Obtain metallic rhenium

Because of the high melting point of rhenium, metallic powders are usually obtained through the reduction of their compounds. Then, like tungsten and molybdenum, the powder is converted to a dense metal using cermet.

Hydrogen reduction
The main method of industrial production of rhenium powder is hydrogen reduction of potassium perchlorate:

2 re kreo4 + 7 h2 = 2 + 2 koh + 6 h2o.

Some of the difficulties in this process are related to the low melting point (518°) of KReO4. To prevent sintering or even melting of the materials to be recovered, reduction begins at low temperatures (250-300°). Then the temperature rises slowly (about 2-3 hours) to 500°. With a slow rise in temperature, some materials, even at low temperatures, are reduced to lower compounds and metals. This prevents sintering when the temperature reaches 500° C. In order to prevent sintering, it is recommended to recover the mixture of finely ground potassium perchlorate and double potassium chloride. The latter melts at 770 degrees and is difficult to sinter. In the presence of KCl, the reduction temperature can be increased to 600 ~ 650°.


The hydrogen reduction method is the same as that used to reduce tungsten and molybdenum oxide in an electric furnace.
The salt to be recycled is placed in a furnace tube on a ship moving at a certain speed. For example, a ship can be made of nickel or molybdenum.

Hydrogen must be free of oxygen and water.

Rinse the reduced product repeatedly with hot water until the rhenium powder is removed from KOH and KCl. The powder is then washed with alcohol and dried. Air-dried rhenium powder, reduced from Perrhenate at 500° C, usually still contains a mixture of lower oxides. Therefore, it is recommended that additional recovery be carried out at a temperature of about 1000° C and then rinsed with water. Washing powder with dilute hydrochloric acid is recommended.

The resulting dark grey powder contains 99.0-99.8% Ee. The recovery rate is 85-95%. Washing water contains a great deal of rhenium. It is necessary to extract rhenium from it. The solution can be concentrated by evaporation. The rhenium compound is then converted to perchlorate by adding hydrogen peroxide, and potassium perrhenate is then isolated.

Electrolytic deposition of rhenium in aqueous solution
In order to obtain the rhenium coating, the conditions of electrolytic deposition of Rhenium were studied. The best results can be obtained when working in sulfuric acid bath.

A dense gloss coating is obtained under the following conditions: perrhenate potassium concentration 10 g/L, pH=1, current density 8A/dm2, temperature 70℃, low current output (not exceeding 15%).

The optimum acidity of the electrolyte must be maintained strictly.
The release of rhenium in citrate solution (500 g/ L citric acid and potassium perchlorate), ammonium citrate solution (50 g/ L citric acid, potassium perchlorate and ammonia solution, pH=9.5) and other solutions was studied.



 

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