Technology Zone
Separating mixed waste into clean, saleable streams is the hardest step in recycling. This zone covers magnetic, eddy-current and density separation, screens, and sensor-based sorting with NIR, X-ray, LIBS, AI and robotics — 24 equipment types, 229 manufacturers.
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What this zone covers
Every separator exploits one physical difference between what you want and what you do not: size (screens), density and shape (air classifiers, ballistic separators, wet tables), magnetism (overband and drum magnets), electrical conductivity (eddy-current separators), colour, spectrum or shape (optical sorters with NIR, VIS, X-ray, LIBS or AI cameras). A sorting line is a sequence of such steps; the order matters as much as the machines, and the cheapest separation goes first.
Trommel, disc and vibrating screens split the stream by size and remove fines; ballistic separators split 2D (flat, light) from 3D (rigid) and fines in one pass; air classifiers, drum separators and windsifters pull light films and paper from heavy fractions. Mechanical steps are robust and cheap per tonne and set up every downstream sensor step by delivering a narrower, more uniform stream.
Overband, drum and pulley magnets remove ferrous metal early to protect equipment and produce a saleable scrap fraction. Eddy-current separators throw non-ferrous metals (aluminium, copper, brass) out of the stream by inducing currents in them; their performance depends on particle size, belt speed, rotor frequency and a thin, single-layer feed. Stainless steel needs a sensor sorter or a special high-gradient magnet.
An optical sorter scans a single layer of material on a fast belt, identifies each object by its near-infrared spectrum (polymer type), colour, X-ray transmission (density, halogens) or laser-induced spectrum (metal alloys), and ejects it with a timed air jet. Modern machines add AI object recognition for shapes and packaging types. Purity and recovery are traded against each other through the ejection settings; throughput per metre of belt width is the sizing number.
Purity is the share of the target material in the product; recovery is the share of the target material in the feed that ends up in the product. No separator gives 100 % of both, and the market sets the purity; recovery is what remains. Rescanning rejects, adding a quality-control sorter on the product and keeping the burden depth low on every belt are the usual routes to a better balance.
| Parameter | Typical range | Rule of thumb |
|---|---|---|
| Optical sorter belt speed | 2.5–4.5 m/s | Faster belts spread the material; single-layer presentation is the aim |
| Optical sorter throughput | 3–12 t/h per metre belt width depending on bulk density | Size on burden depth (one layer), not on the nameplate |
| Sorting purity / recovery | 95–99 % purity at 85–95 % recovery in one pass | Tighten purity and recovery drops; rescan the reject to recover it |
| Eddy-current particle size | 5–150 mm; best above 10 mm | Below 5 mm use high-frequency rotors or a fines eddy-current unit |
| Overband magnet suspension height | 300–500 mm above belt for 1,000–1,400 mm belts | Every centimetre of extra height costs field strength; keep burden depth low |
| Ballistic separator | Paddle inclination 15–25°; 10–40 t/h per unit | Steeper for more 3D in the heavy fraction, flatter for cleaner 2D |
| Trommel screen | 10–15 rpm; 40–60 % of critical speed | Hole size 2–3× the particle size you want to pass |
| Air classifier | Air speed 10–25 m/s at the separation zone | Adjust for the heaviest light fraction you want to lift, not the lightest |
| Symptom | Likely causes | What to do |
|---|---|---|
| Optical sorter purity drops | Burden too deep (objects overlap); dirty or misaligned lamp and sensor; wet or dusty material; ejection timing off | Reduce feed rate or widen belt, clean optics daily, dry or de-dust upstream, recalibrate ejection |
| Eddy-current recovery falls | Particle size too small; belt too fast or too slow; splitter position; ferrous contamination heating the rotor | Screen to size classes, tune belt speed and splitter, magnet upstream |
| Screen blinds | Wet, sticky or fibrous material; near-size particles; wrong aperture shape | Disc screen or flip-flow screen for sticky material, ball cleaning, coarser first cut |
| Film and paper in the heavy fraction | Air classifier air speed too low; ballistic paddle angle too flat; material clumps | Raise air speed, steeper paddles, bag opener upstream |
| Magnet misses ferrous | Suspension too high; burden too deep; belt too fast; magnet dirty | Lower the magnet, spread the burden, self-cleaning belt maintenance |
| Wrapping around shafts and screens | Wires, tapes, strapping, textiles | Pre-shredding, anti-wrap discs, regular cleaning stops, ballistic separator ahead of screens |
| Throughput below design | Uneven feed (surges); bottleneck at one machine; too much moisture | Metering drum or feeder at the head, balance the line, check moisture of incoming material |
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Equipment Guide
Jiangsu Keson Environment Technology Co., Ltd.
Jiangsu Keson Environment Technology Co., Ltd. is a high-tech enterprise specializing in environmental protection, industrial, energy, low-carbon intelligent equipment system R&D, intelligent equipment manufacturing, comprehensive solutions of solid waste low-carbon & resource recovery, and investment, construction and operation.
AIK Technik AG
AIK Technik AG are a system supplier as a plant engineering for the treatment and recovery of residual materials. We are committed to reducing environmental impact for future generations and to achieving maximum sustainability using specialized processes and technologies.
Bollegraaf Group
Bollegraaf Group is a world-leading expert and innovator in the waste sorting and recycling sector. Furthermore, our reputation is based on the unique quality of equipment in terms of separation performance, robustness, and ease of maintenance. A premium quality complemented by our engineering expertise allows delivering the best solutions to the specific challenges of each of our customers.
Eriez
Established in 1942, Eriez is a global leader in separation technologies. Eriez Recycling Products work successfully to separate and recover metals in a variety of applications - from municipal solid waste and shredded automobiles, plastics, electronic waste and foundry sand.
Cleansort GmbH
With many years of experience in innovative recycling solutions, we at Cleansort develop sorting solutions that are geared towards maximum efficiency and sustainability. Through advanced technology and a strong commitment to resource efficiency, we help you boost profits while safeguarding the environment.
Cross Wrap Ltd.
Cross Wrap's speciality is in automated bale handling and material flow solutions for the global recycling, waste, and industrial sectors. It's known for its innovative Bale Wrapping and Bale Dewiring machines, designed to improve safety and efficiency in material processing.
Machinex Industries Inc.
Machinex Industries offers complete engineering design, manufacturing and installation of Material Recycling Facilities. As a leader in sorting technologies, Machinex Industries provides turnkey systems: Single-Stream, Mixed Waste Processing, Construction & Demolition, Commercial and Industrial Waste, front-end processing for Waste-to-Energy plant.
Sense2Sort – Toratecnica
Sense2Sort Toratecnica is specialized in sensor-based sorting equipment for metal sorting applications in recycling. The company leads in automated spectroscopy sorting technologies, such as XRF (X-Ray Fluorescence) and LIBS (Laser-Induced Breakdown Spectroscopy), and offers all common sensor-based sorting technologies and consults on plant design.
Ask the Expert
Engineers and product specialists who answer technical questions from readers. The answer comes back to you by e-mail; when we publish it, other readers benefit too.
Laetitia Paveau
Pellenc ST
Laetitia is the Marketing and Communications Director at Pellenc ST. An engineer by training, she has spent over 20 years driving innovation…
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Tom Jansen
TOMRA Recycling
With more than 20 years of experience in sensor-based sorting technologies, Tom Jansen is VP, Head of Segments at TOMRA Recycling, where…
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Ivan Hondekyn
Valvan nv
Ivan Hondekyn has been part of the Valvan team for over 25 years, bringing a rare depth of expertise across design, project…
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Eric van Looy
Sense2Sort – Toratecnica
Eric van Looy has been active in the recycling industry for over three decades and is regarded as a pioneer in the…
Ask a questionMarket & Technology Focus
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Questions and answers
Cheapest and most robust first: remove fines and oversize by screening, ferrous by magnet, light 2D by air or ballistic separation, then non-ferrous by eddy current and finally the expensive sensor-based sorters on a stream that is already narrow in size and composition. Every step upstream makes the next one cheaper and more accurate.
In one pass typically 95–99 % purity at 85–95 % recovery on a well-prepared single-layer feed. The final percentage points come from a quality-control sorter on the product or a rescan of the rejects, and from material preparation: dry, de-dusted, screened to a narrow size range.
NIR identifies polymer types and paper grades but cannot see black plastics; VIS colour cameras sort by colour; X-ray transmission separates by density (metals, halogenated plastics, inert material); X-ray fluorescence and LIBS identify metal alloys; AI object recognition classifies shapes and packaging that spectra cannot. Most modern sorters combine two or three.
The force on a particle scales with its size and conductivity, so small aluminium pieces are barely deflected at standard rotor speeds. Screen the feed into size classes, use a high-frequency (eccentric) rotor for fines, keep the belt at the right speed for the size class and set the splitter for that class alone.
Take them out before they reach rotating parts: a bag opener and a coarse pre-shredder cut long items, a ballistic separator removes many of them, and anti-wrap discs and shaft guards limit the damage. Schedule short cleaning stops rather than waiting for a jam.
It depends on burden depth, not tonnage: a sorter sees one layer, so throughput is belt width times speed times bulk density of a single layer — commonly 3–12 t/h per metre of belt width. A light, bulky stream such as film needs far more belt width per tonne than dense flakes.
Input composition (regular manual sampling), product purity and recovery per step, burden depth on the sensor belts, moisture of the incoming material, and the reject composition — that last one tells you where recoverable material is lost and which step to tune.
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