Process for Gold and Silver Leaching with Thiourea Solutions

Abstract

The present invention concerns the mining and mineral treatment industry. Specifically, it relates to a solution composition that permits the use of thiourea. Specifically, the patent refers to a process to form a solution that improves, on one hand, the velocity of gold and silver extraction, from minerals and other materials that contain them, improving the stability of the thiourea in the leaching solution and, on the other, the direct electrorecovery of said metals from the aforementioned solution. The invention consists of the leaching solution that, beforehand or simultaneously, has been subjected to a controlled electro-oxidation to produce formamidine disulfide (FADS) which acts as an oxidizing agent for the mineral phases that contain the gold and silver. In the preferred mode, the FADS is present as 10 to 30% of the total thiourea contained in the solution and the electrodeposition of the metals is performed in the same cell (cathodic compartment) in which the FADS is formed (anodic compartment).

Description

FIELD OF THE INVENTION [0001] The present invention concerns the mining and mineral treatment industry. Specifically, it relates to a process that uses thiourea, electro-oxidized under controlled conditions, to form in-situ an oxidizing agent capable of dissolving gold and silver from minerals which contain them and the electrolytic recovery of said metals in the same process. BACKGROUND OF THE INVENTION [0002] At present, the processing of gold and silver ores fundamentally depends on the form in which they are found in the mineral, using for this flotation, amalgamation and / or leaching. In this last technique, the solution employed plays an important role in the efficiency and environmental impact of the process. [0003] Basically two commercially implemented leaching techniques exist: cyanidation produces the highest yields in the majority of cases, however, with the problems of toxic residues and low efficiency in refractory minerals (those that contain organic material, arsenic ...

AI Technical Summary

Benefits of technology

[0007] One objective of the present invention is to avoid the harmful effects of the external oxidizing agents on the thiourea solutions.

[0008] Another consists in recovering the gold and silver in their metallic form, once extracted from the mineral, in such a way that the electrical energy is employed in an optimal manner, by oxidizing part of the thiourea to formamidine disulfide in one of the compartments (anodic) and, in the other (cathodic), reducing the dissolved gold and silver reducing to their metallic state.

[0010] In summary, our invention reduces the inconveniences of the instability of thiourea in the presence of strong oxidants, permitting at the same time a clean recovery of the metallic values, and constitutes an improvement of the solution employed for leaching gold and silver from minerals and other materials that contain them, employing thiourea. These improvements are characterized by the controlled electro-oxidation of 10 to 30% of the thiourea originally in the solution and the simultaneous electrowinning of the gold and silver from said solution. On the other hand, it consists of a process which allows the application of this solution in a process which extracts and recovers the metallic values from the minerals which contain them.

Problems solved by technology

Basically two commercially implemented leaching techniques exist: cyanidation produces the highest yields in the majority of cases, however, with the problems of toxic residues and low efficiency in refractory minerals (those that contain organic material, arsenic or manganese) or those that contain high concentrations of silver sulfides.

One of the great obstacles for the industrialization of the thiourea process to extract silver and gold is the instability of the thiourea solutions themselves.

Another impediment related to the use of thiourea is that the methods employed for precious metal recovery from the leaching solutions results in their contamination, limiting the possibility of their recycle within the process.

Additionally, there exists a disequilibrium with respect to the utilization of electrical energy; on one side of the electrolytic cell, the thiourea is being partially oxidized while, on the other side, separated by a membrane, the generated potential is being wasted on a sacrifice reduction process.

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