Apatite HFSEs

The Phalaborwa complex ia the northeastern Transvaal is a complex volcanic orebody. Different sections are mined to recover magnetite, apatite, a copper concentrate, vermicuhte, and baddeleyite, Hsted in order of aimual quantities mined. The baddeleyite is contained in the foskorite ore zone at a zirconium oxide concentration of 0.2%, and at a lesser concentration in the carbonatite orebody. Although baddeleyite is recovered from the process tailings to meet market demand, the maximum output could be limited by the requirements for the magnetite and apatite. The baddeleyite concentrate contains ca 96% zirconium oxide with a hafnium content of 2% Hf/Zr + Hf. A comminuted, chemically beneficiated concentrate containing ca 99% zirconium oxide is produced also. 

The silicate minerals account for aU the HREE budget and 50-90% of the LREE, strontium, and Zr-Hf in apatite-free peridotites. 

From a materials perspective there are two possible reasons why dental enamel shows the large variations in mechanical properties shown in figure 1 firstly, chemical variations in apatite composition and, secondly, changes in enamel structure with position from the occlusal surface to the EDJ. The chemical composition of enamel can be examined with a lateral resolution of 1-10 pm with electron microprobe analysis. Enamel structure can be obtained with SEM. To perform an accurate microprobe analysis, natural and synthetic minerals are used as standards to calibrate the instrument. This is fairly routine for geologists and earth scientists who are able to obtain chemical compositions with an accuracy of <0.1% for a wide range of elements simultaneously (including Na, Mg, Al, Si, P, K, Ca, Ti, Cr, Mn, Fe, Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, Yb, Hf, Ta, Pb, Th, U, F and Cl). In enamel only a few of these (Na, Mg, Al, P, K, Ca, Ti, Cl and F) are above the detection limit. The Ti is likely to be an impurity or contaminant rather than a constituent of enamel. This technique does not work for lighter elements such as C, S, O and N which may be present in enamel. 

Fluoride is the most unique halide chemically and is the most common halide in igneous rocks. The igneous minerals fluorspar (CaF2) and apatite (Cas(F,OH)(P04)3) are both insoluble in water. Fluoride can substitute for OH- to some extent in soil minerals. This mechanism is probably also responsible for F retention by aluminium and iron hydroxides in acid soils. Fluoride also associates strongly with H+. HF is a weak acid, pK = 3.45. 

Information about the salinity of a magmatic volatile phase based on apatite chemistry can be attained only if the ratio of hydrogen to other cations in the volatile phase is known or assumed because ratios of CI/H2O and F/H2O yield fugacity ratios of HCI/H2O and HF/H2O, respectively and not salinity. 

Figure 28. Apatite-fluid partitioning, (a) Plot of logs of activity ratios (HF/H2O versus HCI/H2O) in fluid with composition fields of apatite indicated. From Zhu and Sverjensky (1991). (b-d) Isopleths showing mole fractions of apatite components calculated from data in (a) and assuming ideal mixing. Note that high concentrations of F-apatite are possible in fluids considerably more dilute in HF than is the case for Cl-apatite.

Korzhirtskiy MA (1981) Apatite solid solutions as indicators of the fugacity of HCl and HF in hydrothermal fltrids. Geochem Inti 3 45-60... 

Yaidley BWD (1985) Apatite composition and fugacities of HF and HCl in metamorphic fluids. Mineral Mag 49 77-79... 

Fowler SW, Buat-Menard P, Yokoyama Y, Ballestra S, Holm E, Van Nguyen H (1987) Rapid removal of Chernobyl fallout from Mediterranean sttrface waters by biological activity. Nature 335 622-625 Fujimaki H (1986) Partition coefficients of Hf, Zr, and REE between zircon, apatite, and liquid. Contrib Mineral Petrol 94 42-45... 

Schweitzer MH, Johnson C, Zocco TG, Homer JR, Starkey JR (1997) Preservation of biomolecules in cancellous bone of Tyrannosaurus rex. J Vert Paleo 17 349-359 Shaw HF, Wasserburg GJ (1985) Sm-Nd in marine carbonates and phosphates Implications for Nd isotopes in seawater and crastal ages. Geochim Cosmochim Acta 49 503-518 Shemesh A (1990) Ciystallinity and diagenesis of sedimentary apatites. Geochim Cosmochim Acta 54 2433-2438... 

Williams CT, Potts PJ (1988) Element distribution maps in fossil bones. Archaeometry 30 237-247 Wittmers LE, Aufderheide AC, Wallgren J, Rapp G, Alich A (1988) Lead in Bone IV Distribution of lead in the human skeleton. Arch Environ Health 43 381-391 Wood BJ, Blundy ID (1997) A predictive model for rare earth element partitioning between clinopyroxene and anhydrous silicate melt. Contrib Mineral Petrol 129 166-181 Wright J, Seymour R S, Shaw HF (1984) REE and Nd isotopes in conodont apatite variations with geologic age and depositional enviromnent. In Conodont Biofacies and Provincialism. Clark DL (ed) Geol Soc Am Spec Paper, p 325-340... 

Fujimaki H., 1986, Partition coefficients of Hf, Zr and REE between zircon, apatite and liquid. Contrib. Mineral. Petrol., 94, 42-45. 

As mentioned in Chapter 5, phosphate rock contains many impurities both in the apatite itself and in accessory minerals. These impurities partidpate in numerous side reactions. Most phosphate rocks have a higher Ca0 P205 ratio than pure fluorapatite. The additional CaO consumes more sulfuric add and forms more cal-dum sulfete. The HF formed by the reaction reads with silica and other impurities (Na, K, Mg, and Al) to form fluosilicates and other more complex compounds. A variable amount of the fluorine is volatilized as Sip4, HF, or both. The amount volatilized and the form depend m phosphate rock composition and process conditions. 

Apatite Ca5(F, aXP04)3 NaOH, Na2C03 Caustic starch, HF, lactic acid Oil acids and Ta oil R-710, 765, 845 Alcohols, pine oil ... 

Figure 2-37 Primary crystal formation in apatite-ieucite glass-ceramics. Crystals of NaCaPO precipitate as very tiny species at 580 C after 15 min. SEM (10s, 2.5% HF).

Figure 2-38 Crystallization of needlelike apatite in the volume of the glass-ceramic after heat treatment at 700 C/8h aixl additionally at 1050°C h. SEM (10 sec, 2.5% HF). SEM micrograph of a representative microstructure arrows indicate the needlelike apatite and its special circled environment (diffusion area).

Figure 2-41 SEM image (etching 10 sec, 3% HF) of the microstructure of apatite-leucite glass-ceramic for dental restorations. Heat treatment of the glass powder at SSO C/I h and 1050°C/1 h. The apatite crystals measure approximately 0.1-0.5 and 1-2 pm in diameter. The leucite crystals measure approx. 2 pm.

Figure 3-8 SEM image showing dendritic surface crystallization of leucite in leucite-apatite glass-ceramics at 900°C, heat-treated for 1 h, etched for 10 sec with 3% HF (Haiand et al., 2000c).

Figure 4-49 SEM image showing the microstructure of apatite-ieucite glass-ceramic (dentin). Etched in 3% HF for 10 sec.

Aplitic albite zone Albite. Quartz ("muscovitei Muscovite, Ta, oxide minerals, beryl, (apatite, tourmaline, cassiterite) (ihnentie, zircon, sulfides) Fine-grained undulating layers, fracture fillings, rounded blebs, diffuse veins Na (Be, Ta, Sn, Zr, Hf, Ti)... 

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