Influence of reactivation conditions on the physio-chemical properties of activated carbon

Abstract

Several market studies predict an increasing demand for Activated carbons (AC) in the future. To reduce the amount of fresh AC, reactivated AC can be used. Therefore, the present study deals with the systematical investigation and optimization of thermal reactivation of AC used for water purification in rotary kilns. The aim is to restore the adsorption properties as far as possible with minimal energy input. In this study, AC from wastewater and drinking water treatment were selected. The experiments follow a statistical design of experiments, varying the heating rate, heating time and composition of gas atmosphere on reactivation process. To analyze the quality of reactivation, besides structural, also several chemical and energetic properties of ACs were selected. In terms of structural properties, the large difference concerning the inner surface between fresh and exhausted wastewater carbon (50.8%) can be restore by thermal reactivation with temperatures of 900 °C up to 91.3%. For drinking water carbon, the difference in internal surface area between fresh and exhausted AC was much smaller (14.9%). Temperatures in the range of 600 °C are already sufficient to restore the internal surface almost completely. The composition of the gas atmosphere is of minor importance for both AC. With regard to surface chemistry, it was found for both carbons that weak acids adsorb on the carbons during application in water purification. The acids partially desorb during thermal reactivation. However, at the same time a slight change in surface chemistry occurs and the surface chemistry becomes more aromatic character.