Results and discussion
3.1. Heavy metals distribution in the waste
The multiple box and whisker plots for the distribution of thirteen
heavy metals along with F− and CN− concentrations among
the eleven thermal processes waste are shown in Fig. 1. The normality
of the data for each heavy metals in each process were
checked with the skewness and kurtosis as well as Shapiro–Wilk
test. Shapiro–Wilk test is more suitable for the sample size less than
50 [13]. The non-normal data were transferred logarithmically to
ensure normal distribution. Most of the heavy metals showed a
wide variation in their concentrations, and the highest medians
were shown by Cu (3.58–209,000 mg/kg), Ni (BDL–1560 mg/kg), Pb
(7.22–5132.25 mg/kg) and Zn (83.02–31,419 mg/kg) (Supplementary
material Table S2).