JP4100695B2 - Method for separating and recovering Ru from a solution containing a platinum group - Google Patents

Description

  The present invention relates to a method for separating Ru from a solution containing a platinum group, for example, a solution after leaching of copper electrolytic slime.

As a method for separating Ru, an oxidative distillation method using the volatility of ruthenium tetroxide (RuO ₄ ) is known. For example, as described in the Journal of the Atomic Energy Society of Japan, Vol. 28, pages 493 to 500 (Non-patent Document 1), ruthenium tetroxide volatilized through chlorine gas into a solution in which an oxidizing agent is added to a residue containing platinum group and dissolved in an alkali There is a way to recover. However, when chlorine gas is passed through, if the chlorine absorbed in the aqueous solution decomposes into hypochlorous acid and hydrochloric acid and the liquidity becomes acidic, oxidative distillation does not proceed. Therefore, it is necessary to repeat distillation by adding alkali to increase the yield. There is.

  Japanese Examined Patent Publication No. 1-30896 (Patent Document 1) discloses a method of oxidizing Ru and Os from a solution containing gold and platinum group into tetraoxide with sodium bromate and removing it by distillation. The amount of oxidizing agent that converts the total amount of Ru and Os to tetroxide is said to be 7 to 10 times the stoichiometric amount, but the response when the Ru concentration in the solution changes is specifically disclosed. Absent. That is, when the Ru concentration is low, the oxidant is insufficient at 7 to 10 times the stoichiometric amount, and when the Ru concentration is high, the oxidant is excessively dissolved at 7 to 10 times the stoichiometric amount. .

The present inventors have disclosed a method for separating and recovering Ru from a solution by distillation from a solution containing a platinum group as in Japanese Patent Application No. 2003-128828 (Patent Document 2). That is, a solution containing a platinum group is distilled as ruthenium tetroxide using, for example, sodium bromate (NaBrO ₃ ) as an oxidizing agent, and Ru is separated and recovered. However, before adding the oxidizing agent, adjust to pH = 1, add sodium bromate about 3 times the equivalent of Ru in the solution, then convert to ruthenium tetroxide, heat to 80 ° C and flow in air in a distillation flask. Although distillation was performed for about 4 hours, Ru could not be completely separated by one distillation operation, and the distillation operation was repeated twice. This is because as the distillation proceeds, sodium bromate is decomposed by the reaction with the acid and the acid is consumed, and the pH rises to about 4 to 5 and the oxidative distillation does not proceed. When acid is added to lower the pH, the oxidant decomposes and consumes the acid. Therefore, after all the added oxidant is decomposed, it is necessary to readjust the pH to 1 and perform distillation again .
Further, ruthenium tetroxide vapor was introduced into a hydrochloric acid solution and converted to ruthenium chloride for recovery. However, for efficient recovery, distillation was performed while flowing air. However, when air is blown into the distillate, harmful ruthenium tetroxide vapor leaks from the connecting portion, and when the plug is clogged, there is a risk that the connecting portion may be disconnected or burst. When gas is blown into the liquid, there is a problem that crystals are likely to be deposited and clogged at the tip of the tube where the gas and the liquid are in contact.
In addition, when air was blown into the liquid in the reaction vessel, mist containing platinum group elements other than Ru was scattered together with ruthenium tetroxide vapor, and a mist trap was provided to reduce the purity of ruthenium chloride recovered with hydrochloric acid solution. However, the ruthenium tetroxide staying in the mist trap is gradually decomposed to change to less volatile ruthenium dioxide, resulting in a reduction in the recovery rate.

Kazuo Watari, et al., The Journal of the Atomic Energy Society of Japan, 1986, 28, 493 pages to 500 pages JP 1-30896 Japanese Patent Application No. 2003-128828

  The present invention has been made to solve the above-described drawbacks, and an object thereof is to provide a method for efficiently separating Ru from a platinum group-containing solution by oxidative distillation.

As a result of examining the method for separating Ru from the platinum group-containing solution by oxidative distillation, the pH range in which sodium bromate can convert Ru to ruthenium tetroxide is in the range of 0.5 to 2.5, and the pH is reduced by decomposition of the oxidizing agent. It has been found that a sufficient concentration of oxidant is necessary to efficiently convert Ru to ruthenium tetroxide before it rises. Furthermore, as a result of repeated research on the distillation method used to efficiently distill harmful ruthenium tetroxide, it is important to distill while flowing air under reduced pressure and to prevent clogging in the tube. I found.

:
That is, the present invention
(1) A solution containing at least one platinum group from Ru and Pt, Pd, Rh, and Ir is adjusted to pH = 0.5 to 2.5, and Ru is converted to ruthenium tetroxide using sodium bromate as the oxidizing agent. The solution containing the platinum group added in excess so that the sodium bromate concentration is 80 g / L or more in addition to 1 equivalent of the amount of sodium bromate added to the ruthenium tetroxide oxidation from Ru. In the method of separating and recovering Ru from
In the oxidative distillation, air is flowed under reduced pressure using a suction pump to transfer ruthenium tetroxide from the reaction tank into the hydrochloric acid solution, and water is flowed to the air introduction pipe of the reaction tank to prevent clogging. A method for separating and recovering Ru from a platinum group-containing solution.
( 2 ) In the oxidative distillation described in (1) above, the ruthenium tetroxide is preceded by
During transfer from the serial reactors in hydrochloric acid solution,
A trap tank is provided, a sodium bromate solution as an oxidant is disposed in the tank, and ruthenium tetroxide is passed through the aqueous solution of the tank to prevent generation of ruthenium dioxide, while removing Ru from a solution containing a platinum group. How to separate and recover.
I will provide a.

By separating and recovering Ru from a solution containing a platinum group using the method and apparatus of the present invention,
(1) Ru can be separated from a solution containing at least one platinum group from Ru and Pt, Pd, Rh, and Ir by one distillation operation.
(2) The ruthenium tetroxide can be prevented from being decomposed and ruthenium can be efficiently recovered.
(3) High-quality ruthenium can be easily obtained.
(4) Stable operation can be performed without blocking the piping in the distillation apparatus.

Details of the present invention will be described. An object of the present invention is to efficiently separate Ru from a solution containing a platinum group and recover the separated Ru.
The oxidative distillation method has long been known as a method in which Ru is converted into volatile ruthenium tetroxide, distilled, and led to a hydrochloric acid solution or a sodium hydroxide solution for recovery. However, in order to convert Ru into ruthenium tetroxide, an oxidizing agent having a high oxidation potential is required. Since the platinum group is recovered from the solution containing the platinum group from which Ru has been separated, it is possible to select an oxidizing agent that can be easily separated without contaminating the liquid with heavy metals, and alkali metal salts of perchloric acid, chloric acid, and bromic acid. Or chlorine gas and ozone gas are mentioned.

In the method using chlorine gas, as described above, when the chlorine absorbed in the aqueous solution decomposes into hypochlorous acid and hydrochloric acid and the liquidity becomes acidic, oxidative distillation does not proceed. It is necessary to repeat. In order to absorb the gas into the aqueous solution, it is difficult to rapidly increase the oxidant concentration in the liquid.
The method using ozone gas can suppress the pH fluctuation of the liquid and can continue the reaction. However, since the amount of ozone gas dissolved in the aqueous solution is extremely small, there is much ozone gas that is not absorbed, and Ru Is difficult to convert to ruthenium tetroxide.
The method using an alkali metal salt of perchloric acid, chloric acid, or bromic acid has a fixed pH range in which Ru can be converted to ruthenium tetroxide, and the pH changes due to decomposition of the oxidizing agent during distillation. If sufficient separation is not achieved by this distillation, the oxidant is decomposed and the pH is adjusted again, followed by redistillation.

The inventors have found that when sodium bromate is used as the oxidizing agent, the pH range in which Ru can be converted to ruthenium tetroxide is in the range of 0.5 to 2.5. Therefore, it is desirable to set the pH of the solution containing the platinum group to 0.5 to 2.5 before adding sodium bromate. However, in this pH range, sodium bromate is decomposed by the acid and consumed, and the pH rises to about 4 to 5 and becomes stable.
In order to sufficiently separate Ru by one distillation, it is necessary to carry out the oxidation reaction promptly by sufficiently increasing the concentration of the oxidizing agent. It was found that the concentration of sodium bromate is preferably 80 g / L or more in order to recover a high purity platinum group element from the liquid excluding Ru.
Since sodium bromate is used in the oxidation reaction, the amount of sodium bromate to be added is 1 equivalent of the reaction for converting Ru to ruthenium tetroxide, and the concentration of sodium bromate is 80 g with respect to the solution containing the platinum group. It is the amount that is more than / L. It is desirable to add sodium bromate rapidly at once to a solution containing a platinum group because pH increases due to decomposition by acid simultaneously with addition of sodium bromate.
In addition, when the pH at which sodium bromate is added is less than 0.5, a reaction to convert Ru to ruthenium tetroxide starts when sodium bromate is decomposed with an acid and the pH is increased to 0.5. Excess oxidizing agent to be adjusted must be added and is not efficient.

Next, the reason why the oxidative distillation is used to prevent clogging by flowing air under reduced pressure using a suction pump and flowing water to the air introduction pipe of the reaction tank will be described. Ruthenium tetroxide vapor is introduced into a 6N hydrochloric acid solution and converted to ruthenium chloride for recovery, but the boiling point of ruthenium tetroxide is about 130 ° C, which is higher than the boiling point of water.
For this reason, in order to efficiently recover ruthenium tetroxide, it is desirable to carry out distillation while flowing air.However, when air is blown into the distillate, harmful ruthenium tetroxide vapor leaks from the connection part or is blocked. When it occurred, there was a risk of pressure being applied and the connecting part coming off or bursting.
Since ruthenium tetroxide has strong oxidizability, it is not preferable to use resin or metal as the material of the device, and it is preferable to use glass or quartz. Therefore, in the present invention, Ru was separated and recovered from a solution containing a platinum group by producing a distillation apparatus shown in FIG. 1 using heat-resistant glass.
Ru puts a 6N hydrochloric acid solution in the absorption tank, and injects ruthenium tetroxide vapor into the liquid and recovers it as a ruthenium chloride solution. By using the absorbing solution in the previous stage during the next distillation, almost the entire amount of Ru can be recovered.
Distillation is preferably carried out at 70 to 95 ° C because ruthenium tetroxide has a high boiling point of about 130 ° C. If the temperature is low, the distillation time will be longer. The volume increases and the concentration of the recovered liquid becomes dilute. At 70 to 95 ° C., almost the entire amount of Ru in the reaction vessel can be transferred to the absorbing solution in one hour or longer.
The ruthenium chloride solution in the absorption tank is recovered as ruthenium powder by a known method. Examples thereof include a method of reducing to ruthenium powder by adding a reducing agent such as formic acid, and a method of adding ammonium chloride and decomposing it in a reducing atmosphere as a precipitate of ammonium ruthenate chloride.

The reason for preventing clogging by flowing water through the air introduction pipe of the reaction tank will be described. In order to sufficiently separate Ru in a single distillation, it is necessary to carry out the oxidation reaction quickly by sufficiently increasing the concentration of the oxidizing agent. At least when the concentration of sodium bromate is 80 g / L or more Desirably, 99.9% or more of Ru can be volatilized.
If the sodium bromate concentration is less than 80 g / L, Ru will remain in the reaction tank, which may interfere with the recovery of other platinum group elements. It is necessary to separate.
Since salt concentrations of sodium bromate, sodium bromide, sodium chloride and the like produced by distillation reaction are high in the reaction tank, salt may be deposited and clogged at the lower end of the air introduction pipe which is in contact with air. For this reason, obstruction | occlusion can be prevented by flowing a small amount of water through the air introduction pipe and dissolving the deposited salt. The amount of water flowing into the air introduction pipe is not particularly limited as long as it can prevent clogging, but as a guide, it is about 1/100 to 1/10 of the liquid volume in the reaction tank per hour .

The reason why a trap tank is provided will be described. In order to efficiently transfer the ruthenium tetroxide produced in the reaction tank to the absorption tank, the ruthenium tetroxide is volatilized while blowing air into the liquid in the reaction tank, and the air containing ruthenium tetroxide is absorbed into the absorption tank. Infuse. When air is blown into the reaction vessel containing platinum group elements other than Ru, a part of the reaction vessel liquid becomes mist and sent to the absorption vessel together with the air containing ruthenium tetroxide, and the absorption solution contains platinum other than Ru. Group elements are mixed.
For this reason, a trap tank containing a sodium bromate aqueous solution is provided between the reaction tank and the absorption tank, and air containing ruthenium tetroxide is passed through it to collect mist containing platinum group elements other than Ru. In order not to move to the absorbent. Since a part of ruthenium tetroxide was collected in the trap tank, the trap tank was heated so that ruthenium tetroxide was volatilized.
The reason why sodium bromate is added to the trap tank is that ruthenium tetroxide is decomposed into ruthenium dioxide in a reducing atmosphere, so that an oxidizing atmosphere is maintained and decomposition of ruthenium tetroxide is prevented. The sodium bromate concentration in the trap tank may be any concentration that maintains an oxidizing atmosphere, and is generally 5 to 50 g / L.

Example 1
Examples of the present invention will be described below. Examples were carried out using the distillation apparatus shown in FIG. 7 L of hydrochloric acid acidic solution containing Ru and a platinum group element adjusted to pH 1 was put into a reaction tank (1) installed in a mantle heater. When sodium bromate was added to this, ruthenium tetroxide was produced, so air was passed through the liquid at 10 L / min while heating to 80 ° C.
At this time, pure water was allowed to flow through the air introduction pipe at a rate of 0.1 L / hour to prevent clogging. Air containing ruthenium tetroxide vapor is led to a 3% sodium bromate solution in a trap tank (2) heated to 80 ° C. and led to an absorption tank (3,4) containing 6N hydrochloric acid solution. Vapor is recovered as a ruthenium chloride solution.
Since the air passing through the absorbing solution contains bromine gas decomposed by sodium bromate, bromine is absorbed in a 16 mass% sodium hydroxide solution and exhausted by an exhaust pump. Distillation was performed by blowing air at 80 ° C. for 2 hours.

Table 1 shows the results of the liquid composition, liquid volume and Ru distribution ratio of Example 1. In Example 1, the sodium bromate concentration added to the reaction vessel liquid before distillation was such that 1 equivalent of 33 g / L of Ru oxidation reaction, and the sodium bromate concentration of the reaction vessel liquid after distillation was 89 g / L. To 122 g / L.
The Ru concentration in the reaction tank after distillation was 0.005 g / L, and Ru could be separated from the reaction tank. Almost all platinum group elements other than Ru remain in the reaction tank, and the absorption tank contains no platinum group elements other than Ru. Moreover, by providing two absorption tanks, almost the entire amount of Ru was recovered and Ru could be separated from other platinum group elements.

(Example 2)

Hereinafter, Example 2 will be described in Table 2 based on the results of the liquid composition, liquid amount, and Ru distribution ratio of Example 2. In Example 2, the sodium bromate concentration added to the reaction vessel liquid before distillation was 61 g / L, which is one equivalent of the oxidation reaction of Ru, and the sodium bromate concentration in the reaction vessel liquid after distillation was 160 g / L. It was set to 221 g / L.
The Ru concentration in the reaction tank after distillation was 0.001 g / L or less, and Ru could be separated from the reaction tank. Almost all platinum group elements other than Ru remain in the reaction tank, and the absorption tank contains no platinum group elements other than Ru. Moreover, by providing two absorption tanks, almost the entire amount of Ru was recovered and Ru could be separated from other platinum group elements.

(Comparative Example 1)

Hereinafter, Comparative Example 1 will be described. Comparative Example 1 was carried out using the same apparatus and procedure as in the Example, except that the amount of sodium bromate added was reduced. Table 3 shows the results of the liquid composition, liquid volume and Ru distribution ratio of Comparative Example 1. In Comparative Example 1, the sodium bromate concentration added to the reaction vessel liquid before distillation was 28 g / L, which is one equivalent of the oxidation reaction of Ru, and the sodium bromate concentration in the reaction vessel liquid after distillation was 56 g / L. The amount was 84 g / L.
The Ru concentration in the reaction vessel after the distillation was 0.026 g / L, and Ru remained in the reaction vessel. This is because the sodium oxalate concentration added in addition to 1 equivalent necessary for oxidation is as low as 56 g / L, so that the ability to fully oxidize Ru does not remain. When other platinum groups were recovered from the reaction tank liquid after the distillation, sufficient quality could not be obtained, which hindered the operation.

(Comparative Example 2)

Hereinafter, Comparative Example 2 will be described. Comparative Example 2 was carried out by the same apparatus and procedure as in the Example except that pure water was put into the trap tank instead of the sodium bromate aqueous solution. Table 4 shows the results of the liquid composition, liquid volume and Ru distribution ratio of Comparative Example 2. In Comparative Example 2, the sodium bromate concentration added to the reaction vessel liquid before distillation was 70 g / L, which is one equivalent of the oxidation reaction of Ru, and the sodium bromate concentration in the reaction vessel liquid after distillation was 140 g / L. The amount was 210 g / L.
The Ru concentration in the reaction tank after distillation was 0.005 g / L, and Ru could be separated from the reaction tank. Almost all platinum group elements other than Ru remained in the reaction vessel. However, the Ru amount in the two-stage absorption tank was as small as 55% of the Ru amount contained in the reaction tank before distillation. This is because pure water was put in the trap tank instead of the sodium bromate aqueous solution, and ruthenium tetroxide was decomposed in the trap tank and changed to a black precipitate of ruthenium dioxide. Ruthenium dioxide cannot be distilled because of its low vapor pressure. For this reason, the amount of Ru recovered in the absorption tank is reduced, and it is not efficient even if the ruthenium dioxide is separately reduced.

(Comparative Example 3)

Hereinafter, Comparative Example 3 will be described. Comparative Example 3 was carried out with the same apparatus and procedure as in the Example, except that pure water was not allowed to flow through the air inlet tube of the reaction vessel. Table 5 shows the closed state of the inlet pipe when pure water is passed through the air inlet pipe of the reaction tank and when pure water is not passed.
When pure water was allowed to flow through the air introduction tube of the reaction tank, the air introduction tube was not blocked during distillation. On the other hand, when pure water was not passed through the air introduction pipe as in Comparative Example 3, the air introduction pipe was blocked and distillation could not be continued. This is because salts such as platinum group salt, sodium bromate and sodium bromide which are reaction products were dissolved in the reaction tank and crystallized inside the pipe, resulting in clogging.

It is explanatory drawing of the Ru distillation apparatus used by the Example and the comparative example.

Claims (2)

A solution containing one or more platinum groups from Ru, Pt, Pd, Rh, and Ir is adjusted to pH = 0.5 to 2.5, and Ru is converted to ruthenium tetroxide using sodium bromate as an oxidizing agent. Distill and add Ru from a solution containing platinum group that is added in excess of sodium bromate so that the amount of sodium bromate added to 1 equivalent of ruthenium tetroxide is oxidized and the sodium bromate concentration is 80 g / L or more. In the separation and recovery method,
In the oxidative distillation, air is flowed under reduced pressure using a suction pump to transfer ruthenium tetroxide from the reaction tank into the hydrochloric acid solution, and water is flowed to the air introduction pipe of the reaction tank to prevent clogging. A method for separating and recovering Ru from a platinum group-containing solution. The oxidative distillation according to claim 1 , wherein a trap tank is provided while ruthenium tetroxide is transferred from the reaction tank into the hydrochloric acid solution, and a sodium bromate solution as an oxidizing agent is disposed in the tank, A method for separating and recovering Ru from a solution containing a platinum group, wherein ruthenium tetroxide is used to prevent ruthenium dioxide from being generated and mist is removed.