Optimization of the conditions for adsorption of fluoride in aqueous solution by carrot residue using central composite design of experiment

Abstract

This study employs the use of carrot residue (CR) treated with dilute hydrochloric acid to remove fluoride ions in aqueous solution. The adsorption process parameters of pH, time of contact, adsorbent mass and initial ion concentration were optimized at ambient temperature by the use of central composite design of experiment. The CR absorbent was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microcopy (SEM). Quadratic model was used to correlate the variables to the responces obtained from the design matrix in the laboratory and analysis of variance was used to test the significance of the independent variables and their interactions. Predicted values of % adsorption at optimum conditions for commercial activated carbon (AC) which served as control and CR were validated. From the results obtained, the optimum adsorption conditions were pH 5, time of contact 96 min, mass of adsorbent 1g and initial ion concentration of 10mg/L with desirability of 1. The design predicted values and experimental values obtained for AC were 85.63% and 87.59%, while those of CR were 87.67±0.02% and 90.25±0.02% respectively. From the results obtained, it was concluded that CR was as effective and a better adsorbent for removal of fluoride ions in aqueous solution than AC. Therefore, CR is a potential alternative to AC for fluoride adsorption in aqueous solution.

Keywords: Carrot Residue; Adsorption; fluoride; central composite design