A Method for Quantification of Zn in Waste Tire and Its Derived Char Samples

Due to the unique properties of waste tire and its derived char samples, conventional methods are unable to quantify Zn in those samples accurately. This study develops a method for accurate quantification of Zn in waste tire and its derived char samples. The method consists of customized ashing, borax-fusion, acid dissolution, and solution analysis for the quantification of Zn. The novelty of the method mainly lies in the customized ashing program specifically designed for waste tire and its derived char samples, with a low final temperature of 400 °C, a low heating rate of 5 °C/min, and multiple holding stages. The accuracy of the method is validated by various purposely prepared standards with known Zn contents. Our results clearly demonstrate that the conventional method largely underestimates the Zn content of waste tire and its derived char samples by up to ∼21% depending on the waste tire sample, while the developed method with a customized ashing program can achieve accurate quantification of Zn in various samples with an error less than 2%. Moreover, various occurrence forms of Zn, including the water-soluble, acid-soluble, and acid-insoluble Zn, are also determined by a multistep extraction process, which is crucial for understanding Zn transformation during the thermochemical processing of waste tires.