Removal of sulfate ions from aqueous solutions by precipitation using calcined hydrocalumite as a precipitating agent

Hydrocalumite (Ca2Al(OH)(6)Cl.2H(2)O) was synthesized and calcined at different temperatures to evaluate its application as a precipitating agent for sulfate removal. At a precipitating agent dosage of 2 g L-1, the greatest sulfate removal was 64.8 +/- 4.0% in 120 min of reaction with the hydrocalumite calcined at 100 degrees C. Anion removals of 90-100% were achieved by increasing the precipitating agent dosage, using an initial concentration close to 950 mg (SO4-2) L-1 in all tests. The sludge produced in the sulfate precipitation process using hydrocalumite calcined at 100 degrees C was heat treated and reused as precipitating agent on sulfate removal process to determine the number of possible cycles to work with the studied material. The solid samples obtained were characterized using X-ray diffraction, scanning electron microscopy coupled with dispersive energy spectroscopy, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Along with characterizing the samples, hydrocalumite synthesis was confirmed, since the collapse of the layered double hydroxide's structure was observed at 400 degrees C and sulfate precipitation by the formation of ettringite and gypsum. The reuse of the thermally treated sludge was not feasible due to the great reduction in the sulfate removal, since only two cycles of treatment and reuse were possible. A new route of precipitation of sulfate present in aqueous media was revealed in this study, which presented a strong potential for application in the treatment of industrial effluents, since it is simple, fast and efficient.