Abstract
Research was carried out at Ngurdoto research station in Tanzania to ascertain the potential development of a water filter made of bauxite, gypsum and magnesite in an attempt to enhance the availability of low-fluoride water. The materials were sourced within Tanzania. The X-Ray fluorescence technique showed that the major components of the materials were: bauxite: Al2O3 (30.33%), SiO2 (15.0%) and Fe2O3 (14.3%); gypsum: CaO (28.09%), SO3 (34.96%), and SiO2 (9.01%); and magnesite: MgO (34.57%) and SiO2(19.3%). The materials were calcined at 350, 400, 450 and 500°C. The activated materials were then mixed in mass ratios of 1:2:3, 1:3:2, 2:1:3, 2:3:1, 3:1:2 and 3:2:1 (bauxite: gypsum: magnesite). One gram of each composite was employed in the batch defluoridation of 1 L of water with fluoride concentration of 12.62 mg/L. The highest defluoridation capacity, 11.89 mg F-/g, was obtained with the 3:2:1 to 500°C composite. The quality of the treated water fell short of WHO standards on sulphates and iron but residual concentrations of Cl-, Al3+, Ca2+, Mg2+, Fe2+ were within the prescribed limits. Sorption behavior followed strongly to Langmuir isotherm, except for the 450°C calcined samples for which the Temkin isotherm behavior was pronounced. Despite the limitations of high residual sulphates and iron, a composite filter of bauxite, gypsum and magnesite was shown to be workable. Key words: Defluoridation, bauxite, gypsum, magnesite, composite, calcine, isotherm.
Highlights
Fluoride and human healthFluoride has been identified as a cause of dental and skeletal fluorosis world over (Maliyekkal et al, 2010; Rango et al, 2010; Peter, 2009; Onyango et al, 2009)
The maximum defluoridation capacity, 11.86 mg F/g, was obtained for the 3:2:1 composite calcined at 500°C
The recommended upper limit for sulphates in water being 400 mg/L, this calcine composite had a limitation of high residual sulphates, 2200 mg/L
Summary
Water defluoridation by bauxite-gypsum-magnesite (B-G-Mc) based filters calcined at 350 – 500°C. Research was carried out at Ngurdoto research station in Tanzania to ascertain the potential development of a water filter made of bauxite, gypsum and magnesite in an attempt to enhance the availability of low-fluoride water. The materials were calcined at 350, 400, 450 and 500°C. One gram of each composite was employed in the batch defluoridation of 1 L of water with fluoride concentration of 12.62 mg/L. The quality of the treated water fell short of WHO standards on sulphates and iron but residual concentrations of Cl-, Al3+, Ca2+, Mg2+, Fe2+ were within the prescribed limits. Despite the limitations of high residual sulphates and iron, a composite filter of bauxite, gypsum and magnesite was shown to be workable
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