Extraction and separation of uranium, thorium and rare earth by TBP-HNO3 system
First, the principle of the process
Extraction of thorium and uranium from a nitric acid solution using TBP is one of the most effective methods. During the extraction process, Th(NO 3 ) 4 and TBP generate Th(NO 3 ) 4 · 2TBP, and silicate silicate and TBP generate UO 2 (NO 3 ) 2 · 2TBP can be extracted. However, the distribution ratio of uranium is higher than that of strontium and is more easily extracted. Since the separation coefficient of uranium and thorium varies with the concentration of TBP, that is, the separation coefficient at low concentration is higher than that at high concentration. Therefore, the separation process uses a method of preferentially extracting uranium at a concentration of 5% TBP, followed by extraction of lanthanum and rare earth with 40% TBP (see Figure 1). It is also possible to extract ruthenium, uranium and rare earth by first 30% TBP extraction, and then extract and separate uranium and plutonium with 5% TBP concentration, followed by extraction and purification of ruthenium by 40% TBP (see Figure 2).
FIG 2 TBP- kerosine Extraction RE / Th / U Process
In addition, the distribution ratio of hydrazine is related to the concentration of hydrazine in the aqueous phase and the concentration of nitric acid. When the concentration of rhodium in the aqueous phase is low and the concentration of TBP in the organic phase is high, the concentration of D th nitric acid increases. Conversely, if the concentration of rhodium in the aqueous phase is high, D th is not affected much by the acidity.
If the solution contains tetravalent cerium , it is difficult to separate because it is similar to hydrazine. When extracting hydrazine, hydrogen peroxide can be added to reduce tetravalent cerium to trivalent, and the separation coefficient of cerium and lanthanum can be increased to enhance the separation effect of cerium and lanthanum.
In this process, uranium is extracted with 5% TBP, and the uranyl nitrate-containing solution obtained by back-extracting is purified by oxalic acid precipitation to remove strontium and rare earth, and then ammonia gas is introduced to precipitate uranium ammonium urate. The remaining uranium extract contains antimony, rare earth and impurities such as iron and titanium . The solution is extracted with 40% TBP, and the anti-extraction solution is subjected to concentrated crystallization to recover cerium nitrate. The residual liquid of the extracted ruthenium can be used to recover rare earth.
Second, the process
The process flow of extracting and separating uranium, thorium and rare earth by TBP-HNO 3 system is shown in Fig. 1.
Figure 1 Process of extracting and separating uranium, thorium and rare earth from TBP-HNO 3 system
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