## Recycled Plastic Contamination Detection: X-Ray Sorting System Technology
### Introduction
Contamination detection is critical for producing high-quality recycled plastics. X-ray sorting systems identify and remove foreign materials based on density and atomic composition differences.
### X-Ray Detection Principles
**Working Mechanism**:
– X-rays penetrate plastic material
– Different materials absorb X-rays at different rates
– Detector array captures transmission image
– Software classifies materials in real-time
**Detectable Contaminants**:
– Metals (aluminum, steel, copper)
– Glass and ceramics
– Stones and minerals
– PVC (chlorine detection)
– Rubber and silicone
### System Components
**X-Ray Source**:
– Energy: 50-150 kV
– Power: 100-1000 W
– Fan-beam or line-scan configuration
– Shielding for operator safety
**Detector Array**:
– Scintillator crystals + photodiodes
– CdTe or CZT semiconductor detectors
– Spatial resolution: 0.5-2 mm
– Line rate: 1-5 m/s
**Ejection System**:
– High-pressure air nozzles (6-8 bar)
– Precision valve control (response <1 ms)
- Multi-zone ejection for complex objects
### PVC Detection
**Chlorine Signature**:
- PVC contains 57% chlorine by weight
- X-ray absorption significantly higher than PE/PP
- Detection sensitivity: <1% PVC in PET stream
- Critical for bottle-to-bottle recycling
**Fluorescence Option**:
- XRF (X-ray fluorescence) for elemental analysis
- Identifies bromine (flame retardants)
- Detects heavy metals (lead, cadmium)
### Performance Specifications
**Detection Rates**:
- Metal >2mm: >99%
– Glass >3mm: >95%
– PVC in PET: >98%
– Stones >5mm: >90%
**Throughput**:
– Belt speed: 1-3 m/s
– Belt width: 600-2000 mm
– Capacity: 1-10 tonnes/hour
### Integration with NIR Sorting
**Combined Systems**:
– NIR for polymer identification
– X-ray for contamination removal
– Sequential or parallel configuration
– Comprehensive quality assurance
**Economic Benefits**:
– Reduced downstream equipment damage
– Improved pellet quality
– Lower rejection rates
– Higher selling prices
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**Keywords**: X-ray sorting, contamination detection, plastic recycling quality, PVC detection, sorting technology