Uranium plants

Phytoremediation methods for radionuclide decontamination do not involve hyper-aeeumulators, except possibly for uranium. Plants require a long period of eontact with a contaminant to evolve the ability to hyper-aeeumulate, and most uranium ores are located underground and so are not in eontaet with plants. Soils with high concentrations of uranium are present only where uranium is or has been mined or processed, but these have only been in existenee for a few deeades. 

Occasionally, the water used for solution makeup to the scrub or strip circuits, because of impurities, can cause subsequent emulsions and cruds. At one uranium plant in South Africa, deionized water was used to prepare the ammoniacal strip solution, rather than normal plant water, which tended to cause crud formation [53,54]. 

Some of the important but expensive rare metals are usually extracted as by-products of other metal separation processes. Selenium and tellurium are recoverable from copper refinery slime by pressure leaching (M40), scandium from uranium plant iron sludge (R15), uranium from gold cyanida-tion residues (G3), silver from aqueous chlorination process for the treatment of slimes, and gravity concentrates from gold ores (V2). A host of other processes are in use. 

The oxidizing atmosphere during the pretreatment of the ore helps to break up chemically the naturally occurring stable bonds in the solid, resulting in better dissolution rates. In a process developed for the recovery of scandium from uranium plant iron sludges (R15), the calcination of the sludge at 250°C was found to be very effective in the removal of organic materials and appreciably decreased the consumption of acid. 

When the component of interest is moisture content, special precautions must be taken to keep the sample dry so that moisture is not absorbed. Collecting samples in the rain without providing proper protection for them will obviously produce a bias. Gy (1992, pp. 295-296) reports that in a particular uranium plant, samples are handled and split in special climate-controlled environments to avoid changes in moisture content. 

Leaching and Extraction of Mineral Values from High Concentration of Solids A uranium plant had 10 large slurry tanks for leaching and extraction (approximately 14 m in diameter and 14 m high). They had about 14,000-m capacity. 

Fig, 2.3. Pachuca leaching tanks at Western Reefs Uranium Plant, South Africa (Arden, T.V. Ref. 1). 

Fio. 2.6. Counter-current decantation washing at the Port Pirie Uranium Plant (Almond, J.N. Ref. 4). 

One of the resin poisons of considerable importance in the South African uranium plants is the very stable cobalti-cyanide complex, or series of complexes, which form as a result of leaching the ore with cyanide solutions. These are used for the extraction of gold before the final leach with sulphuric acid for uranium extraction. The cobalti-cyanide complex can sometimes be removed from the resin by treatment with 2M potassium thiocyanate solution. This is expensive and not always satisfactory under plant conditions since it is beheved that several different compounds are responsible, some of them polymeric complexes and some are retained by the resin to a greater extent than others. The most satisfactory procedure is to prevent the absorption of cobalti-cyanide by removing it from the ore. This is accomplished by means of a water wash of the ore between cyanida-tion and sulphuric add leaching. However, cobalt poisoning remains a problem at some of the South African refineries, particularly that at West Rand. The resin is in fact usually replaced when its cobalt content reaches 2-5 per cent. ... 

When a is close to 1 the minimum reflux ratio is large. At the feed point in the uranium plant enriching to 90% the minimum reflux ratio is 29,100, but at the product end of the... 

The uranium content in plants can serve for monitoring contaminants in the environment (Caldwell et al. 2012). Samples of plants, soil, sediments, water, and common biota were collected from flve distinct sites in the vicinity of a uranium processing facility with the objective of studying transport pathways and selecting the plants that are efficient bioaccumulators of uranium. Plant root samples were dipped... 

In 1997, only two phosphate facilities in Louisiana produced 950,000 kg of commercial uranium, which accounted for about 16% of the uranium produced internally in the USA. The Department of Energy (DOE) refers to these facilities as Nonconventional Uranium Plants (Connett, 2003). 

On the other hand, as discussed later, uranium prices and plutonium credits are expected to rise over the life of the plant whilst fabrication costs per kg and reprocessing costs per kg should fall as a result of technical progress and the increasing scale of plants. The latter feature affects the cost of natural uranium plants with their relatively low burn-up (9000-10,000 MWd/tU) more than enriched reactors such as LWRs. If account of all these factors is taken the minimum economic size of HWRs is substantially reduced and HWRs which have costs equal to those of LWRs at the beginning of their life reach substantially lower costs than LWRs at the end of their life (and integrated over the whole life) as illustrated in Fig. 11,... 

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