Effective adsorption of sulfur dioxide by activated carbons containing calcium carbonate from deinking paper sludge

Abstract

Two activated carbons have been prepared by chemical activation of deinking paper sludge with K₂CO₃, with further carbonization in N₂ (AC-N₂) or CO₂ (AC-CO₂) and characterized in terms of proximate analyses, adsorption/desorption of N₂, skeletal and bulk pycnometry, acid/base and Boehm’s titrations, X-ray diffraction and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) analyses. A commercial activated carbon (AC-COM) was subjected to the same characterization program for comparison purposes. Surface area/porosity followed the trend: AC-CO₂ < AC-N₂ < AC-COM, revealing a good development of porosity in samples prepared in the laboratory but not approaching that of the commercial sample. Surface basicity, in turn, followed the trend: AC-CO₂ > AC-N₂ ≫ AC-COM, due to the presence of CaCO₃, which is a basic salt, in the carbons prepared. The three adsorbents were tested in the adsorption of SO₂, where a proper selection of carbon particle size that maximized pore diffusion control led to a higher SO₂ uptake. Adsorption equilibrium was successfully fitted to Langmuir and Freundlich isotherms. Final adsorption capacity was governed by textural properties, while adsorption affinity was influenced by both surface basicity and porosity.