Solution Application

The lixiviant solution can be spread over the pan through the process of drops or dew with perforated plastic tubing, for aspersion with loaders, and, in special cases of low velocity of percolation, through the wells which are formed on the surface containing the solutions with entablature. The flux of alimentation varies within a very ample range between 2 and 35 ml/sec. By square meter of the irrigated surface, and including more in beds of good permeability.

Among the diverse methods for recuperating the gold and silver from the solutions of cyanidation in heap leaching, the cemnetation of dust of zinc of Merril-Crowe and of the adsorption with activated carbon are outstanding due to their major use. The final one mentioned can also go accompanied of an optional precipitation of the silver with the sulphur of sodium when the relation silver/gold in the solution is very high.

The absorbant properties of the activated carbon above the gold in sollutions of cyanide are known since the end of the past century, but its industrial use was restricted for a very long time due to the lack of an efficient procedure of desorption from the loaded carbon, having to recurr to the calcination. This disadvantage, together with the technological advances reached in the precipitation with zinc, made to diminish the interest for the activated carbon.

The situation, nonetheless, started to change starting from the year 1950 with the development of a method by part of the U.S. Bureau of Mines which allows the re-use of the carbon. From that time on, other methods of desorption have been developed and numerous processes for recuperating the gold and silver using activated carbon have been proposed. The option for precipitation of Merril-Crowe for treating the solutions of cyanidation in heap leaching is sustained better yet in the capacity available of the circuit of some existent conventional plant, on the contrary, the adsorption with activated carbon is preferred, not only for being more efficient for processing diluted solutions of gold and silver, which besides, do not need to be clarified, but also because it involves lower costs of capital and of operation.