Adsorption Performance and Mechanisms of Tetracycline on Clay Minerals in Estuaries and Nearby Coastal Areas

Clay minerals in sediments have strong adsorption capacities for pollutants, but their role in the distribution of antibiotics in estuaries and nearby coastal areas is unclear. We evaluated the clay mineral montmorillonite (SWy-2) adsorption capacity for tetracycline (TC). We assessed the adsorption capacity of SWy-2 for TC by measuring the removal percentage of 30 mg/L TC over time. The effects of pH and ionic strength on the TC adsorption onto SWy-2 were investigated. We analyzed the kinetics of TC adsorption using a pseudo-second-order model and determined the adsorption isotherm using the Langmuir equation. SWy-2 particles were characterized using zeta potential, Fourier transform infrared (FTIR), and X-ray diffraction (XRD) analyses before and after TC adsorption. The removal percentage of 30 mg/L TC by SWy-2 reached 70.76% within 0.25 h and gradually increased to 78.64% at 6 h. TC adsorption was influenced by pH and ionic strength, where low pH enhanced and high ionic strength reduced the adsorption. The kinetics of TC adsorption followed a pseudo-second-order model, and the adsorption isotherm adhered to the Langmuir equation. The saturated adsorption capacity (q(max)) of SWy-2 for TC was 227.27 mg/g. Zeta potential, FTIR, and XRD analyses confirmed that electrostatic interactions and chemical bonds played a significant role in the TC adsorption by SWy-2. SWy-2 clay mineral exhibits a substantial adsorption capacity for TC, indicating its potential as an effective sorbent to mitigate antibiotic contamination in estuaries and nearby coastal areas. The observed effects of pH and ionic strength on TC adsorption have implications for the environmental fate and transport of antibiotics. The pseudo-second-order kinetic model and Langmuir isotherm equation provide valuable insights into the adsorption behavior and capacity of TC on SWy-2. Characterization analyses support the involvement of electrostatic interactions and chemical bonds in the SWy-2-TC adsorption mechanism.