Cyano and acylamino group modification for tannery sludge bio-char: Enhancement of adsorption universality for dye pollutants

Abstract

Tannery sludge biochar (BC) has been widely studied and shown promising prospects in dye wastewater treatment. Dye wastewater is a complex mixture, including cationic and anionic dye pollutions. However, the unmodified BC usually exhibits low adsorption ability for anionic dye pollutants because of the electrostatic repulsion by negatively charged biochar surfaces. Herein, inspired by the great complexation of polyacrylamide flocculant for dye pollutants, the polar functional groups (cyano and acylamino groups) were introduced into BC via the secondary pyrolysis with melamine and KOH. The modified tannery sludge biochar (MBC) had excellent adsorption abilities for both cationic dye (cationic blue X-GRL) and anionic dyes (reactive red X-3B, direct yellow RS and acid blue 2GL) used in textile dyeing processes. Moreover, to separate the MBC from solution quickly, the iron oxide particles were in-situ loaded on MBC to obtain the magnetic MBC. Adsorption kinetic, isotherm and Gaussian calculation analyses demonstrated that the adsorption processes for dye pollutions were exothermic, spontaneous and chemical interacted. The excellent adsorption universality of magnetic MBC for both cationic and anionic dyes may benefit the large-scale application of tannery sludge biochar in dye wastewater treatment.