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Zheng WANG University of Nottingham, Ningbo, China
Supervisor: Prof. Nick Miles, Dr Philip Hall
Particle Separation Techniques for WEEE Recycling
Background • 20-25 million tonnes WEEE
production worldwide per year. (Robinson, 2009)
• More than 70% shipped to developing countries.
• Environmental polluting recycling.
!
Pollute the Environment
Threat Human health
Discarded Resources
Material Concentration in UK WEEE stream
Aluminium 20-200 kg/t
Iron 100-420 kg/t
Copper 20-90 kg/t
Silver 21.41 g/t
Gold 6.45 g/t
Platinum Group Metals 2.14 g/t
Objectives: • Environmental friendly
method for WEEE recycling.
• Particle segregation to separate metallic fractions.
(WRAP, 2012)
Particle Separation Techniques Explored
Pneumatic separation • Particle segregation induced
by pulsation of air. • Principle: Stokes’ law and
terminal velocity
Vibratory separation • Brazil nut effect: !
(Gupta and Yan, 2006)
A. Bed at rest B. Air pulsation and differential
acceleration C. Hindered settling D. Consolidation trickling
(Kudrolli, 2004)
Inverse density segregation: • Dense particles have more
momentum, travel further. • Bottom voids filled by lighter
particles. • Inverse density segregation.
Pneumatic Separation - Sample Preparation
!!• !!
!!
!!!!0%
5%
10%
15%
20%
25%
30%
Particle size (mm)
Mass percentage in each size fraction
• Waste computer mother boards (lithium
batteries and heat sinks removed)
• Shredding: CSF570 hammer mill (Fengli
Pulverization Equipment Co., Ltd), 10 mm
aperture size on the discharge plate
• Sieving: particle size distribution
Pneumatic Separation Process
Bed height = 100mm, superficial velocity of air pulsation = 4m/s!
Light-to-dense fraction weight ratio: 1:6 – 1:9; throughput: 150kg/h!
Pneumatic Separation – Result
Before separation, density =2.27 g/cm3, metal content 34.6%
Dust collected in the dust extraction unit
Bottom fraction – metallic fraction density =2.34 g/cm3, metal content 45.1%
Top fraction – non-metallic fraction density =1.96 g/cm3, metal content 14.0%
Vertical Vibratory Separation • Investigate vibration parameter for
separation of irregular shaped particles • Cutting mill grinded copper (density =
8.76g/cm3) & polypropylene (density = 0.91g/cm3) particles, particle size less than 850µm
• Volume Ratio (mimic metallic/non-metallic fractions): Light material : Dense material = 3:1. Dr. Helena Webster, 2009
10mm thin cell with slopped design
Dr. Muddasar Habib, 2010 T-shape cell design
Previous work with 90-125µm bronze and glass spheres
Copper particles Polypropylene particles
Vibratory Separator Separation chamber
Supporting frame
Vibration table
Pneumatic piston
Separation chamber
Vibration monitoring
Thin cell design for fast segregation, powered by pneumatic piston.
Vertical Vibratory Separation
Copper and polypropylene particles, less than 850µm!
Bed height = 40 mm, slope = 15°; Vibration : �=5, f=30�2Hz
Conclusion & Future work Pneumatic separation
• Experiment with reduced particle size (better liberation of metal)
• Multi-stage process to improve separation efficiency.
• Scale up design, longer retention time to enhance the concentration effect.
Vibratory separation
• Suitable vibration condition: bed height 30-50mm, vibration intensity Γ= 4-6, frequency ! = 30±5 Hz
• Continuous separation experiment and examine the separation efficiency.
• Particle segregation of three-phase system: copper, glass and polypropylene particles.
• Separation of shredded printed wiring boards.
Scale up design, throughput 2 tone/hr.