Fertilizer manufacturing, uranium

In the fertilizer manufacturing scheme, the wet process phosphoric acid most commonly ensues from dissolution of sedimentary phosphate rock in sulfuric acid. Such acid solution contains around 1 g 1 1 uranium which is recovered as the byproduct. This task is accomplished by three well-proven extraction processes, some salient details of which are presented in Table 5.10. 

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). 

The aquilibrium in Eq. (19.4-5) is especially unfavomble at high temperatures, requiring an expensive cooling step before uranium extraction, followed by reheating before the phosphoric acid can be concentratnd to levels required for fertilizer manufacture.33 M... 

Lichens were applied to delineate the distribution of airborne chemical elements emitted by industrial plants such as metal works and foundries (Belandria et al., 1991 Kansanen and Venetvaara, 1991 Manninen et al., 1991 Perkins, 1992 Zanini et al., 1992 Galley and Lloyd, 1993 Caniglia et al., 1994 Jovanovic et al., 1995), chlor alkali plants (Makholm and Bennett, 1998), fertilizer manufacturers and strip mines (Palomaki et al., 1992 Tynnyrinen et al., 1992), mercury mines (Bargagli, 1990 Lupsina et al., 1992) and uranium mines (Fahselt et al., 1995 Jeran et al., 1995). 

Ring, R.J., Manufacture of phosphatic fertilizers and recovery of by-product Uranium—a. review. Report AAEC/E-355. Australian A.E.C. Res. Establ., Lucas Heights, 1975. 

An especially intriraing use of liquid-membrane technology, reported for the first time recently by Fox and Hayworth et al.," is the recovery of uranium from wet process phosphoric acid (WPPA). In the manufacture of fertilizer fiom phosphate rock, the acid is solubilized by treatment with sulfuric acid. In addition to HjP04, this crude leachate can contain up to 0.18 g/L of uranium. Under oxidizing conditions this occurs as the uranate ion, UO . Solvent extraction (SX) processes have been developed to recover die uranium values. One of the most common of these uses a mixture of di-(2-ethylhexyl) phosphoric acid (D2EHPA) and trioctylpbosphine oxide (TOPO) in kerosene solution. The chemistry of solvent extraction is as follows ... 

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