Kinetics of ionic dyes adsorption with magnetic-modified sewage sludge



Sewage sludge is modified by pretreatment with a synthetic ferrite process, which turns the sewage sludge into an absorbent for ionic dyes and the adsorbent can be removed by a magnetic field. When Fe3O4 is synthesized on the surface of sewage sludge, the surface potential of particles is manipulated by adjusting the pH. For Fe3O4 synthesis, the molar ratio of Fe2+ to Fe3+ was 1. In our experiment, two magnetic adsorbents are made (A5 and A10) using 5 g and 10 g doses of sewage sludge, respectively. A5 is used to adsorb Procion Red Mx-5B (PR) and A10 is used to adsorb Methylene Blue (MB). The specific surface area of A5 is 49.08 m2/g. The ideal pH for PR adsorption is found to be 3 with a maximum adsorption capacity of 0.031 mmol/g (18.83 mg/g). For A10, the specific surface area is 39.84 m2/g, and ideal pH is 6 for MB adsorption with maximum adsorption capacity being 0.078 mmol/g (25.06 mg/g). The kinetics study reveals that MB and PR adsorptions fit well a pseudo-second-order kinetic model, and the values of activation energy calculated from the rate constants are 42.82 kJ/mol and 47.19 kJ/mol for MB and PR, respectively. MB and PR adsorption can be characterized as activated chemical adsorption. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 905–912, 2014