Effective removal of chromium, copper, and nickel heavy metal ions from industrial electroplating wastewater by in situ oxidative adsorption using sodium hypochlorite as oxidant and sodium trititanate nanorod as adsorbent

Abstract

Sodium hypochlorite and synthesized sodium trititanate nanorods (Na2Ti3O7, 186 × 1270 nm) were used as the oxidant and adsorbents for in situ oxidative adsorption treatment of actual electroplating wastewaters containing Cr(VI) (2.6‒5.2 mg∙L‒1), Cu2+ (2.7‒5.4 mg∙L‒1), and Ni2+ (0.2705‒0.541 mg∙L‒1) ions at pH of 8.8‒9.1 and 20‒60 °C. The as-synthesized sodium trititanate nanorods were characterized by XRD, HRTEM, N2 adsorption/desorption, SEM, EDX, and Zeta potential techniques. The concentrations of heavy metal ions in wastewaters were analyzed by ICP technique. After in situ oxidative adsorption treatment under the concentrations of 25 g∙L‒1 for sodium hypochlorite and 125 mg∙L‒1 for sodium trititanate nanorods at 60 °C for 5 h, the heavy metal ion concentrations could be reduced from initial value of 2.6 to final value of 1.92 mg∙L‒1 for Cr(VI), 3.6 to 0.17 mg∙L‒1 for Cu2+, and from 0.2705 to 0.097 mg∙L‒1 for Ni2+, respectively. Cr(VI), Cu2+, and Ni2+ ions could be effectively removed by the in situ oxidative adsorption method. The in situ oxidative adsorption processes of Cr(VI), Cu2+, and Ni2+ ions are satisfactorily simulated by the pseudo-second order adsorption kinetics and Langmuir adsorption isotherm, respectively. Adsorption thermodynamics analyses reveal that the oxidative adsorption processes of Cr(VI), Cu2+, and Ni2+ ions are spontaneous and endothermic. The oxidation degree of metal-contained complexes influences the values of thermodynamics functions.