Introduction

With the development of country's economy and population, the amount of scrap tires is increasing and represent a major ecological issue since it occupies a large area and non-biodegradable¹. In many countries, scrap tires are recycled to obtain valuable products such as fuel derived from tires, and used in asphalt, in paving roads and floors, with all these uses, large quantities of old tires are remain discarded annually^2,3. Therefore, it is necessary to explore other applications like utilize as an adsorbent. Scrap tires include (30% W/W) carbon black, which has properties similar to activated carbon but less surface area.^4,5

Many factories use methylene blue dye (MB) to color their products. It is used in textile, wool, cotton, plastics and pharmaceutical industries. This dye is visible even in low concentrations⁶ and may absorb or reflect sunlight in the water, which affects the growth of bacteria and when human take these dyes, it causes different diseases, including eye irritation and diseases related to the digestive system, so it was necessary to remove these dyes from the water.^7,8

There are many ways to remove dyes from the water and between these methods, adsorption technique is the perfect way for being an economical and easy and does not produce wastes are difficult to get rid of them.⁹

We found a lot of researchers using old tires in the process of adsorption to remove organic and inorganic contaminants and dyes from their solutions. Hamadi et al ¹⁰ studied the removal of Cr (VI) from aqua. solution by adsorbent derived from the used tires, Amenaghawon study the Adsorption of Toluene from aqua. Solution in Scrap Tires¹¹ F.A. Aisien et al studied Ethylbenzene adsorption from aqua. solution by Scrap tires¹, F.Calisir et al, studied elimination of Cupper (II) from its solutions using scrap tire rubber¹², Knocke and Hemphill studied adsorption of Mercury (II) on scrap tire rubber.¹³

Many studies have shown that the irradiation process of recycled rubber improves its mechanical and morphological properties. Yassin et al¹⁴ investigated the effect of irradiation on the physiochemical properties of waste tire rubber and noted that ionizing radiation provides a solution to the problem of tire recycling due to its ability of crosslinking or the cleavage of a wide range of materials. Borriello et al studied the effect of irradiation on the thermoplastic polymers¹⁵. Telnov et al. explained that an electron beam with ranging energy from (6 - 10) MeV could provide an alternative method of recycling waste rubber and to reactivate based on butyl rubber¹⁶. Shanmugharaj et al,¹⁷ studied the effect of ultraviolet radiation in the presence of allylamine on crumb rubber and the results of the study showed improvement in tensile strength and elongation, which had ascribed to the energized crumb rubber surface. Adnan et al² studied the  "Mechanical and Curing Properties of Crumb Rubber Irradiated in Polar Media Filled the Tire Tread Blend ". High polar media such as Acetic acid and Trichloroacetic acid (TCA) show better tensile and elongation properties.

 This study focused on the possibility of using rubber granules after exposure to radiation in trichloroacetic acid (TCA) and to investigate the possibility of improving their adsorption capacity.

Materials and protocols

The crumb rubber (CR) utilized for this investigation had brought from General Motors Company in Najaf City, Iraq. There was no steel content. The CR size 0.04 to 0.6 mm was utilized in this work. At that point, washing the CR with refined distilled water to expel any foreign materials, then it was dried at 50-60°C for 4 h and stored in containers for following apply.¹⁸

Adsorbate (MB) Preparation

Methylene Blue ( C₁₆H₁₈N₃SCl ) was utilized to prepare the stock solution(1000 ppm) by dissolving 0.5 g in 500 ml distilled water. A series of diluted dye solutions were prepared (1-30) ppm. The PH of the solution was adjusted using diluted solutions of (0.1 M NaOH) and (0.1 M HCl) .

Modification of Crumb Rubber

Samples were taken from a crumb rubber with different sizes (0.04-0.6 mm) and subjected to gamma rays with TCA solution (20%W/V) to increase its surface activity during the adsorption process. The samples were placed in plastic bags and exposed to radiation from 60-Co source at dose 0.5 kGy/h. After that the samples were cleaned with water and dried at 50° C for 6 hours and then place in containers inside the desiccator for later use.

Batch Experiments

Experiments were conducted in batch mode. 0.5 g of modified CR was taken with 50 ml solution from different concentrations of MB dye placed in the Erlenmeyer flasks in a water bath with a shaker (120 rpm). Several variables were studied, such as time period, PH of the medium, concentration of dye, quantity of CR and granule size. Each time one of the variables was studied and the other variables were kept constant, thus obtaining the optimum conditions for the adsorption process. The solution was agitated until both the solid and the liquid medium reached equilibrium at which point the dye concentration on both mediums was constant. The solutions were filtered at the end of each experiment using Whatman No.1 filter paper, and the remaining concentration of dye was measured spectrophotometrically at λmax 665 nm.

The adsorption capacity of CR for MB q_e was expressed the amount of MB retained by CR. This is expressed as:

Where: C_o is the initial dye concentration (mg/L), C_e is the equilibrium con.(mg/L), V is the solution volume (L) and W is the amount of CR (g).

Percentage removal (%R) of MB was calculated utilizing this equation:

Results and Discussion

Impact of contact time

Different contact time at initial concentration of MB (20 ppm) was done in a batch sorption test. The Erlenmeyer flasks were taken out the water path-shaker at periodic intervals and the samples were filtered, the filtered solution was used to determine the MB concentration. The concentration of MB in solution was analyzed using a UV-VIS spectrophotometer by measuring the absorbance at λmax 665 nm. Adsorption of MB on CR is shown in fig. (1).

Initially, the number of active sites is very large which allows adsorption to take place very easily. But as the time passes, the active sites get saturated thus slowing down the removal of dye. The figure shows that the highest removal is at the equilibrium time of 45 minute, and after this time we notice that the concentration of the dye remains constant. Runping et al, reported that the equilibrium time of MB adsorption by  other adsorbent (tree's leaves) was 30 min.¹⁹

Figure 1: Variation of MB percentage removal vs. time by modified crumb rubber (Condition: 20 ppm primary dye conc., PH=9, 0.5 g adsorbent, agitation speed 120 rpm)   Click here to view figure

Impact of PH

One of the most important factors affecting the process of adsorption is the PH, as it affects the protonation and deprotonation of adsorbent surface in addition to the formation of new species of solute. The effect of the PH on the adsorption process was studied in a range from 3 to 9. Acidic and basic solution was adjusted using 0.1M HCl and 0.1M NaOH, other conditions were kept constant. Fig. (2) shows the influence of PH on the removal of MB.

Fig. (2) clearly shows that the highest dye removal is at pH =9 and that the least removal is in the acidic medium and this is due to a number of reasons that may relate to the dye and the PH of the medium. The surface may contain active sites in large numbers and the adsorption of the dye is related to these sites. It also relates to the surface chemistry of the solute at the low PH. The surface of the CR is surrounded by hydrogen ions that may compete with the dye ions on the active sites on the surface. The surface may get a negative charge, which may lead to electrostatic attraction between the surface and dye molecules. Other adsorbent material such as oak sawdust gave the same results for the effect of the PH on adsorption of MB²⁰, Satish Patil et al, found the  maximum removal of methylene blue by teak tree was at PH=11²¹.

Figure 2: Variation of MB percentage removal vs. PH of medium by modified crumb rubber (Condition: 20 ppm primary dye conc., contact time 45 min, 0.5 g adsorbent)   Click here to view figure

Influence of primary dye concentration

Fig. (3) illustrates the adsorption capacity of MB dye for different concentrations, which is clearly increased with the primary concentration of dye. This is explained by the fact that when the dye concentration is increased in the solution, the driving force of the mass transfer increases, so the dye molecules transfer from the bulk solution to the surface of CR. Ould Brahim reported similar observation when he was studied the removal of  Azo Dye by adsorption on AC Prepared from used tires²²

fig3

Figure 3: Variation of MB adsorption capacity vs. primary dye concentration by modified crumb rubber (Condition: PH=9., contact time 45 min, 0.5g adsorbent)   Click here to view figure

Determination of the optimum quantity of adsorbent

The study of the amount of absorbent gives an idea about the effect of it on the dye adsorption process with a minimum dosage. The results of this study are represented on the fig. (4) And it is shown that the percentage of dye removal increases with increasing the quantity of the absorbent and this is due to the increase in the number of effective sites with increasing the quantity of the absorbent. Similar observations were reported in other studies ^{23 ,24}

fig4

Figure 4: Variation of MB percentage removal vs. adsorbent dosage by modified crumb rubber (Condition: PH=9. contact time 45 min, 20 ppm primary dye conc.)   Click here to view figure

Conclusions

This study showed the possibility of using modified rubber granules (irradiated in TCA solution) as an adsorbent to remove MB dye from solution. The irradiation process has improved the surface properties of the adsorption process. The adsorption process affected by many factors, these factors can be optimized In order to obtain the best removal of MB dye.  Modified rubber granules can be used to remove other dyes and can also be used in the removal of heavy metals from the aquatic environment. The use of crumb rubber provided cheap and available adsorbent, in addition to the safe disposal of solid waste.

Acknowledgment

I address my thanks to the staff of Department of Chemistry in College of Science / Al-Nahrain University especially for Dr. Emad-Yousif for their help in supporting this project.

References

1.  Aisien, F. A., Amenaghawon, N. A. & Akhidenor, S. A. Adsorption of Ethylbenzene from Aqueous Solution Using Recycled Rubber from Scrap Tyre. J. Sci. Res. Reports 2, 497–512 (2013).
2. Alshukri, A. A. et al. Mechanical and Curing Properties of Crumb Rubber Irradiated in Polar Media Filled the Tire Tread Blend. J. Comput. Theor. Nanosci. 14, 5253–5260 (2017).
3. Wulandari, P. S. & Tjandra, D. Use of Crumb Rubber as an Additive in Asphalt Concrete Mixture. in Procedia Engineering (2017). doi:10.1016/j.proeng.2017.01.451
4. Gupta, V. K., Gupta, B., Rastogi, A., Agarwal, S. & Nayak, A. Pesticides removal from waste water by activated carbon prepared from waste rubber tire. Water Res. 45, 4047–4055 (2011).
5. Makrigianni, V., Giannakas, A., Deligiannakis, Y. & Konstantinou, I. Adsorption of phenol and methylene blue from aqueous solutions by pyrolytic tire char: equilibrium and kinetic studies. J. Environ. Chem. Eng. 3, 574–582 (2015).
6. Fungaro, D. A., Grosche, L. C., Pinheiro, A. S., Izidoro, J. C. & Borrely, S. I. Adsorption of methylene blue from aqueous solution on zeolitic material and the improvement as toxicity removal to living organisms. Orbital Electron. J. Chem. 2, 235–247 (2010).
7. Amel, K., Hassena, M. A. & Kerroum, D. Isotherm and Kinetics Study of Biosorption of Cationic Dye onto Banana Peel. Energy Procedia 19, 286–295 (2012).
8. Alam, M. S., Khanom, R. & Rahman, M. A. Removal of congo red dye from industrial wastewater by untreated sawdust. Am. J. Environ. Prot. 4, 207–213 (2015).
9. Saritha, B., Rajasekhar, K. & Kiso, K. Equilibrium Studies of Methylene Blue from Aqueous Solution Using Low Cost Adsorbent. Int. J. Innov. Res. Sci. Eng. Technol. 4, 6821–6828 (2015).
10. Hamadi, N. K., Chen, X. D., Farid, M. M. & Lu, M. G. Q. Adsorption kinetics for the removal of chromium (VI) from aqueous solution by adsorbents derived from used tyres and sawdust. Chem. Eng. J. 84, 95–105 (2001).
11. Application of Recycled Rubber from Scrap Tyres in the Adsorption of Toluene from Aqueous Solution *. J. Appl. Sci. Environ. Manag. Sept 17, 411–417 (2013).
12. Calisir, F. et al. Removal of Cu(II) from aqueous solutions by recycled tire rubber. Desalination 249, 515–518 (2009).
13. Knocke, W. R. & Hemphill, L. H. Mercury (II) sorption by waste rubber. Water Res. 15, 275–282 (1981).
14. Yasin, T., Khan, S., Shafiq, M. & Gill, R. Radiation crosslinking of styrene--butadiene rubber containing waste tire rubber and polyfunctional monomers. Radiat. Phys. Chem. 106, 343–347 (2015).
15. Burillo, G. et al. Polymer recycling: potential application of radiation technology. Radiat. Phys. Chem. 64, 41–51 (2002).
16. Telnov, A. V et al. Radiation degradation of spent butyl rubbers. Radiat. Phys. Chem. 63, 245–248 (2002).
17. Shanmugharaj, A. M., Kim, J. K. & Ryu, S. H. UV surface modification of waste tire powder: characterization and its influence on the properties of polypropylene/waste powder composites. Polym. Test. 24, 739–745 (2005).
18. Nassar, E. F., Zageer, D. & Khlaf, M. S. Elimination of Lead Ions from Aqueous Environment by Waste Tires Rubber. Orient. J. Phys. Sci. 2, 1–7 (2017).
19. Han, R. et al. Biosorption of methylene blue from aqueous solution by fallen phoenix tree’s leaves. J. Hazard. Mater. 141, 156–162 (2007).
20. Abd El-Latif, M. M. & Ibrahim, A. M. Adsorption, kinetic and equilibrium studies on removal of basic dye from aqueous solutions using hydrolyzed oak sawdust. Desalin. Water Treat. 6, 252–268 (2009).
21. Patil, S., Renukdas, S. & Patel, N. Removal of methylene blue , a basic dye from aqueous solutions by adsorption using teak tree ( Tectona grandis ) bark powder. Int. J. Environ. Sci. 1, 711–726 (2011).
22. Brahim, I. O., Belmedani, M., Belgacem, A., Hadoun, H. & Sadaoui, Z. Discoloration of Azo Dye Solutions by Adsorption on Activated Carbon Prepared from the Cryogenic Grinding of Used Tires. Ital. Assoc. Chem. Eng. 38, 121–126 (2014).
23. Hefne, J. A., Mekhemer, W. K., Alandis, N. M., Aldayel, O. A. & Alajyan, T. Kinetic and thermodynamic study of the adsorption of Pb (II) from aqueous solution to the natural and treated bentonite. Int. J. Phys. Sci. 3, 281–288 (2008).
24. Gecgel, U., G., O. & G.C., G. Removal of Methylene Blue from Aqueous Solution by Activated Carbon Prepared from Pea Shells (Pisum sativum). J. Chem. 2013, 1–9 (2013).