Selection Of Clay Adsorbents And Determination Of The Optimum Condition For Defluoridation Of Ground Water In Rift Valley Region

People in several regions of the Rift Valley of Ethiopia are sufferingrnfrom skeletal and non-skeletal fluorosis as result of consuming water containingrnexcessive fluoride. Defluoridation of drinking water using variety of material hasrnbeen suggested by different researchers. This study assesses the fluoridernadsorption characteristics of clays collected from different areas in Ethiopia.rnBombawoha clay, Combolcha clay and Muger clay 2 were found to have the betterrnpotential as fluoride adsorbents.rnThe effect of contact time, amount of adsorbent dose, pH, particle size, heatrntreatment of adsorbent and initial concentration of fluoride was investigated. Thernadsorption was rapid during the first one hour. The adsorption efficiency ofrnfluoride was increased with adsorbent dosage. The defluoridation capacity wasrnappreciable with in acidic pH range. Clay adsorbents treated in the range betweenrn400 to 600oC gave better fluoride removal. The fluoride adsorption efficiencyrndepends directly with initial fluoride concentration. The adsorption data were wellrnfitted to the Langmuir isotherm model with adsorption capacity of 0.136, 0.168,rnand 0.191 for Bombawoha clay, Combolcha clay and Muger clay 2 respectively.rnLaboratory scale column were conducted and showed good removal of fluoride.rnAt breakthrough the three clay samples Bombawoha clay, Combolcha clay andrnMuger clay 2 showed 0.1248, 0.235, 0.239 mg/g of adsorption capacity, 1.64, 1.1,rn1.02 mg/L of residual fluoride and 300, 500, 500 mL of breakthrough volumernrespectively.

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