JP3480216B2 - Separation method of platinum and ruthenium - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for separating each platinum group element from an aqueous solution containing a platinum group element generated in a nonferrous metal smelting process or the like, and more particularly to a method for separating platinum and ruthenium.

[0002]

2. Description of the Related Art When each platinum group element is separated from an aqueous solution containing a platinum group element generated in a non-ferrous metal smelting process, for example, palladium (Pd) is widely used as an extractant for selectively extracting osmium (Pd). Various methods have been adopted for each element, such as Os being volatilized and safely and easily separated.

Among them, platinum (Pt) and ruthenium (R
u) is relatively difficult to separate, and Rev. Met is industrially used.
Al. Madrid, 31 (4), 1995, the oxidative distillation method is mainly used. The oxidative distillation method is a volatile ruthenium oxide (VIII) which is obtained by oxidizing ruthenium with a strong oxidizing agent such as halogen.
After generating RuO ₄ , the aqueous solution is heated to separate ruthenium oxide as a gas, which is then collected by the absorbent.

However, since RuO ₄ is chemically unstable as compared with osmium (VIII) OsO ₄ which is also separated by the volatilization method, an accident of explosion due to self decomposition has been reported. Moreover, since RuO ₄ has a strong oxidizing action, a high degree of corrosion resistance is essential for the gas recovery device. The biggest problem is that ruthenium must be completely volatilized as RuO _{4 in an} aqueous chloride solution.
It is necessary to raise the pH of the liquid to 4 or more and suppress the reduction by chloride ions, but under this condition, the platinum group element contained at the same time is precipitated or hydrolyzed, and the subsequent solvent extraction or ion exchange step The fact is that it forms a hydroxo complex, which is a problem with.

To avoid this, after the distillation of RuO ₄ was completed, it was necessary to add a large excess of hydrochloric acid again to the aqueous solution and continue heating at high temperature to return the hydroxo complex to the chloro complex. However, if such a method is adopted, the hydrochloric acid leachate is neutralized before distillation, and acidified with hydrochloric acid again after distillation, so that the consumption of alkali and acid is very large and economically problematic. There was also a problem that crystals of alkali chloride crystallized out when acidified and the platinum group partially precipitated.

On the other hand, a solvent extraction method is partially used as a method for separating ruthenium. This solvent extraction method is a method of reacting ruthenium with nitric acid in a reducing atmosphere to extract a nitrosyl complex of ruthenium. However, in the coexistence of platinum, both of them are extracted by tributyl phosphate, so that they cannot be separated from each other, and it is necessary to separate and collect platinum in a separate step in advance.

[0007]

SUMMARY OF THE INVENTION In view of such conventional circumstances, the present invention eliminates the risk of explosion, does not require a device having a high degree of corrosion resistance, and is more complicated and costly to neutralize and re-use. It is an object of the present invention to provide a method for achieving mutual separation of platinum and ruthenium by an extraction operation using a single extractant, which does not require dissolution treatment.

[0008]

To achieve the above object, a first method for separating platinum and ruthenium provided by the present invention is to provide an aqueous solution containing platinum and ruthenium with a hydrochloric acid concentration of 1 to 12 mol / l. And, the redox potential is adjusted to 350 to 700 mV with respect to the silver-silver chloride electrode, and then the aqueous solution is mixed with tributyl phosphate to selectively extract platinum into the organic phase.

A second aspect of the present invention, which comprises platinum and ruthenium,
The method for separating is to adjust the hydrochloric acid concentration of an aqueous solution containing platinum and ruthenium to 1 to 12 mol / l, and then mix the aqueous solution with tributyl phosphate to extract platinum and ruthenium into the organic phase, and then The organic phase is separated and hydrochloric acid is mixed so that the hydrochloric acid concentration becomes 1 to 12 mol / l, and the redox potential of the mixture is set to 35 with respect to the silver-silver chloride electrode.
By adjusting to 0 to 500 mV, ruthenium is back-extracted into the aqueous phase, and platinum is selectively left in the organic phase.

Furthermore, the third aspect of the present invention of platinum and ruthenium
The method of separation is that the concentration of hydrochloric acid in the aqueous solution containing platinum and ruthenium is adjusted to 1 to 12 mol / l, and the redox potential is adjusted to 350 to 700 mV with respect to the silver-silver chloride electrode, and then the aqueous solution is mixed with tributyl phosphate. By doing so, platinum is selectively extracted into the organic phase, and then the organic phase is separated and mixed with hydrochloric acid so that the hydrochloric acid concentration becomes 1 to 12 mol / l, and the redox potential of the mixture is adjusted to the silver-silver chloride electrode. By adjusting to 350 to 500 mV, ruthenium co-extracted in the organic phase is back-extracted into the aqueous phase, and platinum is selectively left in the organic phase.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Although both tetravalent platinum and tetravalent ruthenium chloro complex ions are extracted by tributyl phosphate, they are difficult to be extracted when they are reduced to a lower valence. Further, when comparing the tetravalent platinum and the tetravalent ruthenium chloro complex ions, the ruthenium chloro complex ion has a property that it is more easily reduced.

The present invention utilizes such properties of platinum and ruthenium to reduce a liquid containing tetravalent platinum and a tetravalent ruthenium chloro complex ion to the reduction potential of the tetravalent ruthenium complex ion, By mixing this solution with tributyl phosphate, the trivalent ruthenium chloro complex ion is left in the aqueous phase, and only the tetravalent platinum chloro complex ion is selectively extracted into the organic phase.

The present invention will be described in more detail below. Generally, a platinum group element-containing raw material recovered from a smelting system, scrap, or the like is dissolved with hydrochloric acid and chlorine, which are the most practical dissolving agents, or aqua regia. Since these solubilizers are strong oxidizers, all the dissolved platinum group elements have the highest oxidation number in hydrochloric acid and are present as chloro complex ions.

When this aqueous solution contains platinum and ruthenium, when a reducing agent is allowed to act on it, as can be seen from the comparison of the following chemical formulas 1 and 2, the tetravalent ruthenium chloro complex at a higher potential than the tetravalent platinum. The ions are reduced to trivalent chloro complex ions that are not extracted by tributyl phosphate.

[0015]

Embedded image [PtCl ₆ ] ^2- + 2e = [PtCl ₄ ] ^2- + 2C
l ^-; 0.68V

Embedded image [RuCl ₅ OH] ^2- + H ⁺ + e = [RuCl ₅ ] ^2-
+ H ₂ O; 1.30V (For Formulas 1 and 2, the potential is the value for the hydrogen electrode)

The concentration of hydrochloric acid at the time of extraction is required to be the minimum concentration at which the chloro complex of platinum is stable and can be present in the free acid state which is extracted into tributyl phosphate, and is extracted from tributyl phosphate and lost from the aqueous phase. Considering the amount of hydrochloric acid generated, a hydrochloric acid concentration of approximately 1 mol / l or more is required. The extraction rate of platinum increases as the concentration of hydrochloric acid increases, and reaches a maximum at 4 to 6 mol / l. A further decrease in the platinum extraction rate with an increase in the hydrochloric acid concentration is slight, and the maximum concentration is 12 mol / l where the hydrochloric acid concentration becomes a saturated concentration at room temperature.

Regarding the redox potential, judging from the above chemical formula 2, it is possible in principle to reduce ruthenium even at a fairly high potential, but in order to actually achieve mutual separation, a lower potential, That is, it is necessary to set the voltage to 700 mV or less with respect to the silver-silver chloride electrode. But 35
If it is less than 0 mV, the reduction of platinum is also started and the extraction rate of platinum decreases, so it is necessary to control the potential to 350 mV or higher.

The reducing agent added to the liquid for adjusting the oxidation-reduction potential may be of any type as long as it is a compound that can be adjusted within a predetermined potential. However, when the potential is locally excessively lowered, the platinum group element is deposited as a metal, and once deposited, it is not easily dissolved even if the potential is raised again a little,
A reducing agent having an excessively low reduction potential is not preferable. In consideration of the subsequent purification step, the inclusion of metals other than alkali metals should be avoided. Further, since the reduction efficiency is generally lowered under acidic conditions, a reducing agent that works reliably and at room temperature even under such conditions is desired.

Considering these conditions, together with the price which is important in industrial practice, sulfur dioxide or sulfite,
Alternatively, a hydrazinium salt is preferable as the reducing agent used in the present invention. Among these, since hydrazinium salts easily form sparingly soluble salts with platinum group elements, sulfur dioxide or sulfite is judged to be the most suitable reducing agent.

Next, each method of the present invention will be specifically described. In the first separation method, tetravalent ruthenium is reduced by adjusting the hydrochloric acid concentration and the redox potential of an aqueous solution of platinum and ruthenium. After that, by extracting with tributyl phosphate, platinum is selectively extracted from the aqueous solution into the organic phase of tributyl phosphate, and ruthenium remains in the aqueous phase, so that both can be separated.

When a natural mineral is used as a raw material, ruthenium often coexists with iridium (Ir), rhodium (Rh) and the like. Like ruthenium, the chloro complex ion of tetravalent iridium has the property of not being extracted by tributyl phosphate when it is reduced.
It occurs at a potential of 0-600 mV. Therefore, this 350-
By adjusting the redox potential to 600 mV, iridium can be left in the aqueous phase together with ruthenium and separated from platinum. Further, rhodium has an unstable tetravalent oxidation number and exists as trivalent, so that rhodium is not always extracted into tributyl phosphate regardless of the potential. still,
As described above, palladium can be easily separated by a known extractant, and osmium can be easily separated by a volatilization method.

In the second method for separating platinum and ruthenium,
First, both platinum and ruthenium in the aqueous solution are extracted into tributyl phosphate, and then hydrochloric acid is added to the separated organic phase and the potential is adjusted with a reducing agent to reduce the tetravalent ruthenium into ruthenium in the aqueous phase. Back-extract, leaving platinum in the organic phase. In the case of this second method, it is difficult to back-extract ruthenium unless the reduction potential is made lower than that of the first method, and it is necessary to adjust it to 350 to 500 mV specifically. When iridium and rhodium coexist, iridium is back-extracted with ruthenium into the aqueous phase,
Rhodium is not initially extracted into tributyl phosphate.

The third method for separating platinum and ruthenium is a combination of these first and second separating methods,
After extracting platinum into the organic phase under reducing conditions by the first method, hydrochloric acid is added to the organic phase and the redox potential is adjusted to extract a small amount of ruthenium extracted with platinum in the organic phase and, if present, Iridium is reduced and back extracted into the aqueous phase, leaving platinum in the organic phase. Therefore, according to the third separation method, ruthenium and iridium coextracted in the organic phase can be further removed, and more complete separation can be achieved.

[0024]

EXAMPLES Example 1 As a stock solution, Pt: 31.2 g / l, Ir: 1.2 g / l
An aqueous solution containing 1, Ru: 1.2 g / l and hydrochloric acid 4.5 mol / l was prepared. The potential of this aqueous solution was 885 mV against the silver-silver chloride electrode.

Sodium bisulfite and equimolar hydrochloric acid were added to this aqueous solution to carry out reduction, and a sample was taken from the aqueous solution while the potential dropped, and each sampling solution and tributyl phosphate were mixed with O / A = 1 / The mixture was shaken and mixed at 1 for 10 minutes. Then, the organic phase and the aqueous phase were analyzed, and the extraction rate of each element was obtained. Table 1 below shows the relationship between the redox potential of the liquid with respect to the silver-silver chloride electrode and the extraction rate of each element.

[0026]

[Table 1]

As can be seen from the results shown in Table 1, when the equilibrium potential (oxidation-reduction potential of the liquid after extraction) is 700 mV or less, the extraction rate of ruthenium into the organic phase sharply decreases.
Also, it is found that when iridium coexists, the extraction of iridium into the organic phase is suppressed by reducing the potential to 600 mV or less.

Example 2 The stock solution used in Example 1 was shake-mixed with tributyl phosphate for 10 minutes, Pt: 25.8 g / l, Ir: 0.0
An organic phase containing 91 g / l, Ru: 0.38 g / l was obtained.

This organic phase was mixed with 3 mol / l hydrochloric acid and O / A.
= 1/1 and mixed with 3 mol / l hydrochloric acid containing 4.5% by weight of sulfur dioxide SO ₂ to reduce the mixture. The organic phase and a considerable amount of the aqueous phase were sampled while the potential decreased, and the back extraction rate was calculated from the analysis of both. The result is the redox potential (Ag / AgC) of the back extract.
It is shown in Table 2 together with 1).

[0030]

[Table 2]

From these results, it can be seen that in the back extraction, the ruthenium back extraction is incomplete unless the oxidation-reduction potential is 500 mV or less. The same applies to iridium.

Comparative Example 1 As in Example 2, the stock solution used in Example 1 was shake-mixed with tributyl phosphate for 10 minutes, and Pt: 25.
8 g / l, Ir: 0.91 g / l, Ru: 0.38 g / l
An organic phase containing was obtained. This organic phase is mixed with water and O / A = 1
The mixture was mixed at 1/1 and the mixture was reduced with sodium sulfite. The organic phase and a considerable amount of the aqueous phase were sampled while the potential decreased, and the back extraction rate was calculated from the analysis of both, and the results are shown in Table 3.

[0033]

[Table 3]

In this comparative example, the concentration of hydrochloric acid in the aqueous phase contained only 0.5 mol / l, which corresponds to the concentration of hydrochloric acid co-extracted with the platinum group element in the stock solution, and therefore, regardless of the potential. Since the platinum group elements in the above were back-extracted, mutual separation was not possible at all.

Comparative Example 2 Tributyl phosphate containing Pt: 28.8 g / 1 was mixed with 2 mol / l hydrochloric acid at a phase ratio O / A = 1/1 and reduced with 6% aqueous sulfite. . Sampling the organic phase and a considerable amount of the aqueous phase while the potential is decreasing,
From the analysis of both, the platinum concentration in the organic phase and the back extraction rate of platinum into the aqueous phase were calculated, and the obtained results are shown in Table 4 below.

[0036]

[Table 4]

From the results shown in Table 4, the redox potential was 350 m.
It can be seen that below V, platinum is back-extracted into the aqueous phase even if the hydrochloric acid concentration is 1 mol / l or more.
At the potentials in Table 4, ruthenium is completely back-extracted in any case, so platinum and ruthenium cannot be separated from each other.

Example 3 Pt: 32.4 g / l, Rh: 16.6 g / l, Ir:
1.19 g / l, Ru: 1.29 g / l, and hydrochloric acid 4.5
An aqueous solution containing mol / l was prepared. The potential of this aqueous solution was 842 mV against the silver-silver chloride electrode. Sodium hydrogen sulfite and equimolar hydrochloric acid were added to this aqueous solution to reduce it to 421 mV, and the obtained aqueous solution was used as a stock solution.

Meanwhile, 39 ml of 11.6 mol / l hydrochloric acid was dissolved in 411 ml of tributyl phosphate to prepare a hydrochloric acid-added tributyl phosphate. Further, 4.5 mol / l hydrochloric acid was prepared as a cleaning liquid for cleaning (scrubbing) the organic phase of tributyl phosphate.

Using the above stock solution, hydrochloric acid-added tributyl phosphate and washing solution, three extraction stages as shown in FIG.
A batch simulation test assuming multi-stage countercurrent extraction of two stages of scrubbing was performed by a batch operation as shown in FIG. 2 with a phase ratio of the extraction stage O / A = 5/6 and a phase ratio of the scrubbing stage 5/1. did. Even if no reducing agent is added in the scrubbing stage, the potential of the extraction stage is 350 to 700 m.
At V, the scrubbing stage potential was maintained at 350-500 mV.

The composition of the organic phase and the aqueous phase of each stage is shown in Table 5 below.
Table 6 below shows the distribution of each element in the extraction residual liquid of the third stage of extraction for recovering platinum group elements other than platinum and the organic phase of the second stage of scrubbing for recovery of platinum. In Tables 5 and 6, E1 to E3 are extraction stages and S1 is
~ S2 stage means a scrubbing stage.

[0042]

[Table 5] Composition of potential residue (g / l) Composition of organic phase (g / l) Stage (mV) Pt Rh Ir Ru Pt Rh Ir Ru E1 407 0.23 16.5 1.22 1.21 0.64 0.087 <0.005 0.008 E2 398 0.87 13.5 0.93 1.02 0.49 0.083 <0.005 0.006 E3 417 5.07 13.1 0.91 0.95 30.7 0.087 <0.005 0.002 S1 403 1.27 0.12 0.008 0.011 28.9 0.064 <0.005 0.001 S2 438 0.94 0.010 <0.005 <0.001 28.6 0.058 <0.005 0.001

[0043]

[Table 6] Platinum group partitioning between organic phase and aqueous phase recovered in countercurrent multi-stage continuous extraction (%) Pt Rh Ir Ru E E-stage raft solution 0.96 99.72> 99.7 99.94 S2-stage organic phase 99.04 0.28 <0.3 0.06

As can be seen from the above results, by combining a washing stage in which extraction under reducing conditions and back extraction of impurities are combined, 99% or more of platinum in the organic phase and 99% of ruthenium in the raffinate of the aqueous phase are combined. % Or more could be distributed respectively. In addition, in this example, since the redox potential was maintained at 600 mV or less, the iridium (IV) complex ion can be reduced to trivalent, and 99% or more of the trivalent trivalent rhodium originally exists in the aqueous phase. I was able to.

[0045]

According to the present invention, there is no danger of explosion,
It does not require equipment with a high degree of corrosion resistance, does not require complicated and expensive neutralization and re-dissolution processing, and separates platinum and ruthenium by an extraction operation using a single extractant, tributyl phosphate. Can be achieved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a multistage continuous countercurrent extraction operation according to a third embodiment.

FIG. 2 is a conceptual diagram of batch simulation for reproducing the multistage continuous countercurrent extraction shown in FIG. 1 by batch operation,
○ and □ represent shaking and mixing for 10 minutes, and → represents migration of the liquid.

[Explanation of symbols]

TBP Hydrochloric acid-added tributyl phosphate

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22B 1/00-61/00

Claims (4)

(57) [Claims] 1. An aqueous solution containing platinum and ruthenium is adjusted to have a hydrochloric acid concentration of 1 to 12 mol / l and an oxidation-reduction potential of 350 to 700 mV with respect to a silver-silver chloride electrode, and then the aqueous solution is mixed with tributyl phosphate. The method for separating platinum and ruthenium is characterized in that platinum is selectively extracted into the organic phase. 2. After adjusting the hydrochloric acid concentration of the aqueous solution containing platinum and ruthenium to 1 to 12 mol / l, the aqueous solution is mixed with tributyl phosphate to extract platinum and ruthenium into the organic phase, and then the organic phase is extracted. The organic phase is separated and hydrochloric acid is mixed so that the hydrochloric acid concentration becomes 1 to 12 mol / l, and the redox potential of the mixture is set to 35 with respect to the silver-silver chloride electrode.
A method for separating platinum and ruthenium, characterized in that ruthenium is back-extracted into an aqueous phase and platinum is selectively left in an organic phase by adjusting to 0 to 500 mV. 3. An aqueous solution containing platinum and ruthenium is adjusted to have a hydrochloric acid concentration of 1 to 12 mol / l and an oxidation-reduction potential of 350 to 700 mV with respect to a silver-silver chloride electrode, and then the aqueous solution is mixed with tributyl phosphate. By doing so, platinum is selectively extracted into the organic phase, and then the organic phase is separated and mixed with hydrochloric acid so that the hydrochloric acid concentration becomes 1 to 12 mol / l, and the redox potential of the mixture is adjusted to the silver-silver chloride electrode. To 350 to 500 mV, the ruthenium co-extracted in the organic phase is back-extracted into the aqueous phase, and platinum is selectively left in the organic phase. Separation method. 4. The method for separating platinum and ruthenium according to claim 1, wherein sulfur dioxide or sulfite is used as a reducing agent for adjusting the redox potential.