A Comparative study of the synthesis of calcium, strontium, barium, cadmium, and lead apatites in aqueous solution

Article abstract of DOI:10.1081/SIM-120030437

The aqueous syntheses of the hydroxy and halo apatites of calcium, strontium, barium, lead, and cadmium were explored. Because these cations represent the main group s- and p-fillers and a transition metal, they present different synthetic challenges. The alkaline earth cations and lead form hydrogen phosphates at slightly acidic and slightly basic conditions, the alkaline earths form the fluorides (MF₂) in the preparation of the fluoroapatites with excess fluoride, and ammonia is required for the preparation of the cadmium apatites through decomplexation. A variety of reagents were utilized with most of the derivatives, but, in general, the source of the cation was its nitrate or halide, and the phosphate is best provided as ammonium hydrogen phosphate. The requirements for pH, heating, and reaction time were also explored. A number of literature syntheses for pure phase apatites could not be reproduced: calcium iodoapatite, strontium fluoroapatite, and cadmium hydroxyapatite. Several apatites were prepared for the first time in aqueous solution: barium fluoroapatite, lead bromoapatite, and cadmium chloroapatite. The relative ease of formation of the compounds is rationalized with arguments based upon lattice and hydration energies.

Full text of DOI:10.1081/SIM-120030437

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A Comparative Study of the Synthesis of Calcium,
Strontium, Barium, Cadmium, and Lead Apatites in
Aqueous Solution
a
a
b
a
Natalie J. Flora , Keith W. Hamilton , Richard W. Schaeffer & Claude H. Yoder
a
Franklin & Marshall College , P.O. Box 3003, Lancaster, Pennsylvania, 17604, USA
b
Kutztown University of Pennsylvania , Kutztown, Pennsylvania, USA
Published online: 16 Nov 2010.
To cite this article: Natalie J. Flora , Keith W. Hamilton , Richard W. Schaeffer & Claude H. Yoder (2004) A Comparative
Study of the Synthesis of Calcium, Strontium, Barium, Cadmium, and Lead Apatites in Aqueous Solution, Synthesis and
Reactivity in Inorganic and Metal-Organic Chemistry, 34:3, 503-521, DOI: 10.1081/SIM-120030437
To link to this article: http://dx.doi.org/10.1081/SIM-120030437
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 3, pp. 503–521, 2004
A Comparative Study of the Synthesis of
Calcium, Strontium, Barium, Cadmium,
and Lead Apatites in Aqueous Solution
1
Natalie J. Flora, Keith W. Hamilton,
Richard W. Schaeffer, and Claude H. Yoder *
1
2
1,
1
Franklin & Marshall College, Lancaster, Pennsylvania, USA
Kutztown University of Pennsylvania, Kutztown, Pennsylvania, USA
2
ABSTRACT
The aqueous syntheses of the hydroxy and halo apatites of calcium, stron-
tium, barium, lead, and cadmium were explored. Because these cations
represent the main group s- and p-fillers and a transition metal, they
present different synthetic challenges. The alkaline earth cations and lead
form hydrogen phosphates at slightly acidic and slightly basic conditions,
the alkaline earths form the fluorides (MF ) in the preparation of the fluoro-
2
apatites with excess fluoride, and ammonia is required for the preparation
of the cadmium apatites through decomplexation. A variety of reagents
were utilized with most of the derivatives, but, in general, the source of
the cation was its nitrate or halide, and the phosphate is best provided
as ammonium hydrogen phosphate. The requirements for pH, heating,
*
Correspondence: Claude H. Yoder, Franklin & Marshall College, P.O. Box 3003,
Lancaster, PA 17604, USA; E-mail: claude.yoder@fandm.edu.
5
03
DOI: 10.1081/SIM-120030437
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

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5
04
Flora et al.
and reaction time were also explored. A number of literature syntheses for
pure phase apatites could not be reproduced: calcium iodoapatite, stron-
tium fluoroapatite, and cadmium hydroxyapatite. Several apatites were
prepared for the first time in aqueous solution: barium fluoroapatite,
lead bromoapatite, and cadmium chloroapatite. The relative ease of for-
mation of the compounds is rationalized with arguments based upon lat-
tice and hydration energies.
Key Words: Apatite; Aqueous synthesis; Pure phase; XRD.
INTRODUCTION
The class of double salts of formula M (PO ) X, where M is a divalent
4 3
5
metal ion and X ¼ OH, F, Cl, Br, I, is known as apatites and is of considerable
biological, environmental, and geological importance. As shown in Fig. 1,
pure phase apatites have been reported for only a fraction of the elements
that form þ2 cations. Although many of these compounds have been made
by high temperature solid state methods, some have also been prepared
much more easily in aqueous solution. We report here our attempts to prepare
the hydroxy and halo apatites of the most frequently studied cations—calcium,
strontium, barium, cadmium, and lead. We believe that this is the first com-
parative study of the aqueous synthetic routes that can be applied to these
compounds. We conclude with a rationalization of the difference in the
conditions that result in successful syntheses.
EXPERIMENTAL
Reagents were of analytical grade. The cation was introduced as the
halide MX , nitrate M(NO ) or, in several cases, as the carbonate MCO or
2
3 2
3
acetate M(C H O ) . Several sources of phosphate were used, including Na
3-
2
3
2 2
.
PO4 H O, NaH PO H O, (NH ) HPO , and H PO . The halides, if not
.
2
2
4
2
4 2
4
3
4
introduced with the cation, were used in the form of NaX or NH X. The
4
reagents were dissolved in distilled H O, stirred at room temperature or elev-
2
ated to a temperature up to 100 8C, and combined with stirring in a 500 mL
Erlenmeyer flask with a Bunsen valve in order to minimize CO contami-
nation. The pH was adjusted with 6 M NH , 6 M NaOH, or ethylenediamine.
2
3
The solution was heated and stirred for a period of time, after which it was
cooled to room temperature and vacuum filtered in a 30 mL glass crucible
of medium porosity. The precipitate was washed three times with 30 mL of

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505

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5
06
Flora et al.
cold distilled water and twice with 30 mL distilled water heated to 70 8C. The
sample was then dried in a 125 8C oven for at least 6 hr. Syntheses using car-
bonate-free water under N gave the same results and indicated that carbonate
contamination was not a problem.
2
The following preparations are for compounds not previously prepared in
aqueous solution:
BaApF. Ba(NO ) (1.40 g, 5.36 mmol) was dissolved in 60 mL H O at
3
2
2
9
0 8C. A sample of 0.079 g NH F (2.13 mmol) was added, and the pH of the
4
solution was elevated to 12 with 6 M NH and maintained at 90 8C. A pH
3
1
2 solution containing 0.424 g (NH ) HPO (3.21 mmol) was added, and the
4 2 4
pH was raised to 12 with ammonia. The solution was stirred and heated for
4 hr, and 0.392 g solid (91.6% yield) was filtered and dried. An XRD of
the dried compound was obtained with a figure-of-merit (FOM) of 4.6.
2
CdApCl. A 60 mL portion of a solution containing 0.781 g (5.66 mmol)
Na HPO was added to a 60 mL solution containing 1.73 g CdCl (9.44 mmol).
2
4
2
The temperature of both solutions was maintained at 80 8C before and after
combination. The pH was elevated to 7 with 3 M NH , and the solution was
3
filtered and dried in a 110 8C oven after stirring for 5 days at 80 8C. The reac-
tion produced 1.14 g solid (68.3% yield). An XRD of a dried sample of the
product was taken, which produced an FOM of 5.6 for CdApCl.
PbApBr. A 1.50 g sample of Pb(NO ) (4.53 mmol) was dissolved in
3
2
6
0 mL water at 90 8C and combined with 0.359 g (NH ) HPO (2.72 mmol)
4
2
4
and 0.186 g NaBr (1.81 mmol) in 60 mL water. The solution was maintained
at pH 9 with 6 M NH for 6 days and then filtered, and the 1.09 g product
3
(85.6% yield) was dried in a 110 8C oven. An XRD was obtained of the dried
product, which indicated that PbApBr had been formed with an FOM of 5.4.
The products were analyzed using a combination of techniques specific
to each compound, including x-ray diffraction (XRD), x-ray fluorescence
1
XRF), ICP-atomic emission (ICP), F NMR spectroscopy, colorimetric
9
(
phosphate analysis, and qualitative tests. Where possible, XRD was used
to determine the identity of the compound by comparing 2u values and
relative intensities with those reported in the International Center for Diffrac-
tion Data (ICDD) PDF-2 Sets 1-44 Inorganics (includes zeolites and minerals)
(
1994).
For XRD analyses, a Philips 3520 XRD system with a monochrometer and
a copper x-ray tube was used with Jade 6.0 data analysis. ICP analyses were
1
9
performed on an ICP SpectroCiros with Smart Analyzer Software. F nuclear
magnetic resonance spectra were examined in acidic solution (Varian Unity
300 operating at 282.23 MHz) to confirm the presence of fluoride.

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Apatites
507
Qualitative tests were also performed on samples dissolved in 3 M nitric
acid. The presence of chloride, bromide, and iodide was confirmed by
the formation of a precipitate upon the addition of silver nitrate. Phosphate pro-
duced a yellow precipitate upon the addition of several drops of ammonium
molybdate reagent.
RESULTS AND DISCUSSION
The most commonly used synthetic route to the apatites in aqueous solu-
tion is the reaction of sodium or ammonium hydrogen phosphate (Na HPO or
2
4
(
NH ) HPO ) or dihydrogen phosphate (NaH PO or NH H PO ) with a
4 2 4 2 4 4 2 4
metal halide or nitrate (with addition of sodium or ammonium halide if the
nitrate was used for the preparation of a halo apatite). This method was
employed for each of the hydroxy and halo apatites of calcium, strontium,
barium, cadmium, and lead. When this method was not successful, or if
other methods had been used by previous workers, then one or more of the
routes listed below as (c) through (h) were attempted. The routes can be sum-
marized as
(
a) (NH ) HPO þ MX .
3 2 4 2
4
2
4
2
(
b) M(NO ) þ (NH ) HPO þ NH X.
4
4
(
c) MX þ Na PO .
2
3
4
(
d) Hydroxy apatite þ NaX/NH X.
4
(
e) M (PO ) þ MX þ HX, followed by removal of acid.
3
4 2
(
f) M(C H O ) þ NaH PO þ MX.
3 3 4
2
3
2 2
2
4
(
(
g) MCO þ HX þ H PO .
3 2 4 2 4
h) M(NO ) þ (NH ) HPO þ NaX/NH X followed by evaporation to
4
dryness and continued heating above 100 8C.
3
2
Regardless of the source of phosphate, the concentration of PO in aque-
4
ous solution is controlled by the pH of the solution. From the dissociation con-
stants of phosphoric acid one can calculate that the principal constituents are
phosphoric acid below pH 2, dihydrogen phosphate between pH 2 and
7, hydrogen phosphate between 7 and 13, and phosphate above pH 13.
Obviously, as the pH increases the concentration of phosphate increases. If
the apatite is sufficiently insoluble, the concentration of phosphate required
for precipitation can be very low.
The pH of the solution can be adjusted by adding a weak base such as
ammonia or a strong base such as hydroxide ion. In most routes, NH is the
3
base of choice and in combination with ammonium ion from NH H PO (or
4
2
4
(
NH ) HPO ) forms a buffer system. The use of ammonium salts rather than
4 2 4

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5
08
Flora et al.
sodium salts is also advantageous because of their generally greater solubility
and consequent decreased potential for cation double salts. A disadvantage to
the use of ammonia is the formation of ammonia complexes with some tran-
sition metal cations. In this study, only cadmium forms an ammonia complex,
2
4
þ
Cd(NH3) (other species containing different numbers of ammonia per cad-
mium are also possible). These complexes can be destroyed by decomplexa-
tion by heating, thereby liberating ammonia.
The routes and conditions for successful preparations in our laboratory are
summarized in Table 1, which presents the route using the letters employed
above, along with any modifications to a particular set of reagents, as well
as the pH, temperature, and time of heating.
The preparation of several compounds, previously prepared in aqueous
solution, could not be replicated in our laboratory in spite of numerous
attempts to duplicate the reported conditions. When literature procedures
could not be duplicated, the preparation was repeated at least three to four
times as presented in the literature, and, generally, another four to six times
using different variations on the literature procedure. Several compounds,
whose aqueous syntheses had not been reported—cadmium bromoapatite,
cadmium chloroapatite, and barium fluoroapatite—were successfully
prepared. The syntheses will be discussed below.
Peak patterns of our products were compared with patterns of compounds
in the XRD database; FOM are given for all products whose patterns contained
all of the lines present in the reference pattern. Although the FOM was not the
determinative measure of goodness of fit, in general the FOM for syntheses
deemed successful was less than 6. For compounds not in the database or com-
pounds not previously prepared in aqueous solution, the cation percentage,
phosphate percentage, and the cation/phosphate ratio are given in Table 2.
In most cases the observed values of the metal to phosphate ratio were within
+0.02 of the theoretical value of 1.67 for the apatite. The metal and phosphate
percentages were generally within 0.7% of the theoretical values.
Calcium Apatites
Although the synthesis of CaApOH was attempted more than 20 times
using five different routes (Methods a, b, c, e, and f), it was not obtained
pure. In almost all cases, lines due to CaApOH appeared in the diffraction
pattern, but, depending on the synthesis, lines attributable to b-calcium
phosphate, monetite (CaHPO ), or Ca H (PO ) were present as well. It is
4
8
2
4 4
interesting to note that bone mineral, though comprised primarily of CaApOH,
also includes calcium phosphate and other calcium phosphate phases.
[1]

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Apatites
509
Table 1. Summary of reagents and conditions for successful preparations of apatites.
Cation/
anion
Temperature
(8C)
Route (alterations)
pH
Time
2
a, b, c, e (in presence of Cl )
Ca/OH
Ca/F
—
12
5
70
37
75
80
75
90
80
90
90
90
90
90
90
90
90
75
75
90
90
90
90
25
75
25
70
80
80
75
100
75
100
90
90
25
95
130
130
130
75
80
130
130
1–5 d
24 hr
18 hr
24 hr
1 d
2
a (in presence of I )
f
a (NaH
2
PO
4
, NaF)
6
2
Sr/OH
a (in presence of Cl )
b
b (NaH PO , in presence of F )
9
12
8
5 d
5 d
2
2
4
b (NaH
b (NaH
2
PO
PO
4
4
)
)
10
10
8
6 d
1 d
2
2
b (in presence of F )
2
b (in presence of F )
5 d
5 d
10
7
2
b (in presence of Br )
b (NaH PO , excess Cl )
2
b (in presence of F )
5 d
1 d
2
Sr/Cl
Ba/OH
7
2
4
12
12
10
10
9
1 d
5 d
b
a
a
Ba/Cl
1 d
2 hr
4 d
b (excess NH
b (excess NH
4
Cl)
F)
Ba/F
4
12
12
9
1 d
2 d
b (excess NH F)
4
Pb/OH
Pb/Cl
b
5 d
b
a (NaH PO )
9
2 hr
0.5 hr
1 d
2
2
4
a (NaH
2
PO
4
)
2
a
g
g
8
1 d
2
18 hr
2 hr
1 d
2
g (Pb(NO
a
3
)
2
)
7
Pb/F
9
1 d
b (NaH
b (NaH
2
PO
PO
4
4
, NaF)
, NaF)
6
1.5 hr
1 d
6 d
2
2
Pb/Br
b (excess NaBr)
b (excess NaBr)
b
9
2
0.5 hr
1 d
2
Pb/I
Cd/OH
b (NaH
b
b (in presence of I )
2
PO
4
, NaI)
4
0.5 hr
1 d
2 d
10
10
7
2
2
b (in presence of I )
a (NaH PO )
2 d
5 d
Cd/Cl
7
2
4
a (NaH
a
a (excess NaBr)
2
PO
4
)
7
7 d
1 d
Cd/F
Cd/Br
8
7
2, 3, 4 d

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10
Flora et al.
Table 2. Characterization data for compounds not previously prepared in aqueous
solution or not present in XRD database.
%
M
%PO4
XRD
(FOM)
M/P ratio by
ICP
Formula
Calcd
Found
Calcd
Found
Cd (PO ) F
5 4 3
n/a
n/a
5.0
4.6
6.8
1.741
1.657
1.675
1.675
1.689
64.9
60.6
74.0
69.3
63.7
68.0
62.5
73.6
70.9
64.2
32.9
30.7
20.3
28.8
32.3
30.2
30.9
19.3
32.4
32.1
Cd
Pb
Ba (PO ) F
5
(PO
4
)
3
Br
5
4 3
(PO )
Br
5
4 3
Cd (PO ) Cl
5 4 3
CaApCl was not produced in pure form from the reaction of calcium
chloride with (NH ) HPO under any of our conditions, which included the
4
2
4
use of pH 5 through 12, temperatures between 25 and 125 8C, reaction
times from 3 hr to 5 days, evaporation of the water from solution, and the
use of 20 : 1 molar ratios of chloride to calcium (using HCl, sodium chloride,
or ammonium chloride). The product of these reactions in most cases con-
tained CaHPO , Ca H (PO ) , or b-calcium phosphate. The results of the pre-
4
8
2
4 4
sent study therefore support the conclusions of LeGeros that “the maximum
chloride incorporation in hydroxylapatite in aqueous systems is 40 mol per-
[2]
cent, while 100% can be incorporated in solid state systems” and Narasaraju
et al. who found that “wet methods are unsuitable for preparation of pure
[
3]
chlorapatite.”
CaApF has been synthesized in aqueous solution
[
4–8]
as well as by other
We found that CaApF formed in the reaction of calcium
[
6,9–11]
methods.
nitrate with ammonium hydrogen phosphate and sodium fluoride: (a) in the
presence of the chloride ion, even when the chloride concentration was 10
times the stoichiometric concentration of fluoride, (b) instead of CaApOH
even at basic pH values. The apatite appears to precipitate immediately, as
pure CaApF was the product after 2 hr, 18 hr, and 1 day. However, the purity
of CaApF appears to be influenced by the temperature of the reaction: the
FOM of the XRD patterns for the products obtained at room temperature
were significantly higher than those obtained at 80 8C. Moreover, twice the
stoichiometric excess of fluoride resulted in CaF (FOM 3.4) even at near
boiling temperatures and stirring in the presence of phosphate, presumably
2
211
due to the insolubility of CaF (K ¼ 4 Â 10 ).
2
SP
CaApBr has not been synthesized in pure form in aqueous solution but has
[
9,12,13]
been synthesized by solid state methods.
were unsuccessful, using a range of conditions that included pH between 2
Our aqueous preparations
and 10, temperatures between 90 and 125 8C (evaporation of water and

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511
continued heating), reaction times of up to 5 days, and bromide concentrations
up to 20 times the stoichiometric. In addition, synthetic CaApOH was heated
and stirred for 3 weeks in the presence of bromide ion. Depending upon
conditions, the products contained lines attributable to CaApOH (FOM
18.5) or CaPO OH (FOM 19.5), and none of the products gave a positive
test for bromide.
3
The one literature report of an aqueous preparation of CaApI utilized stoi-
We were
[14]
chiometric amounts of KI and ethylenediamine to adjust the pH.
unable to replicate these results in five attempts, all employing ethylenediamine
to adjust the pH to 12. Temperatures between 25 and 100 8C, as well as excess
iodide and excess calcium, were applied to the solution. Other methods, such as
removing H O or HI (in the reaction of calcium phosphate with calcium iodide in
2
HI) were also unsuccessful. In nearly all cases, CaPO OH (FOM 7.4), CaApOH
3
(FOM 10.1), or an amorphous mixture was produced.
Strontium Apatites
[5,15–24]
SrApOH has been prepared extensively in aqueous solution.
Unlike
barium, which requires pH values above 12 for the formation of its hydroxy-
apatite, SrApOH forms between pH 7 and 12. In the reaction of strontium nitrate
with (NH ) HPO the hydroxyapatite formed immediately, and was also the pro-
4
2
4
duct after 1 week. However, higher temperatures were required to precipitate
pure SrApOH: a gelatinous solution formed when the reaction took place at
room temperature. The use of sodium hydroxide instead of ammonia appeared
to have no effect on product composition. Similarly, time of reaction appeared
to have no effect on the preparation of SrApOH in basic solution.
Most of the literature preparations reported for SrApCl occur in the solid
[29]
[
25–28]
state. or by self-propagating high temperature synthesis. In our reac-
tion of strontium nitrate with NaH PO and ammonium chloride, SrApCl was
formed. SrApCl is apparently more stable (insoluble) at slightly acidic and
2
4
slightly basic pH values than both SrHPO and SrApOH, a phenomenon
4
that contrasts significantly with calcium apatites.
Although SrApCl formed in the presence of excess chloride ion (5 : 3 : 20
ratios of cation, phosphate, and chloride, respectively), SrApF was not isolated
in reactions that contained more than double the stoichiometric amount of fluo-
ride. Although Lacout et al. synthesized SrApF by boiling Sr(NO ) with
3
2
[21]
(
dure in our hands produced SrF (FOM 4.1).
NH ) HPO and “a large excess” of NH F at pH 11.8 for 1 hr,
this proce-
4
2
4
4
2
Khattech and Jemal reported the preparation of SrApF by addition of
[
18]
Sr(NO ) to boiling (NH ) HPO and NH F at pH 10 with NH .
The
product was ignited at 450 8C. We repeated this preparation, both with and
3
2
4 2
4
4
3

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5
12
Flora et al.
without ignition at 450 8C, but could not obtain SrApF. The preparation was
also attempted using five other methods at different reaction temperatures
and pH values, and different amounts of NaF and NH F. In reactions in
4
which fluoride (from either NaF or NH F) was present in stoichiometric
4
amounts or in slight excess, a mixture of SrApF and SrApOH was formed,
as evidenced by the presence of both SrApOH and SrApF lines in the XRD
1
9
pattern and the presence of a peak in the F NMR spectrum.
Several different synthetic methods for SrApBr were attempted.
Sr(NO ) , (NH ) HPO , and NaBr or NH Br were combined at 90 8C at pH
3
2
4 2
4
4
values of 7, 10, or 12 with an aging period of 2–5 days. In all cases SrApOH
was formed even at pH 7 and with a 30-fold stoichiometric excess of bromide.
It seems that SrApOH forms initially and does not take up any bromide from
the solution. A sample of previously prepared and dried SrApOH was added to
a solution containing NH Br and aged at a pH value of 8 for over 3 weeks,
4
with no incorporation of bromide. In addition, SrBr was heated with Sr -
2
3
(PO ) or (NH ) HPO in distilled water or HBr followed by removal of the
4 2 4 2 4
acid or water by evaporation. This method resulted in either amorphous
mixtures or SrHPO (FOM 12.0).
4
SrApI has not been reported in the literature and our reactions of solutions
of the strontium nitrate and ammonium hydrogen phosphate at 100 8C and pH
6
(to avoid precipitation of SrApOH) resulted in SrHPO (FOM 8.0).
4
Barium Apatites
Barium is known to form the hydroxy-, chloro-, fluoro-, and bromoapatite
analogs, though the fluoro- and bromoapatites have not been prepared in
aqueous solution. Kato et al. reported that barium hydrogen phosphate
forms at pH 3 but is converted to barium hydroxyapatite by aging in the
mother liquor if some chloride ion is present. A higher chloride concentration
[30]
accelerated the conversion to BaApOH. In our 17 attempts to prepare BaA-
pOH, barium chloroapatite (alforsite) formed preferentially when any chloride
2
þ
32
2
was present. When the Ba : PO4 : Cl ratio was 10 : 6 : 1—i.e., when the
amount of chloride was less than stoichiometric—XRD indicated that the pro-
duct was mostly alforsite, with small amounts of BaApOH. Indeed, barium
hydroxylapatite proved to be difficult to prepare in the reaction of barium
nitrate with ammonium hydrogen phosphate. At acidic pH values and up to
pH 8, a mixture whose XRD pattern contained lines attributable to BaHPO4
was formed, whereas Ba (PO ) (FOM 2.2) formed at pH values between 8
3
4 2
and 12. Only at pH 12, after 5 days at 90 8C, was BaApOH (FOM 3.7) formed
in the reaction of barium nitrate with ammonium hydrogen phosphate with
NaOH used to adjust the pH.

ORDER
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Apatites
513
[31]
Although it has been reported that excess barium in the solution facili-
tates transformation to BaApOH this was not substantiated by our reactions
containing double the stoichiometric amount of barium in solution—after
heating the pH 10 solution at 90 8C for 4 days, barium phosphate was the
product.
Barium fluoroapatite was prepared by the reaction of barium nitrate with
ammonium hydrogen phosphate and ammonium fluoride (5 : 3 : 2 mole ratio)
at pH 12 (or above) after heating at 90 8C for 1 day.
BaApBr has not been prepared in aqueous solution, and has only been
BaApI has not been reported in the litera-
[32]
prepared once in the solid state.
ture. We were unable to prepare either derivative using conditions ranging
from pH 8 to 12, reaction times up to 4 days, temperatures of 90 8C, and
both stoichiometric and excess halide. In our attempts to prepare BaApBr,
barium phosphate (FOM 7.0) was the only product at high pH values, heating
between 2 and 5 days above 90 8C, and with Ba : P : Br molar ratios of 5 : 3 : 2
and 5 : 3 : 10. In attempts at BaApI, using NaI and mole ratios of 5 : 3 : 2 and
5 : 3 : 10, barium phosphate (FOM 1.3) was also formed. Interestingly, the pre-
sence of either bromide or iodide did not facilitate the formation of BaApOH.
Cadmium Apatites
The use of cadmium nitrate and hydrogen phosphate and conditions that
ranged in pH from 7 to 12, in temperature from 25 to 100 8C, and in reaction
time from 30 min to 1 week (some syntheses were done in the presence of
halide ions) produced CdApOH only if water was removed from the reaction
for at least 1 day and either ammonium ion was present in the phosphate
source or ammonia was used to adjust the pH. The addition of Cd(NO3)2
and (NH ) HPO dropwise to boiling CO -free water, all at pH 12 with ethyl-
4
2
4
2
[
33]
enediamine,
When NaH PO was added to cadmium nitrate at room temperature, no
did not produce CdApOH.
2
4
precipitate occurred until the pH was elevated from 4 to 7 with ammonia.
Conversion to the apatite occurred by the removal of water at temperatures
between 100 and 150 8C. When Cd(NO ) and (NH ) HPO were combined
3
2
4 2
4
.
at pH 7 with NH , the product was Cd H (PO ) 4H O (FOM 8.7) after heat-
ing and stirring for 2 days. The use of the same procedure with the evaporation
of water for 1 day produced CdApOH.
3
5
2
4 4
2
The lack of success in the preparation of CdApOH from solutions that do
not contain the ammonium ion or ammonia suggests the initial formation of an
ammonium salt or an ammonia complex. This is supported by the fact that
a solution of ammonium hydrogen phosphate and cadmium nitrate which
.
was heated for 30 min produced NH CdPO H O (FOM 13.8).
4
4
2

ORDER
REPRINTS
5
14
Flora et al.
The preparation of CdApCl did not require heating to dryness. However,
lengthy periods of heating (5 days) were required to obtain pure CdApCl.
Even after heating for 5 days, CdClAp was not produced if sodium reagents
were used instead of ammonium salts, or if ammonia was not used to adjust
the pH. It is clear that ammonia or ammonium ion is required even with longer
heating times.
The involvement of ammonium ion or ammonia is also indicated in the
formation of CdApBr and CdApF. Successful synthesis of CdApF from
(
NH ) HPO and NH F with 6 M ammonia to adjust the pH occurred with
4 2 4 4
the removal of water at temperatures between 120 and 150 8C and at pH 7.
The syntheses of CdApBr were unsuccessful regardless of pH or bromide
concentration if the water was not removed by heating. Formation of CdApBr
seemed not to be affected by the amount of heating time within the experi-
mental range of 1–7 days. However, when NaOH was used to adjust the pH
to 7 instead of ammonia and sodium reagents were used instead of ammonium
salts, CdApBr was not obtained. Apparently, the synthesis of CdApBr requires
removal of water as well as ammonium/ammonia in solution.
Synthesis of CdApI, however, was unsuccessful even with the removal of
water and use of ammonium salts and ammonia for pH adjustment. Evapo-
ration of water in the presence of ammonium ion produced CdApOH. The
[34]
apparently successful preparation of Cd (VO ) I
5
suggests that it is not
4 3
simply the size of the anion that determines feasibility of synthesis.
Lead Apatites
The lead apatites are generally referred to as pyromorphites, and many
aqueous preparation methods exist for the hydroxide, fluoride, and chloride
analogs. Over 10 literature methods in aqueous solution have been reported
for hydroxypyromorphite; in fact, PbApOH has been prepared almost exclu-
[
5,15,33,35–42]
276.8
sively in solution.
similar to that of PbApCl,
Its KSP value has been reported to be 10
279.12
,
[
43]
which is 10
.
In five preparations of PbApOH, along with several other attempts in the
presence of other anions, we found that the presence of excess sodium ion in
the solution in the form of Na PO and NaOH for pH adjustment inhibits the
3
4
formation of PbApOH by producing products with lines attributable to either
Pb (PO ) (FOM 4.7) or NaPb (PO ) (FOM 7.8). The latter was produced
9
4 6
4
4 3
2
when the Pb : PO4 : Na ratio was 3 : 5 : 15 with Na PO as the source of
þ
32
þ
3
4
phosphate (pH was adjusted to 9 with NaOH). It is clear that the sodium
salt is more stable in the presence of excess sodium ion than PbApOH.
When lead nitrate and ammonium hydrogen phosphate are combined without
adjustment of the pH, the product is PbHPO (FOM 5.7). As with the barium
4

ORDER
REPRINTS
Apatites
515
and strontium apatites, the hydrogen phosphate is more stable at acidic pHs
than the apatite if no halide is present. PbApOH was formed in the reaction
of lead nitrate with ammonium hydrogen phosphate at pH 9 after heating at
90 8C for 5 days.
PbApCl is among the most insoluble apatites, and, therefore, one of the
easiest to form in aqueous solution even at acidic pH values. Manecki et al.
report that in the presence of aqueous PbCl , CaApCl, CaApF, and CaApOH
2
[
44]
all reacted to form PbApCl. We found that PbApCl formed under any cond-
itions used—varying reactants, temperature, reaction time, and stoichiometry.
PbCl , PbCO , and Pb(NO ) were all used as reagents, as well as NaH PO ,
2
3
3 2
2
4
(
NH ) HPO , and H PO . Reaction times ranged from 30 min to several days
4 2 4 3 4
at temperatures between 25 and 80 8C.
Lead fluoroapatite was successfully prepared using the nitrate and
(
NH ) HPO under varying conditions from pH 2 to 10, 1.5 hr to 1 day,
4 2 4
from 75 8C to boiling, and at stoichiometric fluoride concentrations as well
as in 10-fold excess. Several aqueous preparations have been reported in the
[
5,45–48]
literature.
PbApBr has been synthesized by solid state methods.
Nriagu, PbApBr is intermediate in stability between chloro- and hydroxyl-
[31]
According to
[
49]
pyromorphite.
phite in aqueous solution using the nitrate and (NH ) HPO under varying
We were able to successfully synthesize bromopyromor-
4
2
4
conditions—pH 2 and 9, after 30 min and 6 days, at 90 8C and at room tem-
perature, and in the presence of stoichiometric and excess amounts of
bromide.
The synthesis of PbApI was attempted several times at pH 4 and above
9
5 8C in the reaction between PbI and sodium hydrogen phosphate. PbApOH
2
was ruled out as a possible phase by XRD, and ICP data indicated that the pro-
duct was not PbApI. The use of (NH ) HPO with lead nitrate in the presence
4
2
4
of ammonium iodide at pH 9 (90 8C, 5 days) produced PbApOH (FOM 1.5).
CONCLUSIONS
Many of the trends observed in the formation of the apatites can be related
to differences in solubilities. The success of the preparative route in solution
depends upon the solubility of the apatite relative to byproducts such as the
phosphate, the hydrogen (or dihydrogen) phosphate, other double salts such
as Na M (PO ) X, stoichiometrically different halo or hydroxy phosphates
2
4
4 3
such as the Wagnerite series (M (PO ) X ), and starting materials. Table 3
4
4 2 2
shows that the hydrogen phosphates of calcium, strontium, and lead are
quite insoluble. It is not surprising therefore to find that these compounds
are formed in slightly acidic and slightly basic solution where the hydrogen

ORDER
REPRINTS
5
16
Flora et al.
a
Table 3. Approximate molar solubilities of some simple salts (mol/L).
Ca
Sr
Ba
Pb
Cd
2
4
4
27
MHPO
(PO
4
10
2
10
10
10
0.4
na
0.005
na
na
26
27
M
3
4
)
2
10
10
10
2
6
25
M(OH)2
MF
MCl
MBr2
0.02
3
0.07 (8H O)
2
23
0.1 (8H O)
10
2
22
10
2
23
2
10
2 (6H
5 (6H O)
10
1 (6H
0.3
2
2
O)
2
O)
1 (2H
1 (2H O)
2
O)
0.04
0.03
2
4 (2.5H O)
1 (6H O)
2
3
2
2
2
2
3
MI
2
5
1 (6H
2
O)
2 (15H
2
O)
10
a
Where the solubility refers to a hydrate, the number of waters of hydration is indicated
in parentheses.
phosphate ion predominates. For cadmium, a transition metal, the hydrogen
phosphates do not interfere, probably because of the generally greater solu-
bility (or instability) of transition metal hydrogen phosphates.
Table 3 also shows that the fluorides of all the cations except cadmium are
relatively insoluble. Indeed, in the preparation of the fluoroapatites of the alka-
line earths, the fluorides (MF ) are formed under some conditions. For
2
example, when the mole ratio of strontium to fluoride is above 1 : 2, SrF is
2
formed exclusively, while at lower ratios, the apatite is more favorable. A
similar pattern is demonstrated with the other group II ions: barium forms
BaF when the mole ratio (Ba : F) is 1 : 2, but forms the apatite at a 5 : 2
2
2
11
mole ratio, while the insolubility of CaF (K ¼ 4 Â 10 ) precluded apatite
2
sp
formation (at 1 : 2 Ca : F ratio) even at near boiling temperatures. The forma-
tion of the metal fluoride is not a problem in the syntheses of the lead and
cadmium fluoroapatites. Lead forms the fluoroapatite even with a 10-fold
excess of fluoride and when PbF is used as a reagent and is not fully
2
dissolved. It is clear that for lead, the apatite is significantly more insoluble
than PbF . Excess fluoride did not promote the formation of either CdApF
or CdApOH.
2
The relative ease of formation of the halo derivatives of the alkaline earth
metal apatites can be related to their solubilities. The relative solubilities of
ionic species in water are determined by their heats of dissolution, if the entro-
pies of dissolution can be ignored (as is frequently the case). The heat of
dissolution is the sum of the hydration energies of the ions in aqueous solution
and the lattice energy of the solid compound. For simple salts, variations in
lattice energies can generally be attributed to changes in ionic radii and
ionic charge (assuming similar structures). For the apatites it is probably
true that the lattice energies of the halides of a given cation (for example,
Ba (PO ) X) decrease as the halide size increases. Thus, if lattice energy
5
4 3

ORDER
REPRINTS
Apatites
517
were the dominant variable, the heat of solution of the fluoride would be
more positive than that of the iodide and the fluoride would, therefore, be
less soluble and more easily formed.
2
2
The heats of hydration of the halides vary: F , 2524 kJ/mol; Cl ,
2
2
2
378 kJ/mol; Br , 2348 kJ/mol; I , 2308 kJ/mol. Thus, if the heats of
hydration control the solubility, the fluoro apatite of a given cation would
be the most soluble. Because hydroxide is similar in size to fluoride, the
lattice energy of the hydroxide would be expected to be similar to that of
the fluoride in the absence of hydrogen-bonding. The heat of hydration of
the hydroxide ion (2460 kJ/mol) places it between the heats of hydration
of fluoride and chloride.
Whether the lattice energy or heat of hydration controls the solubility
depends upon the size of the cation. In general, the smaller the cation, the
greater the role of the lattice energy. Table 3 shows that for all of the alkaline
earth cations, the solubilities vary MF , M(OH) , MCl , MBr , indica-
2
2
2
2
tive of the dominance of the lattice energy. However, the fact that the differ-
ence in solubilities between the fluoride and the bromide is greater for Ca(II)
than it is for Ba(II) ions suggests that the hydration energy becomes more
important as the cation increases in size.
This interplay between lattice energy and hydration energy provides a
rationalization of the ease of formation of the alkaline earth halo apatites in
aqueous solution. Experimental results reveal that the ease of formation of
the halo apatites varies: for Ca(II), F . OH . Cl; for Sr(II), Cl . OH . F;
for Ba(II), Cl . F . OH. The relative solubilites of the calcium apatites
therefore appear to be controlled primarily by lattice energy while the solubi-
lities of the barium apatites are influenced by the heat of hydration. The greater
solubility of BaApOH (lowest ease of formation) is not easily rationalized.
The solubilities given in Table 3 also reveal that most of the lead salts are
considerably less soluble than their alkaline earth counterparts. Since Pb(II)
and Sr(II) have essentially the same ionic radii (and Pb(II) has a more negative
heat of hydration) the lower solubility of lead salts and the lead apatites is
almost surely a reflection of considerable covalent interactions between the
ions. The difficulty experienced in synthesizing the iodo derivatives of all of
the cations can also be attributed to the high solubility of the iodo apatites.
Of course, these analyses completely ignore any structural differences
between the various apatites.
The use of ammonium salts, rather than sodium salts, as the source of
phosphate is important because of the relatively greater solubility of the
ammonium double salts. The use of ammonia and/or ammonium salts for
cadmium is likely related to the fact that cadmium forms ammonia complexes,
which keep the cation in solution, rather than in the form of the hydroxide,
which is considerably more insoluble than the hydroxides of the alkaline

ORDER
REPRINTS
5
18
Flora et al.
earth cations. The apatites are then formed by decomplexation of the com-
plexes. The role of the ammonium salts can also be attributed to the reaction
of the ammonium ion with base to form ammonia (which can then complex the
cation) at high pH. The very low solubility of the lead apatites ensures their
formation under almost any conditions.
ACKNOWLEDGMENTS
The authors are indebted to the William M. and Lucille M. Hackman
Scholars Program, the Howard Hughes Medical Institute, and the Camille
and Henry Dreyfus Foundation for a Jean Dreyfus Boissevain Undergraduate
Scholarship for Excellence in Chemistry.
REFERENCES
1
. Horton, M. Bone cell genes, molecular analysis. In Encyclopedia of
Human Biology; Dulbecco, R., Ed.; Academic Press: San Diego, 1991;
Vol. 1, 761–770.
2
3
4
. Legeros, R. The unit cell dimensions of human enamel apatite: effect of
chloride incorporation. Archs. Oral. Biol. 1974, 20, 63–71.
. Narasaraju, T.S.B.; Rai, U.S.; Rao, K. Some physico-chemical aspects of
chlorapatite. Indian J. Chem. 1978, 16A, 952–954.
. Ben Cherifa, A.; Somrani, S.; Jemal, M. D e´ termination de l’enthalpie
standard de formation de fluorapatite de l’hydroxyapatite et de la chlor-
apatite. J. Chim. Phys. 1991, 88, 1893–1900.
5
6
7
8
9
. Jemal, M.; Ben Cherifa, A.; Khattech, I.; Ntahomvukiye, I. Standard
enthalpies of formation and mixing of hydroxy- and fluorapatites.
Thermochim. Acta 1995, 259, 13–21.
. Fabian, R.; Kotsis, I.; Pilter, Z. Comparison of properties of fluorapatites
prepared by solid state reaction and precipitation. Hung. J. Ind. Chem.
1999, 27, 259–263.
. Moreno, E.C.; Kresak, M.; Zahradnik, R.T. Physicochemical aspects of
fluoride-apatite systems relevant to the study of dental caries. Caries
Res. 1977, 11, 142–171.
. Khattech, I.; Jemal, M. Thermochemistry of phosphate products. Part II:
standard enthalpies of formation and mixing of calcium and strontium
fluorapatites. Thermochim. Acta 1997, 298, 23–30.
. Kim, J.Y.; Fenton, R.R.; Hunter, B.A.; Kennedy, B.J. Powder diffraction
studies of synthetic calcium and lead apatites. Aust. J. Chem. 2000, 53,
679–686.

ORDER
REPRINTS
Apatites
519
1
1
0. Fabian, R.; Kotsis, I.; Zimany, P.; Halmos, P. Preparation and chemical
characterization of high-purity fluorapatite. Talanta 1998, 46,
1
273–1277.
1. Loutts, G.B.; Chai, B.H.T. Growth of high-quality single crystals of FAP
Ca (PO ) F] and its isomorphs. Proceedings of SPIE—The International
[
5
4 3
Society for Optical Engineering 1993, 1863, 31–34.
1
1
1
2. Condrate, R.A.; Cornilsen, B.C.; Dykes, E. The Raman spectrum of
calcium bromapatite. Appl. Spectrosc. 1975, 29, 526–527.
3. Dykes, E. Preparation and characterization of calcium bromapatite.
Mater. Res. Bull. 1974, 9, 1227–1236.
4. Phebe, D.E.; Narasaraju, T.S.B. Preparation and characterization of
hydroxyl and iodide apatites of calcium and their solid solutions.
J. Mater. Sci. Lett. 1995, 14, 229–231.
1
5. Mayer, I.; Wahnon, S.; Cohen, S. Mat. Res. Bull. 1979, 14, 1479–1483.
6. Pujari, M.; Patel, P.N. Strontium-copper-calcium hyhdroxyapatite solid
solutions: preparation, infrared, and lattice constant measurements.
J. Solid State Chem. 1989, 83, 100–104.
1
1
1
1
2
7. Pandey, H.C.; Pandey, S.; Patel, P.N. Preparation and x-ray powder dif-
fraction patterns of mixed (Ca þ Sr þ Cd) hydroxyapatites. Chem. Ind.
1980, 14, 571–572.
8. Pandey, H.C.; Pandey, S.; Patel, P.N. Preparation and characterization of
mixed (Ca þ Sr þ Zn) and (Ca þ Ba þ Cd) hydroxyapatites. Chem. Ind.
1981, 1, 32–33.
9. Patel, P.N. Preparation and characterization of mixed (Ca þ Sr þ Mn)
hydroxylapatites. Journal of the Institute of Chemists (India) 1985, 57,
15–17.
´
0. Badraoui, B.; Thouvenot, R.; Debbabi, M. Etude par diffraction des
3
1
rayons X, par r e´ sonance magn e´ tique nucl e´ aire P en phase solide et
par spectrom e´ trie infrarouge des hydroxyapatites mixtes cadmium–stron-
tium. C. R. Acad. Sci. Paris 2000, 3, 107–112.
2
1. Lacout, J.L.; Nounah, A.; Ferhat, M. Strontium–cadmium substitution in
hydroxy- and fluor-apatites. Ann. Chim. Sci. Mat. 1998, 23, 57–60.
2. George, G.; Gupta, S.K.; Rao, P.V.R.; Narasaraju, T.S.B. Preparation and
characterization of phosphate and arsenate apatites of strontium and their
solid solutions. J. Mater. Sci. 1987, 22, 2274–2276.
2
2
3. Yasukawa, A.; Kidokoro, M.; Kandori, K.; Ishikawa, T. Preparation and
characterization of barium–strontium hydroxyapatites. J. Colloid Inter-
face Sci. 1997, 191, 407–415.
2
4. Kurata, S.; Fujiwara, T.; Negishi, H.; Yamazaki, N.; Fujise, S. Preparation
of strontium and barium hydroxyapatite at various pH and temperatures.
Jpn Oral Biol. 1982, 24, 661–667.

ORDER
REPRINTS
5
20
Flora et al.
2
5. N o¨ tzold, D.; Wulff, H.; Herzog, G. Differential thermal analysis of the
formation of pentastrontium chloride phosphate and its x-ray structural
analysis. J. Alloys Compd. 1974, 215, 281–288.
2
6. N o¨ tzold, D.; Herzog, G.; Henke, I. On the influence of substitutions by
ions of the same charge on luminescence of pentastrontium chloridephos-
phate activated by divalent europium. Z. Anorg. Allg. Chem. 1992, 613,
127–131.
2
2
2
7. Khattech, I.; Jemal, M. Thermochemistry of phosphate products. Part I:
Standard enthalpy of formation of tristrontium phosphate and strontium
chlorapatite. Thermochim. Acta 1997, 298, 17–21.
8. Hoekstra, A.H.; Wanmaker, W.L.; Varriet, J.G. The formation of stron-
tium and bariumchlorapatite from strontium and barium orthophosphate
and hydrochloric acid. J. Inorg. Nucl. Chem. 1970, 32, 2445–2448.
9. Kottaisamy, M.; Mohan Rao, M.; Jeyakumar, D. Divalent europium-acti-
vated alkaline-earth metal chlorophosphate luminophores [M (PO ) Cl:
5
4 3
2
þ
Eu ; M ¼ Ca, Sr, Ba] by self-propagating high-temperature synthesis.
J. Mater. Chem. 1997, 7, 345–349.
3
3
3
3
0. Kato, C.; Fujita, K.; Matsuda, K. Effects of various ions on the synthesis
of barium apatite obtained by homogenous precipitation method. Proc.
Schl. Sci. 1999, 34, 71–80.
1. Kato, C.; Fujita, K.; Matsuda, K. Preparation of various barium phos-
phates by homogenous precipitation method. Nippon Kagaku Kaishi
1996, 7, 630–637.
2. Alberius-Henning, P.; Mattsson, C.; Lidin, S. Crystal structure of penta-
strontium tris(phosphate) bromide, Sr (PO ) Br and of pentabarium
5
4 3
tris(phosphate) bromide Ba (PO ) Br. Z. Kristallogr. 2000, 215, 345–346.
4 3
5
3. Mahapatra, P.P.; Sarangi, D.S.; Misra, B. X-Ray, IR and magnetochem-
ical studies on calcium manganese hydroxyapatites. Indian J. Chem.
1993, 32A, 525–530.
3
3
3
4. Henning, P.A.; Moustiakimov, M.; Lidin, S. Incommensurately modu-
lated cadmium apatites. J. Solid State Chem. 2000, 150, 154–158.
5. Bhatnagar, V.M. Preparation and unit cell dimensions of lead hydroxy-
apatite. Rev. Roum. Chim. 1976, 21, 879–880.
6. Yasukawa, A.; Kunimoto, T.; Kamiuchi, K.; Kandori, K.; Ishikawa, T.
Preparation of lead hydroxyapatite particles using acetamide. J. Mater.
Chem. 1999, 9, 1825–1830.
37. Ma, L.Q. Factors influencing the effectiveness and stability of aqueous
lead immobilization by hyhroxyapatite. J. Environ. Qual. 1996, 25,
1420–1429.
3
8. Laperche, V.; Logan, T.J.; Gaddam, P.; Traina, S.J. Effect of apatite
amendments of plant uptake of lead from contaminated soil. Environ.
Sci. Technol. 1997, 31 (10), 2745–2753.

ORDER
REPRINTS
Apatites
521
3
4
4
9. Ma, Q.Y.; Traina, S.J.; Logan, T.; Ryan, J.A. In situ lead immobilization
by apatite. Environ. Sci. Technol. 1993, 27, 1803–1810.
0. Xu, Y.; Schwartz, F.W. Lead immobilization by hydroxyapatite in aque-
ous solutions. J. Contam. Hydrol. 1994, 15, 187–206.
1. Sugiyama, S.; Nakanishi, T.; Ishimura, T.; Moriga, T.; Hayashi, H.;
Shigemoto, N.; Moffat, J.B. Preparation, characterization, and thermal
stability of lead hydroxyapatite. J. Solid State Chem. 1999, 143, 296–302.
2. Laperche, V.; Traina, S.J. Immobilization of Pb by hydroxylapatite. In
Adsorption of Metals by Geomedia: Variables, Mechanisms, and Model
Applications; Jenne, E., Ed.; Academic Press: 1998; 255–276.
3. Nriagu, J.O. Lead orthophosphates. I. Solubility and hydrolysis of secon-
dary lead orthophosphate. Inorg. Chem. 1972, 11, 2499–2500.
4. Manecki, M.; Maurice, P.A.; Traina, S.J. Uptake of aqueous Pb by Cl-,
F-, and OH-apatites: mineralogic evidence for nucleation mechanisms.
Am. Mineral 2000, 85, 932–942.
4
4
4
4
4
4
5. Bhatnagar, V.M. Lead fluorapatite, Pb (PO ) F . Curr. Sci. Lett. 1970,
1
0
4 6 2
30, 132–133.
6. Bhatnagar, V.M. Lead fluorapatite, Pb (PO ) F . Mater. Res. Bull. 1971,
1
0
4 6 2
6
, 1–4.
7. Bhatnagar, V.M. Preparation, lattice parameters, and X-ray powder patt-
erns of lead fluorapatite and lead chlorapatite. Inorg. Nucl. Chem. Lett.
1
970, 6, 913–917.
8. Bhatnagar, V.M. New observations on lead apatites. Rev. Roum. Chim.
970, 15, 955–956.
9. Nriagu, J.O. Lead orthophosphates. III. Stabilities of fluoropyromorphite
and bromopyromorphite at 25 8C. Geochim. Cosmochim. Acta 1973, 37,
4
4
1
1735–1743.
Received January 24, 2003
Accepted November 21, 2003
Referee I: K. Moedritzer
Referee II: T. B. Brill

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