Old Recovery Processes

 

 

Many modern gold recovery processes have been developed considering the efficiency of old recovery processes. Some processes were employed at small scale or others were not employed continuously. For this reason is important to review the main characteristics of the old gold recoveries processes. Gold was extracted from its ores, either direct by washing (gravimetric processes) or metallurgical processes. In the latter it was combined with mercury, lead silver or copper, or brought into aqueous solution. The extraction of gold was performed in the dry way, in the wet way or by means of electrolysis.

Basically, it is important to distinguish the gold extraction in the different categories. By simple washing the extraction is performed by dressing gold-bearing sands, gravel or ores. The extraction of gold in the dry way is effected by converting the gold into a gold-lead or gold-lead-silver alloy and cupelling it. The extraction of gold by combined wet and dry methods may be performed by obtaining gold as a gold-mercury alloy, obtaining gold in aqueous solutions and obtaining gold as a gold-silver or gold-silver-copper alloy, and dissolving the silver and copper out of these alloys. The extraction of gold by means of electric current was performed by obtaining the gold as a gold-silver or gold-copper-alloy and separating these metals from the gold by means of electrolysis.

The separation of gold and silver is known as “parting” and played an important role in the extractive metallurgy of gold. The selection of a method of gold extraction depended on the mode of occurrence of gold and the nature of the substances intermingled with it. Extraction of the gold by washing is only possible in the case of ores carrying native or free gold. Except for the separation of the gold that occurs in coarse grains or large nuggets in alluvial deposits, by handpicking or washing, this method offered important losses of gold. Washing or gravimetric was combined with amalgamation processes.

The dry method of gold extraction consisted in smelting gold ores or auriferous furnace products with lead, lead ores or lead-bearing furnace products. This method was employed not on pure gold ores, but on auriferous and argentiferous lead ores. It was also used with the advantage for auriferous and argentiferous copper ores. It was used on pure gold ores where lead ore and fuel are cheap or where other methods were not applicable owing to the character of the gold ore itself. Extraction of gold means of mercury is known as amalgamation and was used whenever the main proportion of the gold present is capable of being absorbed by mercury. This method was a simple and cheap portion to recover gold, but often failed with ores that contains the gold in affine state or division or enclosed in pyrite.

Extraction of gold by means of aqueous solutions such as chloride or cyanide was employed when the gold was not completely extracted by amalgamation, as is often the case with pyritic ores. This method was used with advantage where amalgamation failed and smelting processes were too expensive. The extraction of gold in the form of gold-silver or gold-copper alloys out of which the silver and copper are subsequently dissolved was a combination of smelting methods or wet methods with parting. Auriferous copper was obtained by smelting gold-bearing copper ores or gold ores with copper ores or mattes. Auriferous silver was obtained by treating gold-bearing silver ores with lead, argentiferous gold was obtained in most methods of gold extraction. The silver and copper are dissolved by acids leaving he gold behind. The extraction of gold by electro-metallurgical processes was considered for the treatment of gold alloys, especially gold-copper and gold-silver alloys.