ARSENIC REMOVAL USING LOCALLY AVAILABLE GYPSUM MINERALS IN TANZANIA

Arsenic is a toxic metalloid causing severe health challenges to the exposed populations. The long exposure of human being to arsenic through water, food or air can lead to malfunction of internal organs such as kidney, liver, and also causes cancer. Thus, the need to develop affordable removal technique for arsenic removal is of important to save human life. Locally available minerals such as gypsum has been used for arsenic stabilization before deposit to landfill. In order to understand the process of arsenic removal, gypsum minerals powder of 0.75 mm grain size were characterized by X-Ray Diffractometry (XRD). The XRD data indicated the presence of calcium sulphate, calcium carbonate, iron sulfide, and arsenic mineral phases of nickel, copper and gallium. The Scanning Electron Microscopy - Energy Dispersive Spectroscopy (SEM-EDS) confirmed the presence of heterogeneous surface providing multiple sites for arsenic adsorption. The application of gypsum on drinking water sources in Tanzania shows 84% As(V) removal and 98% As(III) removal. In natural water, gypsum works on both As(V) and As(III). Gypsum could be recommended for lower concentrations of arsenic as 1g gypsum removes 0.5 mg/g to 80%. The higher arsenic removal was observed at higher doses of gypsum when 10g gypsum was poured in 100 ml of 1 mg/L. However, 1 gram of gypsum could remove 5 mg/L arsenic up to 60% after 3 hours and the removal increases as contact time increased to 3 hours. At 4 hours, the 1 gram gypsum was saturated and concentration remained constant. The adsorption isotherms was observed to fit well with Freundlich isotherm while kinetic study fitted on pseudo second order with R²=0.99. Gypsum is the best adsorbent for arsenic removal at low concentrations as 1g gypsum removed 0.5 mg/L up to 80%. In natural water, gypsum was more effective to remove both As(V) and As(III).