Use of pyrophyllite clay for fluoride removal from aqueous solution

Abstract

The aim of this study was to investigate the removal of fluoride from aqueous solution using pyrophyllite clay as an adsorbent. X-ray fluorescence analysis showed that Si (74.03%) and Al (21.20%) were the major constituents of pyrophyllite. Equilibrium test (adsorbent particle size < 0.15 mm) demonstrated that the maximum sorption capacity of pyrophyllite was 0.737 mg/g. Kinetic test showed that fluoride sorption to pyrophyllite arrived at equilibrium around 24 h. Thermodynamic test indicated that fluoride sorption to pyrophyllite increased with increasing temperature from 25 to 45°C, indicating the endothermic nature of sorption process. Further experiments indicated that fluoride removal was not sensitive to solution pH between 4.0 and 9.0. The influence of sulfate, carbonate, and phosphate on the removal of fluoride was important while the effect of nitrate and chloride was negligible. In addition, among the pyrophyllite thermally treated at different temperatures (untreated, 400, 600, 800, 1,000, 1,000°C), the adsorbent treated at 400°C had the highest adsorption capacity (21% higher than that of untreated pyrophyllite). This study demonstrates the potential use of pyrophyllite for fluoride removal from water.

Keywords:

• Adsorbent
• Batch experiment
• Defluoridation
• Sorption
• Thermal treatment

Acknowledgment

This research was supported by the National Research Foundation of Korea, funded by the Ministry of Education, Science and Technology, Republic of Korea (grant number 2011–0009688).