JPH03102298A - Recovery of palladium - Google Patents

Abstract

PURPOSE:To enable recovery of a palladium Pd by adding an ascorbic acid to a solution containing platinum group elements, such as a high level radioactive liquid waste. CONSTITUTION:After decreasing nitric acid concentration of a high level radioactive liquid waste down to some 0.5 to 0.3M and removing a Zr, a Mo and a Te as a precipitation, a Pd can be solely and selectively recovered by adding an ascorbic acid to make the concentration to be 0.0588M and agitating under room temperature for 15 minutes. In this occasion, by increment of an adding amount of the ascorbic acid, a recovery efficiency of the Pd is much improved. Also, by adding an oxalic acid after addition of the ascorbic acid, the Pd, with transuranium elements and rare earth elements, can be recovered as a precipitation at higher recovery ion efficiency. In this case, the transuranium elements and the rare earth elements can be easily separated from the Pd during a dissolving stage of the oxalic acid.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a palladium recovery method.

Palladium is widely used in electrodes and catalysts, but like other platinum group elements, it exists in relatively small quantities on Earth, and is produced only in a limited number of countries. As a means to alleviate these situations, methods of recovering platinum group elements including palladium from spent nuclear fuel are being considered.

Approximately 1.4 kilograms of palladium are contained per ton of spent nuclear fuel, but it is said that during reprocessing, about 25% is transferred to undissolved residue, and most of the rest is transferred to high-level radioactive waste liquid. There is. The present invention can be used not only to recover palladium from high-level radioactive waste liquids, but also to selectively separate palladium from solutions containing only platinum group elements such as ruthenium and rhodium.

(Prior technology) As methods for recovering platinum group elements from high-level radioactive waste liquid, lead extraction method, molten metal extraction method, solvent extraction method, ion exchange method, adsorption method, electrolytic reduction method, precipitation method, etc. have been studied. However, in either method, the collection operation is complicated, and these methods are not necessarily superior in terms of economy and safety. The precipitation method is considered to be a method that is relatively easy to put into practical use, but the methods considered so far involve adding formic acid to high-level radioactive waste liquid and decomposing nitric acid by heating it, reducing the acidity of the waste liquid. This is a method of recovering platinum group elements as a precipitate by forming a solution with a p112 level. Palladium can be recovered simultaneously with ruthenium and rhodium by this method, but the disadvantage of this method is that zirconium, molybdenum, tellurium, iron, chromium, etc. precipitate at the same time when the acidity of the solution is set to about p12. , it is also difficult to control the acidity of the solution,
There is a possibility that the acidity will be further reduced, and in that case, the types and amounts of precipitated elements will increase significantly.

(Problems to be Solved by the Invention) An object of the present invention is to provide a method for improving these drawbacks, that is, a method for recovering palladium as a precipitate by reducing the types and amounts of impurity elements that are simultaneously precipitated. It is.

(Means for Solving the Problem) As a result of intensive research, the inventor of the present application has determined that zirconium, molybdenum, and tellurium can be precipitated by reducing the nitric acid concentration of high-level radioactive waste liquid to about 0.5 M to 0.3 M. palladium can be selectively recovered as a precipitate by adding ascorbic acid after removing it as a precipitate;
They also discovered that if oxalic acid is added after ascorbic acid, palladium can be recovered as a precipitate at a higher yield along with transuranic elements and rare earth elements. It was discovered that palladium with little contamination could be recovered, and the object of the present invention was achieved.

Note that in the method of adding oxalic acid after ascorbic acid, transuranic elements and rare earth elements will precipitate at the same time as oxalates, but they can be easily separated from palladium at the stage of dissolving the oxalates. <Examples> Next, the present invention will be explained in more detail by showing examples. However, the present invention is not limited to this example.

After adding 1.5 times the equivalent of nitric acid concentration of formic acid to a flask containing a 2M nitric acid solution of the elements shown in column A of Table 1, which simulated a high-level radioactive waste liquid, 2.5 times the concentration of formic acid was added under reflux. Denitrification was performed by heating for an hour. To remove the precipitate, the solution was filtered with Toyo Filter Paper No. 1 after being allowed to cool. Filtered at 5C. The concentration of the element in the filtrate was measured by optical emission spectrometry, etc., and the ratio of the element remaining in the filtrate was determined relative to the amount of the element in the simulated waste liquid using the results, which are shown in Table 1 B4'ljl. Ascorbic acid was added to this filtrate to give a concentration of 0.0588M, and the mixture was stirred at room temperature for 15 minutes.

The resulting precipitate was filtered in the same manner as described above, and the ratio of the elements remaining in the filtrate was determined relative to the amount of elements in the simulated waste liquid initially used. The results are shown in Table 1 CIM. Also, at the same time as ascorbic acid was added, 0.0% of oxalic acid was added. The results obtained when adding 4M are shown in column D of Table 1.

As is clear from these results, most of zirconium, molybdenum, and tellurium, as well as some of ruthenium, rhodium, and iron were precipitated by denitrification, but palladium was transferred to the filtrate. By adding ascorbic acid to this filtrate, only palladium could be selectively recovered as a precipitate without any heating operation. In the experiment, about 85% of palladium was precipitated, but by increasing the amount of ascorbic acid added, the palladium recovery rate can be made higher.Furthermore, when oxalic acid is added, It was found that almost 100% of neodymium, which was selected as a representative of transuranium elements and rare earth elements, precipitated, and at the same time, almost 100% of palladium precipitated.

(Effects of the Invention) Thus, the palladium recovery method of the present invention can selectively recover palladium as a precipitate by adding ascorbic acid to a solution containing a platinum group element such as a high-level radioactive waste liquid.

element Nd Sr. CS Fe Cr Ni Na Ba Rb Te M.O. Zr Ru Pd Rh Column A simulated waste 冫ffl　冫1-i degree (M) 0.127 0.0165 0.0371 0.038 0.0091 0.0060 0.076 0.0207 0.0074 0.0068 0.069 0.069 0.034 0.018 0.0080 Recruitment Column B Ca Denitration Ascol Bic acid (χ) Addition (X) 99103 100 99 100 98 8887 98100 103 102 100 102 100 99 100 96 0.60 5.0 4.7 0.20 7775 101 15 7473 Column D ascorbine acid + oxalic acid Addition (%) 0 91 96 87 lO0 99 97 98 91 0 4.0 0 75 0. 2 71 Procedural master's letter (spontaneous) Flat Fri. 1st year 1st month

Claims (1)

[Claims] A palladium recovery method characterized by recovering palladium as a precipitate by adding ascorbic acid to a solution containing platinum group elements such as high-level radioactive waste liquid.