Enhancing destruction of copper (I) cyanide and subsequent recovery of Cu(I) by a novel electrochemical system combining activated carbon fiber and stainless steel cathodes

Metal recovery is an attractive strategy for treatment of heavy metal wastewater. Heavy metal cyanide complexes are common pollutants in electroplating or mine industry wastewater, which usually hinder metal recovery due to the high stability of these complexes. A novel electrochemical system with activated carbon fiber and stainless steel combined cathodes was constructed for copper (I) cyanide (Cu(CN)(3)(2-)) destruction and Cu(I) recovery. The destruction of cyanide was significantly improved by combining the stainless steel and activated carbon fiber cathodes due to the enhancement of electro-generated H2O2, which was promoted due to catalysis by copper deposited at the cathodes. Both the destruction of Cu(CN)(3)(2-) and recovery of Cu(I) at 75 min attained 95.0 +/- 3.0%, which were higher than values obtained using stainless steel or activated carbon fiber as individual cathodes. The rate of Cu(CN)(3)(2) destruction and Cu(I) recovery increased with increasing pH. The optimal current density was 50 A/m(2), and higher current density caused more side reactions. Cu(CN)(3)(2-) was successively transformed into Cu(CN)(2-), CNO- and Cu(I), and the liberated Cu(I) was recovered as Cu(0) on the stainless steel and activated carbon fiber electrodes.