Removal of cationic and ionic dyes on industrial-municipal sludge based composite adsorbents

The new class of reactive adsorbents obtained by pyrolysis of individual and mixed industrial sludges were used as media for the removal of cationic (Basic Fuchsin) and anionic (Acid Red 1) dyes. Materials were characterized using adsorption of nitrogen, thermal analysis (TA), potentiometric titration, X-ray diffraction (XRD), and scanning eletron microscopy (SEM). Kinetic measurements showed a fast decolorization process. Dye adsorption isotherms were fitted to the Langmuir-Freundlich model isotherm. The limiting capacities for Acid Red were between 35 and 73 mg/g, whereas the capacities for Basic Fuchsin removal ranged between 70 and 127 mg/g. While the Acid Red removal capacity was comparable to that on commercial activated carbon, the sludge-derived materials adsorb more Basic Fuchsin than carbon. The high efficiency of adsorption for both cationic and ionic dyes was linked to surface chemical heterogeneity and a high volume of mesopores. The diversity in surface chemistry, which leads to ion exchange processes, is a result of the presence of minerals, which are formed during pyrolysis.