Pilot-scale removal of uranium from uranium plant wastewater using industrial iron powder in the ultrasonic field

Boosted charge transfer in a naturally formed Ca(Al2Si2O8)/Fe2O3 heterojunction for piezocatalytical formation of H2O2 and solidification of U(VI)

Energy and environmental issues make the generation of H2O2 and the separation of U(VI) from water very important topics. In this work, we disclosed a low-cost, high-efficiency method for separating U(VI) from water based on the naturally formed catalyst (red volcanic stone powders, RVSP) of Ca(Al2Si2O8)/Fe2O3 heterojunction through a piezocatalytic pathway induced by ultrasonication. The charges were found to be elevatedly separated due to the formation of the heterojunction. It is found that under ultrasonication, charges were effectively separated and then reacted with water to form H2O2 with a high yield of 196.7 μmol·g-1 in 4 h, which further solidifies U(VI) to form a solid of UO2O2. The removal rate of U(VI) in water reached 96 % (50 ppm) within 150 min. Furthermore, the results calculated by VASP show that the cyclic variation of the conduction bands under a cyclic force field facilitates the charge separation, and thus may promote piezocatalysis. Most importantly, the application study in real seawater indicates that U(VI) piezocatalysis based on natural minerals has great potential. This work presents a comprehensive investigation of U(VI) piezocatalysis by Ca(Al2Si2O8)/Fe2O3 and provides a new idea for piezocatalytic extraction of uranium.

Degradation of carbamazepine from wastewater by ultrasound-enhanced zero-valent iron -activated persulfate system (US/Fe0/PS): kinetics, intermediates and pathways

Carbamazepine (CBZ) is a common antiepileptic drug. CBZ enters the environment through unreasonable and standardized ways such as human and animal metabolites, discarded drugs, and more than half of its metabolites are released into the environment. Since CBZ is not easy to be degraded, continuous input of CBZ into the water environment will cause long-term impact on the water ecological environment and seriously endanger human health. Aiming at how to degrade wastewater containing carbamazepine, studies were conducted on the degradation of carbamazepine by ultrasound/zero-valent iron/persulfate system (US/F e 0 /PS). Firstly, the removal effects of carbamazepine by different systems, such as ultrasound/sodium persulfate (US/PS), zero-valent iron/persulfate system (F e 0 /PS) and US/F e 0 /PS, were compared; Secondly, the influence of factors, such as ultrasonic power, sodium persulfate dosage, zero-valent iron dosage, reaction temperature, pH, etc., on the reaction was investigated by the control variables method. Results show that ultrasound power, PS concentration, pH and temperature have a great influence on the removal of carbamazepine in US/Fe0/PS reaction system. Besides, the optimum parameters for degradation of carbamazepine with US/F e 0 /PS reaction system were determined ([CBZ]0 = 0.025 mM; [PS]0 = 0.4 mM; Fe0 = 4.0 mg/L; ultrasonic power = 40 W; T = 30 ℃; initial pH = 5.0). Finally, the intermediates and degradation pathways of carbamazepine by US/F e 0 /PS system were analyzed and speculated. It was inferred that two intermediates were generated during the degradation of carbamazepine, mainly through the ring opening and decyclization of piperazine rings. It was proved that process US/F e 0 /PS has a very important application value in the degradation of antibiotic-containing wastewater.

Efficacy and mechanisms of δ-MnO2 modified biochar with enhanced porous structure for uranium(VI) separation from wastewater

Even though uranium (U) is considered to be an essential strategic resource with vital significance to nuclear power development and climate change mitigation, U exposure to human and ecological environment has received growing concerns due to its both highly chemically toxic and radioactively hazardous property. In this study, a composite (M-BC) based on Ficus macrocarpa (banyan tree) aerial roots biochar (BC) modified by δ-MnO2 was designed to separate U(VI) from synthetic wastewater. The results showed that the separation capacity of M-BC was 61.53 mg/g under the solid - liquid ratio of 1 g/L, which was significantly higher than that of BC (12.39 mg/g). The separation behavior of U(VI) both by BC and M-BC fitted well with Freundlich isothermal models, indicating multilayer adsorption occurring on heterogeneous surfaces. The reaction process was consistent with the pseudo-second-order kinetic model and the main rate-limiting step was particle diffusion process. It is worthy to note that the removal of U(VI) by M-BC was maintained at 94.56% even after five cycles, indicating excellent reusability and promising application potential. Multiple characterization techniques (e.g. Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), Brunauer-Emmett-Teller (BET) and X-ray Photoelectron Spectroscopy (XPS)) uncovered that U(VI) complexation with oxygen-containing functional groups (e.g. O-CO and Mn-O) and cation exchange with protonated ≡MnOH were the dominant mechanisms for U(VI) removal. Application in real uranium wastewater treatment showed that 96% removal of U was achieved by M-BC and more than 92% of co-existing (potentially) toxic metals such as Tl, Co, Pb, Cu and Zn were simultaneously removed. The work verified a feasible candidate of banyan tree aerial roots biowaste based δ-MnO2-modified porous BC composites for efficient separation of U(VI) from uranium wastewater, which are beneficial to help address the dilemma between sustainability of nuclear power and subsequent hazard elimination.