JPS61281833A - Purifying method for cerium - Google Patents

Abstract

PURPOSE:To increase the selective extraction rate of Ce and to obtain high- purity Ce compounds in high yield by subjecting a Ce(IV)-nitrate solution to extractive refining together with tributylphosphoric acid or a tributylphosphoric acid-containing extractant by use of synthetic liquid paraffin as extractive diluent. CONSTITUTION:Crude oxides and/or crude hydroxides of Ce are dissolved in nitric acid and the nitric acid solution containing Ce and other rare-earth ions such as La, Pr, Nd, etc., is brought into contact with the tributylphosphoric acid or tributylphosphoric acid-containing extractant dissolved in the synthetic liquid paraffin as diluent. In this way, the oxidation number of Ce is kept tetravalent during the Ce-extracting stage to increase the selective extraction rate of Ce, so that the high-purity Ce compounds can be obtained in high yield. Further, Ce compounds of higher purity can be obtained by providing a washing stage after the above extracting stage.

Description

[Detailed description of the invention] [Objective of the invention] (Industrial use and decomposition) As a rare earth element, cerium has excellent physical and chemical properties, so it can be used as a magnetic material for the glass industry and as a catalyst for automobile exhaust gas. It is widely used for.

In the past, it was difficult to separate rare earth elements because their chemical properties were similar to each other, but in recent years advances in solvent extraction, ion exchange, and other technologies have made it possible for industrial use. Separation is now implemented. Solvent extraction is an effective method, especially when large amounts of raw materials are to be disposed of.

The present invention relates to a method for purifying cerium in large quantities with good yield by using a solvent extraction method using crude oxide and/or hydroxide of cerium as a raw material. The present invention makes it possible to industrially purify cerium with high yield, thereby greatly contributing to the industrial development of optical materials, magnetic materials, catalysts, and the like.

(Prior art) Conventionally, cerium was purified by solvent extraction by dissolving cerium crude oxide and/or crude hydroxide in nitric acid, and using the obtained cerium (IV) nitric acid solution as tributyl phosphorus r1i (hereinafter referred to as TBP). A method of selectively extracting cerium into an organic phase by contacting it with an extraction solvent using an aliphatic hydrocarbon such as n-paraffin, kerosene, or an aromatic hydrocarbon such as toluene as a diluent; A method of extraction using only TBP without using any agent has been carried out. Extraction using plain TBP has a high extraction rate of cerium, but the phase separation property deteriorates, which increases the amount of other rare earth elements that need to be separated, making it difficult to extract and obtain high-purity cerium. There are some drawbacks. In addition, when using hydrocarbons such as kerosene morro-paraffin or toluene as a diluent, the oxidizable substances contained in the system are oxidized during the extraction process due to the strong oxidizing power of cerium (IV value), and the cerium itself is is reduced to m-valent, and as a result, cerium (III) behaves similarly to m-valent non-cerium rare earth ions such as lanthanum, praseodymium, neodymium, etc., and the extraction rate of cerium becomes low. There was a big problem. In order to overcome this difficulty, various methods have been proposed in which an oxidizing agent such as potassium permanganate is co-existed in the extraction system, but all of them have been insufficiently effective.

(Problems to be Solved) The present invention maintains the oxidation number of cerium at IV value during the cerium extraction process, thereby increasing the selective extraction rate of cerium and producing high-yield, high-purity cerium. It is an attempt to obtain. Conventionally, a method has been proposed in which an oxidizing agent such as potassium permanganate or hydrogen peroxide is added to the extraction system to prevent the reduction reaction of cerium from the IV value to the M value, but the experimental results of the present inventors According to the study, no significant effect was observed. If trace amounts of oxidizable substances are present in the extraction solvent, the extraction rate of cerium will decrease, so it is of course important to purify the TBP used as the extractant or the extractant containing TBP. Its selection is an even more important issue as it greatly affects the extraction of

By using the diluent proposed in the present invention, the yield of extracted high-purity cerium compounds can be greatly improved compared to conventional methods, and by providing a washing step after the extraction step, It also becomes possible to obtain a highly purified cerium compound.

[Structure of the invention]

(Means and effects for solving the problem) The present invention dissolves cerium crude oxide and/or crude hydroxide in nitric acid, and dissolves cerium (IV) and other rare earth ions such as lanthanum, praseodymium, and neodymium. TBP containing nitric acid solution dissolved in synthetic liquid paraffin as a diluent
or by contacting with an extractant containing TAP,
The present invention relates to a method for purifying cerium with high yield.

Conventionally, diluents such as kerosene, n-paraffin, or toluene have been used, but when these are used, the extraction rate of cerium decreases due to the presence of oxidizable substances. In order to prevent this, as mentioned above, methods have been proposed in which various oxidizing agents are allowed to coexist in the system, but according to the research results of the present inventors, no significant effect was found in these methods. The inventors of the present invention continued to conduct intensive studies on diluents, oxidizing agents, etc., and found that when synthetic liquid paraffin was used as a diluent, cerium (I) as an oxidizing agent
The present invention was based on the discovery that a high extraction rate can be obtained with almost no effect of V). If synthetic liquid paraffin is used as a diluent, cerium can be extracted with high yield and purity, but this is because conventional kerosene, paraffin, etc. are extracted using fuming sulfuric acid,
This is thought to be because even though it is highly refined using sulfur trioxide or the like, it still contains cerium oxidizable substances derived from raw F1 petroleum. In the case of the synthetic liquid paraffin used in the present invention, highly purified olefins such as raw material C2,03 can be used, so cerium oxidized substances produced during the polymerization reaction process can be relatively easily separated by operations such as distillation. It is presumed that the

Since the substance to be oxidized by cerium that is present in the system during cerium extraction cannot be determined and is not known in detail, it is presumed that it slightly affects the yield during the cerium extraction process.

Although there are various kinds of synthetic liquid paraffins used in the present invention, liquid substances obtained by further refining a liquid mixture obtained by a polymerization reaction of purified C2 and/or C3 lower olefins by operations such as distillation are suitable. , is a substance that can be primarily used as a lubricant. Various synthetic liquid paraffins can be obtained depending on the polymerization reaction conditions, but when carrying out the present invention, those containing 10 to 20 carbon atoms as a main component can be used, such as those containing mainly C12, C1
Five-centered synthetic liquid paraffins and the like are suitable as diluents. Although it is not impossible to use compounds with a higher carbon number than this, they are not preferable because the viscosity increases during extraction. The extractant used in the present invention is TBP or an extractant containing TBP, and extractants that can be used as a mixture with TBP include, for example, neutral organic phosphorus compounds, such as orthophosphoric acid esters, phosphonates, and phosphinates. , any type of phosphine oxide can be used. To give specific examples, dibutyl butylphosphonate, butyl dibutylphosphonate, and tributylphosphine oxide are used as those having a butyl group, and trioctyl phosphate and trioctyl oxide in which the butyl group is replaced with an octyl group are used. Phosphine etc. are also used, but
It is not limited to these. Further, the concentration of the extractant in the extraction solvent is not particularly limited as long as the viscosity of the extraction solvent does not become high, but it is generally said that 5 to 50% by weight is suitable. When carrying out the present invention, a cerium compound can be obtained in a high yield by performing extraction using the synthetic liquid paraffin as a diluent. It is not always sufficient to obtain the compound stably.

To this end, the organic phase obtained by extracting cerium ions can be made highly pure by washing it with 4-11N diluted nitric acid, preferably 7-9N.6 Washing times of 6 times is usually sufficient. However, it is also possible to obtain a cerium compound of 99.99% or more by carrying out the process two or more times. When the present invention is to be carried out industrially, it can be applied to either a batch type or a continuous type (mixer-settler, tower type), but it is often advantageous to use a batch type because it is easy to operate. An example of an embodiment of the present invention will be described below with reference to FIG. The crude oxide and/or hydroxide of cerium 1 is heated and dissolved in concentrated nitric acid 8 in step (2), and diluted with dissolved condensate 9 to obtain a nitric acid refined solution. This solution is used as an extraction solvent in which TBP or an extractant containing TBP is dissolved in synthetic liquid paraffin as a diluent.10. Extracted in extraction step ①. The extraction time is preferably about 2 to 20 minutes, and is not preferably too long. After extraction, the phase is separated into an organic layer 11 and a raffinate 12, and the organic layer is washed with 4N to 11N, preferably 7 to 9N diluted nitric acid 13 in the washing step (1). Thereafter, after washing, the dilute nitric acid aqueous phase 14 and the organic phase 15 are separated.

The dilute nitric acid aqueous phase 14 can be recycled and reused in the cleaning step (2). The organic phase 15 is separated into an organic phase 17 and an aqueous phase 18 by performing back extraction in a back extraction step (2) with an aqueous solution 16 containing hydrogen peroxide in an amount equal to or more than the amount of cerium extracted into the organic phase.
The organic phase 17 is recycled and reused in the extraction step (2). Cerium is recovered from the aqueous phase 18, cerium hydroxide when alkaline water is added, cerium oxalate when M acid or oxalate is added, and cerium oxalate when carbonate or bicarbonate is added. Cerium carbonate is obtained in each case as cerium compound 19. The obtained cerium compound 19 is fired in the firing step (2) at a firing temperature depending on the firing temperature, whereby a high-yield, high-purity cerium oxide 7 can be obtained.

[Example] The present invention will be explained in more detail by referring to Examples below, in which the numbers are as shown in FIG.

(Example 1) Cerium content 176.3% (Ce02 /TREO)
5KCJ of crude cerium hydroxide was heated and dissolved in 35.11% of concentrated nitric acid in step (2), and diluted with dissolved condensate to give 50% of the crude cerium hydroxide. A synthetic liquid paraffin (based on C15) containing 20% (by volume) of a T-BP extractant and a C15-based diluent was added to a solution of Q and garlic.
Extraction solvent 100.1 using Matsumura Sekiyu process oil P-409108>! Extraction was carried out for 3 minutes in step ①. After extraction, separate into organic phase 11 and raffinate 12, and add organic phase 11 to 8.5N
It was washed with nitric acid aqueous solution 801 in step (2). After washing, it is separated into an aqueous phase 14 and an organic phase 15, and the organic layer 15 is filled with 3J of 35% hydrogen peroxide! Aqueous solution containing 100.1! Back extraction was performed in step ①. Thereafter, it was separated into an organic phase 17 and an aqueous phase 18, and diluted ammonia water was added to the aqueous phase 18 to recover cerium hydroxide, which was calcined at 700° C. in step (2) to obtain cerium oxide. The purity of cerium oxide is 99.93
% and the yield was 86%.

(Comparative Example 1) The same operation as in Example 1 was performed except that kerosene was used as the diluent. As a result, the recovered cerium oxide was 99%
．． The yield was 93% and 72%.

(Example 2) The same operation as in Example 1 was carried out, except that in step (1), the extracted organic phase was washed three times with an 8.degree. 5N nitric acid aqueous solution. As a result, the purity of cerium oxide was 99.99%, and the yield was 80%.

(Example 3) Using 5 kg of crude cerium hydroxide with a cerium content of 85.2% (Ce02 /TREO), the diluent was synthetic liquid paraffin mainly composed of CI2 (process oil P-
The purity of cerium oxide was 99.96% as a result of performing the same operation as in Example 1 except that 40910A> was used.
The yield was 90%.

(Example 4) Using the same raw materials and the same extraction solvent as in Example 1, the extraction in step (1) was performed for 3 minutes on the same amount scale, and after extraction, the organic phase 11
and raffinate residue 12. The organic phase 11 was mixed with 35% hydrogen peroxide 3 without performing the washing in post-separation step ①.
Aqueous solution 100 containing 9, i! Back extraction in step (2) was carried out. After that, it is separated into an organic phase 17 and an aqueous phase 18, and the aqueous phase 18
Dilute ammonia water was added to the mixture to recover cerium hydroxide, and this product was calcined at 700° C. in step (2) to obtain cerium oxide. The purity of cerium oxide was 99.2% and the yield was 89%.

[Effects of the Invention] By carrying out the present invention, as detailed in the specification, it is possible to produce a highly purified cerium compound with a high yield of 80% or more, which is very easy compared to the conventional method, and is useful for optical materials, magnetic materials, etc. It can contribute to the development of industries such as materials and catalysts.

[Brief explanation of the drawing]

FIG. 1 is a process diagram showing an actual tM aspect of the present invention.

Claims (3)

[Claims] (1) In a method of extracting and purifying a cerium (IV) nitric acid solution obtained by dissolving cerium crude oxide and/or crude hydroxide in nitric acid using tributyl phosphoric acid or an extractant containing tributyl phosphoric acid, A method for purifying cerium, characterized by using synthetic liquid paraffin as an extraction diluent. (2) Synthetic liquid paraffin is a liquid substance obtained by purifying the product obtained by polymerizing purified lower olefins having 2 and 3 carbon atoms, and is mainly composed of synthetic liquid paraffin having 10 to 20 carbon atoms. The method according to claim 1, which comprises as a component. (3) In the extraction and purification method using tributyl phosphoric acid or an extractant containing tributyl phosphoric acid, the organic phase obtained by extraction is washed with 4N to 11N dilute nitric acid, or The method described in Section 2.