Water defluoridation using MalawiÕs locally sourced gypsum W.R.L. Masamba, S.M. Sajidu * , B. Thole, J.F. Mwatseteza Chemistry Department, Chancellor College, University of Malawi, P.O Box 280, Zomba, Malawi Accepted 15 August 2005 Available online 27 September 2005 Abstract Free fluoride levels above the WHO guideline maximum value of 1.5 mg/l have been reported in several parts of Malawi. Dental fluo- rosis has also been observed in the same areas such that search for local defluoridation techniques has become important in the country. The present research intended to determine the potential of using Malawi gypsum in defluoridation, identify the best pre-treatment of the gypsum and optimum conditions under which effective water defluoridation with the gypsum may be obtained. Laboratory experiments were carried out to explore defluoridation of drinking water using locally sourced gypsum and gypsum calcined at high temperatures. A 400 °C calcined phase of gypsum gave the highest defluoridation capacity of 67.80% compared to raw (uncalcined) gypsum, 200, 300 and 500 °C calcined phases. Powder X-ray diffraction (PXRD) pattern of the 400 °C phase revealed existence of less crystalline CaSO 4 that was thought to be responsible for such relatively high defluoridation capacity. The dependence of the fluoride removal by the 400 °C calcined phase on other drinking water quality parameters was assessed by simple correlation analysis. Reaction kinetics and mechanisms of fluoride removal by the materials were also investigated. It was found that ion exchange was the dominant mechanism through which fluoride was removed from water by the materials. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Water defluoridation; Gypsum; Fluorosis; Powder X-ray diffraction; Reaction mechanisms; Kinetics; Ion exchange 1. Introduction Millions of people particularly in developing countries are suffering from fluorosis due to high fluoride concentra- tions in their drinking water (PHE, 2001). Fluorosis is characterized by discoloured, blackened, mottled or chalky white teeth. In Malawi this problem is common in places such as Nkhotakota, Karonga, some parts of Nsanje, Chikwawa, Machinga, Mangochi, Mwanza and Neno. Free fluoride levels in drinking water of up to 8.6 ppm have been reported at Ulongwe in Balaka, 9.00 ppm in Mach- inga (Sibale et al., 1998), 7 ppm at Mazengera in Lilongwe, 9.6 ppm in Nkhotakota, 8.0 ppm in Karonga, 5.8 ppm in Nsanje and 3.4 ppm in Mwanza (Carter and Bennet, 1973). A fluoride survey in Nathenje showed a positive cor- relation between prevalence of dental fluorosis in children and levels of fluorides in portable water in the area (Msonda, 2003). Several defluoridation methods have been studied and reported as appropriate in countries such as Kenya, Tanzania and India (Susheela, 1992; NFI, 1992; PHE, 2001; REF, 2003). Materials developed for defluori- dation capacity have included alum, zeolites, bauxite and bone char (NFI, 1992; PHE, 2001; REF, 2003). However, some of these, for example zeolites and alum are costly and not readily available in Malawi. Gypsum is readily available in Malawi with yearly production of 1200 tonnes. Studies carried out in India showed that gypsum has some defluoridation capacity (NFI, 1992). As Malawi has not at- tempted to undertake drinking water defluoridation, there is need to explore suitability of locally available materials such as gypsum as a first step to alleviate the problem of fluorosis in the affected areas. The objective of this work was therefore to study the viability of using local gypsum as a water defluoridation material in Malawi. 1474-7065/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.pce.2005.08.029 * Corresponding author. Tel.: +265 1 524 222; fax: +265 1 524 046. E-mail address: sajidu@chanco.unima.mw (S.M. Sajidu). www.elsevier.com/locate/pce Physics and Chemistry of the Earth 30 (2005) 846–849