Phosphorite complexes

Apatite and other phosphorites constitute a substantial resource of rare earths. The REO content is highly variable and ranges from trace amounts to over 1%. Apatite- [1306-05-4] rich tailings of the iron ore at Mineville, New York, have been considered a potential source of yttrium and lanthanides. Rare-earth-rich apatites are found at the Kola Peninsula, Russia, and the Phalaborwa complex in South Africa. In spite of low REO content apatites could become an important source of rare earths because these are processed in large quantities for the manufacturing of fertilisers (qv). 

Owing to the stability of the uranyl carbonate complex, uranium is universally present in seawater at an average concentration of ca. 3.2/rgL with a daughter/parent activity ratio U) of 1.14. " In particulate matter and bottom sediments that are roughly 1 x 10 " years old, the ratio should approach unity (secular equilibrium). The principal source of dissolved uranium to the ocean is from physicochemical weathering on the continents and subsequent transport by rivers. Potentially significant oceanic U sinks include anoxic basins, organic rich sediments, phosphorites and oceanic basalts, metalliferous sediments, carbonate sediments, and saltwater marshes. " ... 

Research on the benthic phosphoms cycle and phosphorites formation in particular was intensified especially in the seventies to early nineties of the last century (e g. Burnet 1977 Burnett and Froelich 1988 Burnett and Riggs 1990 Nolton and Jarvis 1990 Follmi 1996 Gleim et al. 2000). All present result clearly substantiate that the process of phosphogenesis (= the authigenic formation of carbonate fluorapatite - CFA) is highly complex and not completely understood. However, hydroxy-apatite may be the primary authigenic P-... 

Tribasic calcium phosphate can be obtained directly from rock and minerals such as apatite, a complex and impure form of calcium phosphate, or phosphorite, a mineral that... 

Figure 25. Laser-excited luminescence in fossil fish teeth from phosphorite beds in the Senonian Mishash formation, Israel. (A) Uranyl emission at 77 K indicating uranyl aqueous complexes. (B) after annealing at 1000 K the uranyl complexes are dehydrated . (C) Same as in A but spectrum collected at 300 K. From these data it was concluded that the uranyl resides in organic material and not in the apatite structure. Modified after Gaft et al. (1996b).

In addition to change of concentration by mixing processes, the relative concentrations of lanthanides may be changed by oxidation-reduction reactions followed by diflFerential mineral uptake (as for manganese nodules (4, JO), or phosphorites (4)), or by diflFerential solubility or ion-exchange processes aflFected by variations in ionic radius. The lanthanides are the group of elements for which such processes are known to be least effective only two, cerium and europium, are expected to exhibit stable ions other than trivalent, and as summarized by Moeller et aL (13), lanthanide complexes are typically weak, and show within the series, only modest variations in strength. 

A little less sulphuric acid is used than indicated by Equation 12.1. This is to ensure that the product contains no free sulphuric or phosphoric acids which would render it hygroscopic and lead to caking. In practice not all the fluorine is removed from the rock and some hydrofluoric acid can be produced by reaction with silica impurities (12.2). The efficiency of reaction (12.1) depends on the grade of phosphorite rock which is used, and is limited by the crystallisation behavionr of the by-product, calcium sulphate. The latter is complex and is influenced, not only by the silica and fluorine, but by the level of the other impurities which are present. The phosphate rock (phosphorite) should contain not more than about 1% MgO and 5% AI2O3 + Fe203, and the content of other impurity (potentially toxic) elements such as Cd, Se and Ni must be very low. 

Carbonate-fluor-apatite accommodates large quantities of trace elements, mainly uranium, which are potential luminescence centers. It has been proposed that uranium may occur in phosphorites in the following forms as a separate uraninite phase as an adsorbed or structurally incorporated uranyl ion as dominantly a U" replacement for Ca " " to be structurally incorporated appreciably as both and U (Altschuler 1980). The steady-state luminescence of water-organic comlexes is strong and conceales the weaker characteristic luminescence of uranium containing centers, which can be detected by the difference in decay times only. The reason is that the decay time of water-organic complexes is characterized by two time intervales less than 30 ns and more than 10 ms. Since... 

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