Title

MECHANISM OF GOLD CYANIDATION CATALYSED BY ANTHRAQUINONE SULPHONIC ACID

MECHANISM OF GOLD CYANIDATION CATALYSED BY ANTHRAQUINONE SULPHONIC ACID

Authorship

TRINDADE, ROBERTO DE B. E.

TRINDADE, ROBERTO DE B. E.

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DOI

10.5151/2594-5327-C00319-4989-5005

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Abstract

The cyanidation process has been the most widely used to recover gold from its ores since the end of the last century. Alternative reagents, such as thiourea, thiosulphate and thiocyanate, among others, have also been investigated, but the reach of these ones is probably limited to special cases only. Nowadays, it is known that beside the cyanide concentration the rate of gold dissolution is also controlled by the presence of oxygen in solution. Under some circumstances, such as heap leaching for instance, oxygen may be almost completely absent from the leaching solution in some sites of the heap, thus hindering the recovery of gold. Suggestions to overcome this difficulty include the addition of inorganic peroxides and/or of an organic catalyst to the leaching solution. The catalyst would be an additional and recyclable oxidizing agent, as is the case with anthraquinone sulphonic acid (AQ). The present work deals with the mechanism that governs the dissolution of gold in a solution of cyanide + oxygen + AQ from tests carried out on a bench scale with a gold rotating disc. Preliminary results of tests with selected ores are also evaluated. In spite of the positive results achieved with the addition of AQ, a probable mechanism of competitive adsorption among the reagents prevent the dissolution from continually displaying higher rates. Suggestions for improving the process are also addressed.

The cyanidation process has been the most widely used to recover gold from its ores since the end of the last century. Alternative reagents, such as thiourea, thiosulphate and thiocyanate, among others, have also been investigated, but the reach of these ones is probably limited to special cases only. Nowadays, it is known that beside the cyanide concentration the rate of gold dissolution is also controlled by the presence of oxygen in solution. Under some circumstances, such as heap leaching for instance, oxygen may be almost completely absent from the leaching solution in some sites of the heap, thus hindering the recovery of gold. Suggestions to overcome this difficulty include the addition of inorganic peroxides and/or of an organic catalyst to the leaching solution. The catalyst would be an additional and recyclable oxidizing agent, as is the case with anthraquinone sulphonic acid (AQ). The present work deals with the mechanism that governs the dissolution of gold in a solution of cyanide + oxygen + AQ from tests carried out on a bench scale with a gold rotating disc. Preliminary results of tests with selected ores are also evaluated. In spite of the positive results achieved with the addition of AQ, a probable mechanism of competitive adsorption among the reagents prevent the dissolution from continually displaying higher rates. Suggestions for improving the process are also addressed.

Keywords

gold, cyanide, anthraquinone

gold, cyanide, anthraquinone