TREATMENT OF WASTE NITRIC ACID CONTAINING IRON

PURPOSE:To recover nitric acid from waste nitric acid discharged from a process for surface-treating an iron material, to reuse the recovered acid and to enable the discharge of waste liquor after regeneration into the public water area by subjecting the waste nitric acid to oxidation treatment with an H2O2 soln. and by bringing it into contact with a strongly acidic cation exchange resin. CONSTITUTION:Fe and NO2 in waste nitric acid discharged from a process for surface-treating or etching an iron material with nitric acid are oxidized to Fe and NO3, respectively by adding a chemical equiv. of an about 1% aqueous H2O2 soln. to the ions. The waste acid is then passed through a strongly acidic cation exchange resin bed to remove Fe by adsorption and to recover nitric acid. Since the recovered nitric acid is free from nitrous acid, it is reused in surface treatment or other process. By feeding about 10-20% hydrochloric acid to the resin bed, Fe adsorbed on the resin is allowed to be desorbed to regenerate the resin. Since waste liquor after the regeneraion is almost free from a nitrogen compound, it can be discharged into the public water area by carrying out only neutralization.