Batch defluoridation appraisal of aluminium oxide infused diatomaceous earth

Diatomaceous earth (DE) was enriched with aluminium oxide, via the co-precipitation method, to produce a permeable, reactive material (AD) for groundwater defluoridation. The AD was characterized, using appropriate instrumental methods, and the defluoridation potential was evaluated in a batch process. The infusion of amorphous aluminium oxide on the DE was confirmed by X-ray diffraction analysis and the optimum calcination temperature for AD synthesis was attained at a temperature of 250°C. The kinetic analysis of the time-concentration profile of the defluoridation process showed that the pseudo second order gave better description and the value of the approaching equilibrium factor (R_W<0.01) obtained showed that the process drastically approached equilibrium, at the longest operating time of 300min. The value of the Langmuir monolayer sorption capacity (q_e=13.1mg/g) obtained for AD was comparable with what has been reported for other aluminium rich materials, used as sorbents in batch defluoridation processes. Evidences from the results of kinetic analysis and the results obtained from the process variables (i.e. F^- solution pH, ionic strength, and anionic interference) optimization procedures showed that the mechanism of the defluoridation process occurred via inner sphere association, a chemical process that is specific to F^- on the AD surface.