Abstract
To obtain plated products of high quality, cyanide compounds have been widely used in the electroplating process. An appropriate treatment of cyanide compounds in wastewater is required before the wastewater is discharged due to its high toxicity. In the present work, wet oxidation of cyanide in aqueous solution was studied using a batch type-autoclave. The effects of initial concentration of cyanide, pH, pressure, and temperature on destruction of cyanide were investigated. Wet oxidation was performed at various temperatures (383-423 K), pressures (0.1-2.0 MPa), and concentrations of cyanide (100-5000 mg/dm3 as CN concentration). NaCN and Na3[Cu(CN)4] solutions were used as the sample electroplating wastewater. It was found that the rate of CN destruction in NaCN solution increased as the temperature was raised. On the other hand, the destruction rate was almost independent of pressure and initial concentration of CN. When wet oxidation was performed at 423 K and 1.0 MPa for the NaCN solution with CN concentration of 1000 mg/dm3, 99.8% CN was decomposed in 2 hours reaction time. Formic acid (HCOOH) and ammonia (NH3) were identified as the products in the solution after wet oxidation treatment. It was also found that Na3[Cu(CN)4] has a lower percent destruction compared with NaCN in oxygen and nitrogen atmospheres. After wet oxidation in oxygen atmosphere, copper in the Na3[Cu(CN)4] complex was generated as copper oxide (CuO) precipitate.
