Among the gold extraction processes, cyanide leaching occupies more than 85% of the global
gold ore processing volume by virtue of its high recovery rate (generally >90%) and mature
technology system. According to different ore characteristics and production requirements,
five mainstream process schemes, namely heap leaching, CCD, CIP, RIP and CIL, have been derived.
This paper analyzes the differences and selection logic of each method from the technical
principles, process design and application scenarios.
Basic framework of cyanide leaching process
1. Core chemical principles
Cyanide (NaCN/KCN) complexes with gold in an alkaline environment (pH 10-11):
4Au + 8CN- + O₂ + 2H₂O → 4[Au(CN)₂]- + 4OH-
The reaction needs to strictly control the cyanide concentration (0.03%-0.1%), dissolved oxygen
content (≥6ppm) and ore size (-200 mesh share >90%).
2. Factors affecting process selection
Ore grade (g/t)
Mineral embedding characteristics (free gold/encapsulated gold)
Investment scale and operation cost
Restrictions of environmental protection regulations
Five major process technologies
1. Heap Leaching
Technical characteristics:
Applicable to low-grade ore (0.5-1.5g/t)
The ore is crushed to 10-50mm and then stacked and sprayed.
Leaching cycle 30-120 days, recovery rate 60-75
Advantage:
40% reduction in infrastructure costs
No need for complex grinding system
Suitable for arid region operations
Limitations:
Liquid return system is susceptible to rainfall
Cyanide residue in tailings requires strict treatment
2. Counter-Current Decantation (CCD)
Technical Characteristics:
Multi-stage thickener in series to realize solid-liquid separation
Leaching liquid and slurry flow in the reverse direction
The leaching rate can reach 92-95%.
Core equipment:
High-efficiency thickener (diameter ≥30m)
Vacuum filtration unit
Automatic solution blending system
Application Scenario:
Treatment of highly-sludged oxidized ores
Large-scale continuous production (daily processing capacity>3000t)
3. CIP Carbon-In-Pulp Method (CIP)
Technical features:
Direct adsorption of gold-cyanide complexes between activated carbon and slurry
Number of adsorption tower series 4-8 stages
Gold-carrying carbon grade up to 3000-6000g/t
Process Highlights:
Elimination of solid-liquid separation
Reuse rate of carbon regeneration system＞95%.
Suitable for materials containing clay that are easy to settle
4. RIP Resin-In-Pulp method (Resin-In-Pulp)
Technical features:
Strongly alkaline ion exchange resin is used instead of activated carbon
Adsorption capacity is 3-5 times higher than carbon
Better pollution resistance than traditional CIP process
Technical breakthrough:
Applicable to difficult-to-treat ores containing organic carbon or arsenic
Mechanical strength of resin＞Carbon particles, loss rate reduced by 60
Desorption reagent consumption is reduced by 30%.
5. CIL Carbon-In-Leach method
Technical Characteristics:
Simultaneous leaching and adsorption
Reduced slurry cyanidation time to 18-24 hours
Increased recovery to 92-96
Process Innovation:
Elimination of independent leaching tanks, equipment investment reduced by 25
Adsorption of activated carbon in agitation tank
Real-time monitoring of adsorption saturation
Process selection and optimization strategy
Technology combination program
High-grade oxidized ore: crushing → grinding → CIL → desorption electrolysis
Complex and difficult to process ore: roasting → RIP → resin desorption
Low-grade tailings: heap leaching → precious liquid pool → zinc powder replacement
Environmental protection and technological
innovation direction
1. Cyanide risk management
Ozone/hydrogen peroxide oxidation to degrade cyanide in tailings to <0.2ppm.
Anti-leakage double-layer HDPE membrane paving technology
Online cyanide ion concentration monitor (precision 0.01mg/L)
2. Industry Technology Trends
Cyanide-free leaching agent R&D: Industrialization test of thiosulfate/halogen system
Intelligent control system: real-time regulation and control of slurry concentration based on machine vision
Biological leaching assistance: cyanide-generating bacteria to enhance leaching rate