Under surface weathering conditions, primary sulfide minerals undergo oxidation reactions with atmospheric oxygen and aqueous solutions, forming secondary oxidized mineral zones. These oxidation zones typically develop in the shallow portions of ore deposits, with their thickness controlled by regional geological conditions, ranging between 10-50 meters.
Based on the oxidation degree of metallic elements in the ore (i.e., the percentage of oxidized minerals relative to total metal content), ores can be classified into three categories:
Oxidized ore: oxidation rate >30%
Sulfide ore: oxidation rate <10%
Mixed ore: oxidation rate between 10-30%
Common non-ferrous metal oxide minerals mainly include:
Malachite (Cu₂CO₃(OH)₂)
Cerussite (PbCO₃)
Smithsonite (ZnCO₃)
Non-ferrous oxidized ores exhibit the following characteristic features:
(1) Complex ore texture with finely disseminated mineral grains that are difficult to liberate, combined with notable brittleness leading to severe slime generation during fine grinding;
(2) Highly heterogeneous mineral composition where individual deposits often host multiple oxide minerals of the same metal yet with markedly different surface floatability;
(3) Ubiquitous presence of secondary slimes and soluble salts;
(4) Significant property variations between different deposits, and even among mining sections within the same deposit, regarding oxidation degree and ore characteristics.
These inherent properties pose substantial technological challenges for the flotation separation of oxidized ores.
1. Flotation of Lead-Zinc Ore and Their Mixtures
1.1 Oxidized Lead Minerals and Their Flotation Methods
1.1.1. Key Oxidized Lead Minerals:
Industrial Oxidized Lead Minerals:
Cerussite (PbCO₃): Lead content 77.6%, Density 6.5g/cm³, Mohs hardness 3
Anglesite (PbSO₄): Lead content 68.3%, Density 6.3g/cm³, Mohs hardness 3
1.1.2. Sulfidization Flotation Process
1.1.2.1 Base Flowsheet
Oxidized lead minerals → Sulfidization treatment → Flotation using:
Preferred collectors: Advanced xanthates
Alternative collectors: Dithiophosphates (aerofloats)
1.1.2.2 Pretreatment Options
| Method | Details |
| Conventional | Desliming (removes clay/iron hydroxide slimes) |
| Advanced | Sodium silicate addition (0.5-1.5 kg/t as dispersant) |
1.1.2.3 Critical Sulfidization Controls
Reagents: Na₂S/NaHS
Optimum pH: 9-10 (cerussite)
Key precautions:
Avoid Na₂S overdose (causes depression)
Prevent pH >10 (leads to PbS film detachment)
Process optimizations:
✓ Partial NaHS substitution for Na₂S
✓ pH adjustment with (NH₄)₂SO₄ (1-2 kg/t) or H₂SO₄
✓ Staged reagent addition (test-determined)
1.2. Zinc Oxide Minerals and Flotation Methods
1.2.1. Principal Industrial Zinc Oxide Minerals
| Mineral | Chemical Formula | Zinc Content | Density (g/cm³) | Hardness |
| Smithsonite | ZnCO₃ | 52% | 4.3 | 5 |
| Hemimorphite | H₂Zn₂SiO₅ | 54% | 3.3–3.6 | 4.5–5.0 |
1.2.2 Flotation Process Options
1.2.2.1. Hot Sulfidization Flotation
Key Parameters:
Pulp Temperature: 60–70°C (critical for ZnS film formation)
Activator: CuSO₄ (0.2–0.5 kg/t)
Collector: Xanthates (e.g., potassium amyl xanthate)
Applicability:
Effective for smithsonite
Limited efficiency for hemimorphite
1.2.2.2. Fatty Amine Flotation
Process Control:
pH Adjustment: 10.5–11 (using Na₂S)
Collector: Primary fatty amines (e.g., dodecylamine acetate)
Slime Management:
Option A: Pre-flotation desliming
Option B: Dispersants (sodium hexametaphosphate + Na₂SiO₃)
Innovative Approach:
Amine-Na₂S emulsion (1:50 ratio)
Eliminates need for desliming
1.3. Beneficiation Processes for Mixed Lead-Zinc Ores
1.3.1. Process Flow Options
1.3.1.1. Sulfides-First, Oxides-Later Circuit
Sequence:
Sulfide minerals (bulk/selective flotation) → Oxidized lead → Oxidized zinc
Advantages:
Maximizes sulfide recovery before oxide treatment
Reduces reagent interference between mineral types
1.3.1.2. Lead-First, Zinc-Later Circuit
Sequence:
Lead sulfides → Lead oxides → Zinc sulfides → Zinc oxides
Advantages:
Ideal for ores with clear Pb/Zn liberation boundaries
Enables tailored reagent schemes for each metal
1.3.2. Process Optimization Guidelines
Highly oxidized ores (ZnO >30%):
Use amine collectors to co-recover:
Oxidized zinc minerals
Residual zinc sulfides
Typical dosage: 150–300 g/t C12–C18 amines
Process selection criteria:
Requires:
Ore characterization studies (MLA/QEMSCAN)
Bench-scale testing (including locked-cycle tests)
Decision factors:
Oxidation ratio (PbO/ZnO vs. PbS/ZnS)
Mineralogical complexity index
2. Flotation Characteristics of Multivalent Metal Salt Minerals
2.1. Representative Minerals
Phosphates:
Apatite [Ca₅(PO₄)₃(F,Cl,OH)]
Tungstates:
Scheelite (CaWO₄)
Fluorides:
Fluorite (CaF₂)
Sulfates:
Barite (BaSO₄)
Carbonates:
Magnesite (MgCO₃)
Siderite (FeCO₃)
2.2. Key Flotation Properties
| Characteristic | Description |
| Crystal Structure | Dominant ionic bonding |
| Surface Properties | Strong hydrophilicity (contact angle <20°) |
| Native Floatability | Poor (natural recovery <15%) |
| Collector Type | Fatty acids/soaps (e.g., oleic acid, sodium oleate) |
| Reagent Requirements | Mandatory use of modifiers |
| pH Sensitivity | Critical control window (±0.5 pH units) |
2.3. Process Requirements
2.3.1 Reagent System Optimization
Mineral-specific modifier development:
Apatite: Sodium silicate + starch
Scheelite: “Lime-oleate” process (pH 9–10)
2.3.2 Pulp Chemistry Control
Ionic composition monitoring (Ca²⁺/Mg²⁺ interference)
Redox potential regulation (for iron-bearing minerals)
2.3.3 Innovation Priorities
Selective composite collectors (e.g., fatty acid-amine blends)
Smart depressants (pH-responsive polymers)
3. Apatite Flotation Technology
3.1. Mineralogical Characteristics
Chemical formula: Ca₁₀X₂(PO₄)₆ (X = F/Cl/OH)
P₂O₅ content: 40.9–42.2% (primary raw material for phosphate fertilizers)
Reserve status:
80% of China’s proven reserves are sedimentary phosphorite
Dominated by medium-low grade siliceous-calcareous phosphorite
3.2. Ore Characteristics
3.2.1. Gangue Composition
| Type | Separability |
| Siliceous gangue | Easier separation |
| Carbonate gangue | Challenging (lack of selective depressants) |
3.2.2. Key Challenge
Developing high-selectivity depressants for carbonate-apatite separation
3.3. International Best Practices
3.3.1. Reverse-Direct Flotation Circuit (Kara-Tau Deposit Case)
① Ore Preparation
Grinding fineness: 95% passing 0.15 mm
Desliming: Remove 10–20 μm particles
② Reverse Flotation (Carbonate Removal)
pH adjustment: H₃PO₄ to 4–5
Collector: Synthetic fatty acids
③ Direct Flotation (Apatite Recovery)
pH adjustment: Na₂CO₃ to 9–10
Collector: Tall oil
Tailings: Silica residues
3.3.2. Anionic-Cationic Combined Process
Stage 1: Carbonate flotation (anionic collector)
Stage 2: Silica flotation (cationic collector)
Performance: 79% P₂O₅ recovery
3.4. Critical Control Parameters
Grinding optimization (P80 target)
Slime management (cyclone efficiency)
pH precision (±0.2 unit tolerance)
Collector synergy (fatty acid: tall oil = 3:1)
4. Scheelite Flotation Technology
4.1. Comparative Characteristics of Industrial Tungsten Minerals
| Mineral Name | Chemical Composition | WO₃ Content | Remarks |
| Wolframite | (Fe,Mn)WO₄ | 76.5% | Also called iron-manganese tungstate |
| Scheelite | CaWO₄ | 80.56% | Primary flotation target |
| Ferberite | FeWO₄ | 76.3% | – |
| Hübnerite | MnWO₄ | 76.6% | – |
4.2. Beneficiation Method Selection
4.2.1. Conventional Process:
Gravity separation (preferred for coarse-grained, high-density tungsten minerals)
4.2.2. Flotation Applications:
Primary scheelite ore processing
Recovery from gravity concentrate slimes
(Other tungsten minerals rarely processed by flotation due to poor floatability)
4.3. Scheelite Flotation Process
4.3.1. Standard Conditions:
Collector: Sodium oleate
pH Modifier: Na₂CO₃ (maintain pH 9-10.5)
Depressant: Sodium silicate (for silica gangue)
4.3.2. Technical Challenges:
Calcium-bearing gangue minerals (calcite, fluorite, apatite, barite) share similar floatability characteristics with scheelite:
All respond to fatty acid collectors
Require development of high-selectivity depressants
4.4. Process Optimization Strategies
4.4.1. Novel Depressant Development:
Target selective inhibition of calcium-bearing gangue
4.4.2. Advanced Reagent Schemes:
Composite collector systems (e.g., oleate-sulfonate blends)
Synergistic depressant combinations
4.4.3. Circuit Innovations:
Gravity-flotation hybrid flowsheets
Stage grinding with selective liberation
5. Fluorite Flotation Technical Specifications
5.1. Mineral Characteristics
Chemical Formula: CaF₂
Fluorine content: 48.9%
Physical properties:
Density: 3.18 g/cm³
Mohs hardness: 4
Industrial Status: China is a global leader in fluorite production
Primary Applications: Chemical, metallurgical, and ceramic industries
5.2. Beneficiation Method Selection
| Ore Type | Recommended Method | Notes |
| Lump Ore | Hand Sorting / Gravity Separation | Coarse particle processing |
| Fine-grained Ore | Flotation | High-grade concentrate (CaF₂ >97%) |
5.3. Flotation Process Parameters
5.3.1. Basic Conditions
Pulp Temperature: ≥60°C
Water Quality: Soft water (hardness <100 mg/L)
pH Range: 8–9.5
Cleaning Stages: ≥3
5.3.2. Reagent Regime
pH Modifiers: Na₂CO₃ / NaOH
Depressants:
Siliceous gangue: Sodium silicate
Carbonate gangue: Combined depressant (sodium silicate + Al salts)
Barite: Starch / lignosulfonates
Collectors: Oleic acid / vegetable fatty acids / tall oil
5.4. Refractory Ore Processing Strategies
5.4.1. High-Carbonate Type
Depressant Combination:
Tannic acid + quebracho + dichromates
Enhanced Measures:
Synergistic use of sodium silicate + soluble Al salts
5.4.2. High-Barite Type
Pre-treatment Options:
Gravity pre-concentration
Barite priority flotation (petroleum sulfonate collector)
Main Process:
Modifiers: Sodium silicate + BaCl₂
Fluorite flotation: Oleic acid collector
6. Technical Specifications for Soluble Salt Mineral Flotation
6.1. Major Soluble Salt Minerals
| Mineral Class | Representative Mineral | Chemical Formula | Special Flotation Requirements |
| Potash Salts | Sylvite | KCl | Saturated brine medium |
| Sodium Salts | Halite | NaCl | Saturated brine medium |
| Borates | Borax | Na₂B₄O₇·10H₂O | Requires Ba²⁺ activation |
| Colemanite | Ca₂B₆O₁₁·5H₂O | Fatty acid collectors | |
| Boracite | Mg₃B₈O₁₅ | Needs special activation |
6.2. Potash Salt Flotation Process
6.2.1. Feed Characteristics
Common Impurities: Halite, magnesium salts, gypsum, clay
Pretreatment Requirements:
Clay removal: Desliming operation
Particle size: ≥95% passing 0.3mm
6.2.2. Flotation Conditions
Medium: Saturated brine solution (density 1.18-1.20 g/cm³)
Collector Selection:
Amines (for KCl selectivity)
Alkyl sulfates (for KCl/NaCl separation)
Key Parameters:
Pulp temperature: 25-35°C
pH range: 6-8 (neutral)
6.3. Borate Flotation Technology
6.3.1. Standard Processes
Borax Flotation:
Activator: BaCl₂ (optimal)
Collector: Sodium oleate
Calcium/Magnesium Borates: Direct fatty acid flotation
6.3.2. Gangue Management
Clay: Hydrocyclone desliming
Gypsum Depression:
Depressant: Starch (0.5-1.5 kg/t)
Enhanced formula: Starch + phosphates
6.3.3. Technical Challenges
Magnesium Silicate Interference:
Requires selective activators
Recommended: Gravity-flotation combined circuit
6.4. Critical Control Parameters
| Parameter | Technical Requirement |
| Solution Saturation | Online densitometer (1.18-1.20 g/cm³) |
| Collector Optimization | C12-C18 chain length amines |
| Equipment Protection | 316L stainless steel construction |
Industrial Implementation Notes:
Systematic flotation tests must determine:
✓ Optimal grinding fineness
✓ Precise reagent dosages
✓ Pulp temperature range
✓ Number of cleaning stages
