Removal and recovery of chromium from plating waste using chemically activated carbon

This study shows that the chemically activated coconut shell carbon [CSC (HT)] is superior to F-400 and CS(H) for the removal of Cr(VI) from plating waste. The maximum adsorption of Cr(VI) on carbon occurs at a proton to Cr(VI) molar ratio of 2.5 for CSC(HT) and CS(H) and 1.0 for F-400. The adsorbed Cr(VI) can be desorbed via a 1M NaOH to the extent of 60% and the recovered chromate can be used for the passivation of plated components. The exhausted carbon can be completely regenerated using NaOH followed by HCl and thermal activation for repeated use with minimum carbon loss and particle size degradation. In case Cr(VI) recovery is not required, the plating waste can be passed through the column after adjusting the pH of the solution to less than 1.0 to reduce the Cr(VI) to Cr(II) quantitatively for subsequent removal by chemical precipitation.