Flotation of Non-ferrous Metal Ores and Mixed Ores

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

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

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

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

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

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

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

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

Industrial Implementation Notes:
Systematic flotation tests must determine:
✓ Optimal grinding fineness
✓ Precise reagent dosages
✓ Pulp temperature range
✓ Number of cleaning stages