Treatment Studies

Not all the minerals of gold and silver are apt for a treatment of cyanidation. Besides the absence or presence only in limited quantities of cyanidic agents (partially oxidated sulphurs of As, Sb, Zn, Fe and Cu consume the cyanide), carbonaceous material (which absorbs the precious metals placed in the solution), and organic substances (which consume the oxygen carried by the lixiviant solution, vital so that the reaction may be produced), the gold and the silver must be finely particled for a rapid dissolving (9, 12).

In the cyanidation in the heap leaching, the host rock must be, as a matter of fact, porous and permeable to the solution, or produce enough exposition of the particles with the crushing in minerals of low porosity. On the other hand, the presence of excessive quantities of clay in some minerals difficulties or does not allow the percolation of the solution, this inconvenience can be eliminated through an agglomeration of fines.

Even when a mineralogical exam could indicate that a determined mineral of gold or silver is adequate to be cyanized in heap leaching, it is necessary to study its metallurgic behavior through a program of laboratory and pilot tests. Initially, tests of cyanidation are taken into effect in bottles with the objective of determining the degree of extraction and consumption of reactives (NaCN and CaO). If the precious metals are lixiviable to a size of crushing and with an economic consumption of reactivates, we continue with tests of percolation in columns with the crushed mineral to various granulometries (until even as fine as as – 3/8”), a simultaneous system of adsorption with activated carbon being able to be used.

In certain cases in which it is desirable to verify the results of the experiences in columns and to obtain information about the physical characteristics of the heap leaching, one recurrs to pilot tests. These tests can be performed at diverse sizes of the heap leaching, starting off with a few tons in low heap leachings constructed with crushed mineral. For a certain height of operation, Potter recommends a minimum of 500 TM, or on the contrary the inclined area will be excessive compared with the horizontal area, counterfeiting the entering of the oxygen to the bed of the mineral.