Removal of tetracycline by steel slag-red mud composite pellets: Adsorption performance and mechanism

Tetracycline as a common emerging pollutant has received widespread attention worldwide. In this paper, RMSSx:y composite pellets were prepared by an annealing process to adsorb tetracycline (TC) from wastewater using red mud (RM) and steel slag (SS) as raw materials. The RMSS5:5 composite pellets prepared with a mass ratio of 5:5 at a calcination temperature of 900 °C exhibited excellent adsorption properties. The experimental data were analyzed using Langmuir, Freundlich, and Temkin adsorption models. The equilibrium data fitted both the Langmuir and Freundlich models well. Kinetic adsorption data were analyzed using the quasi-primary kinetic model, the pseudo-secondary kinetic model, the intraparticle diffusion model, and the Boyd model. The maximum adsorption capacity of RMSS5:5 for TC reached 183.78 mg/g. Thermodynamic studies revealed the exothermic and spontaneous nature of the adsorption process. The adsorption mechanism involved the complexation of Fe, Ca with TC, hydrogen bonding, electrostatic interaction, and physisorption. In addition, RMSS5:5 possessed excellent magnetic responsive properties and cycling performance. This study successfully prepared an efficient and cost-effective adsorbent with two industrial solid wastes, which has great potential for TC removal from wastewater.