Carbon Regeneration

The absorbant action of the activated carbon is not limited to the cyanide complexes of gold and silver, and to other metallic ions which could be present in the solution competing with these for active places. The activated carbon is capable of absorbing, besides, a great variety of organic substances (greases and oils) and inorganic constituents such as carbonate of calcium and sylice, which are not removed during the desorption, contaminating it with the loss of its activity.

The characteristic procedure of reactivation of carbon consists in first, eliminating the carbonate of calcium and the sylice through washings in heat withdiluted nytric acid (or chloridric if there would be no latter problems of exulceration) and with solution of caustic soda, to after submit it to a direct heating between 600°C and 650°C for a lapse of 30 minutes in an atmosphere whivh lacks oxygen, with the intention of eliminating the contaminating organic matter without producing combustion.

Separation of Gold/Silver with Sodium Sulphur
Due to its minor price and that also the adsorbant capacity of the carbon by the silver is minor than by the gold, the treatment of the rich sollutions in silver makes a considerable increase to the amount of carbon required for absorbing the same economical equivalent. One procedure which avoids the handling of great volumes of activated carbon is to precipitate the silver selectively with sulphur of sodium and, after filtering, absorbing the gold contained in the in the filtering. The key to this procedure radicates in the formation of flocules of Ag2S easily filterable through the adition of lime in doses of the order of 250 ppm (250 g/m3), and agitation of the pulp for about one hour (12). This method is also effective to separate the silver from concentrated eluides of desorption, allowing to obtain a cathodic deposit of gold with low content of silver.