JPH0433733B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to Ru or Ru used in metal electrodes, catalysts, electronic parts, etc. used as anodes of electrolytic cells.
This article relates to a method for distilling Ru salt produced by melting the coating in order to recover and reuse the compound.

(Prior art and its problems) Recently, metal electrodes in which a substrate of a corrosion-resistant metal such as Ti, Zr, Ta, or Nb is coated with Ru or its compound, which has conductivity and corrosion resistance, have been used as anodes, and have excellent chlorine overvoltage characteristics. It is widely used due to its dimensional stability and the spread of the diaphragm method in the alkali industry.

When such an electrode is used in an electrolytic cell, the wear rate of the electrode is low, but in order to maintain the best performance of the electrode, it is necessary to stop using the electrode and regenerate it before the performance deteriorates. It is necessary to use it effectively.

Further, since Ru is particularly rare among platinum group elements, it is necessary to recover it from the electrode coating and reuse it.

To recover Ru from Ru peeled off from metal electrodes, Ru compounds, or coatings containing them,
melting the coating to produce soluble Ru salt;
It is then necessary to volatilize the Ru salt to obtain highly pure Ru.

Conventionally, Ru salts are distilled by continuously blowing chlorine gas into an alkaline solution, lowering the pH of the solution as an oxidizing agent is supplied, and distilling at normal pressure, or by extracting Ru salts with sulfuric acid, by adding an oxidizing agent as
There is a way to volatilize RuO ₄ .

However, in the former method, chlorine gas is injected by bubbling, so chlorine gas cannot be used effectively. In addition, unabsorbed chlorine gas must be treated as a pollution. Furthermore, if the alkali is strong, it will take time for the pH to drop, leading to problems such as a longer distillation time. In the latter method, some RuO ₄ decomposes during distillation and adheres to the inner wall of the container. Furthermore, oxidizing agents other than chlorine gas cannot sufficiently oxidize the Ru compound, resulting in the formation of black precipitates of RuO ₂ in the liquid, resulting in problems such as a decrease in the Ru recovery rate.

(Purpose of the Invention) The present invention has been developed in view of the problems of the conventional methods described above, and it can effectively use chlorine gas, extremely reduce the amount of chlorine gas used for pollution treatment, and shorten the distillation time even if the alkali is strong. , further distilled
RuO ₄ does not adhere to the inner wall of the container, and Ru
The object of the present invention is to provide a method for distilling Ru salt that can sufficiently oxidize the salt and improve the Ru recovery rate.

(Structure of the Invention) The Ru salt distillation method of the present invention involves blowing chlorine gas into a solution obtained by extracting Ru salt with water to saturate it, producing hypochlorite in the extract, and then The method is characterized in that an acid is introduced into the reactor to lower the pH to decompose the hypochlorite and volatilize RuO ₄ , and then the volatilized RuO ₄ is absorbed into hydrochloric acid.

(Example) An example of the Ru salt distillation method of the present invention will be described in the case of a soluble Ru salt produced from RuO ₂ powder. First, to explain the production of soluble Ru salt, 80 g of 85% KOH and 20 g of KNO ₃ are mixed with 300 g of pure water.
ml of this aqueous alkali solution and 10 g of RuO ₂ powder exfoliated from the metal electrode are mixed and stirred in a _nickel crucible. Place in a dryer and dry at 140°C for 6 hours to evaporate water to obtain a dried product with powder particles attached to it. Place the dried product together with the crucible in an electric furnace preheated to 800°C. The mixture was heated for 1 hour to obtain a soluble Ru salt with powder particles attached to it.

However, to explain how to distill this soluble Ru salt, first extract the Ru salt with 200 ml of pure water,
This extracted liquid was put into a distillation column of a distillation apparatus, and chlorine gas was blown into the extracted liquid at 200 ml/min for 10 minutes to saturate it. Then I started bubbling the distillation equipment. At this time, the extract was still strongly alkaline, and hypochlorite was produced in the solution. Next, 30ml of 36% HCl was added to the extract to lower the pH, which resulted in PH=10.
The reaction becomes intense around ~11 and RuO ₄ begins to volatilize, and this volatilized RuO ₄ enters a mist absorption tower heated to 70℃ containing pure water, passes through the pure water, and is dissolved and absorbed by the mist. It became RuO ₄ and entered the Ru absorption tower containing hydrochloric acid, where it began to be absorbed by the hydrochloric acid. At the same time as RuO ₄ begins to volatilize in the distillation column, hypochlorite in the extract begins to decompose, and this gas has oxidizing power, creating an oxidizing atmosphere inside the distillation column and mist absorption column. , RuO ₄ was reliably transported without being reduced and attached to the inner wall of the container. Subsequently, 36% HCl was added to the distillation column to 35ml, and the pH of the extract was lowered to around 7. Most of the _K2RuO4 was oxidized and volatilized, and the mist containing impurities such as K was absorbed in the mist absorption column. It became clean RuO ₄ and was absorbed by hydrochloric acid in the Ru absorption tower. There, 36% goes to the distillation column.
The addition of HCl was stopped, and bubbling was continued for a while to oxidize and volatilize the remaining K2RuO ₄ , and the mist was dissolved and absorbed in the mist absorption tower, and the mist was converted into RuO ₄ and absorbed into the hydrochloric acid in the Ru absorption tower. In addition, when the extract becomes around neutrality, distillation and bubbling while blowing chlorine gas again will convert K2RuO ₄ more completely.
is oxidized, volatilized, and transported.

The recovery rate of Ru absorbed in hydrochloric acid in this way is 99
%, it is extremely efficient.

Another example of the Ru salt distillation method of the present invention _is
-The case of soluble Ru salt produced from RuO ₂ powder will be explained. First, to explain the production of soluble Ru salt, 80g of 85% KOH and 320g of KNO
Dissolve in 150ml of pure water and mix with this alkaline aqueous solution.
4.0 g of TiO ₂ -RuO ₂ powder (containing approximately 11% Ru) was mixed and stirred in a nickel crucible, the aqueous alkali solution was soaked into the entire TiO ₂ -RuO ₂ powder, and the mixed mixture was dried together with the crucible. Place in a machine and dry at 140℃ for 8 hours to evaporate the moisture to obtain a dried product with powder particles attached to it.Put this dried product together with the crucible into an electric furnace preheated to 500℃. By heating for a period of time, a soluble Ru salt mixed with TiO ₂ with powder particles attached was obtained.

However, to explain the method for distilling this soluble Ru salt mixed with TiO ₂ , we first distill Ru with 400 ml of pure water.
Extract the salt and extract the extracted liquid and precipitated TiO ₂
were placed together in a distillation column of a distillation apparatus, and chlorine gas was blown into the extract at 200 ml/min for 15 minutes to saturate it. Then I started bubbling the distillation equipment. The extract at this time was still strongly alkaline, and hypochlorite was produced in the solution. Next, add 20% to the extract.
When 155ml of 6NHCl was added to lower the pH, the pH was 10 to 11.
The reaction becomes intense nearby, and RuO ₄ begins to volatilize.
This volatilized RuO ₄ enters a mist absorption tower heated to 70°C containing pure water, passes through the pure water, the mist is dissolved and absorbed, becomes RuO ₄ , and enters the Ru absorption tower containing hydrochloric acid. , began to be absorbed by hydrochloric acid. At the same time as RuO ₄ begins to volatilize in the distillation column, hypochlorite in the extract begins to decompose, and this gas has oxidizing power, creating an oxidizing atmosphere inside the distillation column and mist absorption column. , RuO ₄ was reliably transported without being reduced and attached to the inner wall of the container. Continue to add 20% 6NHCI to the distillation column up to 178m, and adjust the extract to pH=
When the temperature is lowered to around 7, most of _K2RuO4 is oxidized and volatilized, and the mist is dissolved and absorbed in the mist absorption tower.
It became RuO ₄ and was absorbed by the hydrochloric acid in the Ru absorption tower.
White TiO ₂ precipitated in the distillation column. Therefore, we stopped adding 20% 6NHCl to the distillation column.
Bubbling was continued for a while to oxidize and volatilize the K2RuO ₄ remaining in the distillation column, and the mist was dissolved and removed in a mist absorption column to form RuO ₄ and absorbed into hydrochloric acid in the Ru absorption column.

The recovery rate of Ru absorbed in hydrochloric acid in this way is
Extremely efficient at 99.5%.

As shown in each of the above examples, Ru absorbed in hydrochloric acid is then recovered and purified as H2RuCl6.

(Effect of the invention) As can be seen from the above explanation, the Ru salt distillation method of the present invention involves blowing chlorine gas into a liquid extracted from Ru salt with water to saturate it, and adding hypochlorite to the extracted liquid. Then, acid is added to the extract to lower the pH, decompose the hypochlorite in the extract, and volatilize RuO ₄ , and then the volatilized RuO ₄ is absorbed into hydrochloric acid. Chlorine gas can be used effectively without being wasted, and the amount of chlorine gas to be used for pollution treatment can be extremely reduced. In addition, if the alkali is strong and the PH cannot be lowered simply by blowing in chlorine gas, the PH can be lowered quickly by adding acid, which shortens the time for Ru salt to start distilling.
In the end, the distillation time for Ru salt can be significantly shortened. Furthermore, as soon as RuO ₄ begins to volatilize, hypochlorite decomposes and creates an oxidizing atmosphere, so RuO ₄ is reliably transported without adhering to the inner walls of the device. Furthermore, RuO ₄ is sufficiently oxidized by blowing chlorine gas into the distillation column, decomposing the generated hypochlorite, and adding acid, so that no black precipitate occurs, so RuO ₄ is completely oxidized. It has excellent effects such as significantly improving the recovery rate of Ru to over 99%.

Claims (1)

[Claims] 1 Ru salt is extracted with water, chlorine gas is blown into the solution to saturate it, hypochlorite is produced in the extract, and then an acid is added to the extract to lower the pH and the hypochlorous acid A method for distilling Ru salt, which is characterized by decomposing the salt and volatilizing RuO ₄ , and then absorbing the volatilized RuO ₄ into hydrochloric acid.