Thiol-incorporated activated carbon derived from fir wood sawdust as an efficient adsorbent for the removal of mercury ion: Batch and fixed-bed column studies

Abstract

The thiol-incorporated activated carbon (AC) was produced from fir wood sawdust by treating it chemically with phosphoric acid at five different impregnation ratios and used as adsorbent for Hg2+ ion in batch and fixed bed systems. The raw material and ACs samples were characterized by means of proximate and ultimate, FTIR, SEM, and BET analyses. The BET surface area of the prepared AC enhanced from 1273m2/g to 1789m2/g along with an increase in the impregnation ratio of H3PO4 from 1 to 1.5g/g and then decreased to1593m2/g. AC-H1.5 and the AC-S (modified AC) samples had the highest (1789m2/g) and lowest surface area (1162m2/g). The effects of various parameters such as contact time, adsorbent dose, pH and initial Hg2+ concentration for the removal of Hg2+ were studied in a batch process. The Hg2+ ion removal efficiency increased by increasing the adsorbent dosage from 0.25 to 2g/L and the pH from 2 to 8. The equilibrium data fitted to the Freundlich, Langmuir and Redlich–Peterson isotherms, but gave a better fit to the Redlich–Peterson model. The maximum monolayer adsorption capacity of the mercury ion onto the AC-S sample (129mg/g) was more than that onto the AC-H1.5 (107mg/g). The results showed that the adsorption process fitted the pseudo-second-order kinetic models. In a fixed-bed column adsorption, the effects of bed height, flow rate and Hg2+ concentration on the breakthrough curve were investigated, on which the adsorption capacity predicted both by the Yan and Thomas models was found to be satisfactory with that determined by integrating the total area above breakthrough curves. The desorption of AC adsorbent was investigated with several acids (HCl, HNO3, H2SO4 and H3PO4) and bases (KOH, NaOH and NaCO3).