Before analysis, 100 g of the sample was placed
in a leaching solution (5.7 mL of glacial acetic acid
diluted to 1 L and leached by constant agitation for 18
h. After the leaching operation, 100 mL was extracted;
to which 3 mL of concentrated nitric acid was added
and digested by heating to 90 to 95 °C. After cooling
and evaporation, 3 mL of concentrated nitric acid was
added to the remaining liquid, which was further
heated. Next, concentrated nitric acid was repeatedly
added until the liquid ceased to changed color. Then,
10 mL of hydrochloric acid was added, and the solution
diluted to 100 mL. Finally, the heavy metal
content in the digested liquid was analyzed using an
ICP-OES.