Abstract

Defluoridation was carried out with bauxite, gypsum, magnesite and their composite calcined at 200°C to determine relationship between particle size, capacity and water quality, in an attempt to formulate a composite filter in the ratio of loading capacities. Particles of 0.5 to 1.0, 1.0 to 1.4, 1.4 to 2.0 and 2.0 to 3.0 mm diameter were employed in batch defluoridation. Color, hardness, pH, were determined hourly until fluoride equilibrium was obtained. Results showed that capacities were inversely correlated to particle size obtaining polynomial, linear and logarithmic relations of capacity (mg/g) to particle size (mm);  (composite, gypsum), (bauxite) and  (magnesite). Bauxite, gypsum and composite decreased but magnesite increased pH. Particle size and pH changes were positively correlated, highly for bauxite (r² = 0.915), fairly for composite and magnesite (r² = 0.855 and 0.853, respectively) and lowly correlated for gypsum (r² = 0.562). Smaller particles obtained higher apparent colour, hardness, alkalinity and sulphate. There was no relationship between particle size and . Sorption capacities of these materials increase with decrease in particle size, however decrease in particle size enhances colour, hardness and sulphate levels. In optimizing the materials for defluoridation particle size can be decreased while monitoring colour, hardness, alkalinity and sulphate levels. Particles of diameter 2 mm were optimum in the present experiments.

Key words: Bauxite, composite, defluoridation, gypsum, magnesite.