The evaluation of technological possibilities for final separation of metallic components obtained from scrap tires.

Radvanska, Agata

1. INTRODUCTION

Along with the constant development in vehicle transportation for asphalt communications, the production of new tires grows enormously, so does the volume of waste tires which is about 1 billion tires annually worldwide. Scrap tires treatment varies in different countries, from landfilling, through energetic use (burning), to material recovery and re-use (Pecha et al., 2001). Output products for recycling are rubber granules, metal and textile. Slovakia and EU countries recovers waste tires using the individual components (rubber granules, textile and metal) and currently such material re-use is preferred to other ways of scrap tire treatment (Vozar & Kvasnica, 2005). The potential uses for scrap tires and crumb rubber are the rubberized asphalt pavements, running tracks, synthetic playing fields, playground surfacing, horse arena footing, asphalt additive, asphalt crack sealants, paint non-slip additive and many others. This commodity is inert, environmentally friendly and has good thermal, mechanical and physical properties (Taborsky & Jungman, 2006).

The aim of the paper is to determine the technological and economic feasibility of the secondary separation process to gain as much of components from waste tires that converges to 100%.

Rubber granules are assigned for the production of rubber products, textile components may be burned or used as filler and a metal component are used as a blast furnace burden in metallurgy. Chemical treatment of waste tires--pyrolysis, is a wasteless tire processing, and material is used totally. The pyrolysis products are charcoal, pyrolysis oil and pyrolysis gas. This method could help to get rid of a large number of scrap tires; the drawback is the economic unavailability (Radvanska, 2006).

2. SECONDARY SEPARATION PROCESS REASONABILITY FOR METAL/RUBBER MIXTURE

The Slovak company performing the scrap tires processing currently uses rubber granules for the production of rubber mats, playground and sport surfaces and since 2009 makes testing for the future production of rubberized asphalt in cooperation with the research institute of civil engineering.

Steel components from scrap tires are used as a blast furnace burden and textile components are sent for energetic use in cement plant. Rubber granules accomplish up to 99.9% purity, which meets the requirements for the production of end products. Separated steel is currently pure to about 80%, the remainder consists of rubber, which is not separated during the processes of crushing and magnetic separation; likewise the textile component, which contains 35 to 65% of rubber (Prochazka, 2007).

Metal waste is a component that can be reused in the metallurgical industry. As any other commodity, the price depends on steel quality and purity. Currently, the purity of steel is about 80%, but the proper equipment can increase the purity up to 98%.

This would result in a more favorable price for the producer and better quality of the steel components for the client. There are various companies that offer technological equipment for the steel components secondary separation--single shaft, double shaft or multiple shaft shredders, knife grinders and special crushers.

3. TESTS FOR THE RUBBER CONTENT DETERMINATION IN A METAL WASTE

The test for the rubber content determination in the metal waste was based on the mass difference between these two components. Metal waste is obtained from the scrap tire separation process performed by the technological line ELDAN and Heavy Rasper, where it is shredded and separated from rubber granules using the magnetic separator. Digital scales, laboratory bowls and metal waste sample was used in the test.

One bowl was filled with metal waste from the ELDAN output line and 100 g of it was weighed by digital weighing. Rubber was then manually separated from the metal. Pieces of rubber sized from 3 x 3 mm to 20 x 20 mm, which were not separated from the metal or could not be separated manually, were placed to another bowl assigned for rubber material. Smaller pieces, sized up to 3 x 3 mm, and metal (wire) that was coated with a thin layer of rubber was placed in a third bowl assigned for the metal. After this sorting, bowls were weighed on digital scales; measurements were made in three different periods, when composition of input tires varied slightly. The results of the measurements are presented in Table 1.

From the results it can be concluded that 100 grams of metal waste consists of rubber component of an average of 20% by weight. That means that in 1 tone of metal waste the rubber portion is up to 200 kg which could not be used for the manufacture of end products. The resulting purity of the metal is also important for price fixing. Currently, during the economic crisis it is difficult to determine the proper price for this commodity. Orientation price from the last year for that commodity was 0.27 [euro] per 1000 g of metal waste with 80% purity. Today, the price is significantly lower. If this metal waste is secondarily separated, the metal purity would increase to a value approaching at least 98% and consequently this would reflect in the final quantity of the rubber granules, as well as it would result in higher metal purity, and so better marketability. Results obtained from these tests help to identify weaknesses in the purity of separated metallic components, resulting in worsened marketability in comparison with the 98%--pure metal obtained after the introduction of secondary metal separating equipment.

Metal waste outgoing from HEAVY RASPER, as it was already mentioned, is of 80% purity, unretained metal passes to Fine Granulator and is magnetically separated, where its purity reaches 90%. Secondary separation equipment has to be placed between Heavy Rasper and Fine Granulator as it is shown on Figure 1.

[FIGURE 1 OMITTED]

In the Super Chopper, tires are shredded to the plates with a size approximately 25 x 25 cm. Plates go forward along the conveyor belt to Heavy Rasper, which cuts the plates into smaller pieces sized 18 to 20 mm. In the outlet of Heavy Rasper, the magnetic separator is placed, which separates the rubber granules from the metal components (including the rubber) on its way to FineGranulator 1. Metal components are lead by conveyor belt outside the hall to final separation. Final separation consists of separation mill (knife mill) and a magnetic separator. Mill consists of static and rotary part, containing several knives. Mill shreds metal remainder and by means of a metal sieve separate the remaining rubber from the metal components where the metal is consequently separated by magnetic separator.

Then, the cleaned waste, i.e. metal, passes into the collection containers and rubber goes back into the process before FG1--Fine Granulator. FG1 cuts rubber granules to smaller size. Granules then also undergo through magnetic separator (overhead magnet), which removes part of the metal residue. The unit is plugged to the exhaust system, for textile portion exhaustion. The FG2 cuts rubber granules to even finer fraction, and roller magnet finally separates the metal from rubber. In the final stage, the rubber granules proceed to the last part of the UPC 1750 where size sorting from 0--0.5 mm to 28 - 38 is done by shaker screen. Sorted granules are collected in big bags (weighing 1 050 kg) depending on the fraction.

Currently, the company does not use final separation equipment put in the ELDAN production line. Last year, the metal waste was subjected to testing on the similar separation equipment based on the technology of knife mill and magnetic separator. The device has an output connected to conveyor belt leading from Heavy Rasper, after the first magnetic separation. Separated metal is collected in containers and the rest goes back into the rubber technology line ELDAN. Tests that have been performed, the separated metal purity reaches to 95%, while technology supplier company guarantees the resulting purity of the metal up to 98%. Tests have been based on the weight difference of metal and rubber, while materials were separated manually. Production line without secondary separation showed 80% metal purity, compared to the production line containing secondary separation device, which showed 95% metal purity.

4. EVALUATION OF THE SECONDARY SEPARATION EFFECTIVENESS

If recycling, the aim is to recover the material completely, without any remainder, which would go to landfills. Each company involved in the waste recovery tends to get closely to 100% material re-use.

Currently, the company generates the secondary raw material in the volume--rubber granules 60%, metal 25% (purified to 80%) and textile 15%. After the secondary separation line introduction for metal purification, the efficiency would be increased by means of the 95% metal purity, which would increase the value of commodities, but also extending the marketability of this commodity.

5. CONCLUSION

The research was followed to the efficient use of rubber granules, metal and textile components in the company in Kosice. The proposal is based on secondary separation of metallic components, where an increase in metal purity can be from 80% to 95%. This is reflected in increased marketability, as well as in a higher price per kg of materials. At present the company uses rubber granules for the manufacture of rubber mats, the surface of children's and sports playgrounds and for exportation.

Another possible solution which could have future benefits, is to apply textile components for uses other than energy recovery in cement kilns, as it is common today.

6. REFERENCES

Pecha, C.; Cornej, P. & Vargova, J. (2001). Zhodnocovanie a recyklacia opotrebovanych pneumatik. (Revaluation and recyclation of scrap tires) Journal Strojarstvo. No. 11 (2001). Available from: http://www. strojarstvo. sk/inc/index.php?In=SK&tl=3&tpl= archiv.php&ids=2&cislo=11/2001&idclan=333 Accessed: 2009-01-05

Prochazka, O. (2007). Odstranovani textilu z granulatu drcenych pneumatik, Metoda fluidniho rozdruzovani. (Textile removal from scrap tires granulate) Available from: http://www.waste.cz/waste.php?clanek=pneuaquatest.htm Accessed: 2007-04-22

Radvanska, A. (2006). Spracovanie odpadovych pneumatik. (Scrap tires processing) Journal Strojdrstvo. No. 12. (2006), pp. 2-3.

Taborsky, T.; Jungman, J. (2006). Tires: Energetic and material re-use of scrap tires. Journal Odpadove forum, No. 2 (2006/2)

Vozar, P.; Kvasnica, M. (2005) Komoditny program sektora opotrebovanych pneumatik na roky 2006-2010. (Commodity programme of scrap tires for years 2006 2010) Bratislava: Recycling fund, 2006. 7 pp. Available from: http://www.recfond.sk/index.php?www=sp_file&id_item=3 5, Accessed: 2009-01-11

Tab. 1. Measurement of the metal and rubber portion in metal
waste from scrap tires

 Percentual composition of 100 g
 of metal waste

 Date of Metal Rubber
No. measurement component [%] component [%]

1 12.11.2008 22,5 77,5
2 03.02.2009 18,3 81,7
3 06.04 2009 79,8 20,2