However, we observed that the final pH of the FGD leachate
showed a wide variation. Low pH (2–4) in the samples of PbM and
ZnM; pH 6–7 among CuM, NFe and NFecas samples and above pH 9
in AlM and Fecas samples. The main reason that can be attributed
to high leaching characteristics in FGD is the higher concentration
of CN− and F− in it (supplementary material Fig. S1). The presence
of CN− and halogens increases the aqueous solubility of the metals,
hence repeatedly reported to be the good leaching additives for
heavy metals [29,52].