Sorption Equilibrium and Column Dynamics for Defluoridation of Groundwater Using Modified Bone Char in Adamawa State

Dental and skeletal fluorosis arising from chronic ingestion of high-fluoride groundwater affects significant numbers of people in Adamawa State, North East Nigeria, particularly in the Mubi and Michika axis where geological fluoride enrichment of aquifers has been documented. This study evaluates the equilibrium and column dynamics of fluoride sorption onto bone char modified with aluminium sulphate and lanthanum nitrate, using groundwater samples from Adamawa State with fluoride concentrations of 4.0 to 8.6 mg/L. Bone char was prepared from cattle bones sourced from Yola abattoirs, carbonised at 800 degrees Celsius, and chemically modified. Modified bone char was characterised by XRD, FESEM-EDS, BET, and point of zero charge determination. Batch isotherm experiments were conducted from 2 to 80 mg/L fluoride concentration, and isotherm data were fitted to Langmuir, Freundlich, and Temkin models. Column experiments were conducted using glass columns packed with modified bone char at varying bed heights and flow rates. Breakthrough curves were analysed using Thomas, Adams-Bohart, and Yoon-Nelson models. The lanthanum-modified bone char exhibited a maximum Langmuir sorption capacity of 14.8 mg/g, significantly higher than unmodified bone char (6.3 mg/g). The Thomas model fit the breakthrough data accurately, predicting exhaustion bed volumes in close agreement with experimental results. The column operated effectively at 10 cm bed depth for 360 hours before breakthrough, treating approximately 1,200 L per cycle. The study supports lanthanum-modified bone char column filters as a practical household defluoridation technology for affected communities in Adamawa State. Keywords: defluoridation, bone char, column dynamics, Thomas model, Adamawa State