Sequential application of Fenton and ozone-based oxidation process for the abatement of Ni-EDTA containing nickel plating effluents

Abstract

Treatment of Ni-EDTA in industrial nickel plating effluents was investigated by integrated application of Fenton and ozone-based oxidation processes. Determination of integrated sequence found that Fenton oxidation presented higher apparent kinetic rate constant of Ni-EDTA oxidation and capacity for contamination load than ozone-based oxidation process, the latter, however, was favorable to guarantee the further mineralization of organic substances, especially at a low concentration. Serial-connection mode of two oxidation processes was appraised, Fenton effluent after treated by hydroxide precipitation and filtration negatively affected the overall performance of the sequential system, as evidenced by the removal efficiencies of Ni²⁺ and TOC dropping from 99.8% to 98.7%, and from 74.8% to 66.6%, respectively. As a comparison, O₃/Fe²⁺ oxidation process was proved to be more effective than other processes (e.g. O₃-Fe²⁺, O₃/H₂O₂/Fe²⁺, O₃/H₂O₂-Fe²⁺), and the final effluent Ni²⁺ concentration could satisfied the discharge standard (<0.1 mg L^-1, China) under the optimal conditions (H₂O₂ dosage of 1.0 mL L^-1, Fe²⁺: H₂O₂ mole ratio of 1.46, and reaction time of 10 min for Fenton reaction, initial influent pH of 3.0, O₃ dosage of 252 mg L^-1, Fe²⁺ of 150 mg L^-1, and reaction time of 30 min for O₃/Fe²⁺ oxidation). Furthermore, pilot-scale test was carried out to study the practical treatability towards the real nickel plating effluent, revealing the effective removal of some other co-existence contaminations. And Fenton reaction has contributed most, with the percentage ranging from 72.41% to 93.76%. The economic cost advantage made it a promising alternative to the continuous Fenton oxidation.

Keywords: Fenton; Integrated system; Ni-EDTA; Ozone; Plating effluents.