Modern Mining August 2016

GOLD

go to the 2,4 Mt/month level, then we need to address this issue,” he explained. “The way we intend to do this is to make use of the Withok site which is immediately adjacent to the Brakpan TDF. Earlier this year we received the necessary regulatory approval to incorporate the Withok footprint into the TDF and, once implemented, this will increase Ergo’s deposition capacity from 200 Mt to approximately 800 Mt – enough to receive most of the mine tailings in and around the Johannesburg area and to assure Ergo’s life of mine for at least another 25 years. When exactly we implement the project is dependent on a feasibility study which is currently well advanced and which is looking at all aspects

a record gold production in March last year. “Getting the FFG circuit right was a difficult task, as we were dealing with so many variables that it was difficult to pinpoint exactly why we weren’t getting the recoveries we expected,” Schoeman told Modern Mining . “We were fairly certain that the basic design was sound but we identified over 50 enhancements that we thought could make a difference and system- atically implemented them all. Then we started up the FFG circuit in stages, making sure that each float stream was stable and achieving the desired parameters before we moved onto the next one.” The enhancements included changes to the carbon management circuit, increasing the water storage capacity and management within the plant, modifications to control systems and ensuring increased tailings thickener availabil- ity prior to the low grade CIL circuit. Although the FFG circuit is now working well, Schoeman said that DRDGOLD is con- stantly looking at ways to improve its operation. “We believe we can get even better numbers out of the FFG. For example, we currently have a mill feed of about 80 % passing 35 microns and we mill that down to 80 % passing 24 microns. The optimum is to go down to 20 microns but there is a cost offset. We will get there – it’s a continuous optimisation exercise.” Looking ahead, Schoeman said that Ergo’s total treatment capacity was now 2,4 Mt/ month, with the Brakpan plant (after the recent refurbishment of five CIL tanks) now hav- ing the ability to process 2,1 Mt/month and the Knights facility a further 300 000 tonnes/ month. “The current restraint on our pro- duction is not plant capacity but deposition capacity – specifically the rate at which we can safely deposit material at our Brakpan Tailings Deposition Facility (TDF) – and if we want to

DRDGOLD’s infrastructure extends over a 62 km long portion of the central and east Witwatersrand.

of the Ergo operation,” he concluded. Photos (unless otherwise acknowledged) courtesy of DRDGOLD

The process flowsheet at Brakpan With the FFG now fully operational for well over a year, all the slurry enter- ing the Brakpan plant enters the flotation section after passing over linear screens to remove organic material and debris. After the material is condi- tioned with reagents, it enters the float cells where it is separated into two streams. One stream, the flotation concentrate, contains the sulphides while the second stream, the flotation tails, is made up of lower-grade material which is treated in the Brakpan plant’s main CIL circuit. The concentrate stream is subjected to the new fine-grind process, which involves milling the slurry material with tiny beads using four verti- cal stirred mills (sourced from FLSmidth). At this stage the milled product has been liberated from the sulphides, making recovery of the previously encapsulated gold easier as it comes into contact with cyanide during the leaching process that follows. The dissolved gold is adsorbed onto activated carbon and the ‘loaded carbon’ in each circuit enters the carbon treatment section where the gold is eluted from the carbon. The carbon then returns to the CIL circuit via a regeneration kiln. Once the gold has been eluted, it undergoes electro-win- ning where the gold is precipitated, calcined and smelted in the existing smelthouse. 

August 2016  MODERN MINING  31