A comparative study on adsorption and catalytic degradation of tetracycline by five magnetic mineral functional materials prepared from steel pickling waste liquor.

Palygorskite (Pal), bentonite (Bent), sepiolite (Sep), zeolite (Zeol), and kaolin (Kaol) were used with steel pickling waste liquor to synthesize magnetic palygorskite (Pal@Fe3O4), magnetic bentonite (Bent@Fe3O4), magnetic sepiolite (Sep@Fe3O4), magnetic zeolite (Zeol@Fe3O4), and magnetic kaolin (Kaol@Fe3O4), for adsorption and catalytic degradation of tetracycline (TC), respectively. Through the study of adsorption kinetics and adsorption isotherms, the maximum adsorption capacity of Pal@Fe3O4 to TC was 149.439 mg/g, which was 1.239 times, 2.260 times, 3.161 times, and 3.448 times of Bent@Fe3O4, Zeol@Fe3O4, Kaol@Fe3O4, and Sep@Fe3O4, respectively. The kinetic study of tetracycline degradation demonstrated that the maximum reaction rate constant of Bent@Fe3O4/H2O2 system was K(obs) = 2.12 × 10-2 min-1, which was close to that of Pal@Fe3O4/H2O2, Kaol@Fe3O4/H2O2 system, and was 2.000 times, 2.356 times, 2.650 times, and 4.711 times of Fe3O4/H2O2, Zeol@Fe3O4/H2O2, Sep@Fe3O4/H2O2, and H2O2 system, respectively. The results showed that Pal@Fe3O4 and Bent@Fe3O4 were more advantageous in the treatment of wastewater containing tetracycline, and efficient reuse of exhausted magnetic minerals and deep mineralization of organic pollutants were achieved by constructing an advanced oxidation system. The BET, VSM, SEM, XPS, XRD, and FTIR were used to characterize the five clay minerals before and after magnetic modification. It was speculated that the surface structure - OH groups of clay minerals might be significant factors influencing the adsorption performance of magnetic minerals on TC, and reduction ability of clay minerals to Fe3+ importantly affected the catalytic performance of magnetic minerals. The specific surface area and morphological structure of clay minerals both affected the adsorption and catalytic degradation of TC by the five magnetic minerals.

Effective degradation of tetracycline by magnetic palygorskite synthesized with different dosages of NaOH.

In the process of preparing magnetic palygorskite from waste pickling liquor of the steel industry, the dosage of NaOH will affect the properties of the magnetic palygorskite. The experimental results showed that magnetic palygorskite can be effectively prepared when NaOH dosage is between 255 and 330 g/L. Vibration sample magnetometry proved that different NaOH dosages can affect the saturation magnetization of magnetic palygorskite. The catalytic performance of five catalysts synthesized with different NaOH dosages hardly changed after five cycles of Fenton-like catalytic degradation of tetracycline (TC). The magnetic palygorskite prepared by this method had good catalytic performance even when the catalyst preparation conditions were magnified ten times, which can provide a reference for large-scale preparation of magnetic palygorskite.