A Bulk Handling Systems unit designed to separate cardboard and rigid fibre from newspaper and other flexible fibres. In the primary roller section, slot openings allow the flexible fraction to fall through holes between the rolls, while rigid materials pass over the top. A later section further separates flexible from rigid fibres with the assistance of a fan. According to Kevin Thomas, Director of MRF Operations at Casepak, this machine separates out newspapers and magazines that are “of the correct quality for use as a feedstock for UK recycled paper mills”.

Used as a subsequent step to shredding in recycling processes that involve metals (such as ELV and WEEE recycling). It enables aluminium, magnesium and mixed heavy metals such as bronze, brass and zinc to be separated. Material goes into a series of drums containing fluids of varying densities, which causes certain materials to float while others sink.

A technique for sorting plastics with significant differences in melting temperature (e.g. PVC melts at 200°C, while PET melts at 260°C.). A belt is heated to the lowest melting point of the polymers; the polymer with that melting point adheres to the belt whilst others don’t. Not commonly used – paper labels cause a real contamination risk.

Like trommels (below), these are typically found at the beginning of a recycling line, though they can be placed elsewhere depending on the function they’re serving. Unlike trommels, disc screens can separate material by shape as well as size. As material goes over the inclined rolls of discs, smaller materials are allowed to fall through the openings while larger material is transported to the end of the line. Typically, flattened material is carried to the top of the screen while other, three-dimensional material bounces along the bottom.

Electric currents induced when a conductor is exposed to a changing magnetic field. These have been used in recycling since the latter half of the twentieth century (though French physicist Leon Foucault discovered them in 1855 and Thomas Edison first patented an eddy current devise in 1889). Used to separate non-ferrous metals (mainly aluminium, but also copper) from ferrous metals. It’s complicated stuff, but our insider at Novelis explains it thus: “The eddy current separator conveyor has a high-intensity spinning magnet inside the head drum. This alternating magnetic field generates a magnetic field in the aluminium on the conveyor and this causes the aluminium to be repelled. The other non-metal materials drop off the conveyor in the normal way.”

Used to sort mixed plastic waste since the late 1970s, and based on differences in charges of static electricity. Materials are charged when two non-conductive materials come into frictional contact (think about combing your hair or taking off a jumper), transferring electrons so one material is positively charged. When materials then fall through an electric field, they are attracted to oppositely charged electrodes. Commonly used to recycle plastic insulation from cables and electronics.

rush glass into small pieces through aggressive action of the discs. Glass drops through the spaces between discs, as do other fines.

A method for identifying non-ferrous metals. As material passes along a conveyor belt, small sensors emit electromagnetic waves, which are disrupted when conductors like aluminium and copper pass through them. A computer can then detect these changes and separate material with the use of pneumatic jets, for example.

A very accurate (and very expensive) technology currently used in some plastic sorting plants, and significant because it detects both bioplastics and petroleum-based plastics. In the Closed Loop plant, for example, specimens pass under green and fluorescent lasers that classify them using Raman spectroscopy, which relies on the inelastic scattering of monochromatic light to identify materials. In layman’s terms, energy from the laser is absorbed by the material and then reemitted with a unique spectrum. Raman spectra information can complement infrared spectra information (below), and is very useful for removing contaminants.

LIPS is potentially used in plastic separation. A high-powered laser hits material for a fraction of a second and vapourises a small amount (in the region of nanogrammes and picogrammes) to create a high-temperature plasma plume. All elements emit light in characteristic frequencies when excited to plasma form, so LIPS can, in theory, identify the exact elemental composition of any material.

An industrial instrument having a single row of pixel sensors, instead of a matrix of them. The camera images a constant stream of moving material, and a computer then creates two-dimensional image data, useful in locating items of specific colours, such as different metal or plastic fractions.

Used to separate out ferrous metals (steel and iron and its alloys). Can be overband magnets above belts; drums which can continually remove ferrous metals from streams put into the enclosure; or conveyor belt head pulleys, which cause ferrous metals to be carried round the head whilst other material drops off.

An emerging technology that operates like near-infrared spectroscopy (below), but detects wavelengths farther from the light the human eye sees. The technique allows separation of carbon black filled polymers favoured by the automotive industry, and is being developed to sort paper and cardboard. MIR spectrometers tend to be more inhibited by dirt than their NIR counterparts.

Used to sort transparent or lightly coloured plastics, predominantly. Near-infrared radiation has a wavelength just longer than the light the human eye can detect. Sensors detect the amount of NIR light that materials absorb by sensing the change in the reflected light; if the spectrum matches a reference spectrum, specimens are isolated from other materials. NIR optical sorters can also be used to sort items by colour, but find it extremely difficult to ‘see’ black items.

An emerging process used in mixed plastics recycling. A batch of mixed plastics can be dissolved together in a solvent as polymers dissolve at different temperatures. Polystyrene (PS), for example, will dissolve almost instantaneously; this PS solution will be drained and remaining plastics added to hotter solvent, at which temperature another polymer will dissolve, and so on. Thus, individual polymers can be separated from complex mixtures, regardless of contaminants, and are chemically equivalent to virgin polymers. The process requires a great deal of solvent, though, and as all additives are extracted, polymers must be restabilised.

Used to sort PET from HDPE, for example, as the former sinks while the latter floats.

A type of screen that consists of steel shafts to which rubber or polyurethane stars are fitted. The stars grip large two-dimensional objects like cardboard, newspapers and magazines and carry them up the slope (at around 45 degrees to the conveyor), while three-dimensional objects like plastic bottles, metal cans and glass roll onto a separate belt and fines fall through gaps between stars.

From the German word for drum, trommels are screened cylinders used to separate materials by size, often at the start of a recycling line.

Indicates colour visible to the human eye. Such sensors can separate out materials with certain colours and brightnesses, as well as of certain shapes by analysing surfaces. Used to separate out different metals as well as primary raw materials.

Used in many sorting processes to remove lighter contaminants, such as paper and plastic carrier bags, which could potentially gum up a MRF’s works.

Used to distribute material evenly across an area, which facilitates easy sorting.

A relative newcomer to the sorting scene, this is a disc screen shaped like a ‘V’, as the names suggests. This arrangement increases the screening surface, and is supposedly useful in separating out paper as light material floats up over the top of the screen, while fines fall through spaces between discs and plastic bottles and cans, for example, continue along the base of the ‘V’.

Also known as density-separators or lights separation units, these are often used on fines to separate light, high surface materials (bits of paper, plastic film and wood) from other, heavier substances through combinations of fans and sometimes vacuums.

Differentiates objects by atomic density; was commonly used 20-30 years ago to separate newly-introduced PET from then-common PVC because of the chlorine atoms in the latter. Has fallen out of favour as most plastics are mainly hydrocarbons with similar densities. Still used on mixed municipal waste to sort material streams such as ferrous scrap and organics and is also useful for removing potential contaminants in other processes.

A subset of x-ray sorting in which characteristic secondary (or fluorescent) X-rays are emitted from material that has been hit with high-energy photons (X-rays or gamma rays). Accurately analyses the elemental composition of specimens and is often used to separate different metal alloys, as well as WEEE plastic samples containing heavy atoms.