Water defluoridation with 150–300°C calcined Bauxite-Gypsum-Magnesite (B-G-Mc) filters

Abstract

Research on water defluoridation with composite filters of bauxite, gypsum and magnesite was carried out at Ngurdoto Research Station to determine capacity, nature of fluoride-sorbent interaction and changes in water quality. The objective was to identify an optimum composite filter that would not alter the water quality beyond World Health Organisation recommendations. The three materials were characterized through X-Ray Fluorescence. The major components were Al 2 O 3 (30.33%) for bauxite, CaO (28.09%) for gypsum and MgO (34.57%) for magnesite. The materials were calcined at temperatures of 150, 200, 250 and 300 o C. Six composite filters were prepared for each calcine temperature of bauxite:gypsum:magnesite in the ratios 1:2:3, 1:3:2, 2:1:3, 2:3:1, 3:1:2 and 3:2:1. The highest capacity, 11.77 mg F/g, was obtained with the 3:1:2-200 o C calcine. The optimum filter was however the 1:2:3-200 o C calcine with capacity of 10.19 mg F/g. This filter did not alter the water quality beyond the considered WHO limits. The fluoride-sorbent interaction could best be described by SO , however a composite filter of these materials is plausible.

Ground Water Contamination with Fluoride and Potential Fluoride Removal Technologies for East and Southern Africa

“…Removal of fluoride from water has been researched on employing a number of materials among which are bauxite, gypsum, magnesite and their composite filters [2,46,47], Calcium chloride ( CaCl 2 ) and Sodium dihydrogen phosphate ( NaH 2 PO 4 ) as co-precipitation reagents in contact precipitation [33,34], cow bone char in batch and fixed bed [7,32], fish bone [43], activated carbon and activated carbon loaded separately with alumina, magnesia and calcium [44], and, magnesite [45].…”

“…The negatively charged species would in effect retard fluoride sorption. Formation of positively charged species as shown in Equation 16 would occur in low pH medium hence greater adsorption of fluoride, fluoride being an anion [46,47].…”

Effects of Calcination Temperature of Naturally Occurring Absorbents on Drinking Water Defluoridation

“…Moreover, gypsum calcinated at low temperature of 150 o C to 300 o C gave better performance in fluoride removal though with the highest residual number of other ions such as sulphate and iron, which are not within the recommended standards. However, gypsum calcinated at temperatures above 300 o C introduces less ionic contaminants in treated water (Thole et al, 2011). Results in Table 3 prove the presence of residual sulphate in gypsum calcinated at temperature of 350 o C, but the amount is found to be within the recommended standards and iron level was found to be below the detection limit.…”

“…These techniques face setbacks whereas some are not cost effective and others are less expensive but less effective with low quality of the treated water as well as poor sorption capacity (Al-Hawamdeh et al, 2013;Thole and Mtalo, 2012). Each technique has its benefits and shortcomings that limit its use.…”

“…The use of bone char, interferes with some taboos and religious beliefs of some societies hence it is not accepted globally and when not properly prepared produces low water quality with taste and odour of rotten meat to drinking water. Bauxite and clay increases water turbidity, colour as well as some of the residual ions (Thole and Mtalo, 2012;Feenstra and Erkel, 2007). Despite activated alumina method being popular, it has some limitations such as it is not effective when the total dissolved solids in water exceeds 1500 mg/L.…”