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

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.