Fluoride Removal Using Modified Spent Diatomaceous Earth Adsorbents

Elevated concentrations of fluoride in drinking water are a serious health concern. Dental andrnskeletal fluorosis being the most commonly reported fluoride-related diseases in Ethiopian riftrnvalley. Various naturally occurring materials have been explored as adsorbents for the removalrnof fluoride from water .This study investigate the fluoride removal capacity of spentrndiatomaceous earth from aqueous solution. The spent diatomaceous earth was collected, washedrnand dried in an oven at 110 0C for 24 hrs. The dried 10 gram of spent diatomaceous earth wasrnreacted in 100 ml of 0.1M HCl and dried in an oven at 110 0C .The dried spent diatomaceous arernpowdered, sieved and preserved. The effect of processing conditions (pH, initial fluoridernconcentration, adsorbent dose and contact time) was investigated using batch adsorptionrnexperiments. The adsorption efficiency was increased with increasing contact time and adsorbentrndose and decreased with increasing pH and initial fluoride concentration. At low pH (2)rnmaximum amount of fluoride was adsorbed by acid treated spent diatomaceous earth (58.48).rnResponse surface methodology (RSM) involving Box–Behnken design was used to optimize thernadsorption process of fluoride ions. The second order mathematical model was developed byrnregression analysis of the experimental data obtained from 29 batch runs. The optimum pH,rninitial fluoride concentration, adsorbent dose and contact time were found by desirabilityrnfunction to be 2.02,24.04mg/l, 18.83g and 2.95 hr respectively. Fluoride removal was 43.19% atrnthe optimum combination of process parameters. The results of validation experimentsrnconducted at optimum conditions for the removal of fluoride ions (42.94%) indicate that thernpredicted values are in good agreement with the experimental result. The adsorption data werernwell fitted to the Langmuir and Freundlich isotherm model. The adsorption capacity was 0.321rnmg/g. Acid treated spent diatomaceous earth could be used as adsorbent for fluoride ionrncontaining aqueous solution

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