Heavy Metals Retention on Recycled Waste Glass from Solid Wastes Sorting Operations: A Comparative Study among Different Metal Species

Heavy metals retention [Pb(2+), Cd(2+), Ni(2+), and Cr(VI)] on recycled waste porous glass (RWPG) from solid wastes sorting operations was carried out. To the purpose metals containing solutions in the concentration range 2-4 mg/L, reproducing the average concentration present in, e.g., solid waste leachate from landfills or industrial effluents, were percolated onto columns loaded with RWPG beads with particle size in the range 0.35-1.0 mm and flow-rates between 0.23 and 0.75 L/h. Metals retention mechanism was associated with ion exchange with overall capacities in the following order: Pb(2+) > Cd(2+) > Ni(2+) > Cr(VI) in consideration of the hydrated ion radius and free energy of hydration of the metal ions. The rate controlling step was identified with the ions interdiffusion in the Nernst liquid film around particles. The metals exhausted beads were embedded into cement conglomerates as inert materials thus minimizing metals release in the environment. The prepared mortar specimen showed improved thermal properties as compared to conventional (sand based) composites.