What are the treatment methods for graphite dust and waste electrodes?

Comprehensive Treatment Methods for Graphite Dust and Waste Electrodes

I. Graphite Dust Treatment: Multi-Technology Synergy for Efficient Governance

1. Source Control and Capture Technologies

• Closed Process and Enclosed Hoods: Install enclosed hoods at critical dust generation points (e.g., crushing, screening, conveying) paired with high-efficiency bag filters (e.g., electrostatic-bag composite dust collectors). This reduces dust generation concentration from 2,000–3,000 mg/m³ to an emission concentration of 20–30 mg/m³, achieving 99% dust removal efficiency.
• Explosion-Proof Dust Removal Equipment: Given the conductive nature of graphite dust and its susceptibility to sparking, use explosion-proof dust collectors (e.g., cyclone separators combined with explosion-proof bag filters) to mitigate explosion risks when mixed with combustible materials.
• Wet Dust Collection Systems: Utilize water-based solution sprays to settle dust particles, suitable for tooling applications. Note: Ensure electrode materials are dried (e.g., 60–80°C in a convection oven for 1 hour) to prevent dielectric oil contamination.

2. Air Purification and Emission Control

• Multi-Stage Purification Process: Cool high-temperature exhaust via heat exchangers, then sequentially pass it through a cyclone separator (for large particles), an alkaline scrubber (to neutralize acidic gases), and an activated carbon adsorption tower (for VOC removal). Final discharge occurs through a 15-meter exhaust stack, ensuring compliance with the Air Pollutant Discharge Standard for General Sources (GB 16297-1996).
• Online Monitoring and Optimization: Install sensors for particulate matter and VOC concentrations to dynamically adjust parameters such as scrubber solution pH and activated carbon replacement intervals, maintaining emission concentrations below 120 mg/m³.

3. Auxiliary Control Measures

• Material Moisturization: Apply dust suppressants (e.g., polyacrylamide solution) to ore stockpiles and tailings ponds, maintaining surface moisture at 6–8% to reduce fugitive dust.
• Equipment Maintenance and Worker Protection: Regularly clean filter bags, inspect pipeline seals, and equip operators with N95 respirators and dust-proof clothing to minimize occupational exposure.

II. Waste Graphite Electrode Treatment: Balancing Resource Recovery and Environmental Disposal

1. Physical Pretreatment

• Sorting and Cleaning: Classify electrodes by type (e.g., regular power, high power), remove surface oil and metal impurities, and clean using ultrasonic machines (40 kHz frequency) for 10–15 minutes.
• Crushing and Screening: Use jaw crushers to reduce electrodes to ≤50 mm particles, then sieve via vibrating screens. Retain 5–50 mm particles for regenerated electrode production.

2. Chemical Purification and Regeneration

• High-Temperature Graphitization: Heat particles in a graphitization furnace at 2,800–3,000°C for 4–6 hours to remove volatile impurities (e.g., sulfur, nitrogen), elevating fixed carbon content to ≥99.5%.
• Acid Leaching for Impurity Removal: Immerse crushed particles in 15–20% hydrochloric acid at 80–90°C for 2 hours to eliminate aluminum, iron, and other metal impurities. Neutralize filtrate before discharge.

3. Specialized Alloy Electrode Recycling

• Platinum-Iridium Electrode Separation: For medical-grade electrodes containing platinum-iridium alloys, dissolve platinum in aqua regia (80°C for 3 hours). Extract iridium via molten salt electrolysis (NaCl-KCl system at 700°C) and refine both to 99.99% purity using zone melting.
• Copper-Based Electrode Regeneration: Crush waste copper-graphite electrodes, separate graphite (density: 1.8–2.1 g/cm³) and copper powder (density: 8.9 g/cm³) via flotation, and refine copper powder into high-purity copper through electrolysis (current density: 200 A/m²).

III. Techno-Economic Analysis and Industry Case Studies

1. Cost-Benefit Comparison

• Bag Filters: Initial investment: ~¥500,000; operational cost: ¥0.2/m³ of exhaust gas. Suitable for large-scale graphite electrode enterprises (annual exhaust volume ≥100,000 m³).
• Wet Dust Collection Systems: Equipment investment: ¥200,000; water-based solution cost: ¥0.5/ton of wastewater. Ideal for small-to-medium workshops.
• Waste Electrode Regeneration: Each ton yields 850 kg graphite (¥3,000 value) and 150 kg metals (¥5,000 value), generating ¥8,000 in total revenue. Investment payback period: 1.5–2 years.

2. Industry Case Studies

• Leading Graphite Electrode Enterprise: Adopted a “静电袋式除尘器 (electrostatic-bag filter) + activated carbon adsorption tower” system, reducing particulate emissions from 2,000 mg/m³ to 15 mg/m³ and achieving 95% VOC removal. Annual environmental fines reduced by ¥2 million.
• Medical Electrode Recycling Plant: Recovered platinum-iridium alloys to 99.99% purity via molten salt electrolysis, directly used in pacemaker manufacturing. Saved ¥1.2 million per ton of waste electrodes in raw material costs.

IV. Policy and Regulatory Guidelines

• Emission Standards: Comply with the Graphite Industry Pollutant Discharge Standard (GB 31573-2015), mandating particulate emissions ≤30 mg/m³ and VOCs ≤100 mg/m³.
• Resource Recovery Incentives: Encourage adoption of the Technical Specification for Recycling Waste Graphite Electrodes (GB/T 35164-2017) with tax incentives (e.g., 70% VAT refund for regenerated graphite products).
• Safety Regulations: Follow the Dust Explosion Prevention Safety Code (GB 15577-2018), requiring explosion relief devices (pressure: 0.01–0.02 MPa) and periodic electrostatic grounding inspections for dust removal systems.