Dynamic and controlled rate thermal analysis of halotrichite

Article abstract of DOI:10.1007/s10973-009-0275-1

Three halotrichites namely halotrichite Fe²⁺SO ₄.Al₂(SO₄)₃.22H₂O, apjohnite Mn²⁺SO₄.Al₂(SO₄) ₃.22H₂O and dietrichite ZnSO₄.Al ₂(SO₄)₃.22H₂O, were analysed by both dynamic, controlled rate thermogravimetric and differential thermogravimetric analysis. Because of the time limitation in the controlled rate experiment of 900 min, two experiments were undertaken (a) from ambient to 430 °C and (b) from 430 to 980 °C. For halotrichite in the dynamic experiment mass losses due to dehydration were observed at 80, 102, 319 and 343 °C. Three higher temperature mass losses occurred at 621, 750 and 805 °C. In the controlled rate thermal analysis experiment two isothermal dehydration steps are observed at 82 and 97 °C followed by a non-isothermal dehydration step at 328 °C. For apjohnite in the dynamic experiment mass losses due to dehydration were observed at 99, 116, 256, 271 and 304 °C. Two higher temperature mass losses occurred at 781 and 922 °C. In the controlled rate thermal analysis experiment three isothermal dehydration steps are observed at 57, 77 and 183 °C followed by a non-isothermal dehydration step at 294 °C. For dietrichite in the dynamic experiment mass losses due to dehydration were observed at 115, 173, 251, 276 and 342 °C. One higher temperature mass loss occurred at 746 °C. In the controlled rate thermal analysis experiment two isothermal dehydration steps are observed at 78 and 102 °C followed by three non-isothermal dehydration steps at 228, 243 and 323 °C. In the CRTA experiment a long isothermal step at 636 °C attributed to de-sulphation is observed. Akademiai Kiado, Budapest, Hungary 2009.

Full text of DOI:10.1007/s10973-009-0275-1

J Therm Anal Calorim (2010) 99:501–507
DOI 10.1007/s10973-009-0275-1
Dynamic and controlled rate thermal analysis of halotrichite
´
´
Ray L. Frost Æ Sara J. Palmer Æ Janos Kristof Æ
´
Erzsebet Horvath
´
Received: 24 May 2009 / Accepted: 26 June 2009 / Published online: 25 July 2009
´
´
Ó Akademiai Kiado, Budapest, Hungary 2009
Abstract Three halotrichites namely halotrichite Fe2?
SO4ꢀAl2(SO4)3ꢀ22H2O, apjohnite Mn2?SO4ꢀAl2(SO4)3ꢀ
22H2O and dietrichite ZnSO4ꢀAl2(SO4)3ꢀ22H2O, were
analysed by both dynamic, controlled rate thermogravi-
metric and differential thermogravimetric analysis.
Because of the time limitation in the controlled rate
experiment of 900 min, two experiments were undertaken
(a) from ambient to 430 °C and (b) from 430 to 980 °C.
For halotrichite in the dynamic experiment mass losses due
to dehydration were observed at 80, 102, 319 and 343 °C.
Three higher temperature mass losses occurred at 621, 750
and 805 °C. In the controlled rate thermal analysis exper-
iment two isothermal dehydration steps are observed at 82
and 97 °C followed by a non-isothermal dehydration step
at 328 °C. For apjohnite in the dynamic experiment mass
losses due to dehydration were observed at 99, 116, 256,
271 and 304 °C. Two higher temperature mass losses
occurred at 781 and 922 °C. In the controlled rate thermal
analysis experiment three isothermal dehydration steps are
observed at 57, 77 and 183 °C followed by a non-isother-
mal dehydration step at 294 °C. For dietrichite in the
dynamic experiment mass losses due to dehydration were
observed at 115, 173, 251, 276 and 342 °C. One higher
temperature mass loss occurred at 746 °C. In the controlled
rate thermal analysis experiment two isothermal dehydra-
tion steps are observed at 78 and 102 °C followed by three
non-isothermal dehydration steps at 228, 243 and 323 °C.
In the CRTA experiment a long isothermal step at 636 °C
attributed to de-sulphation is observed.
Keywords Evaporite ꢀ Jarosite ꢀ Halotrichite ꢀ
Sulphate ꢀ CRTA
Introduction
The minerals in the halotrichite group have been known for
a long period of time [1–6]. This no doubt is because of
their occurrence in environmental systems. These minerals
are referred to as the pseudo-alums [7–9], and are often
found in the environment as post-mining phases [7–9]. The
minerals are monoclinic sulphates of general formula
AB2(SO4)4ꢀ22H2O where A is Mg2?, Mn2?, Fe2?, Ni2?
,
Zn2? and/or some combination of these cations and B is
Al3?, Cr3? or Fe3? or even a combination of these cations.
These minerals have often been referred to as the pseudo-
alums. The minerals as with other alums based upon
monovalent cations can be readily synthesised in the lab-
oratory. Ions of metals such as manganese, ferrous iron,
cobalt, zinc and magnesium will form double sulphates.
These sulphates are related to the halotrichites mineral
series and often form solid solutions. These alums are not
isomorphous with the univalent alums. Typically the end
member formulae are FeSO4ꢀAl2(SO4)3ꢀ22H2O (halotri-
chite) or MgSO4ꢀAl2(SO4)3ꢀ22H2O (pickeringite), but other
M2? cations substitute and solid solutions in the series are
extensive. Apjohnite is the manganese equivalent of
R. L. Frost (&) ꢀ S. J. Palmer
Inorganic Materials Research Program, School of Physical
and Chemical Sciences, Queensland University of Technology,
2 George Street, GPO Box 2434, Brisbane, QLD 4001, Australia
e-mail: r.frost@qut.edu.au
´
J. Kristof
Department of Analytical Chemistry, University of Pannonia,
´
PO Box 158, 8201 Veszprem, Hungary
´
E. Horvath
Department of Environmental Engineering and Chemical
Technology, University of Pannonia, PO Box 158,
´
8201 Veszprem, Hungary
123

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R. L. Frost et al.
halotrichite. Wupatkiite is the cobalt analogue, which may
have some other divalent metal substitution for the cobalt
cation [10]. The minerals are all isomorphous and crys-
tallise in the monoclinic space group P21/c [11]. In the
structure of the pseudo-alums, four crystallographically
independent sulphate ions are present [11–15]. One acts as
a unidentate ligand to the M2? ion, and the other three are
involved in complex hydrogen bond arrays involving
coordinated water molecules to both cations and to the
lattice water molecules [13].
quantities of both salts to supersaturate the solution at
353 K, the resulting solution was allowed to cool to room
temperature and centrifuged at 3,500 rpm for approxi-
mately 30 min. To this solution an equimolar amount of
aluminium(III) sulphate and manganese(II) sulphate was
added in filter paper bags and left to stand for approxi-
mately one week. The resulting precipitate was filtered
under vacuum filtration and washed twice with ethanol.
Dietrichite was prepared using identical methods as above
replacing magnesium(II) sulphate for zink sulphate.
The minerals were analysed by X-ray diffraction for
phase purity and by electron probe using energy dispersive
techniques for quantitative chemical composition.
The thermal decomposition of halotrichite related min-
erals jarosites has been studied for some considerable time
[16–20]. There have been many studies on the Fe(II) and
Fe(III) sulphate minerals [21–26]. Interest in such minerals
and their thermal stability rests with the possible identifi-
cation of these minerals and related dehydrated paragenet-
ically related minerals on planets and on Mars. Recently
thermogravimetric analysis has been applied to some com-
plex mineral systems [27–29]. It is considered that TG-MS
analyses may also be applicable to the jarosite minerals [30–
39]. The thermal stability of minerals such as halotrichites
which are only formed from solution is important especially
for the analysis of minerals on planets such as Mars. Ther-
mal analysis has been used extensively for testing the sta-
bility of minerals. To the best of the authors’ knowledge no
thermoanalytical studies of halotrichites have been under-
taken; although differential thermal analysis of some related
minerals has been published. In this work we report the
thermogravimetric analysis of the thermal decomposition
of synthetic halotrichite FeAl2(SO4)4ꢀ22H2O, apjohnite
MnAl2(SO4)4ꢀ22H2O and dietrichite ZnAl2(SO4)4ꢀ22H2O.
Thermal analysis
Dynamic experiment
Thermal decomposition of the samples was carried out
in a Derivatograph PC type thermoanalytical equipment
(Hungarian Optical Works, Budapest, Hungary) capable of
recording the thermogravimetric (TG), derivative thermo-
gravimetric (DTG) and differential thermal analysis (DTA)
curves simultaneously. The sample was heated in a ceramic
crucible in static air atmosphere at a rate of 5 °C/min.
Controlled rate thermal analysis experiment
Thermal decomposition of the samples was carried out in a
Derivatograph PC-type thermoanalytical instrument in an
open ceramic crucible in static air atmosphere at a pre-set,
constant decomposition rate of 0.10 mg/min. (Below this
threshold value the samples were heated under dynamic
conditions at a uniform rate of 1 °C/min.) With the quasi-
isothermal, quasi-isobaric heating program of the instru-
ment the furnace temperature was regulated precisely to
provide a uniform rate of decomposition in the main
decomposition stage.
Experimental
Synthesis of the halotrichites
Halotrichite
Synthetic halotrichite was prepared by dissolving precisely
equimolar masses of iron(II) sulphate and aluminium(III)
sulphate in degassed ultra-pure water (18.2 MX) the
resulting solution was evaporated by a constant stream of
nitrogen isolated from atmospheric conditions by an eth-
ylene glycol gas trap. The solution was left to dry under
the nitrogen for 5 days. Preliminary studies indicated that
the addition of heat to the solution was deleterious to the
process of co-precipitation.
Results and discussion
Dynamic thermal analysis of halotrichite
The dynamic TG pattern together with the DTG and DTA
patterns for synthetic halotrichite are shown in Fig. 1. The
results of the dynamic experiment are summarised in
Table 1. Mass losses observed at 74, 95.5, 102 and 123 °C
are assigned to water loss as is confirmed by ion current
mass spectrometric results. Mass losses of 1.0, 11.5 and
19.7% are observed. Two further decomposition steps
are observed at 319 and 343 °C with mass losses of 2%
each. Three higher temperature decomposition steps are
Apjohnite and dietrichite
A solution saturated by both aluminium(III) sulphate and
manganese(II) sulphate was prepared by adding sufficient
123

Dynamic and controlled rate thermal analysis of halotrichite
503
Fig. 1 Dynamic thermal analysis of halotrichite
Fig. 2 Dynamic thermal analysis of apjohnite
Table 2 Mass loss and temperature data of apjohnite under dynamic
conditions and under CRTA conditions
Table 1 Mass loss and temperature data of halotrichite under
dynamic conditions and under CRTA conditions
Decomposition process
Temperature range (°C)
Mass loss
Decomposition process
Temperature range (°C)
Mass loss
mg
mg
%
%
Dynamic conditions, sample mass: 120.64 mg
Dynamic conditions, sample mass: 29.47 mg
Dehydration
Desulphation
54–211
211–265
265–297
297–434
537–820
820–965
32.8
7.3
27.2
6.1
Dehydration
27–74
0.3
1.0
11.5
19.7
2.0
74–112
3.4
5.8
0.6
0.6
0.5
2.2
2.5
6.0
3.6
3.0
112–299
299–333
333–429
429–553
553–667
667–739
739–875
2.9
2.4
21.6
20.2
17.9
16.7
2.0
1.7
CRTA conditions, sample mass: 194.67 mg
Desulphation
7.5
Dehydration
26–67
67–163
163–263
263–417
10.6
45.0
13.3
5.2
5.4
23.1
6.8
8.5
20.4
CRTA conditions, sample mass: 89.53 mg
2.7
Dehydration
27–88
88–124
124–272
272–426
9.9
12.7
7.4
11.1
14.2
8.3
CRTA conditions, sample mass: 93.21 mg
Desulphation
417–719
719–789
789–869
869–989
23.4
3.3
25.1
3.5
3.6
4.0
25.9
0.5
27.8
0.5
CRTA conditions, sample mass: 55.93 mg
Desulphation
426–542
542–652
652–712
712–795
795–936
1.5
6.8
2.7
12.2
13.4
32.4
1.6
7.5
temperature steps SO2 is evolved which was confirmed by
mass spectrometry.
18.1
0.9
The following decomposition is proposed.
Á
À
Fe2þ SO4 ꢀ Al2ðSO4Þ ! Al2O3 þ FeO þ 4SO3 and 4SO3
observed at 621, 720 and 805 °C with mass losses of 7.5,
8.5 and 20.4% making a total mass loss at these tempera-
tures of 36.4%.
3! 4SO2 þ 2O2
The theoretical mass loss of water calculated using the
halotrichite formula is 35.68%.
Dynamic thermal analysis of apjohnite
À
Á
The dynamic thermal analysis curves for apjohnite are
shown in Fig. 2. The results of the thermal decomposition
of apjohnite are shown in Table 2.
Fe2þ SO4 ꢀ Al2ðSO4Þ3ꢀ22H2O
À
Á
! Fe2þ SO4 ꢀ Al2ðSO4Þ3þ22H2O
A multiple of dehydration steps can be observed up to
400 °C with a total mass loss of 38.7% (the theoretical
value is 44.5%):
The measured mass loss for water is 36.2%. Due to the
non-standardized storage conditions this difference can
be realistic for hydrated minerals. In the three higher
123

504
R. L. Frost et al.
À
Á
Mn2þ SO4 ꢀ Al2ðSO4Þ3ꢀ22H2O
Table 3 Mass loss and temperature data of dietrichite under dynamic
conditions and under CRTA conditions
À
Á
! Mn2þ SO4 ꢀ Al2ðSO4Þ3þ22H2O
Decomposition process
Temperature range (°C)
Mass loss
mg
Based upon the formula above the total theoretical mass
loss is 44.95%.
%
Some water is apparently retained according to ion
current curves to 304 °C. Three additional mass loss steps
at 256, 271 and 304 °C are also assigned to water evolu-
tion. The total observed mass loss is 38.3% which is
somewhat low compared with the theoretical mass loss.
The thermal decomposition steps at 781 and 922 °C are
attributed to the decomposition of the sulphate anions in
the apjohnite. Such decomposition is confirmed by the ion
current curves of SO2 (m/Z = 64) where maxima at 780
and 922 °C are observed. Similar maxima are observed in
the ion current curves of oxygen.
Dynamic conditions, sample mass: 63.47 mg
Dehydration
27–70
0.5
0.8
22.5
3.6
70–164
14.3
2.3
164–227
227–264
264–309
309–413
589–806
2.4
3.8
3.2
5.0
1.8
2.8
Desulphation
23.5
37.0
CRTA conditions, sample mass: 140.24 mg
Dehydration
28–88
16.0
19.3
8.1
11.4
13.8
5.8
88–125
The following decomposition is proposed.
Á
125–215
215–236
236–265
265–409
409–497
À
Mn2þ SO4 ꢀ Al2ðSO4Þ3! Al2O3 þ MnO
2.6
1.9
þ 4SO3 and 4SO3
! 4SO2 þ 2O2
3.1
2.2
6.0
4.3
0.5
0.4
The experimental mass loss of 34.6% fits well to the
CRTA conditions, sample mass: 84.64 mg
Desulphation 497–892
theoretical figure of 36.0%. The overall decomposition is
51.7
61.1
finished by 950 °C.
Dynamic thermal analysis of dietrichite
For halotrichite and apjohnite three mass loss steps are
found. The DTG peak of dietrichite is strongly asymmetric
and the peak may be curve resolved into three components.
The thermal decomposition steps at 746 °C are attributed
to the decomposition of the sulphate anions in the dietri-
chite. Such decomposition is confirmed by the ion current
curves of SO2 (m/Z = 64) where maxima at 631, 666 and
692 °C are observed. Similar maxima are observed in the
ion current curves of oxygen.
The dynamic thermal analysis patterns of dietrichite are
shown in Fig. 3. A summary of results is reported in
Table 3. Thermal decomposition steps are observed at 115,
173, 251, 276, 342 and 746 °C with mass losses of 22.5,
3.6, 3.8, 5.0, 2.8 and 37.0%. The following equation rep-
resents the overall dehydration chemistry
ZnSO4 ꢀ Al2ðSO4Þ3ꢀ22H2O ! ZnSO4 ꢀ Al2ðSO4Þ3þ22H2O
The experimental amount of the crystallization water is
38.5% as compared to the theoretical figure of 44.1%.
Dissimilarly to the two former minerals sulphate decom-
position is carried out in a single mass loss step at 746 °C:
The ion current curves support the concept of dehydration
at 251, 276 and 342 °C with m/Z = 17 and 18 showing
maxima at these temperatures. It is interesting to compare
the high temperature thermal decomposition of dietrichite.
ZnSO4 ꢀ Al2ðSO4Þ ! Al2O3 þ ZnO þ 4SO3 and 4SO3
3! 4SO2 þ 2O2
The theoretical mass loss (35.6%) compares well with the
observed value of 37.0%.
Controlled rate thermal analysis of halotrichite
The controlled rate thermal analyses of halotrichite are
shown in Fig. 4. The results of the Controlled rate thermal
analysis (CRTA) are summarised in Table 1. The CRTA
experiment is undertaken in two sections (a) up to 400 °C
and (b) from 400 to 1,000 °C. The reason for this is that the
derivatograph has a time limit of 900 min. For the second
experiment, the same sample was placed into the crucible,
Fig. 3 Dynamic thermal analysis of dietrichite
123

Dynamic and controlled rate thermal analysis of halotrichite
505
and with a higher heating rate (2 °C/min) was applied
when the pre-set decomposition rate has not been reached
(during the first measurement the heating rate was 1 °C/
min under this threshold). The higher heating rate is needed
to make time and enable the experiment to go in the
900 min. In this way we can resolve the decomposition
stage in the higher temperature range.
sample is cooled to ambient temperatures and adsorbs water
from the atmosphere. This accounts for the dehydration step
observed at 82 °C in Fig. 4. Three isothermal decomposition
steps are observed at 588, 687 and 750 °C and are attributed
to the decomposition of sulphate anions.
Controlled rate thermal analysis of apjohnite
The CRTA (Fig. 4) shows two quasi-isothermal steps at
82 and 97 °C attributed to dehydration. A non-isothermal
higher temperature mass loss is observed at 328 °C and
based upon ion current measurements is attributed to dehy-
dration. In between the two experiments the halotrichite
The controlled rate thermal analysis of apjohnite is shown in
Fig. 5a (up to 430 °C) and 5b (From 430 to 980 °C). The
summary of the CRT analyses are given in Table 2. It is
apparent that there are two isothermal decomposition steps at
57 and 77 °C assigned to dehydration. Two higher dehy-
dration mass loss steps are observed at 183 and 294 °C; the
first step is a short isothermal step and the second is non-
isothermal. Similarly to the dynamic pattern, sulphate
decomposition also takes place in two stages under CRTA
conditions. In addition to the quasi-isothermal step at 692 °C
and the isothermal one at 821 °C, a shoulder peak is observed
at 753 °C. This shoulder peak indicates the possible forma-
tion of an oxy-sulphate intermediate upon heating.
Controlled rate thermal analysis of dietrichite
The controlled rate thermal analysis of dietrichite is shown
Fig. 4 Controlled rate thermal analysis of halotrichite: ambient to
430 °C, 430–980 °C
in Fig. 6a (up to 430 °C) and 6b (from 430 to 980 °C). The
Fig. 6 Controlled rate thermal analysis of dietrichite: a ambient to
430 °C, b 430–980 °C
Fig. 5 Controlled rate thermal analysis of apjohnite: a ambient to
430 °C, b 430–980 °C
123

506
R. L. Frost et al.
2. Caven RM, Mitchell TC. Equilibrium in systems of the type
Al2(SO4)3-MIISO4-H2O. I. Aluminium sulfate-copper sulfate-
water, and aluminium sulfate-manganous sulfate-water, at 30
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thermal analysis patterns (Fig. 6a) show two isothermal
steps at 78 and 102 °C which as for the dynamic thermal
analysis experiment are attributed to dehydration. Three
higher temperature thermal decomposition steps are
observed at 228, 243 and 323 °C and are also attributed to
dehydration of the dietrichite. (The possible isothermal
nature of the higher temperature dehydration steps cannot
be proved because the level of decomposition is under the
set value of 0.1 mg/min.) Similarly to the dynamic exper-
iment sulphate decomposition is a single step process. The
fact that the temperature remained constant at 636 °C for
more than 400 min is a proof that the rate-determining step
of decomposition is the slow heat transport. Providing time
enough for the heat and the mass transport processes to
occur, quasi equilibrium decomposition can be reached.
8. Frost RL, Wain DL, Reddy BJ, Martens W, Martinez-Frias J,
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trimethylammonium bromide modified montmorillonite organo-
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Conclusions
A series of halotrichites also known as pseudo-alums
including halotrichite, apjohnite, and dietrichite have been
studied by both dynamic thermal and controlled rate thermal
analysis. EDX analysis shows the chemical formula of the
minerals to be (Fe2?)SO4ꢀAl2(SO4)3ꢀ22H2O, (Mn2?)SO4ꢀ
Al2(SO4)3ꢀ22H2O, (Zn)SO4ꢀAl2(SO4)3ꢀ22H2O, respectively.
X-ray diffraction showed the minerals to be phase pure
except for dietrichite which showed the presence of minor
gypsum.
10. Williams SA, Cesbron FP. Wupatkiite from the Cameron ura-
nium district, Arizona, a new member of the halotrichite group.
Mineral Mag. 1995;59:553–6.
11. Menchetti S, Sabelli C. The halotrichite group: the crystal
structure of apjohnite. Mineral Mag. 1976;40:599–608.
12. Ballirano P, Bellatreccia F, Grubessi O. New crystal-chemical and
structural data of dietrichite, ideally ZnAl2(SO4)4ꢀ22H2O, a
member of the halotrichite group. Eur J Mineral. 2003;15:1043–9.
13. Ballirano P. Crystal chemistry of the halotrichite group XAl2
(SO4)4ꢀ22H2O: the X = Fe- Mg-Mn-Zn compositional tetrahe-
dron. Eur J Mineral. 2006;18:463–9.
14. Krstanovic I, Dimitrijevic R, Ilic P. Crystallographic study
of halotrichite from Suplja Stena, Avala Mountain. Glasnik
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The thermal decomposition of the halotrichite minerals
occur through a series of isothermal and non-isothermal
steps as is shown by the CRTA experiments. In general a
number of dehydration steps are observed up to around
340 °C. These steps are isothermal in the CRTA experi-
ment. The high temperature of the last dehydration steps
(343 °C for halotrichite; 304 °C for apjohnite; 342 °C for
dietrichite) provides an indication of how strongly hydro-
gen bonded the water is in the halotrichite structure.
With the use of the CRTA technique the thermal
decomposition processes can be standardized. It means that
the decomposition temperatures are independent of the
experimental conditions offering a solid basis for com-
parison when concerning the thermal behaviour of a series
of minerals is evaluated.
17. Kulp JL, Adler HH. Thermal study of jarosite. Am J Sci.
1950;248:475–87.
18. Cocco G. Differential thermal analysis of some sulfate minerals.
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19. Tsvetkov AI, Val’yashikhina EP. Thermal characteristics of
minerals of the alunite group. Dokl Akad Nauk SSSR. 1953;
89:1079–82.
20. Tsvetkov AI, Val’yashikhina EP. Phase conversions of hydrated
iron sulfates (fibroferrite, Fe(SO4)(OH)ꢀ4.5H2O, and melanterite,
FeSO4ꢀ7H2O) by heating. Dokl Akad Nauk SSSR. 1953;93:
343–6.
Acknowledgements This research was supported by the Hungarian
Scientific Research Fund (OTKA) under grant No. K62175. The
financial and infra-structure support of the Queensland University of
Technology Inorganic Materials Research Program is gratefully
acknowledged.
21. Swamy MSR, Prasad TP, Sant BR. Thermal analysis of ferrous
sulfate heptahydrate in air. II. The oxidation-decomposition path.
J Therm Anal Calorim. 1979;16:471–8.
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34. Hales MC, Frost RL. Thermal analysis of smithsonite and
hydrozincite. J Therm Anal Calorim. 2008;91:855–60.
35. Palmer SJ, Frost RL, Nguyen T. Thermal decomposition of hy-
drotalcite with molybdate and vanadate anions in the interlayer.
J Therm Anal Calorim. 2008;92:879–86.
24. Swami MSR, Prasad TP. Thermal analysis of iron(II) sulfate
heptahydrate in air. III. Thermal decomposition of intermediate
hydrates. J Therm Anal Calorim. 1980;19:297–304.
25. Swamy MSR, Prasad TP. Thermal analysis of iron(II) sulfate
heptahydrate in air. V. Thermal decomposition of hydroxy and
oxysulfates. J Therm Anal Calorim. 1981;20:107–14.
26. Banerjee AC, Sood S. Thermal analysis of basic ferric sulfate and
its formation during oxidation of iron pyrite. In: Thermal analy-
sis: proceedings of the 7th international conference, vol. 1; 1982.
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27. Frost RL, Hales MC, Martens WN. Thermogravimetric analysis
of selected group (II) carbonate minerals—implication for the
geosequestration of greenhouse gases. J Therm Anal Calorim.
2009;95:999–1005.
28. Palmer SJ, Spratt HJ, Frost RL. Thermal decomposition of
hydrotalcites with variable cationic ratios. J Therm Anal Calorim.
2009;95:123–9.
29. Carmody O, Frost R, Xi Y, Kokot S. Selected adsorbent materials
for oil-spill cleanup. A thermoanalytical study. J Therm Anal
Calorim. 2008;91:809–16.
30. Frost RL, Locke A, Martens WN. Thermogravimetric analysis
of wheatleyite Na2Cu2?(C2O4)2ꢀ2H2O. J Therm Anal Calorim.
2008;93:993–7.
36. Vagvoelgyi V, Daniel LM, Pinto C, Kristof J, Frost RL, Horvath
E. Dynamic and controlled rate thermal analysis of attapulgite.
J Therm Anal Calorim. 2008;92:589–94.
37. Vagvolgyi V, Frost RL, Hales M, Locke A, Kristof J, Horvath E.
Controlled rate thermal analysis of hydromagnesite. J Therm
Anal Calorim. 2008;92:893–7.
38. Vagvolgyi V, Hales M, Martens W, Kristof J, Horvath E, Frost
RL. Dynamic and controlled rate thermal analysis of hydrozincite
and smithsonite. J Therm Anal Calorim. 2008;92:911–6.
39. Zhao Y, Frost RL, Vagvolgyi V, Waclawik ER, Kristof J,
Horvath E. XRD, TEM and thermal analysis of yttrium doped
boehmite nanofibres and nanosheets. J Therm Anal Calorim.
2008;94:219–26.
31. Frost RL, Locke AJ, Hales MC, Martens WN. Thermal stability
of synthetic aurichalcite. Implications for making mixed metal
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