I. Introduction
Spent anodes (also known as carbon anode butts ) generated from aluminum electrolysis production are high-quality carbon materials characterized by high fixed carbon and high calorific value. However, compared with traditional cupola coke, spent anodes differ significantly in composition, physical properties, and impurity content.
This solution targets two application scenarios—copper smeltingandlead smeltingin cupola furnaces—systematically comparing the characteristics of spent anodes and coke, and proposing differentiated usage strategies, environmental control measures, and equipment configuration requirements.
II. Comprehensive Comparison Between Spent Anodes and Coke
2.1 Comparison of Basic Physical and Chemical Properties
| Parameter | Aluminum Electrolysis Spent Anode | Cupola Coke (High-Quality Foundry Coke) |
| Source | Residual from used aluminum electrolysis anode blocks | High-temperature dry distillation of coking coal |
| Fixed Carbon (%) | 95-97 | 85-88 |
| Calorific Value (kcal/kg) | 7,800-8,000 | 6,000-6,500 |
| Ash Content (%) | 1.5-3.0(extremely low ash) | 12-15 |
| Sulfur Content (%) | 2.0-3.0(typically around 2.5) | 0.5-1.0 (can be as low as 0.6) |
| Volatile Matter (%) | <1.0(extremely low) | 1.0-1.5 |
| Moisture (%) | 0.5-2.0 (hygroscopic) | 7-8 |
| Impurity Characteristics | Contains fluorides, sodium, aluminum and other electrolytes | Ash mainly composed of silicon and aluminum oxides |
| Particle Size | Irregular, requires crushing | Uniform, 80-150mm |
| Physical Strength | Relatively brittle, tends to pulverize at high temperatures | Hard, good high-temperature strength |
| Porosity | High(hygroscopic, highly reactive) | Relatively low |
2.2 Summary of Advantages and Disadvantages
| Dimension | Advantages of Spent Anode | Disadvantages of Spent Anode |
| :— | :— | :— |
| **Thermal Performance** | High fixed carbon, high calorific value (20-30% higher than coke), extremely low ash, less slag | Extremely low volatile matter, high ignition point, tends to pulverize at high temperatures |
| **Impurity Impact** | Low ash, reduces slag volume | **Contains fluorine/sodium electrolytes**, severely corrosive to furnace lining; high sulfur content |
| **Economy** | Industrial waste, usually lower procurement cost than coke | Requires pretreatment (de-shelling, crushing, drying) |
| **Operational Suitability** | — | Non-uniform particle size, porosity absorbs water causing “explosion” risk, difficult combustion control |
III. Spent Anode Pretreatment Requirements (Mandatory Before Charging)
Due to the unique characteristics of aluminum electrolysis spent anodes,charging without pretreatment will lead to serious accidents. The following are mandatory pretreatment procedures:
| Step | Equipment/Method | Purpose | Standard Requirement |
| De-shelling | Rotary drum cleaner / manual hammering | Remove surface electrolyte hard shell (fluorides, cryolite) | Surface hard shell removal rate ≥90% |
| Crushing | Jaw crusher, roll crusher | Achieve uniform particle size | Particle size 40-100mm (similar to coke) |
| Screening | Vibrating screen | Remove powder and overly fine particles | Screen out particles <10mm |
| Drying | Natural drying or drying kiln | Reduce moisture content, prevent “explosion” when charging | Moisture content <1% |
IV. Cupola Furnace Application Scenarios: Copper vs. Lead Smelting
4.1 Copper Smelting Cupola Furnace: Spent Anode as Raw Material + Fuel
Role Definition
- Copper spent anodes themselves arehigh-grade copper raw materials(copper content can reach over 98%)
- The carbonaceous portion provides the heat required for melting
Process Key Points
| Parameter | Requirement |
| Spent Anode Ratio | Can reach 80-100%(only a small amount of coke needed for ignition) |
| Lining Material | Alkaline lining mandatory(magnesia bricks, magnesia-alumina spinel bricks) |
| Slag Basicity | CaO/SiO₂ ≥ 1.5 (increase limestone dosage) |
| Melting Temperature | 1,350-1,450°C |
| Air Distribution | Oxygen-enriched or high-pressure air for enhanced combustion |
Main Risks and Countermeasures
| Risk | Cause | Countermeasure |
| Lining corrosion | Fluorides and sodium introduced by spent anodes | Alkaline lining + high basicity slag |
| Sulfur contamination | High sulfur content in spent anodes | Desulfurization in subsequent refining furnace |
| Poor permeability | Pulverization of spent anodes at high temperatures | Control particle size, moderately increase air flow |
4.2 Lead Smelting Cupola Furnace: Spent Anode as Auxiliary Fuel (Full Replacement Not Recommended)
Role Definition
- Mainly used ashigh-calorific-value auxiliary fuelto partially replace coke
- Full replacement is not recommended (extremely high risk)
Process Key Points
| Parameter | Requirement |
| Spent Anode Ratio | Recommended ≤20%(absolute limit ≤30%) |
| Furnace Type Requirements | Short-shaft furnace, water-cooled furnace wall, forced water-cooled tuyeres |
| Furnace Temperature Control | 1,000-1,150°C(prevent lead volatilization) |
| Heat Sink Measures | Add cold slag or lead blocks to absorb excess heat |
| Reduction Control | Control CO/CO₂ ratio to prevent over-reduction |
Main Risks and Countermeasures
| Risk | Cause | Countermeasure |
| Excessive lead volatilization | High calorific value of spent anodes causing excessive furnace temperature | Water-cooled furnace wall + heat sink + low charge column |
| High sulfur content in crude lead | Sulfur from spent anodes enters lead melt | Electrolytic refining for sulfur removal |
| Unstable furnace conditions | Non-uniform particle size, pulverization of spent anodes | Strict pretreatment + automated control |
| Sharp increase in lead dust in flue gas | Lead volatilization followed by condensation | High-efficiency bag filter + activated carbon injection |
V. Environmental Protection Equipment Configuration Requirements
When using spent anodes (especially at full or high ratios), the concentration of SO₂ and heavy metals in flue gas increases significantly, requiring efficient environmental protection facilities.
5.1 Recommended Process Route
Flue Gas Cooling → Baghouse Dust Collection → Wet Desulfurization → Activated Carbon Injection (for lead furnaces) → CEMS Online Monitoring → Emission
5.2 Environmental Facility Operation Requirements
| Facility | Operation Requirement |
| Flue Gas Cooler | Reduce high-temperature flue gas from 800-1,000°C to 150-180°C |
| Baghouse Dust Collector | Dust removal efficiency ≥99.5%, outlet dust ≤30 mg/m³ |
| Wet Desulfurization Tower | Desulfurization efficiency ≥98% (for full spent anode use) or ≥95% (for low ratios) |
| Activated Carbon Injection System | Mandatory for lead furnaces, used to adsorb volatilized lead dust and heavy metals |
| CEMS Online Monitoring | Real-time monitoring and upload of SO₂, particulate matter, lead (for lead furnaces), O₂, flow rate |
| Desulfurization Backup System | Key equipment one duty/one standby to prevent direct emissions during maintenance |
VI. Comparison of Different Usage Ratio Schemes
| Usage Ratio | Applicability for Copper | Applicability for Lead | Desulfurization Efficiency Required | Main Risks |
| 100% Spent Anode | ✅ Feasible (requires alkaline lining) | ❌ Not recommended | ≥98% | Lining corrosion, lead volatilization |
| 80% Spent Anode + 20% Coke | ✅ Recommended | ⚠️ High risk | ≥98% | Difficulty in temperature control |
| 50% Spent Anode + 50% Coke | ✅ Feasible | ⚠️ Proceed with caution | ≥95% | High sulfur load |
| ≤20% Spent Anode | ✅ Safe | ✅ Recommended for start-up | ≥95% | Controllable risk |
VII. Operation Key Points and Safety Considerations
7.1 Charging Operation
- Adoptlayered charging: Fuel layer (spent anode + coke mixed) → Metal charge layer → Flux layer
- Spent anodes and coke must beuniformly mixedbefore charging; never charge as a separate layer
7.2 Furnace Condition Monitoring
- Installfurnace thermocouplesfor real-time temperature monitoring
- For lead furnaces: immediately reduce spent anode ratio if temperature exceeds 1,200°C
- Regularly inspectlining thicknessto prevent corrosion penetration
7.3 Emergency Response Plan
| Abnormal Situation | Emergency Measure |
| Desulfurization system failure | Immediately stop adding spent anodes, switch to backup system |
| Lining corrosion alarm | Reduce spent anode ratio, increase limestone dosage |
| Excessive furnace temperature (lead furnace) | Increase cold material input, reduce air flow |
| Excessive lead dust in flue gas | Inspect bag filter, increase activated carbon injection rate |
VIII. Summary
8.1 Core Conclusions
- Aluminum electrolysis spent anodes ≠ coke: Their high fixed carbon and high calorific value are advantages, but high sulfur and fluorine/sodium electrolyte content are fatal drawbacks.
- Copper smelting cupola furnaces can use spent anodes on a large scale: Spent anodes serve as both raw material and fuel, with ratios reaching 80-100%, butalkaline lining is mandatorywith controlled slag basicity.
- Lead smelting cupola furnaces require strict ratio control: Recommended ≤20%, with water-cooled furnace walls, heat sink measures, and efficient dust collection systems;full replacement is not recommended.
- Environmental facilities are a prerequisite for use: Regardless of the scenario, using spent anodes requiresbaghouse dust collection + high-efficiency wet desulfurization (efficiency ≥95-98%) + CEMSto ensure compliant emissions.
- Pretreatment is essential: The four steps of de-shelling, crushing, screening, and drying are indispensable; otherwise, serious accidents such as lining corrosion, explosions, and blockages will occur.
8.2 Final Recommendations
| Application Scenario | Recommended Scheme | Spent Anode Ratio | Key Supporting Measures |
| Copper Smelting Cupola Furnace | Full spent anode scheme | 80-100% | Alkaline lining, high basicity slag, refining desulfurization |
| Lead Smelting Cupola Furnace | Auxiliary fuel scheme | ≤20% | Water-cooled furnace wall, heat sink, activated carbon injection |
| Initial Trial Burn | Low ratio start-up | 5-10% | Full-process environmental facilities + online monitoring |
> **One-sentence summary**: Aluminum electrolysis spent anodes are a “high-energy, highly corrosive” special fuel. Copper smelting can use full quantities, but lead smelting can only use small amounts. Regardless, environmental desulfurization and alkaline lining (for copper furnaces) are critical success factors.
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