Effect and mechanism analysis associated with U(VI) removal by Pseudomonas cepacia immobilized on alfalfa fiber

The radioactivity of uranium tailings poses a significant risk to human health and the integrity of ecosystems. Thus, it is imperative that remediation be undertaken in order to safeguard the environment and facilitate sustainable resource utilization in the affected areas. In this study, Pseudomonas cepacia immobilized on alfalfa fiber was evaluated for its use in the removal of U(VI) from simulated uranium tailings wastewater. The maximum U(VI) adsorption efficiency by Pseudomonas cepacia immobilized on alfalfa fiber was 96.68% at 10 mg/L initial U(VI) concentration with a 480-min reaction time, exceeding the maximum U(VI) adsorption efficiency observed for alfalfa fiber or Pseudomonas cepacia alone. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy revealed microbial cells were successfully immobilized on the support materials. Additionally, the pH, dosage, temperature, and coexisting ions also influenced the adsorption efficiency of U(VI). The adsorption removal of U(VI) by Pseudomonas cepacia immobilized on alfalfa fiber was found to align with a pseudo-second-order kinetic model (R² = 0.984). The observed agreement between the kinetic data and the pseudo-second-order kinetic model indicates that the adsorption reaction was predominantly governed by chemical processes. The characteristics of the biosorbents prior to and following adsorption of U(VI) were investigated, revealing that the primary mechanisms for uranium removal were bioreduction (28.94% U(VI) was reduced to U(IV)) and biosorption. Thus, Pseudomonas cepacia immobilized on alfalfa fiber exhibited substantial practical potential as a novel biomaterial with low cost for use in environmental protection.