Studies on modified conditions of biochar and the mechanism for fluoride removal

The modified Mongolian scotch pine tree sawdust char (MMSC), fabricated from the natural Mongolian scotch pine tree sawdust char (MSC) using phosphoric acid-microwave method, was used as the F- adsorbent of aqueous solution. MMSC was prepared according to the optimized method as follows. MSC and 25% (vol) phosphoric acid (v/v = 1:4) were mixed in Bunsen beaker at 25 degrees C for 24 h. The mixer was then radiated for 3 min (Radiation power 630 W), followed by filtration, generating the desired MMSC, which was washed with distilled water until the pH reached around 7.0, and then dried in an oven at 50 degrees C till constant weight for further fabrication. No obvious difference of MMSC and MSC was observed in color. The adsorption capacity of MMSC reached 885 mg kg(-1) for F- in high-fluoride resource water. The concentration was reduced to below the recommended value (1.5 mg L-1) from the concentration of 20 mg L-1 when the high dosage of MMSC was used. Compared with MSC, the MMSC can be used as potential F- adsorbent for high-fluoride resource water treatment. The analysis of removal mechanism provided a theoretical basis for further application.