Adsorption removal of Ni(II) and phenol from aqueous solution by modified attapulgite and its composite hydrogel

Attapulgite (ATP) and its organically modified products have been investigated for potential applications in environmental remediation. In this work, a variety of modifiers with different functional groups, including saturated sodium chloride solution (NaCl), cetyltrimethyl ammonium bromide (CTAB) and humic acid (HA), were used to treat attapulgite clay firstly, and then with the modified ATP as adsorbent and acrylamide (AAm) as monomer, polyacrylamide/modified attapulgite (PAAm/modified ATP) composite hydrogel which could adsorb heavy metal ions Ni(II) and organic pollutants phenol were synthesized. The structure of the raw ATP and modified ATP was specified with Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and Transmission electron microscope (TEM). The experiments indicated that the modified ATP and composite hydrogel possessed good adsorption properties for Ni(II) ions and phenol. The adsorption capacity of PAAm/HA-ATP hydrogel for Ni(II) was as high as 64.3 mg/g, which was 194.9% of pure hydrogel. The adsorption isotherm of HA-modified ATP (HA-ATP) and adsorption kinetics of PAAm/HA-ATP composite hydrogel was particularly concerned. The adsorption isotherm equation fitted well on the Langmuir model and R_L values ranged from 0.04 to 0.12 with different temperatures, indicated that the HA-ATP was a suitable adsorbent for adsorption of Ni(II) ions from wastewater. The obtained kinetics data for Ni(II) ions adsorption onto the PAAm/HA-ATP were described well by the pseudo-second-order model (R² > 0.99). As for the adsorption of phenol, double-modification proved to be the most effective method, and its optimal adsorption capacity was obtained on PAAm/CTAB-HA-ATP hydrogel.