Experimental design for the optimization of preparation conditions of highly efficient activated carbon from Glebionis coronaria L. and heavy metals removal ability

• Glebionis coronaria L. a novel precursor for microporous activated carbon preparation.
• High adsorption capacity of cadmium and cobalt ions from aqueous solution.
• Response surface method for the optimization of preparation conditions and heavy metals removal.
• Proposed model correctly evaluates the effect of the investigated variables.

The objective of this study was the utilization of Glebionis coronaria L. biomass as a new precursor to produce highly efficient activated carbons by potassium hydroxide activation and their evaluation for heavy metals removal. 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 KOH/g carbon) (1–2) were investigated. To reduce the number of experiments, full factorial experimental design at two levels (24) was used 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 activation time was the most significant factor with a positive impact for iodine number and a negative effect on methylene blue index. Further, and in same as, the interaction between activation time and impregnation ratio had a positive effect on iodine number and negative effect on methylene blue index. Therefore, the removal of cadmuim and cobalt ions onto activated carbons was more influenced by activation temperature and activation time with a negative effect. Although, the interaction between activation time and impregnation ratio was the most significant factor influencing the cadmium and cobalt ions removal. Based on the statistical data, the best conditions for the removal of cadmium and cobalt by Glebionis coronaria L. based activated carbons were indicated. Thus, the maximum iodine number and methylene blue index obtained under these experimental conditions were 752.69 mg/g and 284.04 mg/g respectively. Further, the optimized activated carbons were used in sorption isotherm. The maximum sorption capacities obtained with the application of the Langmuir isotherm model are 115.99, 106.93 mg/g for cadmium sorption and 44.85, 46.80 mg/g for cobalt sorption onto AC carbonized at 400 °C, activated at 500 °C during 1 h with an impregnation ratio of 2 g/g and AC pyrolized at 600 °C and activated at 500 °C for 1 h with an impregnation ratio of 2 g/g respectively. Those sorption efficiencies were shown greater than those of a commercial activated carbon used in water treatment.

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