|
In general, the gold heap leaching process is the more common alternative for small miners, but most the time gives lower recoveries (e.g. 60-65%), and the metallurgical performance depends on porosity, permeability, and grade of liberation for allowing a good percolation of sodium cyanide solution through the rock. This type of heap leaching includes a crushing stage before stockpiling the ore.
An alternative is employ heap leaching and activated carbon in columns (CIC) because the number of equipments is cheap and the flowsheet is very simple. In some cases, where there is a good quantity of silver in the pregnant solutions and the option of activated carbon is discarded because its efficiency will be low and won’t absorb all the gold and silver present in the solution. In this case the use of sodium sulphide could reduce the concentration of silver in the pregnant solution employing short times. See table 1.
Table 1. Effect of Sodium sulphide. Dosage 1.6 kg/t.
|
Time (sec)
|
Au (ppm)
|
Ag (ppm)
|
Ag extracted (%)
|
|
0
|
4.70
|
120
|
0.0
|
|
30
|
4.80
|
51
|
57.5
|
|
60
|
4.82
|
45
|
62.5
|
|
120
|
4.75
|
36
|
70.0
|
|
Although sodium sulphide gives good results, there is a disadvantage, flocs and settled sulphides can react with sodium sulphide. These particles could block the pores of activated carbon. For this reason many plants employ the Merril-Crowe process. |
