JP4715621B2 - Method for purifying ammonium hexachloroiridium (IV) containing lead - Google Patents

Description

  The present invention relates to a method for purifying lead-containing ammonium hexachloroiridium (IV), and more particularly, to reliably separate lead from ammonium hexachloroiridium (IV) containing lead regardless of the form of lead contained. In addition, the present invention relates to a method for recovering iridium in a high yield.

  Iridium is used as an industrial material for catalysts, electronic parts and the like together with platinum group elements such as platinum, palladium, rhodium, ruthenium, and osmium. In these fields, high-purity products with particularly few specific impurity elements are required. By the way, platinum group elements are rare in resources, and are rarely produced in natural minerals such as platinum ore containing platinum group elements in high quality. As a raw material for platinum group elements produced industrially, By-products from smelting of non-ferrous metals such as copper, nickel, cobalt, and various used waste catalysts such as automobile exhaust gas treatment catalysts dominate. For example, by-products from this non-ferrous metal smelting process include platinum group elements contained in trace amounts in the smelting raw materials, and the chemical properties of sulfide concentrates such as copper and nickel, and crude metals. It is concentrated inside and further separated by a noble metal concentrate containing a platinum group element as a residue in the main metal recovery step such as electrolytic purification.

  In this concentrate, the main metals such as copper and nickel, as well as other constituent elements such as gold, silver and other precious metals, lead, bismuth, selenium, tellurium, arsenic, antimony, etc. are higher than platinum group elements. Usually coexisting in content. Thereafter, the platinum group element is recovered through recovery of gold and silver. Usually, the platinum group element is once leached into the liquid, and then purified and separated by solvent extraction, ion exchange method, or the like.

In such a platinum group element recovery process, iridium is usually separated and recovered as a hexachloroiridium (IV) acid salt having good crystallinity at the end of the purification process, and is used as a starting material for the product, or metallic iridium and iridium oxide. It can be used as a raw material. In this method of separating as hexachloroiridium (IV) acid salt (for example, see Patent Document 1), it is said that most of the coexisting impurity elements can be separated from the precipitated crystals. However, a salt of another platinum group element, a platinum group element such as lead or tin, and a complex salt of [MX ₆ ] ²⁻ (wherein M represents a metal and X represents a halogen) type are formed. There was a problem that the elements were mixed in iridium and could not be separated.

In addition, a method of reducing an aqueous solution containing iridium and separating the impurity element in a metal state (see, for example, Patent Document 2), and a method of separating the impurity element into a mother liquor by recrystallization purification (see, for example, Patent Document 3). in normally difficult to separate hexachloroiridate (IV) ions: [IrCl _6] ^2- and be the same _[MX ^6] impurity element which forms a ^2-type complexes coexist, as can be to separate them Yes. However, these proposals can deal with all of the impurity elements existing as [MX ₆ ] ^2- type complex salts, but lead has low solubility other than [MX ₆ ] ^2- type complex salts. Since it tends to form a compound, it may behave entirely with iridium, in which case it was very difficult to separate lead from hexachloroiridium (IV).

  On the other hand, as a method for separating a cationic impurity element such as lead from an aqueous solution containing a platinum group element regardless of its form, a method of extracting with a carboxylic acid that is sparingly soluble in water (for example, see Patent Document 4). It has been. However, according to this method, when lead in an aqueous solution containing iridium is extracted and separated, hexachloroiridium (III) ions are hydrolyzed in the process of increasing the pH. As a result, there is a problem that even if the liquid is oxidized again, crystallization of hexachloroiridium (IV) acid salt becomes difficult, and the yield is very low even if crystals are precipitated.

  From the above situation, when separating and recovering iridium from a platinum group element material containing impurity elements, it is required to reliably separate lead regardless of the lead content and to recover iridium in a high yield. ing.

JP-A-2004-99975 (first page, second page) JP 2004-190058 (first page, second page) JP-A-2005-97695 (first page, second page) JP-A-8-225862 (first page, second page)

  In view of the above-mentioned problems of the prior art, the object of the present invention is to reliably separate lead from ammonium hexachloroiridium (IV) containing lead regardless of the content of lead, and to convert iridium in a high yield. It is to provide a method of collecting.

  In order to achieve the above object, the present inventors have conducted extensive research on a method for purifying ammonium hexachloroiridium (IV) containing lead, and as a result, ammonium hexachloroiridium (IV) containing lead, A step of dissolving under specific conditions, a step of selectively extracting and separating lead from the resulting solution with a specific extractant, and a crystal of ammonium hexachloroiridium IV) under specific conditions from the solution from which lead has been separated The iridium salt containing lead as a low-solubility compound can be reliably separated from iridium salts containing a low-solubility compound, regardless of the form of lead, and iridium can be recovered in high yield. The present invention has been completed by finding out what can be done.

That is, according to the first invention of the present invention, there is provided a method for purifying ammonium hexachloroiridium (IV) containing lead, characterized by comprising the following steps (1) to (3).
(1) After adding a lead-containing ammonium hexachloroiridium (IV) raw material into hydrochloric acid having a concentration of 0.5 to 2 mol / L to prepare a suspension having a slurry concentration of 50 to 150 g / L The resulting suspension was heated to a temperature of 40 to 80 ° C., and hydrated hydrazine was added to adjust the redox potential to 300 to 700 mV with respect to the silver / silver chloride electrode. IV) Ammonium acid is dissolved with lead.
(2) By adding neodecanoic acid as an extractant to the resulting solution, and adding the alkali to adjust the pH to 5 to 7, the lead contained in the solution is selectively selected. Extract into extractant and separate.
(3) Using the solution from which lead is separated, the hydrochloric acid concentration is 1 to 5 mol / L, the ammonium chloride concentration is 50 to 150 g / L, and the oxidation-reduction potential in the presence of an oxidizing agent is applied to the silver / silver chloride electrode. After adjusting to 700 to 1100 mV, ammonium hexachloroiridium (IV) is crystallized and recovered by heating to a temperature of 60 to 100 ° C.

  According to the second invention of the present invention, in the first invention, in the step (2), the addition ratio of neodecanoic acid is 0.01 to 10 L with respect to 1 g of lead contained in the solution. There is provided a method for purifying lead-containing ammonium hexachloroiridium (IV), characterized in that it is.

  According to a third invention of the present invention, in the first invention, in the step (2), the alkali is sodium hydroxide, and the lead-containing hexachloroiridium (IV) acid is characterized in that A method for purifying ammonium is provided.

  According to a fourth invention of the present invention, in the first invention, in the step (3), the oxidizing agent is sodium chlorite, and the lead-containing hexachloroiridium (IV ) A method for purifying ammonium acid is provided.

  The method for purifying lead-containing ammonium hexachloroiridium (IV) according to the present invention reliably separates lead from iridium salts containing lead regardless of the form of lead contained, and recovers iridium in a high yield. Its industrial value is extremely high.

Hereinafter, the method for purifying ammonium hexachloroiridium (IV) containing lead according to the present invention will be described in detail.
The method for purifying ammonium hexachloroiridium (IV) containing lead according to the present invention comprises the following steps (1) to (3).
(1) After adding a hexachloroiridium (IV) ammonium raw material containing lead into hydrochloric acid having a concentration of 0.5 to 2 mol / L to prepare a suspension having a slurry concentration of 50 to 150 g / L The resulting suspension was heated to a temperature of 40 to 80 ° C., and hydrated hydrazine was added to adjust the redox potential to 300 to 700 mV with respect to the silver / silver chloride electrode. IV) Ammonium acid is dissolved with lead.
(2) By adding neodecanoic acid as an extractant to the resulting solution and adding the alkali to adjust the pH to 5 to 7 selectively, lead contained in the solution is selectively added. Extract into extractant and separate.
(3) Using the solution from which lead is separated, the hydrochloric acid concentration is 1 to 5 mol / L, the ammonium chloride concentration is 50 to 150 g / L, and the oxidation-reduction potential in the presence of an oxidizing agent is applied to the silver / silver chloride electrode. After adjusting to 700 to 1100 mV, ammonium hexachloroiridium (IV) is crystallized and recovered by heating to a temperature of 60 to 100 ° C.

  In the present invention, the step of dissolving lead-containing ammonium hexachloroiridium (IV) under the above conditions, the step of selectively extracting and separating lead with neodecanoic acid as an extractant from the resulting solution, and lead It is important to perform a series of steps consisting of a step of crystallizing and recovering ammonium hexachloroiridium (IV) from the separated solution under the above conditions. Thereby, it is possible to reliably separate lead from an iridium salt containing lead regardless of the form of lead contained, and to recover iridium in a high yield.

1. Step (1) In the above step, lead hexachloroiridium (IV) acid crude raw material is added to hydrochloric acid having a concentration of 0.5 to 2 mol / L, and the slurry concentration becomes 50 to 150 g / L. After preparing the suspension, the resulting suspension is heated to a temperature of 40 to 80 ° C., and hydrazine hydrate is added to adjust the redox potential to 300 to 700 mV with respect to the silver / silver chloride electrode. This is a step of dissolving ammonium hexachloroiridium (IV) together with lead.

The lead-containing ammonium hexachloroiridium (IV) used in the above step is not particularly limited, and is obtained by separation and purification methods from raw materials containing impurity elements such as lead by various methods. Among them, a hard-to-separate compound in which lead is co-precipitated is included. The lead content in the ammonium hexachloroiridium (IV) containing lead varies depending on the raw material, separation and purification method, etc., but is usually 0.1 to 5% by weight.
The purification method of the present invention can be applied not only to ammonium hexachloroiridium (IV) but also to other iridium compounds such as hexachloroiridium (IV) acid salt. However, ammonium hexachloroiridium (IV) is exclusively used as a precursor of iridium metal, other compounds, and applied products such as catalysts.

  In the above step, ammonium hexachloroiridium (IV) is dissolved by addition of hydrated hydrazine by the reaction represented by the following reaction formula (1). That is, ammonium hexachloroiridium (IV) as it is has low solubility in water, so that it is difficult to chemically separate impurity elements. Therefore, it is reduced to hexachloroiridium (III) acid by a reducing agent to increase the solubility.

Reaction formula (1): 4 [IrCl ₆ ] ² + N ₂ H ₄ = 4 [IrCl ₆ ] ³ + N ₂ + 4H ⁺

  As the reducing agent, it is essential that the reducing agent is a mild reducing agent that does not have a risk of reducing iridium to a metal and that it does not become an impurity with respect to iridium. Examples of such a reducing agent include hydrated hydrazine, hydrazine monohydrochloride, hydrazine dihydrochloride, hydrazine sulfate, sulfur dioxide, sulfite, etc., but hydrazine hydrate is most suitable from the viewpoint of economy. . That is, sulfur dioxide, sulfite, and hydrazine sulfate generate sulfate ions after completion of the reaction, which reacts with lead (II) ions to form insoluble salts of lead (II) sulfate, and metal In many applications such as catalysts, the inclusion of sulfur is undesirable because it is not desired. In addition, hydrazine compounds are less expensive and expensive than hydrated hydrazine.

  In the above step, first, ammonium hexachloroiridium (IV) containing lead is added to hydrochloric acid having a concentration of 0.5 to 2 mol / L, and suspended so that the slurry concentration becomes 50 to 150 g / L. A suspension is obtained. Here, prior to the reduction reaction, it is important to suspend ammonium hexachloroiridium (IV) in hydrochloric acid. This prevents iridium hydroxide precipitates from being formed by the neutralization reaction accompanying the addition of alkaline hydrazine hydrate.

  That is, when the hydrochloric acid concentration is less than 0.5 mol / L, there is a possibility that a hydroxide is locally formed by alkali with hydrazine. On the other hand, when the hydrochloric acid concentration exceeds 2 mol / L, the reducing power of hydrazine decreases. This is because the reducing power of hydrazine decreases as the hydrochloric acid concentration increases.

  Moreover, if the said slurry density | concentration is less than 50 g / L, the yield at the time of crystallization will fall. This is because the lower the slurry concentration, the larger the ratio of the loss due to dissolution to the precipitated crystals. On the other hand, if the slurry concentration exceeds 150 g / L, the possibility of precipitation of hexachloroiridium (III) salt crystals of hydrazine or other salts increases.

In the above step, the resulting suspension is then heated to a temperature of 40 to 80 ° C., and hydrazine hydrate is added to adjust the redox potential to 300 to 700 mV with respect to the silver / silver chloride electrode. .
That is, as the temperature of the reduction reaction, the reduction rate increases as the temperature increases. However, if the temperature exceeds 80 ° C., generation of hydrazinium salt fumes becomes remarkable, which is not preferable. On the other hand, if it is less than 40 degreeC, reaction is slow.

As for the above reduction potential, the standard redox potential of the reaction of [IrCl ₆ ] ² + e = [IrCl ₆ ] ³⁻ is 0.87 V with respect to the hydrogen electrode, and therefore with respect to the silver / silver chloride electrode. The reduction reaction proceeds most at around 0.67V. Therefore, it is an indispensable condition that the oxidation-reduction potential is 700 mV or less with respect to the silver / silver chloride electrode. On the other hand, when the oxidation-reduction potential is less than 300 mV with respect to the silver / silver chloride electrode, unreacted hydrazine remains in the aqueous solution, and crystals of hexachloroiridium (III) salt of hydrazine precipitate.

  In the above step, all the crystals of ammonium hexachloroiridium (IV) are finally dissolved. At this time, when lead forms crystals of the same shape, it is reduced and dissolved according to the following reaction formula (2).

Reaction formula (2): 2 [PbCl ₆ ] ² + N ₂ H ₄ = 2 [PbCl ₄ ] ² + N ₂ + 4H ⁺ + 4Cl ⁻

  However, even when other poorly soluble lead compounds are present, in the above step, hydrochloric acid is added and dissolved in the same manner by heating. Since this hardly soluble lead compound is merely dissolved by the difference in acid concentration and temperature, the iridium compound is crystallized in the subsequent process, and at the same time, it is precipitated again and mixed into the crystal. Therefore, it is important to separate all forms of lead compounds in the following step (2).

2. Step (2) The above step is included in the resulting solution by adding neodecanoic acid as an extractant to the resulting solution and adjusting the pH to 5-7 by adding alkali while mixing. This is a process of selectively extracting and separating lead to be extracted into an extractant.

  In the above step, the solution containing iridium and lead is mixed with neodecanoic acid, and lead is extracted into the extractant. That is, it is possible to extract lead from an aqueous solution containing lead and iridium by adjusting the pH with an alkali and using an acidic extractant. Here, as the acidic extractant, a higher carboxylic acid is particularly preferable because of its high lead extraction rate. As this higher carboxylic acid, neodecanoic acid, for example, Versatic Acid-10 (VA-10, manufactured by Shell Chemical Co., Ltd.) is most suitable. That is, if VA-10 is used, lead (II) ions can be quantitatively extracted even if lead forms a chloro complex salt or an anion that forms a hardly soluble salt coexists.

Scheme ^{(3): Pb 2+ + 2H} -VA + 2OH - = Pb (VA) 2 + 2H 2 O
(Here, H-VA in the formula represents versatic acid.)

  That is, if the pH is less than 5 in the above process, the lead extraction rate is drastically reduced. On the other hand, when the pH exceeds 7, the hydrolysis reaction of hexachloroiridium (III) acid as shown in the following reaction formula (4) easily proceeds, and VA-10 itself is dissolved as a sodium salt. It is inconvenient.

Scheme ^{_{(4): [IrCl 6]}} 3- + H 2 O = [IrCl 5 (H 2 O)] 2- + Cl -

  The alkali used in the above step is not particularly limited, and sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, and the like are also used. Among them, in order to continuously control the pH, the solubility is low. Sodium hydroxide, which is high and easy to use, is preferred.

  The reaction temperature is not particularly limited and is preferably as low as possible to prevent hydrolysis of hexachloroiridium (III) acid. Moreover, when importance is attached to the volatility of the solvent at the time of solvent extraction, it is desirable to carry out at around room temperature.

  In the above step, a normal solvent extraction method is used. For example, using a mixer-settler type solvent extraction device, the above solution and the neodecanoic acid extractant are stirred and mixed in a reaction tank, lead moves into the extractant, and then separated into an aqueous phase and an organic phase. . Here, if necessary, the extractant is mixed with a diluent made of a petroleum solvent to adjust the viscosity to a desired value. A pH adjuster is also added. Furthermore, the lead extracted into the extractant can be recovered by existing methods.

  The addition ratio of neodecanoic acid used in the above step is not particularly limited, and is selected depending on the amount of lead contained in the solution, but 0.01 to 10 L with respect to 1 g of lead contained in the solution. preferable. That is, when the addition ratio of neodecanoic acid is less than 0.01 L with respect to 1 g of lead, the extraction rate of lead is low. On the other hand, when it exceeds 10 L, a large amount of back extraction with respect to lead is required for industrial extraction operation. Since an acid is required and a large amount of diluted waste liquid is generated, it is not preferable.

3. Step (3) In the above step, using a solution from which lead has been separated, the hydrochloric acid concentration is 1 to 5 mol / L, the ammonium chloride concentration is 50 to 150 g / L, and the oxidation-reduction potential is silver in the presence of an oxidizing agent. / After adjusting to 700 to 1100 mV with respect to the silver chloride electrode, it is a step of crystallizing and recovering ammonium hexachloroiridium (IV) by heating to a temperature of 60 to 100 ° C.

  In the above step, hexachloroiridium (III) acid in the solution from which lead has been separated is oxidized according to the following reaction formula (5) to regenerate hexachloroiridium (IV) acid, and then hexachloroiridium (IV) acid. Crystallize the ammonium.

Reaction formula (5): [IrCl ₆ ] ³⁻ = [IrCl ₆ ] ² + e

In the above process, first, using a solution from which lead has been separated, the hydrochloric acid concentration is 1 to 5 mol / L, the ammonium chloride concentration is 50 to 150 g / L, and an oxidizing agent is added to change the oxidation-reduction potential to silver / silver chloride. Adjust to 700-1100 mV with respect to the electrode.
That is, in the steps (1) and (2), a considerable proportion of hexachloroiridium (III) acid is hydrolyzed according to the reaction formula (4). Even if only oxidation is performed as it is, hexachloroiridium (IV) The amount of ammonium acid crystals precipitated is limited. Therefore, it is important to oxidize while adding hydrochloric acid and heating to form a chloro complex again.

Here, the order of adjusting the hydrochloric acid concentration, the ammonium chloride concentration, and the oxidation-reduction potential is not particularly limited, and there is no problem as long as the final state is within the above range.
That is, when the hydrochloric acid concentration is less than 1 mol / L, it is difficult to completely neutralize and remove OH ⁻ when a hydroxy complex is formed. On the other hand, when the hydrochloric acid concentration exceeds 5 mol / L, the solubility of ammonium chloride is lowered, which is inconvenient for the reaction, and the sodium chloride in the liquid tends to crystallize, causing the product to be contaminated.

  Ammonium chloride is also used to complete crystal precipitation of ammonium hexachloroiridium (IV) by a common ion effect. If the ammonium chloride concentration is less than 50 g / L, the effect is insufficient. On the other hand, if the ammonium chloride concentration exceeds 150 g / L, dissolution is incomplete because sodium chloride and hydrochloric acid already coexist in the liquid. The remaining ammonium chloride may be mixed into the crystal as an impurity.

  Further, when the redox potential is less than 700 mV with respect to the silver / silver chloride electrode, the oxidation of hexachloroiridium (III) ion to hexachloroiridium (IV) acid ion becomes incomplete. On the other hand, if the oxidation-reduction potential exceeds 1100 mV with respect to the silver / silver chloride electrode, chlorine gas tends to be generated, and decomposition of ammonium ions starts, which is not preferable.

  The oxidizing agent used in the above process is not particularly limited, and a compound that does not easily remain as an impurity with respect to iridium is used. Hydrogen peroxide, chlorine, sodium hypochlorite, sodium chlorite, chloric acid Among them, sodium chlorite is particularly preferable because it has little self-decomposition and has a high reaction rate.

  In the above step, ammonium hexachloroiridium (IV) is then crystallized and recovered by heating to a temperature of 60 to 100 ° C. That is, although the precipitation of crystals is observed by adjusting the hydrochloric acid concentration, the ammonium chloride concentration, and the oxidation-reduction potential, the amount of precipitation at this stage is insufficient. Increase gradually. Here, when the temperature is less than 60 ° C., the precipitation of crystals is insufficient. On the other hand, if the temperature exceeds 100 ° C., a pressurized container is required, which is not economical.

  The end point of this reaction is determined as follows. That is, in the stage before the temperature rise, the liquid is dark brown, but as the reaction proceeds, it becomes transparent and the liquid is cooled when there is no color change. Thereafter, by filtration, crystals of ammonium hexachloroiridium (IV) having a low lead content, for example, 0.02% by weight or less, which is a detection limit in a normal ICP emission analysis method, are obtained.

  EXAMPLES The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited to these examples. The metal used in the examples was analyzed by ICP emission analysis.

Example 1
First, as the step (1), 1000 g of ammonium hexachloroiridium (IV) containing 0.26% by weight of lead with respect to the whole was suspended in 10 L of hydrochloric acid having a concentration of 1 mol / L. Subsequently, after the suspension was heated to 60 ° C., hydrated hydrazine was added to adjust to 513 mV with respect to the silver / silver chloride electrode, and all the crystals were dissolved.

  Next, as a step (2), the obtained solution was allowed to cool to 25 ° C. Thereafter, 1 L of trade name VA-10 (manufactured by Shell Chemical Co., Ltd.) as an extractant and 1 L of trade name Tecrine N-20 (manufactured by Shin Nippon Oil Co., Ltd.) as a diluent are added to the total amount of the solution, and the mixture is stirred While mixing uniformly, an aqueous solution of sodium hydroxide having a concentration of 18% by weight was added to adjust the pH to 5.9. Subsequently, this pH was maintained, and after the pH was stabilized and the addition of an aqueous sodium hydroxide solution was eliminated, stirring was terminated and the organic phase was separated.

  Finally, in the step (3), 3 L of hydrochloric acid having a concentration of 35% by weight was added to 11.4 L of the obtained aqueous phase solution. The hydrochloric acid concentration at this time was 2.4 mol / L. Subsequently, 1.44 kg of ammonium chloride was added and dissolved. The ammonium chloride concentration at this time was 100 g / L. Subsequently, an aqueous solution of sodium chlorite having a concentration of 25% by weight was added to adjust the redox potential to 880 mV with respect to the silver / silver chloride electrode. At this point, crystal precipitation was observed, but the liquid remained dark brown. Subsequently, when the temperature was raised to 80 ° C., the amount of crystal precipitation gradually increased, and at the same time, the color of the liquid became light. After 1 hour, when there was no change in the color of the liquid, it was cooled to 40 ° C. Thereafter, the crystals were separated by filtration. The obtained crystals were washed with an aqueous ammonium chloride solution having a concentration of 100 g / L, and then dried at 50 ° C. As a result, 962 g of ammonium hexachloroiridium (IV) was recovered. Moreover, when a part of the obtained crystal was decomposed and dissolved in aqua regia and the lead content was analyzed, it was 0.02% by weight or less of the analytical detection limit.

As described above, in Example 1, the following steps (1) to (3) were carried out according to the method of the present invention under predetermined conditions, so that a high yield of ammonium hexachloroiridium (IV) with a low lead content was obtained. It can be seen that the rate is obtained.
(1) After adding and suspending ammonium hexachloroiridium (IV) containing lead in hydrochloric acid, adjusting the oxidation-reduction potential while heating the resulting suspension, hexachloroiridium (IV) Dissolve ammonium acid.
(2) By adding neodecanoic acid as an extractant to the obtained solution and adjusting the pH by adding an alkali, the lead contained in the solution is selectively extracted into the extractant and separated. .
(3) After adjusting the hydrochloric acid concentration, the ammonium chloride concentration and the oxidation-reduction potential using the solution from which lead has been separated, the ammonium hexachloroiridium (IV) acid is crystallized and recovered by heating.

  As is clear from the above, the method for purifying lead-containing ammonium hexachloroiridium (IV) of the present invention is particularly suitable as a purification method used in the field of producing high-purity iridium having a low lead content. .

Claims (4)

A method for purifying ammonium hexachloroiridium (IV) containing lead, comprising the following steps (1) to (3).
(1) After adding a hexachloroiridium (IV) ammonium raw material containing lead into hydrochloric acid having a concentration of 0.5 to 2 mol / L to prepare a suspension having a slurry concentration of 50 to 150 g / L The resulting suspension was heated to a temperature of 40 to 80 ° C., and hydrated hydrazine was added to adjust the redox potential to 300 to 700 mV with respect to the silver / silver chloride electrode. IV) Ammonium acid is dissolved with lead.
(2) By adding neodecanoic acid as an extractant to the resulting solution and adding the alkali to adjust the pH to 5 to 7 selectively, lead contained in the solution is selectively added. Extract into extractant and separate.
(3) Using the solution from which lead is separated, the hydrochloric acid concentration is 1 to 5 mol / L, the ammonium chloride concentration is 50 to 150 g / L, and the oxidation-reduction potential in the presence of an oxidizing agent is applied to the silver / silver chloride electrode. After adjusting to 700 to 1100 mV, ammonium hexachloroiridium (IV) is crystallized and recovered by heating to a temperature of 60 to 100 ° C.   In the step (2), the addition ratio of neodecanoic acid is 0.01 to 10 L with respect to 1 g of lead contained in the solution. IV) A method for purifying ammonium acid.   The method for purifying ammonium hexachloroiridium (IV) containing lead according to claim 1, wherein the alkali in the step (2) is sodium hydroxide.   The method for purifying ammonium hexachloroiridium (IV) containing lead according to claim 1, wherein the oxidizing agent is sodium chlorite in the step (3).