A new phosphine oxide extractant, commercially known as Cyanex 923, has been studied in order to be applied in the recovery of gold from either cyanide or chloride aqueous media.
is extracted by this reagent Au(CN) 2 throughout the whole pH range. The presence of lithium salts in the media improves the extraction. The extraction mechanism proposed can be explained in terms of a solvating reaction, the species formed in the organic phase being the following :
The stripping can be performed by low ionic Li`Au(CN) 2 ~3(R 3 PO). strength solutions such as dilute KCN solutions, and the reaction is enhanced by an increase in temperature. In chloride media, the extractant is able to extract gold (III) in the entire range of acid concentrations. The amount of extraction agent required, to achieve the same level of extraction, in this medium is much lower than in the cyanide media. The temperature has a negative e †ect on the extraction. Another di †erence observed between the two media, is that the presence of ionic salts in chloride media has no inÑuence on the extraction, which may be attributed to the fact that the extracted species, is a protonated HAuCl 4 , instead of an ionic species. 1998