Fluoride removal from aqueous solution by municipal solid waste compost ash: kinetics, and isotherms studies
Mohammad Hossein Saghi, Mehdi Qasemi, Ali Akbar Mohammadi, Mohammad Hassan Kowsari, M. S. Shams
Abstract
Fluoride (F–) is one of the common water pollutants, which causes severe diseases if be present over 1.5 mg/L suggested by WHO for drinking water. There is essential to find a simple and cost-effective method for excess F– removal from contaminated water. In this study, municipal solid waste compost ash (MSWCA) was used to remove F– from aqueous solution. The effect of operational variables such as adsorbent calcination temperature (550–900°C), adsorbent dose (0.25–1.5 g/L), pH (2–12), occurrence of competing anions (HCO3−, CO32−, Cl−, NO3 − and SO42−), adsorption temperature (20–50°C) and mixing time (15–120 min) were investigated. F–adsorption was highest when compost ash calcinated at 550°C. F– removal increased from 42.6 to 87.7% by increasing adsorbent dose from 0.25 to 1.5 g/L. The removal also increased 4.4% when the temperature of solutions increased from 20 to 50°C, an indicative of endothermic process. Furthermore, adsorption increased by increasing pH from 4 to 10 and then decreased with pH up to 12. F− removal reduced about 10% in the presence of SO42−. Based on pseudo- second-order kinetic model, it was found that the process was controlled by chemisorption. The equilibrium data were well fitted with Langmuir model, which implied the F−ions doesn’t interact and adsorbed in monolayer onto MSWA. The Langmuir maximum adsorption capacity was 30.56 mg F/g MSWCA. Due to excellent adsorptive properties, MSWCA presents as a promising material for F− adsorption from wastewaters or landfill leachates.