Technology of Gold Extraction from Mature Dumps by Thiourea Leaching

Tajikistan has a large volume of gold-containing dumps, which on conversion to gold equals similar to 18 t. These dumps are products of amalgamation and cyanidation processes, resulting from treating the ores from Tarorskoe, one of the largest deposits in Tajikistan, and from a few other nearby deposits: Dzhilau, Khirskhon, and Olimpiiskoe. The mineralogical composition of the dumps is represented primarily by quartz, feldspar, and clay minerals. Their average content of gold is rather high, 2.4 g/t. Therefore, it is expedient to treat the dumps on the premises of JV Zerafshan plant (in the city of Pendzhikent, Tajikistan), which processes ores of the Tarorskoe deposit and has an unloaded technological cycle. The treatment of these dumps does not require an ore pretreatment stage, since, for the actual grain-size class (-0.074 mm, 58.11%), the content of cyanided gold is 89.7%. This work presents the results of studying the extraction of gold from the dumps by thiourea leaching. The purpose of this work is to find ways to decrease the consumption of expensive reagent thiourea. It is found that the sample of the dumps contains sorption-active minerals, which lead to the loss of gold with tails. Therefore, it is suggested that raw material should undergo a preliminary acid treatment to reduce the consumption of thiourea and sodium sulfite should be added to the pulp during carbon in thiourea leach. A high degree of extraction (similar to 89%) is achieved when thiourea is loaded in the amount of 2 kg/t, ferric sulfate 7 kg/t, sodium sulfite 12 kg/t, and the initial concentration of sulfuric acid of 0.5% (at the stage of acid treatment). In this case, the consumption of thiourea is 0.8 kg/t. A process flow diagram for the dump treatment is proposed, which includes the following operations: preliminary acid treatment, carbon in thiourea leach, desorption, reactivation, electrolysis, and melting.