Efficiency and mechanism of sorption of low concentration uranium in water by powdery aerobic activated sludge

Abstract

In this study, powdery aerobic activated sludge (PAAS) was first prepared, and the removal rate, sorption capacity and mechanism of sorption uranium on PAAS was investigated. Before and after sorption, the surface morphology and structure of PAAS were characterized systematically using the Fourier transform infrared spectrometer (FTIR), the X-ray photoelectron spectrometer (XPS), and the scanning electron microscope (SEM-EDX). In this work, the sorption mechanism and efficiency of uranium on the PAAS was study with static batch and ion exchange experiments, meanwhile, some influencing factors such as solution pH, contact temperature, adsorbent dose of PAAS and different initial uranium concentrations were studied. The batch sorption experiments illustrated that pH had a little effect in the process of sorption uranium on PAAS and it has a good removal capacity in a wide pH range (pH = 3–8). When the pH of solution was 7, the removal efficiency of about 93% for uranium when the initial concentration of uranium was 10 mg/L and the concentration of PAAS was 1 g/L. The XPS demonstrated that there are some active functional groups for instance carboxyl (-COOH), Hydroxyl (-OH), Amino (-NH2) and so on in the PAAS, and that all can combine with uranium. After sorption, there is an obviously U signal (marked in green) in the PAAS by charactering with the FE-SEM. In addition, kinetic parameters were fitted by the first-order kinetic (R2 = 0.9738) model and the second-order kinetic model (R2 = 0.9998), the pseudo-secondary kinetic model was better to illustrate the sorption process, so the chemical action was dominant, and existed physical sorption. The sorption isotherms date of PAAS was well-fitted to the Langmuir model (R2 = 0.9688). In the experiment of ion exchange, the concentration of Na+ in the solution hardly changed, the release of the other three ions was K+ <Mg2+ <Ca2+. Therefore, the PAAS could be effectively used as a potential adsorbent for uranium sorption from wastewater.