Analysis and identification of metal residues
After digesting and extracting the samples until become transparent solution, the digested samples were analyzed by inductively coupled plasma optical emission spectrometry, VISTA-MPX Axial (ICP-OES) to estimate the type and the concentrations of heavy metals. Mixed standard (23 elements) was used to evaluate heavy metal as barium (Ba), cadmium (Cd), chromium (Cr), manganese (Mn), nickel (Ni), lead (Pb).