J. Chem. Thermodynamics 95 (2016) 142–148
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J. Chem. Thermodynamics
journal homepage: www.elsevier.com/locate/jct
Enthalpy of formation of natural hydrous copper sulfate: Chalcanthite
Mira Bissengaliyeva a, Lyubov Ogorodova b,⇑, Marina Vigasina b, Lyubov Mel’chakova b, Dariya Kosova c,
Igor Bryzgalov b, Dmitrii Ksenofontov b
a
Institute of Problems of Complex Development of Mineral Resources, Ippodromnaya Str., 5, 100019 Karaganda, Kazakhstan
M.V. Lomonosov Moscow State University, Geological Faculty, MSU, Leninskie Gory, 119234 Moscow, Russia
c
M.V. Lomonosov Moscow State University, Chemical Faculty, MSU, Leninskie Gory, 119234 Moscow, Russia
b
a r t i c l e
i n f o
Article history:
Received 3 September 2015
Received in revised form 8 December 2015
Accepted 11 December 2015
Available online 17 December 2015
Keywords:
Enthalpy of formation
Enthalpy of dehydration
Calvet microcalorimetry
Hydrous copper sulfate
Chalcanthite
a b s t r a c t
This paper presents the results of the thermochemical study of hydrous copper sulfate CuSO45H2O
performed on a high-temperature heat-flux Tian–Calvet microcalorimeter. The samples of two natural
chalcanthite (Kosmurun ore deposit, Kazakhstan, and Lavrion deposit, Greece) and synthetic hydrous
copper sulfate (blue vitriol) were characterized by X-ray microprobe analysis, X-ray powder diffraction,
thermal analysis, FTIR and Raman spectroscopy. The enthalpy of dehydration at T = 298.15 K was measured, and the standard molar enthalpies of formation from the elements were determined by the melt
solution calorimetry in accordance with Hess’s law. The values of Df H0m (T = 298.15 K) were found to be
(2267.2 ± 4.1) kJmol1 for natural chalcanthite and (2272.6 ± 6.0) kJmol1 for synthetic hydrous
copper sulfate (blue vitriol).
Ó 2015 Published by Elsevier Ltd.
1. Introduction
Natural hydrous copper sulfate CuSO45H2O, chalcanthite is a
secondary mineral, which is formed in the oxidation zone of copper
sulfide deposits by sedimentation from waters saturated with dissolved copper sulfate, as well as in the areas of volcanic activity.
Under industrial conditions, a synthetic analog of chalcanthite
(blue vitriol) is obtained by slow evaporation of an aqueous solution of copper sulfate or by dissolution of copper in sulfuric acid.
The product is used in chemical and tinctorial industry, and in agriculture as a fertilizer and for pest control.
For physicochemical modeling of stability of hydrous sulfates of
bivalent metals and the sequence of their sedimentation in the
hypergenesis zone of sulfide ores, on the evaporation barrier of
water-salt basins and in hydrothermal solutions containing acidic
sulfate waters near the craters of volcanoes – fumaroles, it is necessary to have reliable thermodynamic data for both hydrous and
anhydrous participants of processes [1]. The data on thermodynamic properties of hydrous and anhydrous copper sulfate available in the literature are limited. In a previously reported study
[2] the enthalpy of formation of anhydrous copper sulfate CuSO4
has been determined from the obtained experimental data on dissolution of copper oxide in sulfuric acid. Based on the data [3,4] on
⇑ Corresponding author.
E-mail address: logor@geol.msu.ru (L. Ogorodova).
http://dx.doi.org/10.1016/j.jct.2015.12.010
0021-9614/Ó 2015 Published by Elsevier Ltd.
the enthalpy of dissolution of synthetic copper sulfate in water,
Bergman [5] calculated the values of Df H0m (T = 298.15 K) for CuSO4.
The available reference books [7–9] also used the results of the
only experimental work [2]. Only one experimental value of the
enthalpy of dissolution of a synthetic crystalline hydrous copper
sulfate in water has been reported in the literature [4]. Based on
the results of this work, the value of the enthalpy of formation of
synthetic CuSO45H2O was calculated in [6], and subsequently this
value was included in the reference books [7,9].
In this work, we carried out the first thermochemical study of
natural chalcanthite and its synthetic analog (blue vitriol) using a
Calvet microcalorimeter and obtained new data on the enthalpies
of dehydration and formation of hydrous copper sulfate from its
constituent elements.
2. Experimental
2.1. Materials, equipment and diagnostic methods
A thermochemical study of natural chalcanthite from the oxidation zone of the Kosmurun ore deposit (the mountain ridge
Genghis, Eastern Kazakhstan) (sample I) has been carried out;
and for comparison we studied a sample from the Lavrion deposit
(Greece) (sample II), as well as a sample of synthetic hydrous copper sulfate (blue vitriol) (sample III) (table 1).
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M. Bissengaliyeva et al. / J. Chem. Thermodynamics 95 (2016) 142–148
TABLE 1
Provenance and mass fraction purity of substances used in this study.
Substance name
Chalcanthite
Chalcanthite
Blue vitriol
Corundum
Platinum
Lead oxide
Boric acide
a
b
Source
Natural (Kosmurun, Kazakhstan)
Natural (Lavrion, Greece)
Synthetic (Mosreactiv Co., Russia)
Mosreactiv Co., Russia
Myprom Co., Russia
Mosreactiv Co., Russia
Mosreactiv Co., Russia
State
Mass fraction purity
Further treatments
a
Crystal
Crystal
Crystal
Crystal
Solid
Powder
Crystal
>0.99
>0.99a
>0.99b
0.999b
0.999b
0.99b
0.99b
Calcination at T = 630 K
Calcination at T = 630 K
Calcination at T = 630 K
None
None
Melting of the mixture of lead oxide and boric
acid in a ratio 2PbO: B2O3 at T = 1073 K
Purity was estimated according X-ray data.
Purity grade as given by the supplier.
Before study the samples of natural chalcanthite were carefully
selected by hand picking under a binocular microscope. Detailed
diagnostics of substances was done with use of modern physicochemical methods.
Chemical analysis was carried out on a microanalyzer
«CAMEBAX SX-50» (Cameca, France). To determine elemental
composition, we used the analytical line Ka and the following
standards: Cu – cuprite (natural); Mg – hornblende (natural); Ca
– tremolite (natural); Co – CoSi (synthetic); Zn – ZnO (synthetic);
Fe – spinel (natural); Pb – nodorite (natural); S – celestine (natural). All synthetic oxides were provided by company Cameca. The
natural minerals were provided by A.E. Fersman Mineralogical
Museum and were tested using standards provided by company
Cameca using the ‘‘Camebax SX-50” and a Jeol JSM-6480LV scanning electron microscope equipped with an INCA-Wave 500 wavelength dispersive spectrometer (Jeol, Japan). The mode of operation
was as follows: accelerating voltage 15 kV; probe current 30 nA.
X-ray analysis was performed using a powder diffractometer
«STOE-STADI MP» (Germany) equipped with a curved Ge(1 1 1)
monochromator which gives strictly monochromatic CoKa1
radiation (k = 0.178897 nm). Data were collected in a regime of
sequential overlapping of scanned regions using a linear
position-sensitive detector with an angle of coverage of 5° at 2h
with a channel width of 0.02°.
IR-spectroscopic investigation was done on a Fourier spectrometer «FSM-1201» (Russia) at room temperature in the air over the
range of wave numbers from (400 to 4000) cm1 with a spectral
resolution of 4.0 cm1. The accuracy of the determination of the
absorption bands frequencies was ±1 cm1. Specimens for the
studies were prepared in the form of tablets pressed from 3 mg
of mineral substance and 250 mg of KBr, as well as in the form of
suspensions of mineral powder in petrolatum oil.
Raman spectroscopic study was carried out on a Raman microscope «EnSpectr R532» (Russia) with a diffraction grating (1800
lines per mm) and a spectral resolution of about 6 cm1. The laser
radiation wavelength was equal to 532 nm, the laser radiation
power on the sample was approximately 15 mW, a single exposure
time was 1 s, signal averaging was done using 50 measurements.
The spectrum was obtained on a non-oriented single crystal of
about 100 lm in size; a diameter of the focal laser spot was
approximately 15 lm.
Thermal behavior of the samples was investigated over the
temperature range from room temperature to 773 K on a Derivatograph Q-1500 D (MOM, Hungary) with a heating rate of
10 Kmin1, weight of the samples was about 90 mg).
2.1.1. Chemical analysis
X-ray microprobe analysis data for the composition of the
samples studied are shown in table 2. The chemical formulas calculated for 2 charges coincide with the theoretical formula of
CuSO45H2O.
2.1.2. X-ray diffraction
The obtained X-ray diffraction patterns of natural minerals and
synthetic blue vitriol are identical; in accordance with the database
of the powder diffraction patterns ICDD No. 01-070-2158 [10] the
studied samples are mono-mineral phases with the structure of
chalcanthite (figure 1). No impurity phases were detected.
2.1.3. FTIR spectroscopy
The IR-absorption spectra of all the samples studied were
similar to each other, the maximum difference in the values of
the wave numbers of the absorption bands did not exceed
4 cm1; the samples did not contain impurities in the noticeable
amounts, and they were monomineral phases. Figure 2
shows the IR absorption spectra for the sample I (Kosmurun,
Kazakhstan).
The spectrum of chalcanthite prepared in a tablet with KBr
(figure 2a) agrees with the spectra presented in [11,12]. It must
be pointed out that this spectrum differs markedly from the
spectrum of sample prepared as a suspension in petrolatum oil
(figure 2b). The latter one coincides with the data [13,14] obtained
by the same method. In opinion of [13], this fact may be explained
by the interaction between chalcanthite and KBr, when the specimen was prepared for research. The range of wave numbers
(400–4000) cm1 registered in the experiment can be divided into
four non-overlapping spectral areas.
The first region (3800–2600) cm1 contains a broad absorption
band with a few maxima over the range of (3480–3160) cm1,
corresponding to valence vibrations of water molecules present
in the structure in different crystallographic positions.
TABLE 2
Chemical composition of the substances studied.
Oxides
CuO
MgO
CoO
ZnO
FeO
CaO
PbO
SO3
H2Ob
a
Sample I
(Kosmurun,
Kazakhstan)
Sample II
(Lavrion, Greece)
Sample III
(Synthetic)
Mass
fraction
Ua
Mass
fraction
Ua
Mass
fraction
Ua
0.3207
0.0001
0.0081
0.000002
0.0074
0.00001
0.0001
0.000008
0.00001
0.0077
0.0045c
0.0076
0.000006
0.000002
0.000002
0.000002
0.3186
0.0005
0.0049
0.0004
0.0005
0.3039
0.369
0.3220
0.0003
0.0001
0.0001
0.0001
0.0002
0.0004
0.0001
0.000004
0.000008
0.000002
0.3128
0.364
0.0087
0.0045c
0.3189
0.361
0.0060
0.0045c
U is the uncertainty of experimental values calculated with 0.95 level of confidence, the uncertainties are calculated on the basis of 10 determinations for each
sample.
b
The water content was determined by the thermogravimetry method.
c
The uncertainty is an instrumental error (MOM recorder).
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M. Bissengaliyeva et al. / J. Chem. Thermodynamics 95 (2016) 142–148
FIGURE 1. XRD pattern of natural chalcanthite from the Kosmurun deposit (sample I). Note that 1 angstrom = 0.1 nm.
FIGURE 3. Raman spectra of natural halcanthite from the Kosmurun deposit
(sample I).
FIGURE 2. FTIR spectra of natural chalcanthite from the Kosmurun deposit (sample
I) (obtained in transmission mode): a – in tablet of KBr; b – in petrolatum oil; c – in
petrolatum oil after heating of initial mineral up to T = 630 K.
The second region (1990–1500) cm1 contains the absorption
band with maxima over the range of (1620–1670) cm1, which
corresponds to deformation vibrations of H2O molecules and confirms the presence of water in the molecular form in the structure
of the mineral.
The third region (1390–760) cm1 contains absorption bands
corresponding to the splitting triply degenerate valence vibration
of the distorted tetrahedra [SO4]2, totally symmetric valence
vibration of tetrahedra [SO4]2- and librations of H2O molecules.
The fourth region (760–440) cm1 contains absorption bands
corresponding to deformation vibrations of distorted tetrahedra
[SO4]2. No impurity phases were detected.
FIGURE 4. Thermogram of natural chalcanthite from the Kosmurun deposit
(sample I).
145
1.0
0.5
6
0.5
d
c
b
a
398.9
400.5
399.2
II
III
CuSO45H2O 249.67
I
The accuracy of determination of the calorimetric experiment temperatures was ± 1 K.
U is the uncertainty of experimental data calculated with 0.95 level of confidence.
N is the number of experiments.
The values of the formula weight was taken from the reference book [9].
1.9
2.5
6
1.7
6
5
CuSO4
159.60d
40.8
40.5
40.5
Ub/kJmol1
Ub/kJmol1
d
Ho(T = 630 K) Ho(T =
298.15 K) /(kJmol1)
Composition of sample,
formula weight/g
Nc
Ho(T = 630 K) Ho(T =
298.15 K) + Ddehydr.Ho(T =
630 K) /(kJmol1)
2.2.1. Tian–Calvet microcalorimetry
The thermochemical study was carried out on a hightemperature heat-flux Tian–Calvet microcalorimeter «SETARAM»
(France). Measurement of the enthalpy of dehydration was carried
out by ‘‘the double drop” method [19]. First, a sample with a mass
of (6 to 12) (±2103) mg was dropped from room temperature
(298.15 K) into an empty platinum crucible in the calorimeter at
the temperature 630 K, which according to the results of thermal
analysis corresponds to completion of the process of total removal
of water. IR absorption spectrum of the product of the heating of
chalcanthite at this temperature (figure 2c) confirmed a complete
dehydration of the substance and registered the change in its crystal structure. The infrared absorption spectrum of newly formed
phase was obtained on suspension of a mineral powder in petrolatum oil (figure 2c) and showed signs of the onset of crystallization
of chalcocyanite [10]. The thermal effect under measurement
included the enthalpy increment of the sample and the
enthalpy of its dehydration {Ho(T = 630 K) Ho(T = 298.15 K)
+ Ddehydr.Ho(T = 630 K)}. Then, the dehydrated sample was dropped
again into the calorimeter at the same temperature, and we measured only the value of its enthalpy increment {Ho(T = 630 K) Ho(T = 298.15 K)}. The sample weight was controlled before and
after experiments.
The enthalpy of formation was determined by the melt solution
calorimetry using a thermochemical cycle including the dissolution of the mineral and its constituent components [19]. We used
the melt with composition 2PbO B2O3 as a solvent; the melt
was prepared by melting of stoichiometric amounts of lead oxide
and boric acid at T = 1073 K (weight accuracy was ±0.2 mg). On dissolution which was carried out by dropping the samples from
room temperature into the melt-solvent at T = 973 K, we measured
jointly the enthalpy increment of the substance and the enthalpy
of its solution {Ho(T = 973 K) Ho(T = 298.15 K) + Dsol.Ho(T =
973 K)}. Masses of the samples upon dissolution were (5 to 13)
Composition of sample,
formula weight/g
The thermochemical studies were carried out on a hightemperature heat-flux Tian–Calvet microcalorimeter ‘‘Setaram”
(France) and differential scanning calorimeter «NETZSCH DSC 204
F1» (Germany) at the ambient pressure of (1004 ± 5) hPa.
Number of
sample
2.2. Thermochemical methods
TABLE 3
Calorimetric data on dehydration of chalcanthite obtained in present work (ambient pressure P = (1004 ± 5) hPa, the uncertainty is presented as 0.95 confidence interval).a
2.1.5. Thermal analysis
The thermograms obtained for the three samples of chalcanthite are identical and consistent with the literature data [18].
On the DTA curve (figure 4) we marked two endothermic effects
associated with two stages of removal of water. The first of them
(two-step) takes place in the temperature range (338 to 403) K
and is characterized by two maxima, it corresponds to the loss of
0.27–0.30 mass fraction (about 4 molecules of water). The second
stage corresponds to the lost of remaining water (0.08 mass fraction) over the range from T = (493 to 538) K.
Nc
2.1.4. Raman-spectroscopy
The Raman spectrum (figure 3) is similar to the Spectra shown
in [14-17]. Anion [SO4]2 shows itself in the spectrum by a group of
lines: a strong line 976 cm1 corresponds to the totally symmetric
valence vibration of the anion; the triplet with frequencies of
(1135, 1086, and 1060) cm1 corresponds to the split triply degenerate antisymmetric valence vibration; the line with a frequency of
603 cm1 belongs to the triply degenerate deformation vibration of
the interior angles S–O–S; line 457 cm1 corresponds to doubly
degenerate deformation vibration of the angles. The group of
high-frequency lines with the frequencies of (3190, 3360, and
3472) cm1 corresponds to the valence vibrations of OH-groups
(in water molecules). No impurity phases were detected.
6
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M. Bissengaliyeva et al. / J. Chem. Thermodynamics 95 (2016) 142–148
TABLE 4
Results of drop solution calorimetry in the melt 2PbOB2O3 for chalcanthite obtained in the present work (ambient pressure P = (1004 ± 5) hPa, the uncertainty is presented as
0.95 confidence interval).a
Number
of sample
Composition
of sample
Formula weightb/g
Ho(T = 973 K) Ho(T = 298.15 K)
+ Dsol.Ho(T = 973 K)/(kJmol1)
Nd
Uc/(kJmol1)
I
II
III
a
b
c
d
CuSO4
CuSO45H2O
CuSO4
CuSO4
159.60
249.67
159.60
419.7
24.1
29.5
1.0
2.9
1.3
1.9
8
7
8
6
The accuracy of determination of calorimetric experiment temperatures was ±1 K.
The values of the formula weight was taken from the reference book [9].
U is the uncertainty of experimental values calculated with 0.95 level of confidence.
N is the number of experiments.
TABLE 5
The standard enthalpies of dehydration and of formation of pentahydrate copper sulfates. The uncertainties are calculated on the basis of the law of propagation of uncertainty.
*
Sample
Ddehydr.Ho(T = 298.15 K)/kJmol1
Ddehydr.Ho(T = 298.15 K)/kJ(mol H2O)1
Df H0m (T = 298.15 K)/kJmol1
Sample I (Kosmurun, Kazakhstan)
Sample II (Lavrion, Greece)
80.6 ± 1.8
80.0 ± 2.2
16.1 ± 0.4
16.0 ± 0.4
Sample III (Synthetic)
81.9 ± 2.5
16.4 ± 0.5
2263.3 ± 5.5
2265.4 ± 5.7
2273.0 ± 9.3*
2272.6 ± 6.0
This value was obtained using solution data for hydrous natural chalcanthite.
(±2103) mg. When using (30 to 35) g of solvent during the (6–8)
solution experiments the ratio of dissolved substance – melt can be
attributed to an infinitely dilute solution with the enthalpy of mixing close to zero.
The calibration of the instrument was carried out on each week
of thermochemical studies according to the enthalpy increments
when dropping the reference substances: platinum (in the experiments on dissolution at 973 K) and corundum a-Al2O3 (when
studying dehydration at T = 630 K). The necessary thermochemical
data for the standards were borrowed from [7]. Used in the calculations were the average values obtained for each temperature.
2.2.2. Differential scanning calorimetry
Measurement of the thermal effects of the dehydration process
of chalcanthite (sample I) was carried out using «NETZSCH DSC 204
F1» (Germany) in aluminum crucibles under nitrogen flow
(20 mLmin1) with a heating rate of 10 Kmin1 over the temperature range from room temperature to 573 K. The instrument was
calibrated according to the temperature and the enthalpy of phase
transition of standard substances (C6H12, Hg, Ga, KNO3, In, Sn, Bi,
99.999% purity) [20].
Thermoanalytical system NETZSCH is located at the Chemistry
Faculty of M.V. Lomonosov Moscow State University, all other
equipment used is located at the Geological Faculty of M.V. Lomonosov Moscow State University.
3. Results and discussion
The calorimetric results from the experiments in Tian–Calvet
microcalorimeter are listed in tables 3 and 4.
3.1. The enthalpy of dehydration
Using the experimental values for dehydration obtained on the
Tian–Calvet microcalorimeter (table 3) and the necessary reference
data for the water [21], we calculated the enthalpy of reaction (1)
according to equation (2). The amount of water removed was 0.369
mass fraction (sample I), 0.364 mass fraction (sample II) and 0.361
FIGURE 5. DSC curves of natural chalcanthite from the Kosmurun deposit (sample
I); thermal effects Q1 and Q2 correspond to two experimentally unseparable
dehydration steps in the first stage of the water removal; thermal effect Q3 relates
to the dehydration process in the second stage.
mass fraction (sample III) that corresponds to a loss of about 5
water molecules in each of the samples studied.
CuSO4 5H2 O ¼ CuSO4 þ 5H2 O ðlÞ;
ð1Þ
Ddehydr: Ho ðT ¼ 298:15 KÞ ¼ fHo ðT ¼ 630 KÞ Ho ðT ¼ 298:15 KÞ
þ Ddehydr: Ho ðT ¼ 630 KÞgCuSO4 5H2 O
fHo ðT ¼ 630 KÞ Ho ðT ¼ 298:15 KÞg
CuSO4 5fHo ðT ¼ 630 KÞ
Ho ðT ¼ 298:15 KÞg H2 O:
ð2Þ
The results obtained for natural samples and synthetic blue vitriol (table 5) are consistent with each other and with the value
(79.45 kJmol1) calculated in [6] according to calorimetrical data
on dissolving of hydrous and anhydrous copper sulfate in water
[4].
The experimental results of the study of the dehydration process for natural chalcanthite (sample I) in the heating mode using
differential scanning calorimetry are given in figure 5 and table 6.
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M. Bissengaliyeva et al. / J. Chem. Thermodynamics 95 (2016) 142–148
TABLE 6
Results of DSC measurements of the dehydration thermal effect of chalcanthite
(sample I).
Mass of sample/mg
Q1 + Q 2
Jg
2.56
3.67
2.16
TABLE 7
Thermochemical values used in the calculation of the standard enthalpies of
formation of the copper sulfate pentahydrate.
Q3
1
1
905.4
935.5
982.0
Component
1
kJmol
Jg
kJmol
225.9
233.4
245.0
297.0
306.7
319.7
74.1
76.5
79.8
Mean value: 235 ± 24*
1
Mean value:
77.0 ± 7.0*
CuO(tenotite)
CaO(s)
CaSO4(anhydrite)
Al2O3(corund)
Al(OH)3(gibbsite)
DHa/kJmol1
Df H0m (T = 298.15 K)b/kJmol1
c
70.10 ± 0.90
21.78 ± 0.29d
131.3 ± 1.6e
107.38 ± 0.59f
172.6 ± 1.9g
156.1 ± 2.0
635.1 ± 0.9
1434.4 ± 4.2
1675.7 ± 1.3
1293.1 ± 1.2
DH = [Ho(T = 973 K) Ho(T = 298.15 K) + Dsol.Ho(T = 973 K)].
The values of Df H0m (T = 298.15 K) are the reference values from [9].
c
The values of DH were calculated using reference data on {Ho(T = 973 K)
Ho(T = 298.15 K)} [9] and experimental values of Dsol.Ho(T = 973 K): c – from [19].
d
The values of DH were calculated using reference data on {Ho(T = 973 K)
Ho(T = 298.15 K)} [9] and experimental values of Dsol.Ho(T = 973 K): d – from [22].
e
The values of DH were calculated using reference data on {Ho(T = 973 K)
Ho(T = 298.15 K)} [9] and experimental values of Dsol.Ho(T = 973 K): e – from [23].
f
The values of DH were calculated using reference data on {Ho(T = 973 K)
Ho(T = 298.15 K)} [9] and experimental values of Dsol.Ho(T = 973 K): f – from [24].
g
The value of DH is the experimental value from [25].
a
b
*
Uncertainties are calculated with 0.95% level of confidence.
The total thermal effect (Q1 + Q2) corresponds to the enthalpy of
the first stage of water removal. The thermal effect Q3 corresponds
to the dehydration enthalpy in the second stage. The enthalpy of
complete dehydration of chalcanthite was found to be equal to
(312 ± 25) kJmol1. This value relates to process of water removal
in the temperature interval (330 to 530) K during heating. The
value of the enthalpy of dehydration obtained by microcalorimetry
method for sample I (table 5) belongs to T = 298.15 K. These data
can be compared with each other after the conversion of DSC data
to T = 298.15 K with considering the enthalpy of vaporization of
water [21]. Estimated value of Ddehydr.Ho(T = 298.15 K)
(90 kJmol1) does not contradict to the value of enthalpy
obtained by means of ‘‘the double drop” method (80.6 ± 1.8
kJmol1) (table 5).
4.2. The enthalpy of formation
Based on the experimental values of the dissolution of three
samples of anhydrous copper sulfate (table 4) in accordance with
Hess’s law, the values of their standard molar enthalpies of formation from the elements were calculated using the reaction (3) and
equations (4) and (5)
CuO þ CaSO4 ¼ CuSO4 þ CaO;
Df H0m ðT ¼ 298:15 KÞchalcanthite
¼ Df H0m ðT ¼ 298:15 KÞdehydr:chalcanthite Drð1Þ Ho ð298:15 KÞ
þ 5Df H0m ðT ¼ 298:15 KÞH2 O ðlÞ:
ð6Þ
The calculated values of Df H0m (T = 298.15 K) of the pentahydrates of
copper sulfate studied are listed in table 5.
The enthalpy of formation of chalcanthite was also determined
using the data on dissolution of natural mineral (sample II) by
reaction (7) and equations (8) and (9).
CuO þ CaSO4 þ 3:33 AlðOHÞ3 ¼ CuSO4 5H2 O þ CaO þ 1:66 Al2 O3 ;
ð7Þ
Drð7Þ Ho ð298:15 KÞ ¼ DHCuO þ DHCaSO4 þ 3:33 DHAlðOHÞ3
DHchalcanthite DHCaO
ð3Þ
1:66 DHAl2 O3 ;
ð8Þ
o
Drð3Þ H ðT ¼ 298:15 KÞ ¼ DHCuO þ DHCaSO4 DHCuSO4 DHCaO;
ð4Þ
Df H0m ðT
¼ 298:15 KÞCuSO4
o
¼ Drð3Þ H ðT ¼ 298:15 KÞ þ
þ
Df H0m ðT
¼ Drð7Þ Ho ðT ¼ 298:15 KÞ þ Df H0m ðT ¼ 298:15 KÞCuO
þ Df H0m ðT ¼ 298:15 KÞCaSO4 þ 3:33 Df H0m ðT ¼ 298:15 KÞAlðOHÞ3
Df H0m ðT
¼ 298:15 KÞCaSO4 ¼ 298:15 KÞCuO
Df H0m ðT
Df H0m ðT ¼ 298:15 KÞCaO 1:66 Df H0m ðT ¼ 298:15 KÞAl2 O3 ; ð9Þ
¼ 298:15 KÞCaO;
ð5Þ
where DH = {H (T = 973 K) H (T = 298.15 K) + Dsol.H (T = 973 K)}
are thermochemical data for anhydrous copper sulfate (table 4)
and constituent components (table 7), the values of the enthalpies
of formation of the latter are shown in the same table. The enthalpy
of mixing for an infinitely dilute solution is close to zero. The
o
Df H0m ðT ¼ 298:15 KÞchalcanthite
o
o
derived values of Df H0m (T = 298.15 K) are equal to: (753.7 ± 5.2)
(sample I), (756.4 ± 5.3) (sample II), and (761.7 ± 5.4) (sample
III) kJmol1 and relate to dehydrated chalcanthite CuSO4 with signs
of the onset of crystallization of chalcocyanite. These values, as
might be expected, are more endothermic than the values of standard enthalpies of formation of crystalline chalcocyanite given in
[7–9]: (770.9 ± 1.1), (771.4 ± 1.2) and (771.4 ± 1.3) kJmol1,
respectively.
The values of standard enthalpies of formation for the copper
sulfate pentahydrates studied were determined using enthalpies
of formation of dehydrated phases given above, and the values of
enthalpies of dehydration of hydrous copper sulfates obtained in
the present study (according to reaction (1)) and given at the end
of the previous paragraph. The calculation was carried out based
on equation (6).
where DH = {Ho(T = 973 K) Ho(T = 298.15 K) + Dsol.Ho(T = 973 K)}
are thermochemical data for chalcanthite (table 4) and constituent
components (table 7).
All the values obtained for the standard enthalpies of formation
of chalcanthite (table 5) are consistent with each other within the
error limits. For the synthetic sample, this value is in agreement
with values for synthetic hydrous copper sulfate Df H0m
(T = 298.15 K) = (2279.7 ± 3.4) kJmol1 given in the reference
book [9]. The average value from three determinations for natural
chalcanthite, equal (2267.2 ± 4.1) kJmol1, can be recommended
as a standard value of the enthalpy of formation of natural chalcanthite. This value is different by 0.5% from that given in the reference book [9] for the synthetic analog.
4.3. Conclusions
The experimental thermochemical study of chalcanthite was
performed using different methods of high temperature Tian–
Calvet microcalorimetry. For the first time, the value of enthalpy
of dehydration was measured and the standard enthalpies of
formation for natural chalcanthite and its synthetic analog (blue
148
M. Bissengaliyeva et al. / J. Chem. Thermodynamics 95 (2016) 142–148
vitriol) were obtained. The new thermodynamic values can be used
for the quantitative modeling of the physicochemical conditions of
weathering processes in hypergenesis zone of sulfide ores.
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JCT 15-600