Chemical regeneration of spent powdered activated carbon used in decolorization of sodium salicylate for the pharmaceutical industry

The purpose of this work was to regenerate spent powered activated carbon (PAC) which was exhausted in the decolorization of sodium salicylate (NaSA) liquor. In this research, a facile procedure of chemical regeneration was performed and a simple and accurate spectrophotometric method was applied. In order to obtain the optimal operation conditions, influences of following parameters were verified: soaking time, heating temperature, acid concentration and reaction time. PAC was also characterized by thermogravimetric analysis (TGA) to investigate the adsorbate-adsorbent interactions and their dependences on temperature. The optimal conditions for PAC regeneration were as follows: NaOH (1 M) soaking time of 1 h, H2SO4 concentration of 0.31 mol L−1 and agitating at 95 °C for 1 h. The peaks of derivative thermogravimetric (DTG) pyrolysis profiles of exhausted PAC appeared at low temperatures (∼180 °C and ∼260 °C), which demonstrated the adsorption of colored contaminants was a weak physisorption. In pilot plant experiments, it was found that after four consecutive adsorption-regeneration cycles, the adsorption capacity of PAC was maintained at high levels, even higher than virgin PAC. Therefore, this method was very simple, economical and had successfully applied in industrial scale.