Poly(acrylamide acrylic acid) grafted on steel slag as an efficient magnetic adsorbent for cationic and anionic dyes

In this study, an efficient magnetic polymeric composite was synthesized from steelmaking waste. Steel slag was modified with acrylamide acrylic acid (SSAA) copolymer for removal of methyl orange MO and methylene blue MB from synthetic solutions. The SSAA composite was characterized by TGA thermogravimetric analysis, SEM scanning electron microscope, XRD X-ray diffraction, BET Brunauer-Emmett-Teller surface area, and FTIR Fourier transform infrared. The adsorption behavior of SSAA for MO and MB was investigated, and the impact of various parameters was examined using one factor at a time (OFAT) and RSM-BBD response surface method-Box Behnken Design. The kinetic data of MO and MB were well described with the second-order kinetic model, and the dominant rate-limiting step is the film diffusion. The isotherms of Dubinin-Raudshkevish (D-R) and Freundlich well described the MB and MO experimental results, respectively. The maximum uptake efficiencies of 97% and 94% and capacities of 47 and 463 mg/g were reported for MO and MB, respectively. The thermodynamic investigations suggested favorable, spontaneous adsorption of MO and MB on the SSAA. Physical adsorption was found to be the dominating mechanism for MB, while the chemisorption mechanism was reported for MO. Those mechanisms were confirmed by the regeneration study, where SSAA was regenerated for MB, and an insignificant drop in the adsorption capacity was noted after five cycles. However, a negligible regeneration of the SSAA was achieved for MO ions, which verifies the chemisorption mechanism. The reported investigations revealed that the SSAA composite could be used for cationic and anionic dyes removal from wastewater, spontaneously and feasibly, as indicated by the thermodynamic study.