Lixiviation in Auriferous Minerals Heap Leaching

The present work describes the operations and processes involved in the treatment of the oxidated minerals of the mineralized body, for the recuperation of gold. The technology which will be applied is resumed in the combined system.

Lixivation in Heap Leaching - Carbon in Collumns – Electrodeposition
The significant increase in the price of gold, initiated in the decade of the seventies (US$ 40 to 180/Oz. Between 1970 and 1975), and afterwards the high increase to more than US$ 500 in 1980, impulsed an intense activity in the search of new technologies for recuperating precious metals, starting from the benefit of ores each time more complex and of low grade (significant increase of the potential reserves of minerals of gold), conducing this fenomenon to a notorious change in the conventional patterns of the extractive industry of the gold. As an important result of these changes, the process of lixiviation in heap leaching appears, whose principal characteristic is its relatively low cost of investment and operation, compared to the system of lixiviation by agitation.

The lixiviation in heap leaching, is a process which can be defined as the percolation of a lixiviant solution through the heap leaching of the minerals of low grade or materials of waste which have been heap leached conveniently over an impermeable base, especially prepared. The application, with success, of the lixiviation in heap leaching mainly in operations of small scale is due to the two recent developments:

1. – The use of cloths or plastic coverings which now are disposed for impermeabilizing the base of the heap leaching completely, in reason of the significant value which the loaded solutions represent.

2. – The use of granular activated carbon which has been perfected for the recuperation of gold and silver. The use of the carbon, instead of the conventional process of precipitation with zinc, allows the design of circuits of low cost with parameters of operation which are more flexible. The use of the activated carbon for purposes of recuperation of precious metals, was initially remmitted to the stages of absorption and direct thermic destruction of the carbon, an operation which resulted to be expensive due to the fact that at the end the carbon would be lost, not being able to be used again; this inconvenient has been overcome with the recent development of the method of desorption or re-extraction (stripping) of the precious metals starting from the heaped activated carbon, which allows that the carbon which is previously reactivated again be used in the circuit of recuperation of gold. In this respect, four methods of desorption exist which can be used according to the requirements and facilities which a plant possesses:

• Conventional Zadra desorption.
• Desorption with alcohol.
• High pressure desorption.
• Anglo-American desorption.

The use of granular activated carbon in the modality of carbon in column (CIC), in conjunction with the lixiviation in heap leaching, is a simple and economical process. For the characteristics of the mineral and the quality of the impregnated solution, this technology for the benefit of the minerals has been chosen. Having implemented the process of desorption with alcohol to the circuit followed by electrodeposition in cells Zadra type.