Adsorption of strontium from aqueous solution using activated carbon produced from textile sewage sludges

Different types of activated carbons were prepared by changing the activation temperatures (400–700 °C) and impregnation ratio (sewage sludge: KOH; 1:1, 1:2) and the removal of Sr+2 from aqueous solution was determined. The maximum adsorption yield (12.11 mg/g) was obtained at 500 °C for 1 h carbonization conditions with impregnation ratio of 1:1. The affecting parameters were analyzed by using central composite design method. The selected parameters were initial pH, temperature, initial strontium concentration and carbon dosage. The analysis of variance was performed in 95% confidence level and checked to fitting of experimental value and predicted value. The significant F was P < 0.05 with a model F value of 19.94 which revealed that this regression is statistically significant. The results of regression analysis indicated that pH and temperature parameters were not individually statistically significant for Sr+2sorption. However, the efficiency of strontium sorption increases with the increase in carbon dosage and decreases with the Sr+2 concentration. Influences of initial pH and temperature, pH and Sr+2 concentration, temperature and carbon dosage and Sr+2 concentration and carbon dosage on the adsorption process were considered statistically significant. Adsorption of strontium was described by Freundlich isotherm as a physical adsorption (E = 7.2 kJ/mol). The adsorption reactions were calculated as endothermic, spontaneous and favorable reactions.