Reduction of chromate in dilute solution using hydrogen in a GBC-cell

Redn. of metal ions in dil. solns. is of a great interest for purifn. of waste waters and process liqs. Hydrogen gas is a very attractive reductant, since its use gives no addnl. pollution. The redn. of chromate in a sulfuric acid medium was studied. A new electrochem. cell, a GBC-cell, which is a combination of a gas-diffusion electrode to 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 soln. is pumped upwards through the bed. Expts. were carried out with H2SO4 solns. initially contg. 70 mol m-3 chromate at various temps., soln. flow rates, H2SO4 solns. initially contg. 70 mol m-3 chromate at various temps., soln. flow rates, H2SO4 concns. and bed thicknesses. Exptl. results for the chromate redn. are described by an empirical relation. The redn. of chromate is a 1st-order reaction in chromate and the apparent rate const. for the chromate redn. increases with decreasing chromate concn. and increasing temp., H2SO4 concn. and bed thickness and is practically independent of the flow rate of the soln. It is concluded that the new GBC-cell is very attractive for the redn. of chromate in dil. solns. and for industrial application on a large scal