Uranium in phosphates

Norman JD, Stumpe LA, Trimm J, et al. 1983. Argon-plasma emission spectrometry of uranium in phosphatic materials (e.g., fertilizers). J Assoc Off Anal Chem 66 949-951. 

Woodis TC Jr., Trimm JR, Holmes JH, et al. 1980. Determination of uranium in phosphate rock and wet-process phosphoric acid by argon-plasma emission spectrometry. J Assoc Off Anal Chem 63 208-210. 

Phosphate rock deposits contain uranium (U), radium (Ra), thorium (Th), and other radionuclides as contaminants. Uranium in phosphate rock deposits throughout the world range from 3 to 400 mg kg (Guimond, 1978). It has been estimated that 1000 kg of Florida phosphate rock contains about 100 pCi each of" U and Ra and 4 pCi of °Th (Menzel, 1968). Some of these elements are retained in the HjPO and the remainder are transferred to the by-products during fertilizer manufacture. For instance it is estimated that 60% of the radioactivity in mined Florida phosphate rock remains with slime and sand tailings during beneficiation (Guimond and Windham, 1975). 

Cathcart, J.B., Uranium in phosphate rock. Geological survey Professional paper. No. 988-A, Washington, D.C. Geological Survey. 

Vucic, N., and Ilic, Z., Extraction and spectrophotometric determination of uranium in phosphate fertilizers. J. Radioanal. Nucl. Chem. Articles 129 (1989) 113-120. 

Tetravalent uranium can be precipitated from aqueous solution as the insoluble oxalate, fluoride, or phosphate. UF4 precipitated from aqueous solution contains water of crystallization. When this compound is heated to drive off the water, it is partially hydrolyzed to an oxyfluoride. The phosphate U3(P04)4 is soluble in hot, concentrated phosphoric acid and appears in this form when uranium in phosphate rock, Ca3(P04)2, is dissolved in sulfuric acid. 

Complex ions are also formed with citrate and anions of other organi acids, thiocyanate and phosphates. The phosphates are important in view c the occurrence of uranium in phosphate minerals, and species such a U02H2PC>4 and U02H3P0 +, and at high concentrations anionic coir plexes are known. 

Today, no active optode is capable of application in industrial environments for process control. Indeed, the required properties such as reversibility, durability, and reliability are very difHcult to obtain. Nevertheless, various approaches have been made in the laboratory, eg, pH measurements in acidic or basic media [34], the detection of uranium in phosphate medium [166], and the continuous measurement of the concentration of vapors in polar organic solvents using blue thermal paper placed in a flow-through cell [153]. Moreover, the features of the flow-injection analysis (FIA) technique [69, 70] are being adapted in the laboratory to process control. 

Barisic, D., Lulic, S. andMiletic, P. (1992). Radium and uranium in phosphate fertilizers and their impact on the radioactivity of waters. Water Research, 26(5) 607-611. Bodelier, Paul, L.E., Peter Roslev, Thilo Henckel and Peter Frenzel (1999). Stimulation by ammonium-based fertilizers of methane oxidation in soil around rice roots. Nature, 403(6768) 421-424. 

Andreou, G., Efstathiou, M., and PashaUdis, I. (2012). A simplified determination of uranium in phosphate rock and phosphogypsum by alpha spectroscopy after its separation by liquid-extraction, J. Radioanal. Chem. 291, 865-867. 

Uranium, not as rare as once thought, is now considered to be more plentiful than mercury, antimony, silver, or cadmium, and is about as abundant as molybdenum or arsenic. It occurs in numerous minerals such as pitchblende, uraninite, carnotite, autunite, uranophane, and tobernite. It is also found in phosphate rock, lignite, monazite sands, and can be recovered commercially from these sources. 

Uranium is present in small (50—200 ppm) amounts in phosphate rock and it can be economically feasible to separate the uranium as a by-product from the cmde black acid (30% phosphoric acid) obtained from the leaching of phosphate for fertilizers (qv). The development and design of processes to produce 500 t U Og per year at Ereeport, Louisiana have been detailed (272). 

Uranium(VI) phosphates have been widely investigated and can be divided in several stmcture types orthophosphates M(U02) (PO4) XH2O, hydrogenphosphates M(U02) (H P04) XH2O, pyrophosphates U 0 P202, metaphosphates (U02) (P03) XH2O, and polyphosphates (U04,(PP,).- Hp (188). 

Determination of uranium with cupferron Discussion. Cupferron does not react with uranium(VI), but uranium(IV) is quantitatively precipitated. These facts are utilised in the separation of iron, vanadium, titanium, and zirconium from uranium(VI). After precipitation of these elements in acid solution with cupferron, the uranium in the filtrate is reduced to uranium(IV) by means of a Jones reductor and then precipitated with cupferron (thus separating it from aluminium, chromium, manganese, zinc, and phosphate). Ignition of the uranium(IV) cupferron complex affords U308. 

In most other countries regulations or recommendations for a decrease of the radon daughter concentrations in homes have not been established. In USA and Canada limits have been given only for special cases, for example building on waste from uranium and phosphate industries (Atomic Energy Control Board, 1977 EPA, 1979 EPA, 1980). In Finland, there are general recommendations for homes (Finnish Radon Commission, 1982). 

In a final example of the use of a sliding activity path, we calculate a speciation diagram, plotted versus pH, for hexavalent uranium in the presence of dissolved phosphate at 25 °C. We take a 10 mmolal NaCl solution containing 1 mmolal each ofUO +, the basis species for U(VI), and HPO4... 

Lanthanides are also found as minor components in other ores, particularly in association with uranium or in phosphate rock. These are often coextracted with the major product and can be economically recovered from the waste streams resulting from the uranium or phosphoric acid extraction. 

The concentration of uranium contained in phosphate rocks (50 200 ppm) is higher than that in seawater (see section 12.3.5). Even though economic recovery of uranium from phosphate rock is difficult, several phosphoric acid plants include operation of uranium recovery facilities. 

Vanadium is not found in its pure state. Small amounts of vanadium can be found in phosphate rocks and some iron ores. Most of it is recovered from two minerals vanadinite, which is a compound of lead and chlorine plus some vanadium oxide, and carnotite, a mineral containing uranium, potassium, and an oxide of vanadium. Because of its four oxidation states and its ability to act as both a metal and a nonmetal, vanadium is known to chemically combine with over 55 different elements. 

Our study of sedimentary apatite from Israel proved that laser-induced time-resolved luminescence is a perspective tool for evaluation of sedimentary phosphate ores with high dolomite content (Gaft et al. 1993b). The idea was based on the fact that natural apatite contains several characteristic luminescence centers, which enables us to differentiate it from dolomite. The most widespread characteristic luminescence center in sedimentary apatite is uranyl (U02) with a typical vibrational green band luminescence under nitrogen laser excitation (Fig. 8.13a,b). Nevertheless, it appears that such luminescence is absent in phosphate rock samples from Florida, evidently because of extremely low uranium concentration (Fig. 8.13c,d). hi order to find potential liuninescence centers, ICP-MS analyses of Florida phosphates was accompHshed. From discovered REE, theoretically Dy + is the best candidate... 

Oxo Ion Salts. Salts of oxo anions, such as nitrate, sulfate, perchlorate, iodate, hydroxide, carbonate, phosphate, oxalate, etc, are important for the separation and reprocessing of uranium, hydroxide, carbonate, and phosphate ions are important for the chemical behavior of uranium in the environment (150—153). 

Chemex [Chemical exchange] A process for separating uranium isotopes, based on the equilibrium between U3+ and U4+ in aqueous solution. U-238 concentrates in the LP+ state and U-235 in the U4+. Uranium in the two valence states is separated by solvent extraction into tributyl phosphate. Developed and piloted in France but not commercialized. 

There are wide variations from the values presented in the table, particularly in areas where uranium minerals are more concentrated. Concentrations of uranium in Louisiana soils ranged from 2.35 to 3.98 pg/g (1.6-2.7 pCi/g) (Meriwether et al. 1988), while uranium concentrations in phosphate rock in north and central Florida ranged from 4.5 to 83.4 pCi/g (6.8-124 pg/g) (EPA 1985J). 

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