Efficacy of Photocatalytic Processes Using Silica and Zirconia Nanoparticles in the Bivalent Nickel Removal of Aqueous Solutions and Determining the Optimum Removal Conditions

Background and Nickel is one of the heavy metals that originates from various industries such as plating and dyeing and leads to many environmental problems، thus، it is important to remove it. The aim of this study was to assess the photocatalytic process by silica and zirconia nanoparticles in nickel removal. In this applied-fundamental study after construcring photoreactor، the performance of silica and zirconia nanoparticles in the removal of nickel were studied by changing variables such as the amount of nanoparticles (0. 5-2. 5 g/L)، pH (3،7،11)، nickel concentration and exposure time of UV (15-75 min). After assessing the synthetic wastewater (n=50) real wastewater (n=10) samples were evaluated according to the resultant optimum conditions. Nickel adsorption isotherm was determined. SPSS was used to analyze the data. Nickel was removed completely under optimum condittions (pH= 11)، 1g/L zirconia، 0. 5g/L silica with exposure time of 30min and 5mg/L synthetic nickel. Removal efficiency of nickel in concentrations of 5، 10، 15، 20 and 25 mg/L at pH= 11 and 1g/L zirconia nanoparticles was 100، 91، 88، 87. 5 and 84%، respectively and with 0. 5g/L dose of silica nanoparticles was 100، 100، 90. 90 and 87%، respectively. According to the coefficient of determination (R2)، Freundlich isotherm for zirconia nanoparticle (R2= 0. 883) and the Langmuir model for silica (R2= 0. 949) were found to be more relevant. Increase in the amount of nanoparticles، UV exposure and pH increased the efficacy of photocatalytic process in nickel removal through production of hydroxyl radicals. Nickel concentration reduced the process efficiency due to inhibition of the reaction of holes (h+) and hydroxyl radicals. Efficiency of photocatalytic process in removal of nickel from a real wastewater due to the presence of other substances (cyanide and zinc) was far less compared to the synthetic solutions. According to nickel removal efficiency from real wastewater (49. 6% and 56% by zirconia nanoparticles and silica، respectively) photocatalytic processes was able to remove about 50% nickel from actual wastewater.