Characteristics and comparative study of a new drinking-water defluoridation adsorbent Bio-F

To evaluate the application potentiality of a new type drinking-water defluoridation adsorbent Bio-F, comparative study on the defluoridation characteristics of common adsorbents activated alumina (AA), bone char (BC), activated clinoptilolite (AC) with Bio-F was conducted. The defluoridation characteristics under different conditions, such as particle diameter, pH, retention time, fluorine concentration, regeneration stability, were investigated by continuous-flow column experiments and static tests. The defluoridation efficiency of high fluoride underground water by four types of adsorbents was also compared. The results showed that F^- adsorption kinetics of Bio-F fitted the Lagergren First-order equation (R = 0.9580). F^- adsorption by Bio-F was found to fit the Langmuir adsorption isotherm (R = 0.9992). The results indicated that the static defluoridation capacity (DC) of Bio-F was 4.0883 mg·g^-1, which was about 1.8 folds and 5.8 folds of those of AA and AC respectively. DC of all four adsorbents was positively correlated with F^- concentration and negatively correlated with particle size. High concentration of CO₃^2- and HCO₃^- reduced the DC of Bio-F (p < 0.05), while high concentration of Ca, NO₃^-, HPO₄^2- favored defluoridation by Bio-F (p <0.001). The optimal retention time of Bio-F was 3-4 min, which was less than that of AC (20 min) and AA (11 min). The DC of Bio-F remained relatively stable in pH 4.0-9.0 and in regeneration since the DC variation was not more than 15%. The above results indicated that Bio-F was superior to AA, BC and AC in drinking-water defluoridation.