Clay-based ceramic materials for water de-fluoridation

Abstract

Long-term consumption of water with fluoride concentration above the WHO recommended limit of 1.5 mg/g may cause fluorosis. Low-income communities living in fluoride endemic regions are more affected as they cannot afford well-established water de-fluoridation technologies. Currently, clay ceramic materials impregnated with silver colloids have been used to disinfect water disregarding the removal of fluoride. This work investigated improving the de-fluoridation capacity of clay ceramic materials with in-situ generated Ca/Mg phosphate system using locally available carbonate rocks as a source of Ca/Mg. To achieve this, clayCa/Mg phosphate system composite ceramic materials were synthesized from varied ratios of

clay (K) to carbonate rock materials (R) (K:R = 0:100, 90∶10, 85∶15, 75∶25 and 100:0), sintered

at various temperatures between 500 and 900 . The materials were characterized using XRF, FTIR, AAS, CHNS-O analyzer and X-ray PDF analysis. The three types of carbonate rock materials investigated were identified to be; high-calcium limestone, magnesium-deficient dolomite and near-stoichiometric dolomite. The magnesium-deficient dolomite gave rise to a Ca/Mg phosphate system that exhibited superior de-fluoridation performance. The material improved in de-fluoridation performance with increase sintering temperature from 500 to 700 , possibly due to an increase in the more soluble magnesium-substituted tri-calcium phosphate (β-Mg x Ca 3-x PO 4 ), CaO and MgO (PDF and FTIR). This work has shown that the de-fluorination performance of clay ceramic materials can be improved with a phosphate system synthesized/formed in-situ using carbonate rocks as Ca/Mg source. The method of improving the de-fluoridation performance of clay ceramic materials introduced in this present study has potential applications in the fabrication of water filters with fluoride removal ability.