Content and speciation of heavy metals in residues of used tires treated with supercritical water

摘要

Used tires were subjected to supercritical water and supercritical water with H_2O_2. The distribution of heavy metals(Pb, Mn, Ni, Cu, Zn, Cd, Cr)in used tires and the corresponding residues were analyzed. BCR sequential extraction procedure was applied to examine the speciation of heavy metals mentioned above. The results showed that: the contents of Mn, Zn, Cu, Pb, Cd increased after supercritical water treatment while that of Cr and Ni decreased significantly. The addition of H_2O_2 was beneficial for the increase of heavy metals concentration and sequestration. The sequestration rate of Mn, Zn, Cu, Pb, Cd, Cr reached to 90% after the addition of H_2O_2, and that of Ni was much lower as 40%. The main speciation of Cr and other heavy metals were in residual form and oxidate form respectively. The speciation of all heavy metals were transferred from the unstable forms of weak acid soluble and reducible to relatively stable forms of oxidizable and residual.