Adsorption of Co(II) from aqueous solution using municipal sludge biochar modified by HNO3

Here adsorption studies were proposed on a carboxylated sludge biochar (CSB) material modified by HNO 3 to assess its capacity in the removal of cobalt from aqueous solution. The as-prepared sludge biochar material was characterized by Brunauer-Emmett-Teller (BET) analysis, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The isotherm process could be well described by the Langmuir isotherm model. The adsorption kinetics indicated that cobalt adsorption followed a pseudo-second-order kinetics model. The mechanism between Co(II) and biochar involved electrostatic interaction, ion exchange, surface complexation and physical function. The adsorption capacity on CSB was as high as 72.27 mg·g −1 , surpassing original sludge biochar (SB) as CSB had abundant oxygen-containing functional groups and many hydroxyls, plus the BET surface areas increased when SB was modified by HNO 3 , which stimulated adsorption effect. Therefore, this work shows that CSB could be used as an efficient adsorbent to remove Co(II) in wastewater. The material has abundant oxygen-containing functional groups, which are beneficial for binding Co(II). The isotherm process could be well described by the Langmuir isotherm model and pseudo-second-order kinetic model. The adsorbent has an efficient adsorption capacity for Co(II), as high as 72.27 mg·g −1 .