Cleaning steel by devulcanizing rubber from used automotive tires

Abstract

In many cases, only a fraction of the steel recovered from end-of-life automobile tires can be recycled. About 10–20% of the steel isolated after grinding/shredding the tires is too contaminated with rubber to be accepted by metal recyclers. We report that complete devulcanization to ‘dissolve’ the rubber from the steel is possible, but not necessary. Much less chemical intervention is required, resulting in lower overall efficiency, and lower environmental impact, if the samples are first: magnetically separated from rubber; swollen with toluene and, after physical agitation, again magnetically separated (to remove up to 90% of rubber present on steel) and finally subjected to chemical treatment to chemically strip the rubber from steel by partial devulcanization (using about 1/10 the catalyst required for complete devulcanization); combining these two means that only about 1% of the B(C₆F₅)₃ catalyst is needed to clean steel compared to complete devulcanization of an as received sample. This process is more cost competitive, the toluene solvent remains internal to the process, and the steel produced is sufficiently clean to be sent to recyclers rather than to landfill.