Electroplating manufacturing processes release industrial effluents that comprise severe levels of heavy metals into the environment. This study investigated the utilization of nanoparticles of zero-valent iron (nZVI) for the treatment of electroplating wastewater industry containing multiple heavy metal ions. In batch experiments using Cu2+ as a single solute, the optimum operating condition was pH 7.3, nZVI dosage 1.6 g/L, time 36 min, temperature 30 °C, and agitation speed 180 rpm, achieving almost 100% Cu2+ removal efficiency. The adsorption mechanisms were illustrated using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FTIR) spectrometer. Moreover, continuous-feed experiments were performed to treat real electroplating wastewater industry via adsorption and sedimentation processes. The system attained removal efficiencies of 91.3% total suspended solids (TSS), 68.3% chemical oxygen demand (COD), 94.2% nitrogen (N), 98.5% phosphorus (P), 66.7% Cr6+, 91.5% Pb2+, 83.3% Ag+, 80.8% Cu2+, 17.4% Ni2+, 47.1% Mn2+, 54.6% Zn2+, 94.7% Fe3+, 100.0% Al3+, and 42.1% Co2+. The removal mechanisms included reduction of Men+ to Me(n-x)+/Me0 by the Fe0 core, adsorption to the oxide shell as Me(OH)x and Me-Fe-OOH, oxidation of Men+ to Me(n+z)+, specific surface bonding, and sequential steps of electron transfer and precipitation. The total cost, including amortized and operating expenses for scaling up the adsorption system, was 4.45$ per m3 of electroplating wastewater. Graphical abstract.
Keywords: Adsorption mechanisms; Cost analysis; Electroplating wastewater; Metal ions; Zero-valent iron nanoparticles.