Activated carbon from Diplotaxis Harra biomass: Optimization of preparation conditions and heavy metal removal

Abstract

Diplotaxis harra biomass was used as a precursor for the preparation of activated carbons by phosphoric acid activation. The effects of several 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. In order to reduce the number of experiments, full factorial experimental design at two levels (24) were carried out to achieve optimal preparation conditions and better conditions for the removal of cadmium and cobalt ions from aqueous solutions. The experimental results showed that the carbonization temperature was more significant with a negative effect for iodine number and methylene blue index. Therefore, activation temperature and activation time present a positive effect for iodine number and negative effect for methylene blue index. The impregnation ratio shows a positive impact for the both indicated responses. The removal of cadmuim and cobalt ions onto activated carbons was more sensitive to methylene blue index. Moreover, the interaction between carbonization and activation temperatures was the most influencing in cadmium and cobalt ions removal with a positive effect. Using this statistical tool, the best conditions for the removal of cadmium and cobalt by Diplotaxis Harra based activated carbons were established. The maximum iodine number and methylene blue index obtained under these experimental conditions were 1058.8 mg/g and 280.4 mg/g respectively. The high sorption capacities were 31.6 mg/g for cadmium and 25.9 mg/g for cobalt. Those characteristics were shown close than those of a commercial activated carbon used in water treatment and those reported by other researchers studying activated carbon preparation from various solid wastes.