[Oxidation buffer capacity of sewage sludge barrier for immobilization of heavy metals]

Benefit from the microbial activities especially the anaerobic sulfate reduction processes, sewage sludge could be used as a barrier to immobilize the heavy metals leached from tailings. With respect to the redox reaction between sewage sludge and acid mine drainage (AMD), oxidation titration test was carried out to study the effect of oxidation buffer capacity (OBC) of sewage sludge on the immobilization of heavy metals. Test results showed that OBC of sludge suspensions was decreased slightly with the solid-liquid ratio of the suspensions, but increased with the anaerobic incubation time, and that more than 50% of OBC was contributed by the sludge existed in strongly-reduction conditions (Eh < or = - 150 mV). During oxidation titration test, Zn was released obviously when Eh > or = - 150 mV, while Cu and Pb released obviously when Eh > or = 150 mV. According to the test results, a mathematical model was established to predict the OBC consumption of the sludge barrier under AMD penetrating conditions. The simulation results showed that a sludge barrier with 2m thickness, even undergone 38 787-years oxidation by AMD under 10m water head, keep in a strongly-reduced condition and, therefore, promote an immobilization of heavy metals from AMD in the barrier.