. 

Anion exchange in hydrochloric acid/acetic acid medium for selective sorption of uranium as its anionic chloride/acetate complex (190, 191). 

Uranium U(VI) (also Fe, Co, Cu, Zn, and Cd) in 10 M HC1 solution is present in the form of the complex uranyl anion U02CI42, which is adsorbed on an anion exchange resin.43 44 Separation and purification of uranium from other elements is possible in sulfuric acid solution. When the H2S04 (aq) concentration is >0.01 M, uranium exists in the anionic forms U02(S04)22- and U02(S04)34. In contrast to uranium, other elements (Fe, Co, Cu, Zn, and Cd) do not form anionic complexes in sulfuric acid solution.34... 

Separation and Purification. In the Purex process discussed here, the uranium, plutonium, and fission products are separated by solvent extraction into three different streams (Fig. 21.20). The plutonium stream goes through anion exchange (discussed later) to reduce traces of ruthenium, and the uranium stream goes through silica gel sorption to reduce traces of zirconium. The fission-product stream, which contains the fission products... 

From the second cycle the plutonium goes through anion exchange for final purification (Fig. 21.21). The principal problem here is due to ruthenium, which is difficult to remove because of its many valence states. The uranium stream goes through silica sorption primarily to remove zirconium, which seems to be carried along as a colloid. 

After irradiation of the uranium target, it is dissolved in nitric acid and the final solution adsorbed on an alumina column that is washed with nitric acid to remove uranium (and other fission products). Molybdenum is finally eluted with ammonium hydroxide and further purified by absorption on an anion exchange column from which ammonium molibdate is eluted with dilute hydrochloric acid after washing the resin with concentrated HC1. The "Mo is obtained in no-carrier-added conditions, and the most common contaminants can be 131I and 103Ru. 

Certain long-chain alkylammonium salts, notably tricaprylmethyl-ammonium chloride (Aliquat 336-S) and tri-/so-octylamine hydrochloride (TIOA) are liquids, sometimes referred to as liquid anion exchangers, which can form extractable ion-pairs or aggregates with anionic metal complexes in the same way, e.g. in sulphuric acid solution uranium is extracted as 2(TIOA—H+), UOtfSOn ... 

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