The feasibility of the rapid degradation of hexachlorobenzene (HCB) by micron-size silver (Ag)/iron (Fe) particles was investigated. Ag/Fe particles with different ratios (0, 0.05%, 0.09%, 0.20%, and 0.45%) were prepared by electroless silver plating on 300 mesh Fe powder, and were used to degrade HCB at different pH values and temperatures. The dechlorination ability of Fe greatly increased with small Ag addition, whereas too much added Ag would cover the Fe surface and reduce the effective reaction surface, thereby decreasing the extent of dechlorination. The optimal Ag/Fe ratio was 0.09%. Tafel polarization curves showed that HCB was rapidly degraded at neutral or acidic pH, whereas low pH levels severely intensified H2 production, which consumed the reducing electrons needed for the HCB degradation. HCB degradation was more sensitive to temperature than pH. The rate constant of HCB dechlorination was 0.452 min- at 85 degrees C, 50 times higher than that at 31 degrees C. HCB was degraded in a successive dechlorination pathway, yielding the main products 1,2,4,5-tetrachlorobenzene and 1,2,4-trichlorobenzene within 2 hr.
