A Flash Chlorination Process was developed as a pre-treatment step to oxidize organic carbon and pyrite present in refractory gold ores. The process deactivates preg-robbing carbon and produces a material suitable for a common cyanidation process. The process is a modification of the classical chlorination process and was developed by Newmont Mining Corporation and the process is based on high shear forces and efficient gas dispersion in to the vessel. The chlorination vessel has been designed with special devices to introduce chlorine gas into the hydrocyclone overflow and the process is able to reduce the typical chlorination time by 60 to 90 times. For this reason the process is called Flash Chlorination.
During the process, some heat is produced in the chlorination circuit as a result of the exothermic reactions produced in the process and the chlorine utilization efficiency is higher than 90% through all the Flash Chlorination Process. Once the refractory gold ore is pretreated, the excess of hypochlorite is neutralized and the material is mixed the oxide ore and processed through a Carbon-in-Pulp or Carbon-in-Leach circuit. A lot of research work has been carried out on direct recovery of gold from the chloride solution and the activated carbon adsorbs efficiently the dissolved gold and the residence time tends to be short. The potential problem of direct recovery is the possible losses of gold and carbon by attrition. The alternative recovery process is a Resin-in-Pulp (RIP) circuit and the type of ion-exchange resin is important due to gold chloride system could attack the resin matrix.
The process can be applied on carbonaceous and sulphidic refractory gold ores with variable amounts of clays and calcareous minerals. The typical carbon content of carbonaceous and sulphidic ores is 3.0-4.5 and 2.5-4.0%, respectively. The typical sulphur content of carbonaceous and sulphidic ores is 0.3-0.7 and 0.4-1.2%, respectively. The typical organic carbon content of carbonaceous and sulphidic ores is 0.3-0.5 and 0.2-0.4%, respectively.
Chlorination of carbonaceous and sulphidic gold ores have been practiced in Nevada since 1971 and the Flash Chlorination process is an alternative with metallurgical and economical benefits that gold companies with preg-robbing problems must consider to develop gold projects that were not developed before due to the lack of appropriate technology.
Flash Chlorination Circuit