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DEWATERING OCTOBER 2017 • E&MJ; 55 www.e-mj.com Once mechanical and electrical instal- lation were completed, the next two stages, i.e., pre-commissioning and commission- ing, were critical to guarantee a smooth and proper plant startup and the related ramp-up stage, as well as to mitigate dam- age risks in the installed mechanisms and peripheral equipment during operations. After completing the required condi- tions during the commissioning process to have both CCD thickeners working, the plant started operations on schedule. Once the upgrade was implemented, the throughput improved by a staggering 60% and the plant now has a processing capacity of 2,500 mt/d, and the subsystem implemented by FLSmidth could allow it to increase to as much as 3,000 mt/d. Taking It to the Next Level The standard cyanide leach process con- sists of grinding the ore, then mixing the ground ore-water slurry with sodium cya- nide and enough quick lime to keep the pH of the solution at about 11. At a concen- tration of 45% solids, the slurry is pumped to a series of agitated mixing tanks sized to provide the required residence time. The metal-bearing liquid then is separat- ed from the leached solids in a decanter, and the tailings are washed to remove metal and cyanide before disposal. The separation and washing of these tailings takes place in a series of units by a process referred to as CCD. The liquor is progres- sively pumped back into the plant from the solids in a counter-current fashion. Volcan currently processed the de- canter underflow through a three-stage CCD circuit and is adding fourth and fifth stages (CCD 4 and CCD 5) to improve the recovery of dissolved metal. "By counter current washing, the dissolved metals — cyanide compounds — are recovered to the maximum ex- tent before the solids are pumped to the Detoxification circuit for the destruction of the residual cyanide before discharge," Gamero said. Maximizing the recovery of cyanide back into the plant reduces the consumption of cyanide for leaching and also reduces Detox chemical con- sumption, thus reducing the plants over- all operating costs. The flocculant dosing system consists of bulk storage of flocculant crystals, feeder, eductor, and three preparation and storage tanks. "Raw water is added at the eductor where it mixes with the flocculant crystals and feeds the three compartment prepara- tion with storage tanks," Gamero said. Beyond normal operating conditions, each thickener can be bypassed and oper- ated separately. "CCD 4 can be bypassed and the feed from the existing CCD 3 can be directed to CCD 5 Mix Tank," Gamero said. "CCD 5 overflow can be sent to the Process Water Tank via a by-pass line. If CCD 5 is not in operation, CCD 4 can still operate. For this operating condition, CCD 4 underflow slurry is sent to the re-slurry tank and raw water is added directly to CCD 4 Mix Tank to provide optimum feed solids density." Following the completion of the proj- ect, FLSmidth continues to work with Volcan in various optimization projects to help improve the productivity of the plant. Currently, a pilot upgrade project is being implemented in the plant — not at indus- trial scale yet — consisting of replacing raw water for acid water coming from an old tailings pond after going through CCD 4 and CCD 5, to obtain a slurry that will go to the detox stage. This upgrade was de- signed to avoid sulphur release caused by the contact between pyrite and air/water. IBIS-ArcSAR Next Generation Radar Revolutionizing Safety in Slope Monitoring IDS GeoRadar Srl Part of Hexagon Via Enrica Calabresi 24, 56121 Pisa (PI) Italy Tel. +39 050 3124 501 sales.mining@idsgeoradar.com www.idsgeoradar.com Criঞcal monitoring to ensure the highest safety standards and manage risk condiঞons with confidence 3D SAR radar for a stunning 360° field of view The widest and longest range (5000 meters), shortest scan ঞme (360° in 40s), and outstanding spaঞal resoluঞon of 10 million pixels Enhanced data interpretaঞon with instant HD picture of monitored area. Built-in GNSS and real ঞme DTM survey Combined, built-in hybrid solar–diesel generator supply system, with opঞonal wind turbine The most advanced automaঞc atmospheric correcঞon in the market Minimal moving parts and low profile design