Highly efficient activated carbon from Glebionis coronaria L. biomass: Optimization of preparation conditions and heavy metals removal using experimental design approach

This study investigates the preparation of activated carbons from Glebionis coronaria L. biomass by phosphoric acid activation and their ability for heavy metals removal from aqueous solution. The effects of four factors controlling the activation process, such as carbonization temperature (500-600 °C), activation temperature (400-500 °C), activation time (1-2 h) and impregnation ratio (g H3PO4/g carbon) (1.5-2) were established. Further, full factorial experimental design at two levels (24) was carried out in order to achieve simultaneously optimal preparation conditions and high removal efficiency of cadmium and cobalt ions. The experimental results indicated that the carbonization temperature was the most significant factor on iodine number and methylene blue index with a negative effect. Therefore, the removal of cadmium onto activated carbons was more influenced by the interaction between carbonization temperature and impregnation ratio. According to statistical data, the best conditions for the removal of cadmium and cobalt by the prepared activated carbon samples were investigated. The maximum iodine number and methylene blue index obtained under these experimental conditions were 794.58 mg/g and 161.92 mg/g respectively. The sorption capacities were 57.87 mg/g for cadmium and 45.75 mg/g for cobalt. These sorption performances were higher than those of a commercial activated carbon (0.85 mg/g for cadmium and 21.24 mg/g for cobalt removal) used in water treatment. Desorption studies using HCl as desorbing agent revealed over 87.14 and 70.18% for cadmium and cobalt, respectively.