Superb Capacity of Magnetic Sludge-Floc-Based Adsorbents for Congo Red: Synthesis and Adsorption Studies

Adsorbents based on sludge flocs derived from wastewater have been widely developed in recent years. Herein, one of the adsorbents (PFloc) was obtained from water produced from oil without further treatment and was eluted via polysilicate aluminium to produce another adsorbent, MPFloc. The physiochemical characteristics of MPFloc and PFloc were characterized by Fourier transform infrared spectroscopy, X-ray diffraction analysis, contact angle measurements, scanning electron microsocpy, thermogravimetric analysis and zeta-potential techniques. The adsorption performance parameters of MPFloc and PFloc were assessed using Congo red (CR). The effect of dosage and settling time on CR adsorption was investigated. The adsorption capacities of adsorbents reached 1924.4 mg and 854.3 mg g−1 (generally below 100 mg g−1), respectively, because of their large quantities of –OH, better dispersion in CR solution, strong positive charge and cross-linked structure. The dynamic adsorption modes of the adsorption data were studied, which indicated that the adsorption process follows a pseudo-second-order model. Moreover, the adsorption isotherms of PFloc and MPFloc were in agreement with the Freundlich and Langmuir models, respectively. The waste utilization and superb adsorption capacity of MPFloc and PFloc provide new insight into the preparation of adsorbents.