Process optimization of potassium hydroxide activated carbon from carob shell biomass and heavy metals removal ability using Box-Behnken design

摘要

This work investigated the utilization of carob shell biomass as a precursor for the preparation of activated carbons by potassium hydroxide activation and their use for heavy metals removal from aqueous solutions. Experimental design approach was adopted for the optimization of preparation conditions and cobalt and cadmium removal efficiency. A Box-Behnken surface statistical design with three factors and three-level combining with response surface modeling and quadratic programming was employed for maximizing cadmium and cobalt ions removal from aqueous solution. Three different factors including impregnation ratio, activation time, and activation temperature were used. Experimental results showed that the activation temperature was the most significant factor with a negative impact for iodine number, methylene blue index, and the removal of cadmium and cobalt ions. Furthermore, the impregnation ratio showed a negative impact for iodine number and methylene blue index. The activation time presented a positive effect for methylene blue index. Moreover, the interaction between activation time and activation temperature had a negative impact for cadmium and cobalt ions removal. Optimal conditions for cadmium removal were achieved with an impregnation ratio of 0.3 g/g, activation time of 1.5 h, and an activation temperature at 400 degrees C. Sorption capacities were determined with equilibrium isotherms. Greater sorption efficiencies acquiring via Langmuir isotherm model were 90.58 mg/g for cadmium removal and 77.24 mg/g for cobalt sorption. These major values were obtained for the activated carbons prepared with an impregnation ratio of 0.3 g/g, activation time of 1.5 h and an activation temperature at 400 degrees C and an impregnation ratio of 0.1 g/g, activation time of 1.5 h and an activation temperature at 400 degrees C, respectively.