Fluoride removal from aqueous solution by municipal solid waste compost ash: kinetics, and isotherms studies.

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. [ABSTRACT FROM AUTHOR]