concentration cyanide solution is required. The cyanide eluted resin is discharged to a resin transfer tank to be pumped back to the adsorption circuit. The resin flow rate through the elution column, and subsequently through adsorption, is determined by the cyanide level in the CIL/CIP discharge, and automatically controlled by a variable speed rotary valve at the outlet of the column. Variations to the basic ReCYN I flowsheet include simultaneous recovery of cyanide and zinc from Merrill- Crowe plant tailings. Zinc is eluted by sulphuric acid at the same time as cyanide but recovered in a separate precipitation step. The combination of co-current adsorption, continuous elution and immediate return of cyanide to the leach circuit makes for a simple and efficient cyanide recovery circuit. RECYN II The presence of sufficient WAD cyanide complexes in the tailings slurry that require a detoxification step to meet discharge compliance is accommodated with ReCYN II. For small quantities of WAD cyanides, less than 100ppm as CN, a combined cyanide and metal adsorption section is used. However, for larger quantities, two-stage adsorption is preferred as shown in Fig. 2 ReCYN II FlOWSHEET.
RECYN II PROCESS FLOWSHEET
Slurry Flow Resin Flow Solution Flow
Carbon Safety Screen U/F Metal Eluted Resin
Resin Sizing Screen
Flocculant
NaSH
Precipitate Thickener
Loaded Resin Screen
H 2 SO 4
NaOH
Copper Elution Column
Metal Adsorption Tank
Filter Feed Tank
Copper Reactor Tank
Loaded Resin Tank
NaCl
Copper Filter
Copper Concentrate
Cyanide Eluted Resin
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. 2 ReCYN II Flowsheet
The metal cyanide complexes are removed before the free cyanide using a similar adsorption circuit for both duties, generally three stages of twenty minutes each, in a co-current flow. Copper elution is more efficient with a higher CN:Cu ratio on the loaded resin thus favouring the staged adsorption steps. The slurry tailings from the metal adsorption stage flows to the cyanide recovery adsorption circuit where the free cyanide is then recovered as per ReCYN I.
ALTA 2020 Gold-PM Proceedings
4
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