Characteristics of equilibrium, kinetics studies for adsorption of Hg(II) and Cr(VI) by polyaniline/humic acid composite

A composite PANI/HA was prepared by adding humic acid (HA) into the chemical polymerization process of aniline monomers. Hg(II) ions and Cr(VI) anions were selected to evaluate the adsorption properties of PANI/HA, and the adsorption data were analyzed. Various factors affecting the uptake behavior such as aqueous pH, adsorbent concentration, ionic strength and competing anions were also studied. The adsorption kinetics followed the mechanism of the pseudo-second-order equation, and the maximum Hg(II) adsorption capacity calculated by Langmuir model was 671 mg g− 1, while the adsorption of Cr(VI) fitted well by Freundlich isotherm. Both ionic strength and certain competing anions had a significant effect on Hg(II) and Cr(VI) adsorption. BET analysis, FTIR spectra and transmission electron microscopy (TEM) were used to investigate the differences between polyaniline (PANI) and PANI/HA. The HA played an important role in modifying the morphology, preventing the aggregation of PANI, and improving the uptake properties of mercury and chromium on this composite in pH 3.0–7.0. The mechanism of Hg(II) and Cr(VI) adsorption was discussed.