Devulcanization and Demineralization of Used Tire Rubber by Thermal Chemical Methods: A Study by X-ray Diffraction

The use of novel methods for the devulcanization and demineralization of used tire rubber (UTR) based on the thermal chemical treatment of this material with LiCl-KCl, LiCl-KCl-KOH, or KOH at relatively low temperatures is investigated. The influence of composition of the reactive system, ratio of reactants to UTR, and maximum heat treatment temperature (i.e., 300, 400, or 500 degrees C) is studied. For comparison purposes, a HNO3 solution is also used. The changes produced in the chemical composition of UTR as a result of the devulcanization and demineralization processes are studied by X-ray diffraction. Sulfur of UTR usually transforms into a metal sulfide or a variety of sulfur chemical species [i.e., Na2Zn-(S2O4)center dot H2O, KAl(SO4)(2), etc.] depending upon the composition of the reactive system. A combination of the treatments of UTR with LiCl-KCl, LiCl-KCl-KOH, or KOH and with HNO3 in aqueous solution is more effective to reduce the ash content in the resultant products. The most promising results are obtained when UTR is treated first with the LiCl-KCl-KOH mixture and then with HNO3 solution. For the resultant product, the ash content is as low as 4.9 wt, whereas for UTR, it is 7.0 wt %, and for the HNO3 solution-treated product, it is 5.8 wt %. The preparation of carbonaceous materials with a low ash content may promote the recovery and use of UTR, and this leads to a decrease in its environmental impact.