LITERATURE REVIEW
ASR can be classified as both hazardous or not hazardous waste. The stringent landfill legislation related to ELV treatment will limit current landfilling practice and impose an increased efficiency of the recovery and recycling of ELVs. Primary recovery techniques recycle up to 75% of the ELV components and the remaining 25% is called ASR. The application in waste-to-energy plants, in cement kilns or in metallurgical processes is significant .Emerging technologies include Gasification and Pyrolysis. The environmental impacts of the processes are acceptable. The ever growing number of vehicles will determine a further rise of automotive shredder residue (ASR) generated for years to come. Landfilling is currently the most widely used solution for this type of residue but due to its complex matrix the final deposit requires great technical and environmental care.
CHARACTERIZATION OF ASR
ASR is a highly heterogeneous material, that is mainly composed of plastics (23 – 41%), rubber/elastomers (9 – 21%), metals (6 – 13%), glass (10 – 20%)(7).The ranges depend on the construction year, brand, engine displacement, employed technology for the treatment of disposing vehicles, the accuracy given during the dismantling operations, type of vehicles, etc. Depending on its origin from the post-shredding scheme, ASR can be classified
• Light fluff: Fraction generated during shredding of the hulk and separated using air classification (ca. 75% of the total ASR; 10–24% of the total ELV)
• Heavy fluff: Fraction remaining after metal separation from the shredded heavy fraction (ca. 25% of the total ASR; 2–8% of the total ELV). • A soil/sand fraction is sometimes reported separately, but is usually included as part of the heavy ASR (ca. 0–2.5% of the total ELV).
Two aspects are concerned as the main issues in secondary raw materials recovery and these are : First of all, to make their use favourable over virgin raw materials the qualitative specifications must be fulfilled and of course to minimize the undesirable components; afterwards, there must exist a constant demand of the secondary raw materials, involving a selling price adequate to cover the recovery process costs. The technologies that may be employed to mobilize valuable components from ASR include mechanical processes (mainly shredding), and physical operations such as dimensional, magnetic, electrostatic and densimetric separation phases and thermal processes. All of which are discussed later.
Table No -1 Composition as wt%, of ASR
Material Gakagno (2001) Mirabile (2002) Marco (2002) Fabrici (2003) Zolezzi (2004) De Marco(2007)a De Marco(2007)b Mancini(2010) Ruffino (2010) Ciacci(2010) Mancini (2011) Santini (2011) ENEA(2011)
Fine material <10 mm 35 – 6.1 75 6.1 53.5 32.3 21.7 17
Fine material <20 mm 69.6 34.5 35.2
Foam – 3.3 7 4.5 0.26 3.5 0.28 5.6
Fabric , fibers 25 10 11 6 5 8 10.5 12.3 15.6 11 17 27 0.9
Soft plastic 20 41 29 22 20 0.26 21 0.47
Hard plastic 7.5 27.6 13.4 24.5 45 32.9 23 9.3
Rubber 20 21 9.7 23 38 4.1 35.1 1.4 6.6 15 15.9 9
Electric material – 3 0.7 0.4 .7 0.44 3.5
Ferrous metals – – 13 6 1.1 6.9 9.5 2.9 8 59
Non ferrous metals 1 0.29 1.4 2
Glass – 16 13 16.5 15 0.09 2.9
Wood – – 16 4 10 0.63 0.4 2.07 1
Paper , cardboard – 1 0.41 0.4 0.4
Others 9 2.2 18 13.4 20.3
Parameters U.M. Matoino(2000) Galvagn(2001) APAT(2002) Mirabile(2002) FAEC(2005) Apat(2006) Manci(2010) Vigno(2010) Marselli(2010) Ruffino(2010) Viotti(2010) Santtni(2011)
Fe % wt. 2.36-2.7 25.7 3-10 3026
Al % wt. 0.62-4.8 4-10 0.76
As mg/kg 4.17 6.42 0.01 15.9 3-6 16 3.44 6.4 1
Cd mg/kg 80 30-70 22.9 62.2 16.32 31.3 22.2 0-30 6 15.2 6.7 9.91-21.1
Cr mg/kg 900 150-200 149 800 136 209 100-200 300 226 535.3 73.1-102
Cr VI mg/kg <5 <1 0.49 <0.05 4.9 <1 33500 5.06 <0.2
Cu mg/kg 5600 7200-21800 25876 12000 2.59 12284 2856 10000-60000 27 6633 5980-21200
Hg mg/kg 3 0.25 3.19 <0.05 0.213 0-0.5 0.8 111 0.31 0.17-0.42
Ni mg/kg 100-150 69.2 700 76.2 260.4 257 50-100 210 191.1 34.8-38.6
Pb mg/kg 2800 2980-3475 2007 2000 1495 6.191 2458 0-5000 4000 410 1808 442-600
Se mg/kg <0.01 2.20 0.56 <0.1
Zn mg/kg 4250-6650 3493 19000 4615 6833 19439 0-15000 3140 14221 1810-6140
Parameter Patiemo
(1998) Maurino
(2000) Galvagno
(2001) APAT
(2002) Mirabile
(2002) Zolezzi
(2004) Vigano
(2010) Ruffino
(2010) Mancini
(2010) Morselli
(2010) Santini
(2011)
Ash 36.2 27.3 44.7 28.2 35.8
C 17.5 40 37.2 48.11 44.5 47 40 46 36.3
H 2.1 50 4.8 307 5.3 5.8 5 5.89 4.67
N 0.5 1 – – 4.5 1.2 2 1.68 –
O 17.4 1.5 – 6.9 19.5 2.5 –
S 0.25 0.95 0.4 0.3 0.2 0.3 0.3 0.4 0.28 6 0.23
Cl 0.05 3.5 2 – 0.5 1.25 0.94 0.95
F – – – – – 0.75 0.017 <0.05
Table No-2 ContantOf Metals In ASR
Table No-3 Elemental Composition And Characteristics Of ASR
As it can be easily observed from Table 1, fines (0–20 mm fraction) can represent up to 70% of the total sample with a mean value of about 35% in wt. The remaining fluff mainly consists of polymers, up to 45%, such as polyurethane (foam rubber), plastics and rubbers. Textiles accounts for about 10% on the total and together with polyurethane foam (PUF) are strictly related to car seats and carpeting (Morselli et al., 2010). Elemental Analysis of ASR from Italian shredder plants is shown in Table 4 while the main metals content is reportend in Table 3. The levels of contaminants such as Pb, Cu, Ni, and Zn poses serious attention on the need to lower concentrations throughout the entire ELV recovery process. Considerable amounts of copper wire fragments, many connected to or intertwined with other materials, were observed. The content of mercury is typically around 0.5 mg/kg, roughly half the Hg present in the ELV before shredding . Cd is typically found at 20–80 mg/kg in ASR, whilst Pb levels are much higher, typically 500–5000 ppm (0.05–0.5%), for chromium (Cr) typically 150–800 mg/kg, for arsenic (As) up to 16 mg/kg. Dealing with the total metal content, an increase of Pb and Zn can usually be observed towards the finest fraction whilst the other metals considered do not exhibit such clear grain-size dependence. Notwithstanding their total metal content, ASR usually does not overpass the threshold values for landfill disposal.
Mechanical recycling and material recovery
Clean recyclates and their potential applications are the basic requirement for the recycling of polymers such as PET, PE and PP.Identification methods of different materials should be improved and for large pieces like PU foam or bumpers must essentially be removed before the shredding process. Materials that are too contaminated for mechanical recycling have as options feedstock recycling (pyrolysis, hydrolysis or depolymerisation) or energy recovery, besides landfill. Mechanical processing can give recyclable recovered fractions or can be used to improve the quality of ASR by removing harmful substances, or increase its worth as a waste derived fuel [4].
Fig. 4 : Process for mechanical separation of ASR [5]
To assure that insulation is stripped off copper wires, the ASR must be reduced to a size less than 7 mm as, and this is achieved by a two-stage comminution process. Before that, to remove a fines fraction smaller than 1.2 mm, the ASR is screened. Then, a rotary shear is used to cut the remaining ASR to a size below 20 mm, followed by the removal of magnetic components, followed by a double shaft cutter with an integrated sieve to reduce the size further below and it is then combined with the 1.2-7 mm fraction from the first screening stage. Next, it must be dried from 5-25 % to less than 2 % moisture before the material can be further separated into different density fraction. After an air classification step (to remove for example foam) the material is passed through a multi-level sieve followed by a zigzag air sifter where the remains are screened in three fractions. The four product fractions obtained are then
1) a magnetic fraction (~95 % iron),
2) a fraction containing copper granules,
3) a mixture of minerals and some metals, and
4) an organic fraction containing ~ 50 %-wt C, ~6 % H, ~ 12 % O, 1~2.5 % Cl, 20~28 % ash, < 0.5 % metal, with a calorific value > 23 MJ/kg.
Metal industry can be targeted for selling off the first two product and further processing of the third fraction is carried out for copper and aluminum recovery. A waste-to-energy process, can be used as carbon source in steel plants or use for methanol production is suggested for the fourth organic fraction.Also another method for ASR processing employed in Japan is as shown .
Annually around 1 million tonnes of Japanese ASR must be processed. Process for the basic separation of the combustible and non-combustible fractions is described by Kusaka and Iida where the ASR issorted, compacted and solidified. Extraction of iron, non-ferrous metals and glass is carried out during the sorting step. The combustible (mainly plastics) part are processed into a fuel suitable for “dry distillation/ gasification” during the compacting/solidification step. Process set-up for ASR sorting, compacting and solidification is pictorially represented in Figure 5. For trapping HCl during the gasification process, slaked limeCa(OH)2 is added. During the shredding stages, large amounts of water are added to the ASR to avoid fires from breaking out [6].
THERMAL TREATMENT
The thermal treatment methods such as co-incineration with other wastes in waste-to-energy (WTE) are for the ASR largely dependent on its organic fraction, (typically about 50 wt%). These promote installations or application as (energy) feedstock in the foundry and cement industries. Whereas the small particle size fraction can largely be handled by thermal treatment the fine ASR fraction often hinders further mechanical recovery. Thus a better and a more cost-effective as well as sustainable alternative to landfillingof ASR is presented. Three different methods undertaken undertaken under the thermal treatment are as follows :
Co-combustion
The application of combustion technologies (i.e. incineration) to treat ASR may be hindered by the fact that ASR constitutes of high amounts of chlorine, heavy metals, and toxins. As a result, thermal treatment in Waste-to-Energy Plants (WTEP) could result in the emission of acidic gases, fine dusts containing heavy metals, and organic pollutants. In general, ASR is not applicable for mono-incineration due to possible carry-over of unburned fines. A mixture with lower calorific wastes enhances the incineration potential and efficiency in waste-to-energy plants along with recovery of energy. De-chlorination techniques for ASR are intensively researched as chlorine presence may lead to due to chemical corrosion and fouling. Advanced upgrading techniques are employed to reduce the high concentrations of persistent organic pollutants (POPs) and heavy metals. Emission of the harmful substances can be limited by optimum control of the process conditions in combination with adequate flue gas cleaning. It is estimated that 95% reuse and recovery target can be met by applying thermal incineration techniques or emerging technologies such as pyrolysis or gasification.
Gasification
Gasification is generally operated at high temperatures (>700–800 °C). Air is used as a gasification agent, and the air factor is generally 30% or 40% of the amount of air needed for the combustion of the organic fraction of the feedstock. Gasification produces mostly a gas phase and a solid residue (char and ashes). The use of air introduces N2 in the gases, thereby considerably reducing the calorific value of the syngas because of the dilution. Gasification has been widely studied and applied for biomass, coal and plastic solid waste. The application for the treatment of ASR make use of a rotary kiln, operated between 850 and 1120 °C with an air factor < 1. Combustion of the gases is completed in a secondary afterburner chamber. The system is completed with a boiler (steam at 43 bar, 430 °C) and turbine. The capacity was on average 2400 kg/h during the tests. The full-scale plant, designed for the thermo-valorization of tyres, was purpose-modified to allow for ASR combustion. Several plant components were specifically modified; for instance, the inlet of the gasification chamber was properly sealed to avoid excess air in the first reaction stage.
Pyrolysis
As is well known, pyrolysis is the thermal degradation of macromolecular materials in the absence of oxygen. The main products of this process are a solid phase (charcoal), a liquid phase (tar) and a gaseous phase. The conventional pyrolysis is carried out at moderate temperatures (300–600 °C) and low heating rates (with vapour residence times of 10 s to 10 min) and gives approximately equal mass fractions of gas, liquid and solid products. Pyrolysis seem to offers an environmentally attractive method for the treatment of ASR. As mentioned above, the process uses medium to high temperatures and an oxygen-free environment to decompose ASR chemically, thus producing minimum emissions of nitrogen oxide and sulphur oxide compared to the commonly practised conventional technology, incineration. Pyrolysis also allows valuable materials to be recovered. This is particularly important when designing plants to meet material recycling targets established by the ELV Directive. The process, generally, begins with preheating of shredded materials being fed to a reactor. In the reactor, depending upon the chosen process parameters, the waste material is heated to the required temperature. The products of pyrolysis represent a significant percent of the initial volume of organic matter that can be converted into energy, to either sustain the process or produce excess power. Processes for the pyrolysis of ASR could specifically be designed to maximize gaseous products or focus on material recovery as a key design requirement. Potential users of pyrolysis char include iron, steel and cement industries.
A review of technologies for the pyrolysis and gasification of (most) wastes worldwide was available as a commercial publication in 2002 [8]. In 2004 an excellent review of pyrolysis and gasification processes for MSW was published [9]. Both indicated a number of processes that had the potential to develop into commercially useful options 10 for SR. Of these, several years later, only one is now considered to be fully commercial – the Ebara plant in Japan [10-12]. Ebara co-processes SR with sewerage sludge (70/30) at around 100,000 tonnes per year using gasification followed by vitrification of the residue in order to produce an ‘inert’ product. Only three other pyrolysis processes are classified as semi- or fully-commercial, and which clearly specify that they can handle ASR as a feed. They are the PKA process, the Pyromelt Process (LurgiEnsorgung), and the TWR process (Siemens; Schwel-Brenn; TWR/Mitsui
COMPACT DISK WASTES
A compact disc is a deceptively simple looking device considering the technology required to make it. CDs consist of three layers of materials:
A base layer made of a polycarbonate plastic.
A thin layer of aluminium coating over the polycarbonate plastic.
A clear protective acrylic coating over the aluminium layer.
A composition for refinishing a compact disk having a plastic surface comprising:
(a) from about 15 to about 25 weight percent of a solvent for the plastic surface;
(b) from about 12.5 to about 35 weight percent of an abrasive particulate;
(c) from about 15 to about 25 weight percent of a petroleum distillate;
(d) from about 2 to about 10 weight percent of a hard wax; and
(e) from about 15 to about 25 weight percent water, where the weight percentages are based on the total weight of the composition.[17]
In order to maintain universal compatibility, the design of the compact disc is according to the norms established by Sony and Philip. Standard CD dimensions are4.72 inches (120 millimetres) diameter and .047 inches (1.2 millimetres) thickness. The positioning hole in the middle is .59 inch (15 millimetres) in diameter. Usually weight of CD is around .53 of an ounce (15 grams). First step in making a compact disc involves preparing a glass \”disc master.\” The encoding of this master is donewith the desired information and then they are put through a series of electroforming steps. In electroforming, with the help of electric currents, metal layers are deposited on the glass master. Then, the information is transferred onto a plastic disc oncethe final master version is ready, its. Application of the reflective aluminium layer, followed by a clear acrylic protective layer, and then lastly the label.[14]
CDs and DVDs consist of the same basic materials and layers but are manufactured differently. A DVD is actually like two thin CDs glued together.
LITERATURE REVIEW
In a conventional method of recycling disks, disks are crushed as they are and molded. In such a case, the components of the protective layers and reflective films are also mixed into the molded product. It is not possible to recover the reflective films only, and the molded product is not transparent. Thus, the molded product is applicable only for limited usage.
Apart from the read-only disks, recordable optical disks are also on the market. Although there are several types that are recordable, the present invention relates to optical disks which have a layered structure, as shown in FIG. 8, including a substrate L7, a dye layer L6, a reflective film L5 and a protective layer L4. Generally, in this type, recording is allowed only once. An example of this type is a CD-R (recordable compact disk). The CD-R includes, for example, a polycarbonate substrate, additives such as an organic dye, for example, a cyanine dye, and a quencher, a gold reflective film, and an ultraviolet-curable resin such as an acrylic resin.
There is a DVD-R (recordable high-density recording disk: digital video disk), in which two layered structures described above are laminated together by means of, for example, an adhesive as shown in FIG. 9. That is, protective layers L11 and L11 are adhered together with an adhesion layer B. and a dye layer L9, a gold reflective film L10, and a protective layer L11 are deposited on a substrate L8 in that order on both sides. In these types of disks, in addition to substrates, expensive gold reflective films are used, and thus, the recovery of reflective films has been desired. For that purpose, although it may be possible to use a solution which dissolves reflective films as described above, only an extremely hazardous solution, for example, aqua regia, can be used. Also, by treating the whole disks at high temperature, organic substances such as substrates are burnt and gold only can be recovered, however, in this method, the substrate resin cannot be recovered.
A method of recycling a disk recording medium includes the steps of retaining the disk recording medium in a liquid medium, the disk recording medium having a layered structure including a substrate, a dye layer, a reflective film, and a protective layer; radiating ultrasonic waves onto the disk recording medium such that the substrate and the reflective film are separated from each other; and bringing a solution into contact with the substrate separated from the reflective film such that the dye layer is separated from the substrate in order to recover the substrate, the solution dissolving the dye layer.
The lacquer and aluminium coatings from the polycarbonate substrate of scrap compact discs so as to reclaim the polycarbonate are removed by a method which includes the steps of immersing the discs in a an alkaline solution, heating the solution to a predetermined temperature and mechanically agitating the immersed discs by applying ultrasonic energy to the solution at a sufficient energy density and for a sufficient time to dissolve the lacquer and the aluminum into the solution. The solution containing the dissolved lacquer and aluminum is decanted from the stripped polycarbonate discs, the discs are washed with water to remove remanent alkaline solution, and then dried. it is possible to strip the protective lacquer layer, whether UV cured or solvent-based, and the underlying aluminium film, from the polycarbonate substrate of compact discs, without causing dissolution of the polycarbonate, by placing a quantity of the discs in a perforated barrel supported for rotation in an ultrasonic tank containing an aqueous alkaline solution of an alkaline salt or a base, a chelating additive and a surfactant, and as the barrel is rotated agitating the discs with ultrasonic energy for a time sufficient to completely remove the coatings from the substrate. The long axis of rotation of the barrel is disposed horizontally, and the barrel, which typically may be sixteen inches in diameter and twenty inches long, has round openings or holes, three to four inches in diameter, in its walls to facilitate flow of the solution to and from the interior of the barrel and floating of removed flakes of lacquer out of the barrel for settling onto the bottom of the tank. Any desired member of discs, up to the capacity of the barrel, are loaded into the barrel.
The tank in which the barrel is supported is filled with an aqueous alkaline solution containing: (1) an alkaline salt or a base which preferably is a mixture of alkali metal phosphate, alkali metal hydroxide and alkali metal carbonate, wherein the metal may be either sodium or potassium; (2) a chelating additive selected from the alkali metal salts of citric acid, ethylenediaminetetraacetic acid (EDTA), gluconic acid and nitrilotriacetic acid, and (3) a wetting agent selected from the group including sodium alkylbenzenesulfonate, napthalenesulfonate, fatty acid esters and sodium lauryl sulfate.
DISPOSAL OF CDs AND DVDs
Disposing of CDs and DVDs is a problematic issue. The discs are made up of layers of different mixed materials, including combination of various mined metals and petroleum derived plastics, lacquers and dyes, which, when disposed of, can pollute groundwater and bring on a myriad of health problems. Most jewel cases are made of polyvinyl chloride which has been thought to produce a higher than normal cancer rate within workers and those who live in the area where it is manufactured. They also release harmful chemicals when incinerated. Unfortunately most CDs and DVDs end up in the incinerator, as they are difficult to recycle. When PVC is processed with regular recyclables, it can sully entire batches, ruin equipment, and bring on health problems, so CDs and DVDs can’t just be tossed in your blue recycling bin, but instead have to be sent to specialized recycling facilities. Due to lack of awareness of these facilities and the inconvenience of packaging up old discs and sending them away, most people resort to tossing them in the trash – in the United States, upwards of 5.5 million software packages end up in landfills and incinerators each year. Even those that do manage to send them to the appropriate recycling facility are adding one more step to their environmentally-damaging journey by sending them on a CO2 producing plane or transport truck. Eliminating the need for CDs in the first places would mean less waste in our landfills and less toxic chemicals in our air, and it’s hard to argue against that [16]. CDs can be recycled for use in new products. Specialized electronic recycling companies clean, grind, blend, and compound the discs into a high-quality plastic for a variety of uses, including Automotive industry parts, Raw materials to make plastics (Discs are ground into a gravel-like substance, which is sold to companies that melt it down and convert it to plastic), Office equipment etc.
FUTURE SCOPE
For Automotive Shredder Residue :
ASR is a potential alternative fuel and mineral feedstock for cement production as about 50wt% of ASR consists of combustible matter such as plastic or rubber, and another 40 wt% is made up of silicates, calcium, aluminium and iron. Given these typical waste characteristics, a cement kiln seems in principle ideal for the use of ASR as fuel. However the use of ASR in the cement industry implies a need to guarantee feedstock quality parameters in order to satisfy kiln operators and certify that no significant increases in kiln emissions will be elicited. The pretreatment and mechanical means, required to process ASR into material suitable for use as coal and mineral substitutes, should be properly assessed. Techniques aimed at reducing contaminant levels (particularly mercury) should be developed. Other problems related to co-incineration of ASR in cement kilns are increased ash formation, clogging of the fuel injection zone, and increased concentrations of hazardous elements in the cement kiln dust. However, the use of ASR in kilns may lead to reduced environmental impacts resulting from less mining, transportation and preparation of coal and mineral ores as well and reduced impacts of SR landfill leachate. Remaining barriers to acceptance include demonstration that a full-scale system will consistently produce high value fuel with low concentrations of hazardous materials. ASR can also be used as an alternate fuel to coal in the iron metallurgical industry with an excellent emission control This can be attributed to the fact that blast furnaces are able to comply with the confined values fixed by national norms without any significant additional investment. Use of such material, especially in the metallurgical sector, offers energetic, environmental and economic advantages without installation of new plants. Nevertheless, the experience gained on this topic is still not sufficient to express its technoeconomic evaluation. In fact, if the process on one hand is certainly efficient energetically, on the other hand, the same appears to provide end products of a modest quality.
For Compact Disk Wastes:
Recycling of compact disc should be considered in the future. Recycling of compact discs is economically valuable because the quality properties of the recycled polycarbonate from old compact disc after being stripped by removing aluminum, lacquer and printing are extremely high, only slightly lower than of virgin polycarbonate. The recycled polycarbonate can be used in other application, which is preferable over final disposal on a landfill.
Each recycling method has some advantages and disadvantages. Mechanical recycling may be regarded as the simple, save and cheap way to recycle the polycarbonate. But chemical
recycling is proved to be effective as being used for example by Bayer AG. Also, another way of recycling of compact disc is by using the recycled disc polycarbonate scrap as a blending resin for other material formulations has been shown to be a viable use for this recycled resin. Already in 1998 the polycarbonate recovered from scrap CDs was amongst the four largest sources for this recyclate. For metals such as aluminium and gold the amount of material that can be recovered is extremely small as compared to the total streams of recycled aluminium and gold [20] This makes their recovery from scrapped CDs (at this moment) economically unattractive and energy consuming.
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