The SART Plant in Yanacocha
The SART plant in Yanacocha has been designed to treat a flow rate of 1200 m3/h and the main objective of the plant is remove the copper and silver present in the cyanide pregnant solution as metallic sulphides of copper and silver. Other aspect very important is the conversion of WAD cyanide in free cyanide. The pregnant solution receives the addition of sulphuric acid and sodium hydrosulphide and the stream is direct to the precipitation tank. During the reaction, copper and silver form copper sulphide and silver sulphide and part of the cyanide is released as HCN gas.
The reactions are performed at pH 4 to 5. The stoichiometric requirement of sodium hydrosulphide is 0.44 g per gram of copper and 0.52 g per gram of silver. The presence of other metals such as zinc, lead, cadmium and molybdenum obliges to increase the dosage of sodium hydrosulphide. Metallic sulphides are thickened and one portion of thickener underflow is recirculated to promote the formation of new metallic sulphides. When the underflow contents 20% to 30% solids, the material is sent to a holding tank, which feeds the filtration circuit. The thickener overflow contents gold and is sent to the neutralization stage with lime where the pH is raised until 10.5-11.0. The main product of the neutralization stage is gypsum, which is thickened and part of the underflow is recirculated to the neutralization plant to promote the formation of gypsum and other part is sent to the Counter Current Decantation (CCD) circuit of the Gold Mill Plant.
The overflow of gypsum thickener is sent to the Carbon-in-Column (CIC) adsorption circuit. This solution has no base metals, but the presence of carbonates produced during the neutralization has an impact on the adsorption efficiency of the carbon. In order to solve this problem, the plant incorporates the addition of antiscalant and periodic acid treatment of the activated carbon. The CIC circuit has two circuits capable to process a total flow rate of 5400 m3/h. The pregnant solution must have copper and silver contents higher than 25 ppm and 6 ppm, respectively. Next graph shows the copper and silver recovery.
Copper and silver Recovery using the SART process