Titanium and its alloys are critical materials in aerospace, medical implants, and chemical equipment due to their high strength, corrosion resistance, and biocompatibility. However, scrap generated during production-comprising 70% chips and 30% bulk pieces-poses both environmental and resource challenges if not properly treated.
Direct disposal of untreated scrap not only wastes strategic resources (producing 1 ton of primary titanium requires 4 tons of rutile ore) but also risks contaminating the environment with oils, oxides, and metallic impurities. Efficient recycling of titanium scrap has thus become a vital focus in global green manufacturing initiatives.
Scrap Classification and Pre-Treatment: The Foundation of Purification
Types and Characteristics of Scrap
Chip Scrap: Generated from turning or milling processes, featuring a large surface area that readily retains cutting fluids and oxide layers, requiring intensive degreasing.
Bulk Scrap: Derived from stamping or cutting operations, with relatively lower contamination but potential inclusions of tool steel fragments.
Melting Residues: Contain high concentrations of oxides, necessitating chemical extraction to recover metallic titanium.
Three-Step Pre-Treatment Process
►Degreasing:
Alkaline cleaning (80°C NaOH solution) to dissolve mineral oils.
Ultrasonic organic solvent (acetone/ethanol) treatment to remove emulsified oils from micro-pores.
►Magnetic Separation: High-intensity magnets (≥0.5 T) remove iron impurities to prevent contamination during melting.
►Crushing and Screening: Bulk scraps are crushed to <5 cm particles to enhance subsequent reaction efficiency.
Chemical Purification: Breakthrough Core Technologies
Pickling Method-Cost-Effective Option
Formula: HF (5–10%) + HNO₃ (20–30%) mixed acid solution.
Function: Dissolves surface TiO₂ and TiN oxide layers with >95% efficiency.
Challenge: Hydrogen embrittlement risk requires post-treatment vacuum annealing (500°C/4 h) for mitigation.
Molten Salt Electrolysis-Deep Deoxidation
Process: Electrolysis in NaCl-KCl-NaF molten salt system (650°C) drives oxygen ions to the anode.
Outcome: Oxygen content reduced below 800 ppm, meeting aerospace-grade TA6V (Ti-6Al-4V) standards.
Vacuum Heat Treatment-Medical-Grade Purification
Conditions: 900°C under high vacuum (10⁻³ Pa) with argon gas protection.
Advantages: Simultaneous hydrogen removal (99% efficiency) and volatilization of metallic impurities (e.g., Cu, Sn).
