Fluoride removal from wastewater using activated clay: A study kinetics and isotherm adsorption

One of the anion contaminants which was found in surface or groundwater was fluoride. It found in water because of geochemical reaction or anthropogenic activities. Fluoride with high concentration in drinking water may be harmful to health, especially teeth and bones. Adsorption process is one of method to overcome high concentration of fluoride in drinking water. Clay as adsorbent was activated by physical activation at 700°C in a furnace for 30 minutes and chemical activation in HCl solution for 60 minutes. This research aimed to examine the kinetics and isotherm adsorption model for this process. The batch sorption experiments were carried out in shaker waterbath by mixing 50 ml beaker glass contained 13 mg/L fluoride solution with 0.75 gram of activated clay with size 100-200 mesh. The temperatures of solution were 45°C and pH of 4. The solution samples were taken every 5 minute until reaching equilibrium. The solution was analyzed for remaining fluoride by using visible spectrophotometer at the maximum wavelength of 570 nm using SPADNS-zirconil acid reagent. From this research, the maximum removal efficiency of fluoride reached 66% with time of equilibrium was 45 minutes and the mass adsorbed was 0.5743 mg/g. The suitable kinetics of the process was pseudo second order model with the value of R² was 0.9911 and fitted well the Langmuir and Freundlich adsorption isotherm models.