In 2017 a decision was made to capitalise on the success of the cyanide recovery circuits and commercialise the technology under the brand name of ReCYN through a new specialist company called GreenGold Technology (GGT). The company is based in Jakarta, Indonesia, taking advantage of the operational expertise gained on the two Indonesian projects. The GreenGold team includes several of the lead engineers that ran the Vitrokele development programme. Since its inception in 2017, the GGT company has advanced the ReCYN technology through studies and research with over 30 projects worldwide for most major gold mining companies. The Martabe ReCYN II plant was the first large scale project (6Mtpa) constructed under the GGT brand, due for completion of commissioning in November 2020. Copper levels in the Martabe ore were at problematic levels and caused processing challenges (3) . In a logical progression of technology development GGT have responded to the needs of the mining industry and developed ReCYN III; combining free and complexed cyanide recovery with gold as a primary recovery circuit, replacing the need for a carbon circuit. Two previous Alta papers, 2017 and 2019, provide information on ReCYN I and ReCYN II, with both processes described below as part of ReCYN III. Flowsheet improvements made since the 2019 Alta Paper are noted in the descriptions. RECYN I The recovery and recycling of "Free" cyanide from the post-leach slurry can be provided as a stand-alone circuit when solution chemistry allows. When the ore is relatively clean from cyanicides and the removal of Free cyanide is sufficient to meet compliance, a ReCYN I flowsheet is applied. A summary flowsheet is shown in Fig.1.
Slurry Flow Resin Flow Solution Flow
RECYN I PROCESS FLOWSHEET
Cyanide Eluted Resin Carbon Safety Screen U/F
Scrubbing Column
Resin Sizing Screen
Loaded Resin Screen
NaOH
Ventilation
Cyanide Adsorption Tank
Cyanide Elution Column
Safety Screen
Recycle Cyanide Solution to Leach Tank
Recycle Cyanide Tank
Loaded Resin Tank
H 2 SO 4
Tailing Dam
Tailings Hopper
Fig. 1. ReCYN I Flowsheet The combination of favourable equilibrium and kinetics allows the use of a co-current adsorption circuit incorporating small tanks, usually 20 mins residence time for each tank. The benefit is reduced equipment complexity, minimised resin inventory, optimised adsorption efficiency and simple control. Resin adsorption kinetics are fast, with adsorption complete in 5 to 15 minutes. However, the use of a continuous co-current adsorption train requires several stages to be used to overcome by-passing. Triple stage agitators ensure complete mixing of the slurry and resin as the low density of the resin bead causes it to float compared to carbon, which tends to sink. A three-stage, co-current, adsorption train uses "conditioned" resin to remove the free cyanide from the slurry. Free cyanide is adsorbed onto the resin by converting CuCN present on the eluted resin to CuCN 3 2- . The treated slurry and loaded resin discharge from the last adsorption tank across a wash screen with the loaded resin stored in an agitated tank to control the feed rate to the elution column. A continuous elution column is selected because of the large resin flow to be eluted and to maximise efficient use of the acid in a counter-current flow regime. Sulphuric acid is used as the eluant to release the CN as HCN in solution. The eluate containing the HCN is fed to the direct neutralisation tank and then recycled to the leach circuit. HCN gas is not generated except in a separate VR (volatilisation-recovery) circuit if a higher
ALTA 2020 Gold-PM Proceedings
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