Coupling adsorption by NiO nanopowder with UV/H₂O₂ process for Cr(VI) removal

Abstract

Chromium enters surface and ground waters through the wastewater of electroplating, textile, metallurgical, dye production, and other industries, leading to numerous adverse health effects. The potential property of nanoparticle adsorption of nickel oxide (NiO) and the economic nature of ultraviolet/hydrogen peroxide (UV/H₂O₂) process have eased the usage of these two processes for chromium removal. In this study, the parameters including chromium concentration, pH, and NiO dosage were examined by the adsorption process. Furthermore, following the separation of NiO nanoparticles by magnet and filtration, in UV/H₂O₂ reactor, the effects of H₂O₂ concentration, radiation time, and pH were studied on the removal efficiency. In the reactor containing NiO, with an increased dose of NiO from 0.2 to 1 g, the removal efficiency increased from 26 to 76%. Moreover, at different pHs (3, 5, 7, and 11) and reaction times (10, 20, 30, and 40 min), the maximum efficiency of 79% was obtained at pH = 3 and reaction time of 40 min. The isotherm of the adsorption followed the Langmuir model. In the UV/H₂O₂ reactor, elevation of H₂O₂ concentration from 20 to 100 µmol resulted in an elevated chromium removal efficiency at pH = 3 from 35 to 95%. In this process, pH = 3 was chosen as the optimum pH. The results indicated that the removal efficiency is highly influenced by pH, reaction time, dose of NiO nanoparticles, and H₂O₂. By optimizing the effective parameters, this process can be used to remove chromium in aqueous solutions.