Plasma-induced reduction of chromium(VI) in an aqueous solution.

An efficient reduction of hexavalent chromium [Cr(VI)] induced by gaseous glow discharge plasma (GDP) generated between a pointed platinum anode and the surface of an aqueous solution has been achieved for the first time. Experimental results show that Cr(VI) could be smoothly reduced to trivalent state [Cr(III)] by using GDP with 500 V as the optimum operating voltage. The rate of Cr(VI) reduction was enhanced by either decreasing the solution pH or adding radical scavengers to the solution. At initial pH 2.0, 100 mg/L of Cr(VI) was completely reduced within 10 min of GDP treatment in the presence of 100 mg/L phenol. A possible reaction mechanism was proposed based on the reduction kinetics. Energy efficiency of Cr(VI) reduction in GDP was compared with that in other competitive processes.