Rapid reduction of Cr(VI) coupling with efficient removal of total chromium in the coexistence of Zn(0) and silica gel

The effect of silica gel on the efficiency enhancement of Zn(0) for the reduction of Cr(VI) and removal of total chromium was investigated in this study. The batch experiment was carried at 4 <= pH <= 10 with 50 mu M initial Cr(VI) concentration, and mass loading of 0-40 g/L for silica gel and 0-8 g/L for Zn(0). Results showed limited Cr(VI) reduction in the Zn(0)/H2O system, which was attributed to the formation of passivating films on the Zn(0) surface. However, a complete reduction of Cr(VI) by Zn(0) in the presence of silica gel could be achieved at the all tested pHs. The rate of Cr(VI) reduction was markedly enhanced with a pH decrease, an increase of silica gel or Zn(0) loading, and specific surface area of silica gel. Almost complete removal of total chromium was also observed, suggesting that Cr(III) yielded from the reduction of Cr(VI) was adsorbed onto the silica gel and ZnO surface or existed in Zn-Cr mixed oxides or other Zn-Cr co-precipitates. The possible pathways for Cr(VI) reduction and total chromium removal were proposed in this study, revealing the potential mechanism responsible for the rapid reduction of Cr(VI) coupling with the efficient removal of total chromium in the coexistence of Zn(0) and silica gel. (C) 2012 Elsevier B.V. All rights reserved.