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Nuclear reactors and their fuel cycles
Published in R.J. Pentreath, Nuclear Power, Man and the Environment, 2019
Uranium ore usually needs to be at least 0.05% by weight of U3O8 if it is to be mined economically at present. The uranium is extracted and begins its cycle (figure 4.6) by being concentrated in a process referred to as milling. The ore is crushed and ground and the uranium leached out by a variety of methods, usually dependent upon the lime content of the ores. There then follow a variable number of complex treatments involving some form of decantation, filtration, flocculation and so on, culminating in a recovery process achieved by chemical precipitation, ion exchange or solvent extraction. These processes result in a dried powder containing 70 to 90% by weight of uranium as U3O8, or its equivalent. When it is in the form of ammonium diuranate it is referred to as ‘yellow-cake’. The milling process thus separates the uranium isotopes from the original ore, the majority of the uranium daughter products remaining in the depleted ore – the tailings. Tailings are usually pumped into ponds where solids can settle out and shorter-lived radionuclides decay away. The resultant clear liquid may be filtered, neutralized, and discharged into streams or allowed to evaporate off. The final waste product inevitably contains a large quantity of radium and its daughters, their rate of emanation being dependent upon the exposed surface area and weather conditions -particularly wind speeds. There may be further complications when the tailings are extremely fine and prone to being wind blown.
Urban Sources of Micropollutants: from the Catchment to the Lake
Published in Nathalie Chèvre, Andrew Barry, Florence Bonvin, Neil Graham, Jean-Luc Loizeau, Hans-Rudolf Pfeifer, Luca Rossi, Torsten Vennemann, Micropollutants in Large Lakes, 2018
Jonas Margot, Luca Rossi, D. A. Barry
As the pollution in runoff water is in many cases (apart from pesticides) associated with particulate matters (e.g., for heavy metals, PAHs, PBDEs) (Gasperi et al., 2014), most of the technologies proposed for the treatment of such waters are mainly based on particle removal. For an optimal treatment, ideally, a combination of three processes is recommended: decantation, filtration and adsorption. The role of decantation is to remove most of suspended solids (TSS) by using either settling tanks or hydrocyclones. As the settleability of TSS is often low in stormwater, a filtration step through a bed of sand, organic matter (vegetation, compost, wood chips, etc.), of soil and/or of other media (textile, zoelite, activated carbon, etc.) is then recommended. The goal of the filtration is: (i) to retain the remaining fine particles and the pollutants associated; (ii) to promote the biodegradation of the pollutants by the microorganisms present in the filter; and (iii) to adsorb the dissolved pollutants onto the filter substrate, which can be organic (e.g., compost, soil, activated carbon) or mineral (e.g., zeolites, iron or aluminium oxides, ion-exchange resin). More detailed information on the design of such processes can be found, for instance, in the ASTRA guideline (ASTRA, 2015).
Decolorization of water through removal of methylene blue and malachite green on biodegradable magnetic Bauhinia variagata fruits
Published in International Journal of Phytoremediation, 2022
Okan Bayram, Elif Köksal, Fethiye Göde, Erol Pehlivan
The BV fruits were collected and they were cut into small pieces (2–4 mm) with a scissor. The pieces were washed several times with deionized water. The pieces were dried in air for a day, kept in an oven at 60 °C for 24 h, then these pieces were pulverized with a blender and placed in a desiccator. The pulverized particles were dried for 4–5 h at 60 °C again, then they were stored in plastic containers for sorption studies. 5 g dried biosorbent was added into a batch type reactor. Then, FeCl3.6H2O (6 g) and FeSO4.7H2O (4 g) were added to the reactor containing 50 mL pure water. To adjust pH of the reaction medium, 1 M solution of ammonia is added to the reactor vessel in drops. The pH of the reaction medium was 10 and the reaction was held at 70 °C for 1 h. During the experiment, the suspension in the reaction vessel was stirred for 1 h to obtain nM-BVf. nM-BVf was filtered under vacuum, after that, washing operations with deionized water were carried out several times. Then, the nM-BVf suspension was settled from the suspension by decantation. The nM-BVf survived at 70 °C in an oven all night long (Mahdavi et al.2013, Koesnarpadi et al.2020, Abate et al.2021). The possible reaction is described below.
Biosorption of methylene blue and malachite green on biodegradable magnetic Cortaderia selloana flower spikes: modeling and equilibrium study
Published in International Journal of Phytoremediation, 2021
Şerife Parlayıcı, Erol Pehlivan
CSFs were washed in pure water several times. The spikes obtained in herbal form were meshed (2-4 mm) with a knife and then dried in the oven. nM∞CSFs were synthesized by a simple chemical precipitation method (Figure 2). Grinded CSFs (5 g) were put in a batch-wise reactor and then FeCl3·6H2O (6 g) and FeSO4·7H2O (4 g) were transferred into the reactor containing 50 mL pure water. The pH of the reaction medium was adjusted to 10 by adding 1 M ammonia solution by dropwise and the reaction was held at 50 °C for 1 h. During the experiment, the suspension in the flask was stirred for 1 h. nM∞CSFs was filtered in a vacuum and then washed with pure water for several times to dispose of unnecessary dirtiness. Then the nM∞CSFs suspension was settled from the mother liquid phase by decantation. The nM∞CSFs were dried during the night in an oven at 40 °C. The reaction occurs as shown in Equations (1)–(5) (Mahdavi et al. 2013):
Ultrasound-assisted synthesis of 1, 8-dioxodecahydroacridine derivatives in presence of Ag doped CdS nanocatalyst
Published in Journal of Dispersion Science and Technology, 2020
Divya Verma, Vikash Sharma, Shubha Jain, Gunadhor Singh Okram
In a typical synthesis, 2 mmol of Cd(NO3)2·4H2O (≥98%, Merck) and 7 mmol of thiourea (99%, Merck) as Cd and S sources, respectively, were dissolved in 50 mL of diethylene glycol (DEG, ≥98.5%, Merck). The mixture was transferred to a three-neck round bottomed flask (RBF) and heated in N2 atmosphere. The solution immediately turned gradually more and more yellowish in color at 97–100 °C indicating the formation of CdS NPs. This was maintained at 175–180 °C with a continuous flow of nitrogen gas for 2 h to complete the reaction. Then, the solution was allowed to cool naturally. The precipitate was removed from the suspension by 12 min centrifugation at 12,000 rpm and decantation. The precipitate was then dispersed in ethanol and subjected to 2 min of probe ultrasonication for uniform dispersion. The dispersed precipitate was then centrifuged for another 5 min at the same rpm, followed by 2 min of sonication. These cleaning steps were repeated three times. Finally, the transparent layer of ethanol was discarded and the precipitate was vacuum-dried at 60 °C for 1 h; this catalyst was denoted as CdS0. For Cd1-xAgxS, x = 0.02, 0.04, 0.06 catalysts (denoted as CdS2, CdS4 and CdS6 respectively), appropriate amounts of Cd(NO3)2·4H2O were replaced by AgNO3 (99%, Merck) while the other parameters remained the same.