Adsorption kinetics of three fluoroquinolone carboxylic acids on red clay soil in five types of aqueous solutions

View large Download slide View large Download slide Close modal The adsorption and desorption kinetics of antibiotics on natural soils in various aqueous solutions are crucial for understanding their occurrence, transport, and bioavailability in the environment. This study investigated the adsorption and desorption kinetics of three fluoroquinolone carboxylic acids (FQCAs), namely ciprofloxacin, ofloxacin, and levofloxacin, on red clay soil using batch experiments conducted with pure water, treated wastewater effluent, lake water, river water, and stormwater runoff. The research identified pH, electrical conductivity (EC), and organic suspended solids (OSS) as primary water quality parameters that negatively impacted the adsorbed and desorbed masses of FQCAs at equilibrium. Higher pH, EC, and OSS significantly reduced the initial adsorption rates and adsorption efficiencies and promoted initial desorption and desorption efficiencies. FQCAs adsorption processes exhibited a rapid phase mainly governed by external mass transfer and a slower phase primarily limited by intra-particle diffusion, both influenced by boundary layer effects. The adsorption removal of FQCA's ranged from 65.82 to 98.33%, but desorption was only 1.35–3.09%. These findings highlight the potential of red clay soil as an effective and environmentally friendly adsorbent for mitigating FQCA pollution. Future research should focus on investigating FQCA degradation after adsorption in soil and their transport dynamics under diverse field conditions. Measured q e and average adsorption rate over the first 20 s showed strong negative correlations with pH (pH > 7), electrical conductivity, and organic suspended solids. The q e of ciprofloxacin, ofloxacin, and levofloxacin was higher in pure water (PW) and lower in treated wastewater and lake water. Both adsorption and desorption exhibited a fast phase and a slower phase. High adsorption capacities and low desorption were observed. Lower desorption was observed in PW.