Treatments of alkaline non-cyanide, alkaline cyanide and acidic zinc electroplating wastewaters by electrocoagulation

Treatments of alkaline non-cyanide, alkaline cyanide and acidic zinc electroplating rinse wastewaters were investigated in an electrocoagulation (EC) reactor using Fe plate electrodes. This is the first study involved with removals of zinc and cyanide together from three different wastewaters in the literature. The effects of the operating parameters namely, initial pH (pHi), current density and operating time on the removal efficiencies were evaluated. The removal efficiencies and operating costs were determined as 99.8% for Zn and 0.74 €/m3 at a pH of 7, 80 A/m2 and 60 min for alkaline non-cyanide, 99.9% for Zn, 99.9% for CN and 1.72 €/m3 at a pH of 9.5, 60 A/m2 and 60 min for alkaline cyanide, and 99.9% for Zn and 2.26 €/m3 at a pH of 8, 80 A/m2 and 60 min for acidic zinc electroplating wastewaters, respectively. Moreover, toxicity test was conducted to obtain information about the toxic effect of the raw and treated wastewaters. The toxicity results indicated that all the raw wastewaters contained hardly toxic effect (EC50 for acidic, alkaline cyanide and alkaline non-cyanide were 0.62, 5.25 and 3.38). On the other hand, the treated wastewater was non-toxic. This study revealed that the EC process with Fe electrode was very effective for removal of zinc and cyanide ions from different zinc electroplating rinse wastewaters.