Adsorption of Tetracycline by Shrimp Shell Waste from Aqueous Solutions: Adsorption Isotherm, Kinetics Modeling, and Mechanism

The highly efficient removal of tetracycline (TC) from an aqueous solution was accomplished by using the raw shrimp shell waste (SSW) as an environmentally friendly adsorbent. The SSW without any treatment removed TC more efficiently than the SSW after being treated with HCl and NaOH solutions. The SSW was characterized using nitrogen adsorption-desorption isotherms, scanning electron microscopy alongside energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, a thermogravimetric-derivative thermogravimetry analyzer, and a zeta-potential analyzer. The maximum adsorption capacity of 400 mg/L SSW was 229.98 mg/g for 36 h at 55 degrees C. Both the Langmuir isotherm model and the pseudo-second-order kinetic model well described the experimental data. According to the values of the Gibbs free energy and enthalpy changes, the TC adsorption by SSW proved to be spontaneous and endothermic. The TC adsorption process was controlled by intraparticle diffusion and liquid film diffusion.