Background and purpose: Fluoride is one of the common anion in water that its concentration varies in different water supplies. Most of the body's requirement for fluoride is supplied through drinking water. Fluoride in low concentration is essential for human health but in high concentration is very hazardous for human health. The efficiency of modified-clay and lime-marl were investigated in this research as an adsorbent for the elimination of fluoride from aqueou solution.

 Methods: In this study, the capability of modified-clay and lime-marl to adsorb fluoride ions was conducted using a series of batch tests in a shaker-incubator instrument. The effect of experimental parameters such as pH (4,7,10),  adsorbent dosage (1,5,10 g/L), initial fluoride concentration  (5,10,15 mg/L) andcontact time (15-120 min) were evaluated. The morphological and micro-structural character of  modified-clay and lime-marl have performed by using X-ray diffraction (XRD). The formation of the carboxylic functional groups was verified by Fourier transform infrared spectra (FT-IR).

 Findings: results well demonstrate higher removal efficiency of fluoride was 95.23% and 28.71 by clay-modified and lime-marl, respectively; at 10 mg/L of fluoride concentration and 60 min contact time. The adsorption kinetics fitted well using the pseudo second-order kinetic model; however, equlibrium data were best fitted onto Langmiur isotherm model. The maximum adsorption capacities of modified-clay and lime-marl for fluoride were found to be 4.43 mg/g and 1.32 mg/g, respectively.

Conclusion: According to our finding, it proposed that adsorption process by using modified clay is very efficient and economic process for fluoride removal from aqueous solution.