Simple metal electrode reaction

A characteristic of this type of reaction is that the system potential is independent of pH and is only related to the ion activity in the solution. The general formula of the reaction is:

The greater the value of the E system, the system of larger ions are reduced to precipitate metals trend; the other hand, if the smaller the value of the system E, the greater the tendency of the metal is oxidized, the oxidation reaction if the final product is readily soluble Then the metal dissolves.

In heap leaching, the dissolution and leaching of copper , gold and silver and the dissolution of most metals belong to this type of reaction. For heap leaching with natural copper in the ore, when an oxidant is present, the reaction can be expressed as:

When replacing the scrap iron copper leaching solution to form a copper sponge, which reaction is as follows:

This reaction involves two simple metal electrode reactions. The copper dissolution reaction is as described above, and the other electrode reaction and its potential relationship are as follows:

Electric type of displacement reaction:

When a sufficient amount of iron is present, the reaction proceeds until almost all of the copper ions have been deposited. Because when ε = 0, aCu ^{2 +} /aFe ^{2 +} =10 ^{- 26.3} .

For gold ore heap leaching, the gold in the ore is essentially natural gold, and its leaching reaction can be expressed as:

Its potential is: E=1.3+0.0591lgaAu ⁺ (9)

Such a high potential indicates that it is impossible to oxidize and leaching gold by using oxygen or other oxidizing agent in an aqueous solution. In the production practice, people use the complexation of gold with cyanide and chloride to reduce the concentration (activity) of metal ions in the solution, thereby reducing the potential of the system. The complexation reaction is as follows:

It can be seen from Table 1 and Table 2 that the standard reduction potential of the above reaction is -0.68 V, and the stability constant of the complex ion is 2 × 10 ³⁸ . It can be seen that when there is free CN ^- , the activity of metal ions in the solution can be significantly reduced. . At this time, the potential of the gold cyanide heap leaching is:

Table 1 Common monovalent gold complex formation potential

Table 2 Commonly used gold junction ion stability constants

For the gold cyanide complex ions in the cyanide heap leaching solution, some of the heap leaching fields adopt a zinc replacement process, and the chemical reaction is as follows:

Another metal electrode reaction and its potential relationship included in this reaction are as follows:

It should also be pointed out that in the heap leaching process of gold, copper, silver and other ores, the extract of high-grade copper oxide ore is subjected to extraction-back extraction to obtain a stripping solution with high copper content (35-50 g/L); gold ore By the adsorption-desorption of carbon, a desorption liquid having a high gold content (0.3 to 8 g/L) is obtained, and these solutions are obtained by electrowinning to obtain electrolytic copper and gold mud, respectively. These electrowinning processes also belong to the metal electrode reaction.

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