Electrolytic recovery of chromium salts from tannery wastewater

Tannery wastewater collected from a local leather industry in Peshawar, Pakistan was subjected to DC electrolysis in a simple cell having two static sheet electrodes and stirring assembly after proper dilution and adjustment to desired conditions. One percent HNO 3 and 1% NaHCO 3 were used as electrolytes and pH adjusters. The latter salt also worked as sodium source for anodic deposition of Na 2 Cr 2 O 7 . Various combinations of electrodes were tested and conditions optimized for best electrode couple with increased recovery and removal of chromium in the form of Cr(OH) 3 and/or Na 2 Cr 2 O 7 at cathode and anode, respectively. The recovery of 99% chromium was achieved after 2 h electrolysis at a cell potential of 1.0 V, pH 5.0 and stirring rate of 500 rpm using Pb sheet as anode and Cu sheet as cathode. The most interesting and novel finding of this work was the recovery of the mentioned salt(s) alone at Cu cathode or Pb anode or collectively at both electrodes by proper control of pH. Such treatment not only minimizes the environmental water pollution, but results in the formation of useful products employed for recycling purpose in tannery or other related industry to make the process economical.