Ore Flotation in Supergene Environments
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# 1. Supergene Enrichment Overview
Supergene processes occur near the Earth’s surface, where weathering and oxidation alter primary (hypogene) sulfide ores. Key features:
– Oxidation Zone: Sulfides (e.g., pyrite, chalcopyrite) oxidize to sulfates, oxides, and hydroxides (e.g., hematite, goethite).
– Supergene Zone: Below the water table, metals like copper reprecipitate as secondary sulfides (e.g., chalcocite, covellite), enriching the ore grade.
# 2. Challenges in Supergene Ore Flotation
– Mineralogy Complexity: Mixed primary/secondary sulfides and oxides complicate separation.
– Surface Reactivity: Oxidized minerals may have poor floatability due to hydrophilic surfaces.
– Gangue Interference: Clays or iron oxides can slime coatings 
consume reagents.
# 3. Flotation Strategies for Supergene Ores
## A. Sulfide-Dominant Supergene Ores
(e.g., chalcocite-enriched copper deposits)
– Collectors: Thiol-based (e.g., xanthates) for secondary sulfides.
– Activators: Copper sulfate for oxidized zones.
– Depressants: Sodium sulfide (Na₂S) to remove oxidation layers.
## B. Mixed Oxide-Sulfide Ores
(e.g., copper oxide + chalcocite)
– Sulfidization: Treat oxides with Na₂S/NaHS to create a pseudo-sulfide surface for xanthate adsorption.
– Sequential Flotation: Float sulfides first, then oxides using fatty acids or hydroxamates.
## C. Gold/Silver Supergene Ores
– Free gold may need gravity separation before flotation.
– Activated carbon can recover preg-robbed gold from oxidized minerals.
# 4. Reagent Optimization
– pH Control: ~9–11 for sulfide flotation; lower (~7–9) for sulfidized oxides.
– Frothers/Modifiers: Pine oil or MIBC as frothers; sodium silicate disperses clays.
# 5. Case Example: Porphyry Copper Deposits
– Supergene zones often yield high-grade chalcocite blankets.
– Flotation recovers >85% Cu by targeting secondary sulfides with xanthates