Efficient fluoride removal by preparation, characterization of pyrolysis bone: Mixed level design experiment and Taguchi L8 orthogonal array optimization

Abstract

Mixed level design experiment and Taguchi orthogonal array design L8 (4^1, 2^2) was applied to optimize pyrolysis process for preparing bone char in order to remove fluoride from real groundwater. Taguchi analysis is through selecting high signal-to-noise ratio as a better response. Estimated effects index based on the least squares approach indicated that the pyrolysis temperature had a main effect on bone char preparation using pyrolysis process. The bone char obtained at pyrolysis temperature = 550 °C had the highest adsorption capacity with maximum saturation experimental adsorption capacity of 12.05 mg/g. Specific surface area and Barrett-Joyner-Halenda area of the bone char obtained from pyrolysis of animal bones were 118 m2/g and 120 m2/g, respectively. The experimental adsorption results were better fitted to the Langmuir isotherm and the pseudo second-order kinetic model. Thermodynamic information indicated that fluoride adsorption process onto pyrolysis bone char followed spontaneously (∆Go = −4.972–4.296 kJ/mol), an endothermic (∆Ho = 5.59 kJ/mol) and nature randomness (∆So = 0.033 kJ/mol·K). Accordingly, the bone char obtained using pyrolysis process under optimum conditions demonstrated higher adsorption capacity compared to commercial bone chars applied for fluoride removal from groundwater.