JP3835487B2 - Rhodium purification method - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a rhodium purification method capable of separating and purifying rhodium in a high yield from a mixture of rhodium and other elements generated in a non-ferrous metal refining step and a treatment step of a platinum-containing spent catalyst.
[0002]
[Prior art]
As a purification method of rhodium, using the difference in complex stability of the nitrite complex salt, precipitates other than rhodium are precipitated, rhodium is left in the mother liquor, and then separated as crystals, and other platinum group elements are removed. As described in JP-A-4-22402, the method of adsorbing other platinum groups to strongly basic anion exchange resins and the separation of other base metals are described in JP-A-3-277730. There is known a method of adsorbing to a strongly acidic cation exchange resin as described in Japanese Patent Publication No. JP-A.
[0003]
[Problems to be solved by the invention]
However, in the method of mutual separation utilizing the complex stability of nitrite complex salt, rhodium also precipitates a considerable part in order to hydrolyze other impurities at a relatively high pH, and the purity of rhodium is sufficiently high. When this operation was repeated until the end, there was a problem that only about 20% of the initial rhodium could be recovered.
[0004]
On the other hand, when other platinum groups are separated by the anion exchange method, there is a problem that the adsorbed ions are not completely in the form of a chloro complex and are eluted together with rhodium, and the base metal element coexisting with the cation exchange method. On the other hand, when the chloro complex is separated, it is not adsorbed unless the chloro complex is completely decomposed. Therefore, even if the anion exchange method and the cation exchange method are combined, it is difficult to separate other platinum group and base metal elements.
[0005]
The present invention selectively and quantitatively separates impurities that have not completely formed a chloro complex and impurities that coexist as a chloro complex in which chloride ions are highly coordinated from rhodium, It is an object of the present invention to provide a method for recovering rhodium with high yield.
[0006]
[Means for Solving the Problems]
As a result of researches to solve the above problems and achieve the above object, the present inventor has found that, among impurities coexisting in rhodium, most of low basic impurities such as platinum group elements are tributyl phosphate. Extraction into the organic phase using the properties of forming adducts, and even if cationic impurities form chloro complexes, extraction with the carboxylic acid type takes advantage of the property of forming salts with carboxylic acids. In addition, the chloro complex salt of rhodium forms a sparingly soluble salt with an alkali cation having a large ionic radius, and is separated from impurities that cannot be separated by any method, and finally heated in a hydrogen stream. This is based on the knowledge that the components other than the metal component can be volatilized and removed. That is, in the present invention, an aqueous solution containing rhodium and chloride ions, in which impurities coexist, is mixed with tributyl phosphate, and then the aqueous phase is mixed with a higher carboxylic acid that is sparingly soluble in water. A method for purifying rhodium, in which a compound that forms a chloro complex salt of poorly soluble rhodium is dissolved, and the deposited crystals are thermally decomposed in a hydrogen stream, more specifically, an aqueous solution containing rhodium and chloride ions in which impurities coexist. Is mixed with tributyl phosphate to extract impurities, and while maintaining the pH of the obtained aqueous phase at 4 to 7, the aqueous phase is mixed with a higher carboxylic acid that is sparingly soluble in water. Extracted into an organic phase , ethylenediamine is dissolved in a newly obtained aqueous phase, and the precipitated crystals are thermally decomposed in a hydrogen stream.
[0007]
[Action]
The present invention has been made on the basis of the above knowledge, and among the impurities coexisting in rhodium, most of the low basic impurities such as platinum group elements are extracted with tributyl phosphate , and then are difficult to dissolve in water. Extract and remove most of the cationic base metal with a soluble higher carboxylic acid, add a compound that forms a chloro complex salt of poorly soluble rhodium, and precipitate rhodium as crystals, etc. In this method, the crystals separated from the impurities and finally precipitated are thermally decomposed in a hydrogen stream. That is, in the tributyl phosphate extraction step, the impurity element is extracted as a free acid of chloride or chloro complex ion. Platinum is the element that is most likely to accompany rhodium ions and is large in quantity, but since this element is extracted as a free acid of a chloro complex ion, the coexistence of hydrochloric acid is indispensable. Although the minimum required amount of hydrochloric acid is 2 times mol with respect to platinum, more complete extraction can be achieved by the presence of 2 to 7 mol / l hydrochloric acid in the aqueous phase during the extraction equilibrium. Unlike the anion exchange resin, this extractant is characterized by being capable of quantitatively extracting elements that have not completely formed chloride or chloro complex salts because extraction is performed by a solvation reaction. is there.
[0008]
In the extraction step using carboxylic acid, base metals that easily form cations are extracted by a cation exchange reaction. Copper, nickel, lead, etc., which are particularly abundantly contained as impurities, form chloro complex salts in chlorides and are incompletely reactive with strongly acidic sulfonic acid type cation exchangers, but are weak bases. Therefore, it is easy to form a stable bond with a weakly acidic carboxylic acid type cation exchanger, and a salt can be quantitatively formed even with ions initially present in the state of a chloro complex. As the carboxylic acid type cation exchanger, the extractant is suitable for this purpose because the extractant has a larger capacity for holding the metal and the selectivity with the platinum group is higher than that of the ion exchange resin. Industrially produced products include Versatic Acid-10 (VA-10, Shell Chemical Co., Ltd., trade name), naphthenic acid, etc., and petroleum-based solvents are used to reduce the viscosity. Good phase separation is achieved when diluted. In the carboxylic acid type extractant, hydrogen ions are released into the liquid simultaneously with the progress of the reaction. Therefore, it is necessary to raise the pH with an alkali or the like. However, if the pH is too high, the carboxylic acid becomes an alkali salt. In order to dissolve in the aqueous phase, it is desirable to maintain the pH in the range of 4-7.
[0009]
In the crystallization process of chloro complex salt, the hardly soluble salt of hexachlororhodium (III) acid, which is the chlorine complex salt of rhodium coordinated with the most chlorine, is precipitated to separate it from impurities that could not be separated in the above process. . As the cation source, volatile and decomposable ions having a large cation radius and difficult to remain in the subsequent dry hydrogen reduction process are suitable, and ammonium salts and polyethylene polyamines can be used. In view of the low solubility and easy industrial availability, ethylenediamine is suitable.
[0010]
Finally, the obtained crystals can be reduced in a hydrogen stream to remove volatile chlorides and obtain metal rhodium with very low impurities.
[0011]
【Example】
Next, examples of the present invention will be described.
Example
(1) Rh 75.4 g / l, pt 2.81 g / l, Pd 0.18 g / l, Fe 0.0012 g / l, Cu 0.05 g / l, Pb 0.11 g / l, Ni 0.03 g / l 2230 ml of an aqueous solution containing 1 and 5.5 mol / l of HCl was concentrated to 1460 ml and mixed with tributyl phosphate at a phase ratio of O / A = 1 / l for 10 minutes. As a result of analyzing the extraction residual liquid, it was lowered to Pt 0.09 g / l and Pd 0.004 g / l.
[0012]
(2) Mixing the tributyl phosphate extraction liquid with 50 V / V% VA-10 Cleansol G (Nippon Petroleum Corporation, trade name) so that the phase ratio is O / A = 1 / l. Extraction was performed with NaHCO ₃ such that the pH of the aqueous phase was 5.9. As a result of analyzing the extracted residual liquid, the base metal ions were reduced to Cu <0.001 g / l, Ni 0.001 g / l, Fe <0.001 g / l, and Pb <0.003 g / l.
[0013]
(3) To the extraction residual liquid of VA-10, 1560 ml of 6N HCl was added, and then ethylenediamine was added until the pH of the liquid became 0 while maintaining the liquid temperature at 18 ° C. The obtained crystal was maintained at 450 ° C. for 1 hour in a hydrogen stream. The quality of each element in the obtained rhodium is Pt 36 ppm, Pd 14 ppm, Fe <1 ppm, Cu <1 ppm, Pb <10 ppm, Ni 0.4 ppm, and the weight of Rh is 145.9 g. The yield based on the liquid was 86.8%.
[0014]
【The invention's effect】
The present invention relates to a platinum group impurity that does not completely form a chloro complex in the stock solution, or a cationic base metal that coexists as a chloro complex in which chlorine is highly coordinated and is difficult to separate with a cation exchange resin. Even if impurities coexist, it can be selectively and quantitatively separated from rhodium, and further, rhodium can be recovered in a high yield.

Claims (1)

An aqueous solution containing rhodium and chloride ions and coexisting with impurities is mixed with tributyl phosphate, the impurities are extracted, and then the aqueous phase is made into water while maintaining the pH of the obtained aqueous phase at 4-7. Rhodium, which is mixed with a slightly soluble higher carboxylic acid, further extracts impurities into the organic phase, dissolves ethylenediamine in the newly obtained aqueous phase, and thermally decomposes the precipitated crystals in a hydrogen stream Purification method.