[Adsorption Characteristics of Fluoride in Low-Concentration Water by Aluminum and Zirconium-Modified Biochar]

To deal with problems such as the difficult treatment of low-concentration fluoride-containing water and water pollution caused by excessive fluoride (F^-) discharge, aluminum and zirconium-modified biochar (AZBC) was prepared and its adsorption characteristics and adsorption mechanism for low-concentration fluoride in water were studied. The results showed that AZBC was a mesoporous biochar with uniform pore structure. It could rapidly adsorb F^- from water and reach adsorption equilibrium within 20 min. When the initial ρ(F^-) was 10 mg·L^-1and the AZBC dosage was 30 g·L^-1, the removal rate was 90.7%, and the effluent concentration was lower than 1 mg·L^-1. The pH_pzc of AZBC was 8.9, and the recommended pH in practical application was 3.2-8.9. The adsorption kinetics accorded with pseudo-second order kinetics, and the adsorption process accorded with the Langmuir model. The maximum adsorption capacities at 25, 35, and 45℃ were 8.91, 11.40, and 13.76 mg·g^-1, respectively. Fluoride could be desorbed by 1 mol·L^-1 NaOH. The adsorption capacity of AZBC decreased by approximately 15.9% after 5 cycles. The adsorption mechanisms of AZBC were the combination of electrostatic adsorption and ion exchange.Taking actual sewage as theexperimental object, when the AZBC dosage was 10 g·L^-1, the ρ(F^-) was reduced to below 1 mg·L^-1.