Recycled Plastic Contamination Detection: X-Ray Sorting System Technology

## 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