JP7017780B2 - Rhodium recovery method - Google Patents

Description

The present invention relates to a rhodium recovery method.

Rhodium is one of the rarest and most expensive precious metals, and its production areas are unevenly distributed, so recycling is essential for stable supply. For example, rhodium is used as a catalyst for purifying automobile exhaust gas together with platinum and palladium, and when recycling, a technique for selectively recovering rhodium from a solution containing platinum or palladium is required.

Generally, a method such as an electrolytic precipitation method, a cementation method, an ion exchange method, or a solvent extraction method is used for recovering a noble metal. Among these methods, a solvent extraction method having excellent economic efficiency and operability is widely used. For example, a method for selectively recovering palladium from a solution containing a plurality of noble metals by a solvent extraction method using a dialkyl sulfide is known (Patent Document 1). However, since rhodium does not have an extractant that can be efficiently and selectively recovered, it has been recovered from the extraction residue after extracting other precious metals (Patent Document 2). Such a method has a problem that the recovery cost is high because the recovery of rhodium, which is the most expensive precious metal, is postponed.

An example using a pyridine ring-containing compound has been reported as a rhodium recovery technique by a solvent extraction method (Patent Document 3). The extractant can separate rhodium from the base metal, but does not describe the separation from platinum or palladium. Further, in the example using the imidazole derivative, the separation between gold and platinum and rhodium was achieved to some extent, but the separation from palladium was not possible (Patent Document 4). It has been reported that separation of platinum and palladium from rhodium is possible by using an amide-containing tertiary amine compound (Patent Document 5). In this method, all metals are extracted into the organic phase by contacting the organic phase containing the extractant with the aqueous phase containing platinum, palladium and rhodium. Then, by contacting the organic phase with a high-concentration hydrochloric acid solution, only rhodium is back-extracted into the aqueous phase to selectively recover rhodium. However, in such a method, since at least two extraction steps are required to separate rhodium, there is a problem that a large amount of waste liquid is required and the cost is increased due to the increase in the steps. In addition, since rhodium is a method of selectively removing only rhodium from the extractant by utilizing the fact that rhodium is less likely to be adsorbed by the extractant than platinum and palladium, it is a principle to recover only rhodium at the initial extraction stage. Is impossible.

In addition, the present inventors have proposed a method for recovering rhodium by adding a predetermined amine to a hydrochloric acid solution containing rhodium to form a precipitate (Patent Documents 6 and 7).

Japanese Unexamined Patent Publication No. 9-279264 Japanese Unexamined Patent Publication No. 2004-332401 Japanese Unexamined Patent Publication No. 5-295458 Japanese Unexamined Patent Publication No. 2013-032563 International Publication No. 2009/001897 Japanese Unexamined Patent Publication No. 2017-179409 International Publication No. 2017/170444

However, in the recovery methods described in Patent Documents 6 and 7, it is necessary to add an excessive amount of amine to rhodium in order to sufficiently recover rhodium, and there is room for improvement in terms of cost and efficiency. .. It is an object of the present invention to provide a new rhodium recovery method which is advantageous in terms of cost and efficiency.

Rhodium chloride anions are difficult to form ion pairs, and there has been no example of analyzing the structure of ion pairs. Therefore, although the detailed structure of the precipitates produced in Patent Documents 6 and 7 was unknown, in general, an ion pair in which three ammonium cations are bonded to a trivalent rhodium chloride anion is formed. It was thought to be done.
However, the present inventors have performed single crystal X-ray measurement, powder X-ray measurement, thermoweight analysis, XPS measurement, etc. on the precipitate to obtain six ammonium cations for one rhodium chloride anion. It was found that the complex was surrounded by and contained three chloride anions to cancel the entire charge.
Based on the above findings, the present inventors can recover rhodium by a new method by using an amount of amine necessary and sufficient to form the complex and an organic solvent capable of dissolving the complex. We found that there was, and completed the following invention.

The first invention recovers rhodium from a mixture containing rhodium using a rhodium recovery agent containing at least one amine compound selected from an aromatic primary amine compound or an aliphatic primary amine compound. The rhodium recovery agent, the mixture, and the organic solvent are added to hydrochloric acid to form a complex of the amine compound represented by the formula (1) and rhodium chloride, and the complex is used as the organic solvent. It is a method of recovering rhodium.

（式（１）中のＺは、アミン化合物の残基を表す。）

(Z in the formula (1) represents a residue of the amine compound.)

In the first invention, the molar ratio (NH ₂ / Rh) of the amino group of the amine compound to rhodium in the mixture is preferably 6 or more and less than 20.

In the first invention, the organic solvent is preferably any one or a mixture of chloroform, dichloromethane, toluene and xylene.

In the first invention, the aromatic primary amine compound is preferably a compound represented by the following formula (2).

（式（２）中のＸは、炭素数２以上１２以下の直鎖または分岐鎖のアルキル基、または、炭素数２以上１０以下の直鎖または分岐鎖のアルコキシ基である。）

(X in the formula (2) is a linear or branched alkyl group having 2 or more and 12 or less carbon atoms, or a linear or branched alkoxy group having 2 or more and 10 or less carbon atoms.)

In the first invention, the aliphatic primary amine compound is preferably a compound represented by the following formula (3).

（式（３）中のＹは、炭素数６以上１４以下の直鎖または分岐鎖のアルキル基である。）

(Y in the formula (3) is a linear or branched alkyl group having 6 or more and 14 or less carbon atoms.)

In the first invention, the concentration of hydrochloric acid is preferably 2 mol / L or more and 12 mol / L or less.

The present invention is a novel rhodium recovery method that is advantageous in terms of cost and efficiency.

It is a schematic diagram which shows the structure of a single crystal obtained by the single crystal X-ray diffraction measurement. It is a powder X-ray diffraction pattern (Calculated) predicted from a single crystal and a powder X-ray diffraction pattern (Measured) of a precipitate. It is an XPS spectrum of a precipitate prepared using 4-hexylamine. It is a thermogravimetric analysis result of the precipitate prepared using 4-hexylamine. It is a figure which showed the rhodium extraction rate when the addition amount of 4-butylaniline was changed. It is a figure which shows each metal extraction rate at the time of using 4-hexylaniline. It is a figure which shows the rhodium precipitation rate at the time of changing the addition amount of 4-butylaniline. It is a figure which shows the rhodium extraction rate at the time of changing the hydrochloric acid concentration using 4-hexylaniline. It is a figure which shows the rhodium extraction rate at the time of changing the shaking time using 4-hexylaniline.

[Rhodium recovery method]
The present invention is a method for recovering rhodium from a mixture containing rhodium by using a rhodium recovery agent containing at least one predetermined amine compound, and by using a predetermined rhodium recovery agent and an organic solvent. It is a method of forming a predetermined complex and recovering the complex in an organic solvent. If the recovery method of the present invention is described for each step, it can be divided into, for example, an addition step, a mixing step, and a rhodium recovery step, which will be described below in that order.

<Addition process>
In the addition step, a rhodium recovery agent, a mixture containing rhodium, and an organic solvent are added to hydrochloric acid.
The present invention is characterized in that rhodium is recovered from a hydrochloric acid solution containing rhodium by using a predetermined rhodium recovery agent and an organic solvent, and there is also a form in which other parts that do not affect the characteristics are appropriately modified. Included in the scope of the invention. For example, the addition here also includes a form in which a rhodium recovery agent and an organic solvent are added to a hydrochloric acid solution in which rhodium is dissolved from the beginning without adding a mixture containing rhodium to hydrochloric acid.

(Rhodium recovery agent)
The rhodium recovery agent used in the present invention contains at least one amine compound selected from an aromatic primary amine compound or an aliphatic primary amine compound.
The aromatic primary amine compound is preferably a compound represented by the following formula (2).

（式（２）中のＸは、炭素数２以上１２以下の直鎖または分岐鎖のアルキル基、または、炭素数２以上１０以下の直鎖または分岐鎖のアルコキシ基である。）

(X in the formula (2) is a linear or branched alkyl group having 2 or more and 12 or less carbon atoms, or a linear or branched alkoxy group having 2 or more and 10 or less carbon atoms.)

The alkyl group of X preferably has 3 or more and 11 or less carbon atoms, and more preferably 4 or more and 10 or less. Further, it is preferably a linear alkyl group. Preferred alkyl groups of X include butyl groups, hexyl groups and decyl groups.

The alkoxy group of X preferably has 3 or more and 9 or less carbon atoms, and more preferably 4 or more and 8 or less. Further, it is preferably a linear alkoxy group. Preferred examples of the alkoxy group X include a butoxy group and an octyloxy group.

The aliphatic primary amine compound is preferably a compound represented by the following formula (3).

（式（３）中のＹは、炭素数６以上１４以下の直鎖または分岐鎖のアルキル基である。）

(Y in the formula (3) is a linear or branched alkyl group having 6 or more and 14 or less carbon atoms.)

The alkyl group having Y is preferably 7 or more and 13 or less carbon atoms, and more preferably 8 or more and 12 or less carbon atoms. Further, it is preferably a linear alkyl group. Examples of the alkyl group which is preferable Y include an octyl group and a dodecyl group.

As the rhodium recovery agent used in the present invention described above, it is preferable to use an aromatic primary amine compound from the viewpoint of selective extraction of rhodium.

In the rhodium recovery agent used in the present invention, the complex with rhodium described later may be dissolved in an organic solvent, and the rhodium recovery agent itself does not necessarily have to be dissolved in an organic solvent. In that respect, it is different from the conventional solvent extraction method, and the range of application of the recovery agent is widened in that a recovery agent that cannot be used by the conventional solvent extraction method can be used.

The amount of the rhodium recovery agent added may be an amount necessary and sufficient for forming the complex shown below. Therefore, the molar ratio (NH ₂ / Rh) of the amino group of the amine compound constituting the rhodium recovery agent to rhodium in the mixture is preferably 6 or more and 20 or less, and the upper limit is 12 or less from the viewpoint of efficiency. It is more preferably less than 10, further preferably 9 or less, and particularly preferably 8 or less. Further, from the viewpoint of appropriately forming the complex shown below, the lower limit is preferably 6 or more, but the amount of amine may be reduced while slightly reducing the efficiency, and from that point of view, the lower limit is 6. May be slightly lower than. However, even in that case, the lower limit is preferably 5.8 or more, and more preferably 5.9 or more, from the viewpoint of recovery efficiency.

(Mixture containing rhodium)
The mixture contains at least rhodium and may further contain other metals and noble metals. According to the findings of the present inventors, even if the mixture contains at least one selected from palladium and platinum as a noble metal other than rhodium, rhodium can be preferentially recovered by the rhodium recovery agent of the present disclosure. For example, the catalyst for purifying automobile exhaust gas itself can be applied as a mixture.

(Organic solvent)
As the organic solvent used in the present invention, various ones can be used without particular limitation as long as the complex described later can be dissolved. Further, two or more kinds of organic solvents may be mixed and used. Examples of the organic solvent include chloroform, dichloromethane, toluene and xylene, and a mixture thereof may be used. Further, as the organic solvent, a solvent that is completely compatible with water cannot be used.

(hydrochloric acid)
The concentration of hydrochloric acid used in the present invention preferably has a lower limit of 2.0 mol / L or more, more preferably 3.0 mol / L or more, still more preferably 4.0 mol / L or more, from the viewpoint of rhodium extraction rate. 9.0 mol / L or more is particularly preferable. Further, in the method of the present invention, the following complex can be dissolved in an organic solvent (preferably a chlorine-based organic solvent) even in high-concentration hydrochloric acid, so that the upper limit of the hydrochloric acid concentration is not particularly limited, but practically. Is preferably 12.0 mol / L or less, more preferably 10 mol / L or less, further preferably 9.0 mol / L or less, and particularly preferably 8.0 mol / L or less.
Further, from the viewpoint of exhibiting high rhodium selectivity, the concentration of hydrochloric acid is preferably 2.5 mol / L or more. Further, in the present invention, the rhodium recovery agent recovers not only rhodium but also other noble metal elements in hydrochloric acid having a concentration of less than 2.0 mol / L.

<Mixing process>
In the mixing step, the above-mentioned rhodium recovery agent, a mixture containing rhodium, an organic solvent, and hydrochloric acid are mixed to form a complex of an amine compound and rhodium chloride.
Mixing can be done by shaking or stirring. The shaking conditions and stirring conditions are not particularly limited, and the conditions that have been adopted so far in solvent extraction can be appropriately adopted. The shaking and stirring time is preferably 1 minute or longer, more preferably 5 minutes or longer, and even more preferably 10 minutes or longer. The upper limit is not particularly limited, but it is preferably 60 minutes or less from the viewpoint of efficiency because the effect of stirring is not seen when the time is about 60 minutes or more.

(Complex)
The structure of the complex of the amine compound and rhodium chloride formed in the rhodium recovery method of the present invention is as follows.

（式（１）中のＺは、アミン化合物の残基を表す。）

(Z in the formula (1) represents a residue of the amine compound.)

Rhodium forms a trivalent rhodium chloride anion ([RhCl ₆ ] ^3- ) in hydrochloric acid. Until now, the structure of the complex was unknown, but it was thought that a person skilled in the art would form an ion pair in which three ammonium cations were bound to a trivalent rhodium chloride anion. .. However, the present inventors have found that the complex of the above formula (1) is formed by various analyzes, which will be shown later.
In the complex of the formula (1), six ammonium cations and three chloride anions are complexed with respect to the trivalent rhodium chloride anion.
In formula (1), Z represents a residue of the above-mentioned amine compound. Therefore, when the amine compound is an aromatic primary amine compound, Z represents "X-Ph-", and when the amine compound is an aliphatic primary amine compound, Z represents "Y-". ..

In the present invention, the rhodium recovery agent does not necessarily have to be dissolved in an organic solvent, as described above, but the complex of the formula (1) needs to be dissolved in an organic solvent. From that point of view, a suitable organic solvent is selected.

<Rhodium recovery process>
The complex dissolved in the organic solvent formed in the above-mentioned mixing step can be recovered, and rhodium can be recovered after a predetermined purification operation. The purification operation is not particularly limited, and examples thereof include a method of extracting only rhodium with a basic aqueous solution and a method of burning a complex.

<Reference example 1>
4-Hexylaniline was added to a 6 mol / L hydrochloric acid solution containing 100 ppm of rhodium so that the molar ratio with rhodium (NH ₂ / Rh) was 30, and the mixture was shaken for 3 hours. The generated precipitate was collected by filtration and washed with 2 mol / L hydrochloric acid water. The obtained precipitate was dried under reduced pressure at room temperature, and then powder X-ray diffraction measurement (FIG. 2), XPS measurement (FIG. 3) and thermogravimetric analysis (FIG. 4) were performed. Further, this precipitate was dissolved in 1 mol / L hydrochloric acid water and left for a long period of time to prepare a single crystal. Single crystal X-ray diffraction measurement was performed on the obtained single crystal (FIG. 1).

As a result of single crystal X-ray diffraction measurement, the complex is expected to have the structure shown in FIG. FIG. 2 shows a powder X-ray diffraction pattern. The upper row is a powder X-ray diffraction pattern expected from a single crystal, and the lower row is a powder X-ray diffraction pattern of the precipitate after rhodium recovery with hexylaniline. From the fact that the two data are almost the same, it was confirmed that the precipitate formed during rhodium recovery is a complex with Rh: amine of 1: 6, which is the same as that of the single crystal.

Further, from the XPS measurement results shown in FIG. 3, the atomic ratio of the precipitate calculated from the XPS peak is N: Cl: Rh = 6.1: 8.8: 1.0, whereas FIG. 1 The atomic ratio (theoretical value) obtained from the structure of N: Cl: Rh = 6: 9: 1.

Further, as shown in FIG. 4 by thermogravimetric analysis (under an air atmosphere), the obtained precipitate was subjected to thermogravimetric analysis at 700 ° C., and as a result, a residue of 8.6% was obtained. Further, it has been reported that RhCl ₃ produces Rh ₂ O ₃ by combustion in an oxidizing atmosphere of 900 ° C. or lower (Thermochimica Acta, 2005, 435, 151-161.). Then, the theoretical value of Rh ₂ O ₃ when the complex shown in FIG. 1 was burned was 8.5%, which was almost the same as the theoretical value and the result of thermogravimetric analysis.
From all the above analysis results, it was clarified that the precipitate was a complex consisting of [RhCl ₆ ] ^3- and 6 amines.

<Reference example 2>
Aniline, 4-butylaniline, 4-hexyloxyaniline, 4-phenoxyaniline, and n-octylamine were used in place of 4-hexylaniline as the amine compound in the same operation as in Example 1, and precipitation was performed. Obtained. The obtained precipitate was subjected to thermogravimetric analysis. The results are shown in Table 1.

From the results shown in Table 1, the residue of the precipitate was almost in agreement with the theoretical value in each case. From this, it was found that amines other than 4-hexylaniline also formed a complex of Rh: amine = 1: 6.

<Example 1>
To 3 mL of a 6 mol / L hydrochloric acid solution containing 100 ppm rhodium, 4-butylaniline was added so that the molar ratio (NH ₂ / Rh) with rhodium was 3, 6, 9 and 30, respectively, and 0.75 mL of chloroform was added. In addition, it was shaken for 30 minutes. The aqueous layer was recovered and the concentration of rhodium contained in the aqueous solution was analyzed by ICP to calculate the proportion of rhodium transferred to the organic layer (rhodium extraction rate). The results are shown in FIG. The results of the molar ratio 6 are also shown in Table 2.
It was found that when the molar ratio (NH ₂ / Rh) was 6 or more, a high extraction rate of more than 50% was exhibited.

<Example 2>
As the amine compound, 4-hexylaniline, 4-decylaniline, 4-butoxyaniline, 4-octyloxyaniline, n-octylamine, and n-dodecylamine were used instead of 4-butylaniline in the same manner as in Example 1. An experiment was carried out by operation, and the rhodium extraction rate was calculated. The results are shown in Table 2.

<Example 3>
The experiment was carried out in the same manner as in Example 1 using 4-butylaniline as the amine compound, 4-hexylaniline as the organic solvent, chloroform and toluene as the organic solvent, and the rhodium extraction rate was calculated. .. The results are shown in Table 3.

溶媒を替えた場合でも、高いＲｈ抽出率を示した。

Even when the solvent was changed, a high Rh extraction rate was shown.

<Example 4>
Add 4-hexylaniline to 3 mL of 6 mol / L hydrochloric acid containing 100 ppm each of palladium, platinum and rhodium so that the molar ratio to rhodium (NH ₂ / Rh) is 6, and then add 0.75 mL of chloroform to 30 Shake for a minute. The aqueous layer was recovered and the concentrations of palladium, platinum and rhodium contained in the aqueous solution were analyzed by ICP to calculate the proportion of metal transferred to the organic layer (metal extraction rate). The results are shown in FIG.
As shown in FIG. 6, Rh could be selectively extracted. The extraction rates were 0% for Pd, 1% for Pt, and 70% for Rh.

<Comparative Example 1>
4-Butylaniline was added to 3 mL of a 6 mol / L hydrochloric acid solution containing 100 ppm of rhodium so that the molar ratio (NH ₂ / Rh) with rhodium was 3, 6, 9, 12, 15, 20, and 30, respectively. After shaking for 3 hours, the precipitate was separated by centrifugation. The supernatant was collected and the concentration of rhodium contained in the aqueous solution was analyzed by ICP to calculate the proportion of rhodium contained in the precipitate (rhodium precipitation rate). The results are shown in FIG. The results of the molar ratio 6 are shown in Table 4.
When the molar ratio (NH ₂ / Rh) was 9 or less, the Rh extraction rate was almost zero, and even when the molar ratio was 15, the extraction rate was about 50%.

<Comparative Example 2>
Using 4-butoxyaniline and n-octylamine instead of 4-butylaniline as the amine compound, an experiment was carried out in the same manner as in Comparative Example 1 to calculate the rhodium precipitation rate. The results are shown in Table 4.

アミンを変更した場合であっても、表４に示したモル比では、Ｒｈ抽出率はゼロであった。

Even when the amine was changed, the Rh extraction rate was zero at the molar ratios shown in Table 4.

<Example 5>
Add 4-hexylaniline to 3 mL of a 1-8 mol / L hydrochloric acid solution containing 100 ppm rhodium so that the molar ratio to rhodium (NH ₂ / Rh) is 12, add 0.75 mL of chloroform, and shake for 30 minutes. I let you. The aqueous layer was recovered and the concentration of rhodium contained in the aqueous solution was analyzed by ICP to calculate the proportion of rhodium transferred to the organic layer (rhodium extraction rate). The results are shown in FIG.

<Example 6>
Add 4-hexylaniline to 3 mL of a 6 mol / L hydrochloric acid solution containing 100 ppm rhodium so that the molar ratio to rhodium (NH ₂ / Rh) is 12, and then add 0.75 mL of chloroform for 1 minute and 5 minutes, respectively. It was shaken for minutes, 10 minutes, 20 minutes, 30 minutes, and 60 minutes. The aqueous layer was recovered and the concentration of rhodium contained in the aqueous solution was analyzed by ICP to calculate the proportion of rhodium transferred to the organic layer (rhodium extraction rate). The results are shown in FIG.

Claims (6)

A method for recovering rhodium from a mixture containing rhodium by using a rhodium recovery agent containing at least one amine compound selected from an aromatic primary amine compound or an aliphatic primary amine compound. Recovery of rhodium, in which a rhodium recovery agent, the mixture and an organic solvent are added to hydrochloric acid to form a complex of an amine compound represented by the formula (1) and a rhodium chloride, and the complex is recovered in an organic solvent. Method.

(Z in the formula (1) represents a residue of the amine compound.) The method for recovering rhodium according to claim 1, wherein the molar ratio (NH ₂ / Rh) of the amino group of the amine compound to rhodium in the mixture is 6 or more and 20 or less. The method for recovering rhodium according to claim 1 or 2, wherein the organic solvent is any one or a mixture of chloroform, dichloromethane, toluene, and xylene. The method for recovering rhodium according to any one of claims 1 to 3, wherein the aromatic primary amine compound is a compound represented by the following formula (2).

(X in the formula (2) is a linear or branched alkyl group having 2 or more and 12 or less carbon atoms, or a linear or branched alkoxy group having 2 or more and 10 or less carbon atoms.) The method for recovering rhodium according to any one of claims 1 to 3, wherein the aliphatic primary amine compound is a compound represented by the following formula (3).

(Y in the formula (3) is a linear or branched alkyl group having 6 or more and 14 or less carbon atoms.) The method for recovering rhodium according to any one of claims 1 to 5, wherein the concentration of hydrochloric acid is 2 mol / L or more and 12 mol / L or less.

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