Advantages of recycling

Recycling diverse materials involves recovering and reusing them instead of of landfilling or incinerating the waste. These materials are processed and repurposed for new projects, conserving natural resources like forests for wood production and animal skins for leather production by reducing the demand for new raw materials. This process also minimizes environmental impact by lowering greenhouse gas emissions from decomposition and incinerating, as well as reducing the energy consumption associated with producing new materials. Additionally, recycling can lower overall costs for processes. For example, recycling aluminum can save up to 90% of the energy required compared to extracting aluminium from raw materials. Fewer mines are needed to obtain raw materials, resulting in less environmental pollution. By reusing electronic waste and ensuring quality control, fewer hazardous substances pollute the environment. Recycling also saves water, as recycling processes require less water than using raw materials. For instance, each ton of recycled paper can save thousands of liters of water, thousands of kilowatt-hours of electricity, and over a dozen trees. Recycling organic waste, such as sewage sludge, food, yard trimmings, and agricultural residues, transforms them into valuable resources like compost and biogas. This process is crucial in waste management strategies by diverting organic waste from landfills, where it decomposes anaerobically and produces methane - a potent greenhouse gas. Technological advances now allow for the extraction of valuable minerals that were previously not economically feasible to recover, including trace amounts of metals like gold, silver, copper, and rare earth elements.

Retsch equipment is used broadly in the sector of recycling:

• Quality control and processing. The quality control process and re-using process both begin with the pre-crushing and size reduction to prepare the materials for analysis or further use. At this stage, RETSCH provides an extensive selection of machines essential for these tasks, for a better overview, the section QC/processing is splitted in different areas by recycling material. Sieving and fractionizing as well as pellet pressing belongs to this chapter.
   
• In R&D, mechanochemical methods offer new pathways for the recycling of waste materials such as plastics, plant matter, or food residues, with Retsch ball mills playing a key role in these emerging processes.
   
• Retsch also offers equipment for waste management e.g. secondary fuels or soil remediation

Construction materials

Typical recycled construction materials include concrete, cement, bricks and asphalt. After being crushed, concrete can be repurposed as aggregate for fresh concrete or as base material for roads. Similarly, asphalt from roads and roofing shingles can be processed into new asphalt.

The above materials are all hard and brittle, so that typically Jaw Crushers are used for initial size reduction. Retsch’s offering of crushers provides suitable models for feed sizes up to 350 mm. Benchtop units like the BB 50 are designed for lower sample throughput, whereas the largest model BB 600 processes up to 3.5 t/h. For crushing rather sticky material like asphalt, embrittling the sample with liquid nitrogen and using a crusher with front door for easy access to the grinding chamber is beneficial. Ideally, the pre-crushing step results in particle sizes around 3-5 mm, which can be reduced further by fine grinding. Here, ball mills are commonly used, covering a wide range from small sample volumes to about 200 g per batch and typically providing grind sizes down to 100 µm. For the sticky asphalt sample, cryogenic grinding is recommended to avoid caking effects.

A good alternative to ball mills are Vibratory Disc Mills such as the RS 200 or RS 300. These mills produce very fine particles in the shortest amount of time.

Insulation materials are usually not as hard and brittle as the above-mentioned sample materials. Here Cutting mills in combination with ball mills can be used to pre-cut and pulverize such samples. See section “Glass”.

Metals

There are two main categories of metals that are recycled: ferrous metals, which contain iron and steel, and non-ferrous metals, which contain aluminum, copper, lead, zinc, and tin, as well as precious metals like gold and silver. Grinding and crushing of metal samples can be challenging due to their high ductility and abrasiveness – the risk of damaging a mill needs to be considered. Normally melting is the most common method of recycling metals, but sometimes mechanical crushing is required or is the better choice. To shred materials consisting of thin foil like tin or aluminum cans, a cutting mill like the SM 300 is suitable. Bottom sieves with apertures sized 4 to 20 mm are typically used. The resulting flakes have a particle size of approximately 5 mm. Employing a 6-disc rotor, which proves to be more durable than a parallel section rotor, has shown to be advantageous.

Hard and brittle materials such as metal alloys, tungsten carbide   or brittle mixtures of different metallic elements are submitted to primary size reduction in a jaw crusher, with the BB 500 model being particularly suitable. Finer grinding can follow in a Cross-Beater Mill SK 300 or a Vibratory Disc Mill RS 200 where grind sizes below 200 µm can be obtained. However, as these samples are commonly strongly abrasive, this will also lead to abrasion in the machines used.

The re-use of excess metal powders from additive manufacturing processes is a field where RETSCH sieving machines contribute to the recycling process. Sieving machines like the Vibratory Sieve Shaker AS 200 basic are used to separate metal powder particles into fractions, which are left after the 3D printing process. The fraction with the fine particles may be reused for the next printing process. RETSCH also offers size reduction equipment like the powerful jaw crusher BB 500 which is suitable for pulverizing incorrect green bodies or hard and brittle sprue parts produced by metal injection molding. The obtained powder is then returned to the production process.

Another important aspect of metal recycling is the re-use of iron slags which is a waste product during the steel production. Slags can be re-used as building materials especially in concrete production to reduce the clinker or cement content. Another optionis the re-use as fertilizers. Slags can be best crushed in jaw crushers and then pulverized in ball mills or vibratory disc mills, similar to the examples given for construction materials.

Textiles and leather

The Cutting Mill SM 300 is the most suitable mill to pre-cut soft sample materials. The parallel-section rotor and bottom sieves of 2 - 6 mm aperture are typical for this application. A cyclone helps to discharge the fluffy sample from the grinding chamber. Depending on the material, e.g. for more tough leather articles, cryogenic grinding may be required in the pre-cutting step. Here, immersing the sample for some minutes in liquid nitrogen embrittles the sample. In the case of cryogenic grinding, it is better to use the more robust 6-disc rotor.

The fine grinding step is either done in a Ball Mill or in the Ultra-Centrifugal Mill ZM 300. Embrittling the pre-cut fibrous samples may help to get fine ground particles. As the fibers do not keep the low temperatures and tend to warm up quickly, mixing with dry ice is superior to embrittling with liquid nitrogen. For this, the fibers are mixed 1:2 with dry ice snow and the complete mixture is fed into the ZM, usually equipped with a 0.5 mm ring sieve and operated at 18000 rpm. For cryogenic grinding, a cyclone should be used. Another way to get very fine particles of textiles is to use either the CryoMill or the MM 500 control. The MM 500 control offers larger grinding jars than the CryoMill and two grinding stations. Both mills embrittle the sample by using liquid nitrogen for cooling. In both cases first a pre-cooling time of 10-20 min is required to freeze the samples. The sample is then ground in ca. 10 cycles of about 1 min at 30 Hz with 1 min cooling breaks.

Electronic scrap

Electronic scrap is a valuable resource as it generally contains a much higher percentage of precious metals than is found in the same amount of ore. For materials analysis, electronic scrap can in most cases be pre-crushed in a Cutting Mill. The powerful SM 300 allows for cutting of hard and massive electrical components such as computer boards. Depending on the feed size, manual pre-crushing is required so that the samples can be fed to the mill. For tough samples, the use of the 6-disc rotor with robust cutting plates is beneficial. Usually, a 6 or 8 mm bottom sieve is used to obtain 5 mm particles. In a subsequent fine-grinding step, either a ZM 300 or a RS 200 is most commonly used. The embrittling with dry ice can be beneficial to pulverize the samples to about 0.5 mm particles in the ZM 300. Samples with increased metal parts are better ground in the RS 200 or the larger RS 300 as they are more suitable for this abrasive material than the ZM 300. When grinding metallic products, it is important to remember that metal parts cannot be pulverized by impact forces. If they are ductile, they will flatten or form lumps in a the RS or the ball milling process.

Organic waste

Bioorganic   waste sample are very common like garden waste or food residues and versatile. They can be ground in Rotor Mills much easier when they are dried to prevent blockages and sticky effects. Dried sewage sludge is commonly ground to about 2 mm particles in a Cutting Mill, here the basic model SM 100 a good choice. About 100 g sample require – depending on the sample properties like feed size and moisture residues – between 2-4 min. Garden residues containing twigs and other tough plant waste need to be pre-cut in the SM 200 or in the strong SM 300 models with higher speed and using the robust 6-disc rotor. Fine-grinding can be done in Planetary Ball Mills like the PM 200 or the Ultra Centrifugal Mill ZM 300, depending on the required sample throughput and final fineness. Food residues like orange peel also need drying before grinding in a Rotor Mill. Larger sample quantities such as 1 kg can be processed in the Rotor Beater Mill SR 300. As those samples tend to get warm during grinding, slow feeding is required, and the use of the distance rotor is beneficial. About 25 min are required for the 1 kg sample, when a 1.5 mm bottom sieve is used.

Mining waste

Mining waste is usually hard and brittle, therefore the best instrument to crush ore residues are Jaw Crushers. The BB 500 for example is capable to crush 8 kg gold ore to 5 mm particles in about 2.5 min. For fine grinding of mining samples, Vibratory Disc Mills are preferred. The RS 200 efficiently grinds up to 250 ml samples in only a few minutes, whereas the RS 300 is suitable to grind up to 2 l samples in one batch. Typical fineness of the ores is below 100 µm and suitable to prepare samples for XRF analysis.

Ceramics

Differentiating between various ceramic materials for reuse are pivotal in conserving natural resources and preventing environmental degradation. The recovery e.g. of valuable metals from spent catalysts, such as platinum and palladium, not only supports economic sustainability but also reduces the demand for mining activities. Ceramic bodies or misformed parts represent a unique opportunity for recycling and resource efficiency within the ceramics industry. These materials can be ground down and reused in the production of new ceramic items, significantly reducing waste and the need for virgin raw materials.  Initial   Crushing of ceramic material is easily done in Retsch Jaw Crushers. Depending on the feed size and the sample throughput, the most suitable model can be selected. Fine grinding is then performed in a Ball Mill for smaller sample volumes, like the MM 400. For larger sample quantities, the Disc Mill DM 200 or the vibratory disc mill RS 300 can be used. With this combination of pre-grinding and pulverisation, up to 3 kg samples can be crushed to about 100 µm particles in about 30 min. For harder samples, the Jaw Crusher, the Ball Mills and the RS 300 for example work with tungsten carbide accessories.

Secondary fuels and Waste management

"Secondary fuels" or “refused derived fuels” (RDF) are energy-rich fuels derived from various types of waste that would otherwise end up in landfills, such as industrial waste, municipal solid waste, biomass waste, and non-recyclable plastic waste. Combustible RDF can be used to heat cement kilns or in power stations as a substitute for conventional fossil fuels. In order to analyse the halogen content, water content, ash content and calorific value of RDFs, these heterogeneous material mixtures have to be pulverised. Usually, a Cutting Mill is required for the first size reduction step. Here, dependent on the sample composition, the 6-disc rotor is used, if more tough sample material like wood or hard plastic needs to be crushed. If the sample is more foil, paper and textile based, the V-rotor can be used. In both cases, as secondary fuels are usually light materials, the use of the cyclone unit is beneficial to enhance sample discharge from the grinding chamber and to avoid that the material warms up. In a fine grinding step, either the ZM 300 is used to process larger sample quantities up to several 100 g, or the CryoMill for small sample quantities up to 5 g. Usually, finer particles can be obtained with the CryoMill compared to the ZM 300. Ring sieves finer than 0.75 mm should not be used for such samples, as clogging may occur. Cryogenic grinding – thus mixing the sample with dry ice prior to grinding in the ZM 300, is essential in the case. Also here, the use of the cyclone is recommended.

Pressing stable pellets for XRF analytics

Solid, high-quality pellets are an important precondition for reliable and meaningful XRF analysis. With the PP 40, RETSCH offers a Pellet Press which produces strong pellets with a smooth surface. The PP 40 features an individual pressure force regulation in the range of 0 to 40 t. The PP 40 combines the advantage of a small benchtop model with high press forces, which are built automatically in up to three steps, ensuring that even difficult materials are pressed perfectly. For example, it turns out to be beneficial for the pellet stability when the forces like 10 tons, 20 tons and 30 tons in three subsequent steps of each 20 seconds holding time are programmed. The particles get the time to settle with the result that stability is enhanced. The pellets can be pressed in aluminum cups for further stability. Of all measured do not help, the mixing the sample material with a binder like Licowax is good method to stabilize even the most difficult samples like metal powders. About 10-15 g sample are mixed with 2 g licowax and pressed in three steps as described above. For mixing, the MM 400 is a good solution. This Mill can be equipped with an adapter to hold 8 conical centrifuge tubes. The samples are all mixed automatically, equally and in a reproducible way.

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RETSCH offers a comprehensive portfolio of instruments for recycling processes - from quality control and sample preparation to innovative mechanochemical methods. Whether pre-grinding, sieving, pelletizing or the use of ball mills for sustainable recycling solutions: We have the right instruments for your requirements.

Our global network and experts are available to provide you with personalised advice. Contact us and work with our specialists to find the best solution for your application!