[Characteristics of fluoride removal by activated iron-manganese nodules]

Adsorption of fluoride on FeCl3-activated manganese-iron nodules was investigated in this study. Influences of contact time, temperature and coexistence anions on F- adsorption were carried out in terms of batch tests. It was found that the fluoride adsorptions onto activated material achieved equilibrium gradually at about 48 h. The adsorption capacity increased with the increase in reaction temperature. Furthermore, the adsorption isotherm can be described as Langmuir and Freundlich models. Thermodynamical study reveals that fluoride adsorptions on the activated material are spontaneous and endothermic. In addition, the presence of coexistence anions shows negative effect on removal of fluoride. Column studies demonstrate that the activated adsorbent could efficiently adsorb F-. Concentrations of Fe and Mn in effluents meet Chinese sanitary standard for drinking water. Effectiveness of adsorbent for fluoride removal increases after regeneration, and the average capacity is up to 1.340 mg/g with 2 cycles of desorption and regeneration. Results of X-ray diffraction (XRD) and scanning electron microscopy (SEM) manifest that high adsorption capacity arose from conglutination of Fe oxides/ hydroxides to the surface of nodules and subsequently adsorption of F- on the fresh Fe hydroxides. Therefore, the activated absorbent has high adsorption capacity and stable property for F- removal, which shows that it is a potential material for F- removal in practice.