Journal of Applied Electrochemistry, Vol.24, No.10, 1028-1036, 1994
Reduction of Chromate in Dilute-Solution Using Hydrogen in a Gbc-Cell
Reduction of metal ions in dilute solutions is of great interest for purification of waste waters and process liquids. Hydrogen gas is a very attractive reductant, since its use gives no additional pollution. In this paper the reduction of chromate in a sulphuric acid medium has been studied. A new electrochemical cell, a GBC-cell, which is a combination of a gas-diffusion electrode in direct contact with a packed bed of carbon particles, is introduced. Hydrogen gas flows along the hydrophobic side of the gas-diffusion electrode and a chromate solution is pumped upwards through the bed. Experiments were carried out with H2SO4 solutions initially containing 70 mol m-3 chromate at various temperatures, solution flow rates, H2SO4 concentrations and bed thicknesses. Experimental results for the chromate reduction are described by an empirical relation. It has been found that the reduction of chromate is a first-order reaction in chromate and the apparent rate constant for the chromate reduction increases with decreasing chromate concentration and increasing temperature, H2SO4 concentration and bed thicknesses and is practically independent of the flow rate of the solution. It is concluded that the new GBC-cell is very attractive for the reduction of chromate in dilute solutions and for industrial application on a large scale.
Keywords:CONVERSION