SU436799A1 - The method of cleaning amalgams formed in the process of electrolysis with a mercury cathode - Google Patents

Description

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There is no known method of purification of amalgams formed during the process of electrolysis with a mercury cathode, before their decomposition by washing with liquid ammonia.

However, this method is only acceptable for cleaning amalgams from colloidal and mechanical impurities.

In order to efficiently clean amalgam from metallic impurities, such as potassium, a method has been proposed, but using an electrolyte with a cation of the same base metal as the washing reagent, the average activity of which is no less than an order of magnitude higher than the average activity of the electrolyte subjected to electrolysis. When an amalgam is transferred to a new electrolyte, the greater the amalgam potential shift occurs, the more the electrolyte activities differ.

With a new potential value, the content of impurity deposited on the amalgam exceeds the equilibrium value for a given potential, which causes the reverse transition of impurity from the amalgam to the solution as a result of equivalent exchange with the base metal cations and the amalgam so that it is clear of impurity.

Of practical interest is the effect achieved when the ratio of average coefficients of electrolyte activity at the stages of formation and washing of the amalgam is not less than 10. The cleaning effect increases with an increase in the indicated ratio of average activities.

When the amalgam contacts the electrolyte solution with the same-cation of high average activity, the base metal is practically not lost.

After purification of the A. Malgam of impurities by the proposed method, it is sent to a decomposer to obtain a highly pure metal in the form of its compound or in an elemental state (with subsequent extraction on a solid cathode).

The method allows the amalgam to be purified from metallic impurities whose standard potentials are close to the potential of the base metal, in particular, potassium, calcium, lithium, magnesium, rubidium, cesium and barium.

Example. The resulting irie electrolumine sodium chloride 0.25% sodium amalgam, containing as an impurity 0.009% potassium, is brought into contact with a 40% solution

caustic soda. The initial potassium content in caustic soda is 0.0014%. After contact of the amalgam with an alkali solution for 4 seconds, the potassium content in the solution increases to 1.28%. In the amalgam after washing it with a solution of alkali, the calcium was not detected, and the content of sodium was practically unchanged.

The amalgam purification data provided in this example refers to the electrolysis of a sodium chloride solution whose average activity coefficient is 0.76. (s) Concentration of sodium chloride 305 g / l (5.2 M-Cf). Thus, the average activity of the electrolyte is a 0.765, 2 4.

 activity coefficient of 40% (14.3 at 80 ° C is equal to 4.3 (). Therefore, the average activity of alkali

and Tr-s ;; 4.3.14, 4.

Prevention of Invention

The purification method for amalgams formed in the process of electrolysis with a mercury cathode, and their decomposition by washing with a liquid reagent, is the same. In order to increase the purity of the mixtures of metallic character, such as potassium, an electrolyte with the same base metal cation is used as the washing reagent, the average activity of which is no less than an order of magnitude of the average activity of the electrolyte subjected to electrolysis.