Characterization of zinc carbonate hydroxides synthesized by precipitation from zinc acetate and potassium carbonate solutions

Article abstract of DOI:10.1016/j.materresbull.2004.05.023

Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation of a white solid, whose composition and structure depend on the initial concentrations of the reagents. Hydrozincite, Zn₅(CO₃)₂(OH)₆, forms when the K₂CO₃ concentration is low and a new K-containing zinc carbonate hydroxide phase forms when the K₂CO₃ concentration is high. The chemical formula of the new phase has been determined to be Zn(CO₃)_0.61(OH)_0.78·0.233K ₂CO₃ by TGA, CHNO and AA analysis. The new phase is insoluble in water and extensive water washing of the new phase does not change its composition or structure, suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified CO ₂ causes disproportionation to separate phases of ZnCO₃ and K₂CO₃. Pure ZnCO₃ was synthesized for comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal synthesis of ZnCO₃.

Full text of DOI:10.1016/j.materresbull.2004.05.023

Materials Research Bulletin 39 (2004) 1939–1948
Characterization of zinc carbonate hydroxides synthesized
by precipitation from zinc acetate and potassium
carbonate solutions
*
S. Zhang, H. Fortier, J.R. Dahn
Department of Physics and Atmospheric Science, Dalhousie University, Halifax, N.S. Canada B3H 3J5
Received 28 April 2004; accepted 28 May 2004
Abstract
Addition of potassium carbonate solution to zinc acetate solution at room temperature causes the precipitation
of a white solid, whose composition and structure depend on the initial concentrations of the reagents.
Hydrozincite, Zn (CO ) (OH) , forms when the K CO concentration is low and a new K-containing zinc
5
3 2
6
2
3
carbonate hydroxide phase forms when the K CO concentration is high. The chemical formula of the new phase
2
3
ꢀ
has been determined to be Zn(CO3)0.61(OH)0.78 0.233K CO by TGA, CHNO and AA analysis. The new phase is
2
3
insoluble in water and extensive water washing of the new phase does not change its composition or structure,
suggesting the new phase is a single phase compound salt. Exposure of the new phase to a stream of humidified
CO causes disproportionation to separate phases of ZnCO and K CO . Pure ZnCO was synthesized for
2
3
2
3
3
comparison by a new procedure under atmospheric conditions instead of the more common hydrothermal
synthesis of ZnCO3.
#
2004 Elsevier Ltd. All rights reserved.
Keywords: A. Inorganic compounds; B. Chemical synthesis; C. Thermogravimetric analysis (TGA); C. X-ray diffraction
1
. Introduction
Zinc carbonate compounds are used in respirators to remove toxic gases such as SO and HCN [1]. In
2
reference [1], several synthesis methods are described, one of which involves the mixing of zinc acetate
and potassium carbonate solutions, thought to yield soluble potassium acetate and insoluble zinc
carbonate. The ‘‘ZnCO ’’ is precipitated on a suitable activated carbon to make an impregnated carbon
3
for respirator applications.
*
Corresponding author. 1 902 494 2991; fax: þ1 902 492 5191.
E-mail address: jeff.dahn@dal.ca (J.R. Dahn).
0025-5408/$ – see front matter # 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2004.05.023

1
940
S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
The search for new impregnants for respirator applications has led us to carefully examine the
compounds produced during the reaction between solutions of Zn(CH COO) and K CO . ZnCO exists in
a well-known crystal structure called Smithsonite, and is easily identified by X-ray diffraction [2]. We were
3
2
2
3
3
initially surprised to learn that ZnCO is not a product of the reaction between Zn acetate and potassium
3
carbonate solutions. Instead, under some conditions hydrozincite (Zn (CO ) (OH) ) [3] forms as we will
5
3 2
6
show in this paper and under other conditions an unknown phase forms which we identify here.
In order to identify the new phase, we reviewed the literature on zinc carbonate hydroxides. Sawada
ꢀ
et al. [4] suggested the formation of Zn CO (OH) 2H O, another zinc carbonate hydroxide, when ZnO
4
3
3
2
powder was exposed to an atmosphere of carbon dioxide and water vapor. In reference [5], Ohkum
et al. reported two more forms of zinc carbonate hydroxide: Zn CO (OH) and another phase whose
2
3
2
structure and composition were not determined. One of the applications of zinc carbonate hydroxide is
in the production of nanometer-sized ZnO powder by decomposition at relatively low temperature. ZnO
is of extensive interest to industry. For example, it is used in ZnO varistors for protection of electronic
devices [6]. It is also used as a functional component in catalysts used in the chemical industry. The
decomposition kinetics of zinc carbonate hydroxides have been studied extensively [7,8]. These zinc
carbonate hydroxides exhibit a general chemical formula, Zn(CO ) (OH)
x
with 0 ꢁ x ꢁ 1. The end
3
2À2x
members are ZnCO and Zn(OH) , respectively, for x ¼ 1 and x ¼ 0. The value of x can presumably be
3
2
controlled by the synthesis procedure. Cu forms similar carbonate hydroxide compounds exhibiting the
form, Cu(CO ) (OH)
. CuCO3 (x ¼ 1), Cu (CO ) (OH) (x ¼ 0.67, which is the mineral
3
x
(2À2x)
3
3 2
2
Malachite) and Cu (CO )(OH) (x ¼ 0.5, which is the mineral Aurichalcite) are several examples.
2
3
2
Here, we study the reaction between solutions of Zn(CH COO) and K CO at room temperature.
3
2
2
3
We show the range of synthesis conditions that yield hydrozincite and those that yield the previously
unknown new phase. As we will show, the new phase is a water insoluble zinc carbonate hydroxide-
ꢀ
potassium carbonate-compound salt with approximate composition Zn(CO3)0.61(OH)0.78 0.233K CO .
2
3
In order to distinguish the unknown phase from ZnCO we also synthesized pure ZnCO for
3
3
comparison. Initially we were surprised that pure ZnCO was not commercially available, but later
3
learned that hydrothermal synthesis conditions are commonly required to obtain anhydrous ZnCO [7].
3
We developed a synthesis of anhydrous ZnCO under atmospheric pressure that is also reported here.
3
2
. Experimental section
2
.1. Synthesis of ZnCO3
ZnCl and K CO (Aldrich) were used as reagents. 100 ml of 0.05 M ZnCl solution were mixed
2
2
3
2
while stirring with 100 ml of 0.05 M K CO solution previously saturated with CO . The mixture was
2
3
2
then placed in a water-ice bath for 24 h. Then it was stored at room temperature for another 24 h. The
precipitated material was washed with distilled water until the wash water had a neutral pH. The
precipitate was recovered by filtration and then dried at 120 8C in air for 2 h. The resultant product is
called sample A and will later be found to be ZnCO3.
2
.2. Studies of the reaction between Zn(CH COO) and K CO solutions
3 2 2 3
ꢀ
Zn(CH COO) 2H O and K CO (Aldrich) were used as the reagents to make five samples whose
3
2
2
2
3
ꢀ
syntheses are described in Table 2. 0.0073 mol of Zn(CH COO) 2H O in a 0.55 M aqueous solution
2
3
2

S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
1941
Table 1
Conditions used for synthesis of samples B–F
Sample
Conc. Zinc acetate(mol/L)
Moles Zinc acetate (mol)
Conc. K
2
CO
3
(mol/L)
Moles K
2
CO
3
(mol)
B
C
D
E
F
0.55
0.55
0.55
0.55
0.55
0.0073
0.0073
0.0073
0.0073
0.0073
2.64
1.98
0.99
0.50
0.20
0.02
0.02
0.02
0.02
0.02
and 0.02 mol of K CO in an aqueous solution of molarity specified in Table 1 were mixed while
2
3
stirring at room temperature. After 10 min of reaction, the precipitates were allowed to settle and were
kept at room temperature for 24 h. The precipitates were subsequently rinsed with distilled water until
neutral pH was reached. The precipitates were recovered by filtration and dried at 120 8C in air for 2 h.
The resulting samples are designated samples B–F, as indicated in Table 1.
2
.3. X-ray diffraction measurements
X-ray powder diffraction (XRD) was performed using a Siemens D-5000 diffractometer equipped
with a diffracted beam monochromator and a Cu target X-ray tube. Data were collected every 0.058
with a 10 s count time. A zero background sample holder (Si (510) wafer obtained from ‘‘The Gem
Dugout’’, PA, USA) was used when only a small amount of sample was available, for example after
TGA measurement. A well-type sample holder requiring about 0.5 ml of sample was used for
measurements when larger amounts of sample were available.
2
.4. Thermal analysis
TGA measurements were made at 5 8C/min from room temperature to 500 8C in air on all
six synthesized samples using a TA instruments TGA 51 thermogravimetric analyzer. Upon
completion of the TGA measurements, the products were examined by XRD. Differential Scanning
Calorimetry (DSC) measurements were made in air at 5 8C/min on sample A, B and D using a Dupont
9
10 DSC.
2
.5. Chemical analysis
Several samples were sent for CHNO (carbon–hydrogen–nitrogen–oxygen) analysis (Canadian
Microanalytical Sevices Ltd., Delta B.C., Canada) and AA (Atomic Adsorption) analysis (Department
of Mining and Metallurgical Engineering, Dalhousie University). Table 2 lists the results of both
analyses.
2
.6. Test of the stability of sample B
Sample B was stored in a sealed vial for 4 months where the sample was only in contact with a very
limited amount of carbon dioxide and moisture. Some of the stored sample was placed in a flowing

1
942
S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
Table 2
AA and CHNO analysis results for samples A–F
Sample
CHNO analysis (wt.%)
AA analysis (wt.%)
C
H
N
O
Zn
K
A
B
C
D
E
F
8.86
6.73
6.33
4.43
5.70
5.31
0.25
0.59
0.66
1.36
1.44
1.10
<0.3
<0.3
<0.3
<0.3
<0.3
<0.3
36.06
33.65
34.37
32.67
33.81
32.42
47.8
44.4
0.26
12.32
52.6
0.04
atmosphere of dry carbon dioxide for 4 days. Another portion of the stored sample was placed in a
flowing stream of water-saturated carbon dioxide gas generated by bubbling CO through water at room
2
temperature. The sample was exposed to the H O/CO mixture for 4 days. The samples after storage
2
2
and after exposure to different atmosphere were examined by XRD measurements.
3
. Results and discussion
3
.1. Identification of three compounds by XRD
Fig. 1 shows the X-ray diffraction profiles collected on the series of samples (B–F) prepared from the
zinc acetate and potassium carbonate solutions. Samples B and C show similar patterns and samples D,
E and F show a different common pattern. For comparison, the XRD pattern of sample A, ZnCO , is
3
also shown in Fig. 1. The XRD patterns of samples (B–F) do not match the pattern of sample A which
matches perfectly to JCPDS card 8-449, the pattern of ZnCO . Samples D, E and F match the pattern
3
for Zn (CO ) (OH) (JCPDS card 19-1458) or Zn(CO ) (OH) which is called hydrozincite.
1.2
5
3 2
6
3 0.4
However, samples B and C, which have almost the same diffraction pattern, could not be identified
using the known patterns in the powder diffraction file. To our knowledge, the unknown phase
represented by samples B and C has not been reported in the literature. We have determined the
chemical formula of this unknown phase, as will be shown in the following section, but we have not
solved its crystal structure. Some of the Bragg peaks are broad and some are quite narrow. We do not
know if the broad peaks arise from a low symmetry crystal structure having overlapping peaks or from
a structure that has a large fraction of defects like stacking faults that selectively broaden Bragg peaks
with certain Miller indices [9]. The grain size of the crystallites of three samples which are essentially
pure phases was estimated using the width of strongest diffraction peak and the Scherrer formula [10],
to be 54 nm for sample A, 4.4 nm for sample B, and 4.2 nm for sample D.
Fig. 2 shows TGA profiles of samples A, B and D. Zinc carbonate hydroxides exhibiting general
formula Zn(CO ) (OH)
(0 ꢁ x ꢁ 1) are expected to thermally decompose according to:
3
x
2À2x
ZnðCO Þ ðOHÞ
! ZnO þ ð1 À xÞH O " þ xCO "
(1)
3
x
ð2À2xÞ
2
2
According to Eq. (1), the solid remaining after TGA should be ZnO. Fig. 3 shows the XRD patterns of
the solid remaining after TGA to 500 8C for each of samples A, B and D. For samples A and D, only

S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
1943
Fig. 1. XRD profiles collected on the precipitates recovered from the reaction between zinc acetate and potassium carbonate
solutions as described in Table 2. The six panels show the diffraction patterns of samples A–F, respectively. Sample A is
ZnCO
3 2 3
(JCPDS 8-449); Samples B and C are K CO -containing zinc carbonate hydroxide; and samples D, E and F are
Zn (CO ) (OH) (JCPDS 19-1458).
5
3 2
6
Fig. 2. TGA patterns of samples A, B and D. The measurements were made using a scan rate of 5 8C/min in air.

1
944
S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
Fig. 3. XRD profiles of the TGA products (heated to 500 8C in air) derived from (a) ZnCO
3
(Sample A); (b)
ꢀ
(
Zn (CO ) (OH) ) (Sample D) and (c) Zn(CO ) (OH)0.78 0.233K CO (Sample B). Panel (d) shows the diffraction pattern
5
3 2
6
3 0.61
2
3
of commercial K CO after heating to 500 8C for comparison to panel (c). Only ZnO is observed in panels (a) and (b) but both
2
3
2 3
ZnO and K CO are both observed in panel (c).
ZnO is observed. However, sample B shows another phase in addition to ZnO. In order to identify the
additional phase, we compared it to the diffraction pattern of K CO heated to 500 8C. As Fig. 3 shows,
2
3
the agreement between the peaks from the additional phase and the peaks from heated K CO is good.
2
3
From the XRD measurements of the samples after TGA, we conclude that samples A and D contain
only Zn cations and that sample B contains both Zn and K cations. Sample B was made in a process
that included numerous water washes to neutral pH so that all washable K CO and K(CH COO)
2
3
3
would have been removed from the sample. Therefore, we believe that sample B is a K-containing
compound salt.
3
.2. Determination of x in Zn(CO ) (OH)
3
for samples A and D using TGA
x
2À2x
The weight loss in the TGA curves of Fig. 2 can be used to calculate x in Zn(CO ) (OH)
3
for
x
2À2x
samples A and D according to Eq. (1). We calculate x ¼ 1.0 for sample A and x ¼ 0.43 for sample D,
which agree well with the theoretical values for ZnCO (x ¼ 1) and hydrozincite (x ¼ 0.4). The TGA
3
measurements confirm the phase identification by XRD as stated above. The formula for sample D
suggested by TGA measurement is Zn(CO3)0.43(OH)1.14. Table 3 lists the calculated weight percentages
of the elements based on this suggested chemical formula and the measured values.

S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
1945
Table 3
Comparison between calculated and tested content for sample D
Calculated
Tested
Test method
Zn content (wt.%)
K content (wt.%)
C content (wt.%)
59.14
0
52.6
0.04
4.43
1.36
32.67
73.54
AA
AA
4.67
1.03
35.16
73.61
CHNO
CHNO
CHNO
TGA
H content wt.%)
O content (wt.%)
TGA residual: ZnO (wt.%)
The calculation was based on the suggested chemical formula: Zn(CO
3
)
0.43(OH)1.14.
After TGA, sample B retains 77% of its mass as shown in Fig. 2. Along with other information, this
is used to determine the tentative formula of this unknown phase in the next section.
3
.3. Tentative formula of K-containing zinc carbonate hydroxide (sample B)
Based on the evidence that ZnO and K CO were present in the residue of sample B after TGA, a
2
3
ꢀ
] b[K CO ], for the unknown phase was proposed with b/a and x to be
2 3
formula, a[Zn(CO ) (OH)
3
x
2À2x
determined. AA analysis was used to measure the K and Zn contents and b/a was determined to be
.233. Using this value of b/a, x was then determined using the mass fraction remaining after TGA and
0
was found to be x ¼ 0.61. Therefore, the tentative formula of this K-containing zinc carbonate
ꢀ
hydroxide is Zn(CO ) (OH)
3
0.233K CO . The calculated content of carbon based on this formula
2 3
0.61
0.78
is 6.86%, which agrees well with 6.73% determined by CHNO analysis. Table 4 lists the calculated
weight percentages of the elements based on the suggested chemical formula and the measured values,
showing good agreement.
Initially, we hesitated in the identification of the unknown phase according to the model above.
However, there are analogous compound salt phases known where Cu replaces Zn. One is
ꢀ
ꢀ
ꢀ
KCu (CO ) (OH) 4H O (JCPDS 28-746) [11] or Cu(CO ) (OH)0.5 0.25K CO 2H O and the other
3
2
3 2
2
3 0.75
2
2
ꢀ
ꢀ
ꢀ
is KCu (CO ) (OH) 2H O (JCPDS 30-932) or Cu(CO ) (OH)0.64 0.227K CO 0.91H O.
2
2
.2
3 2
1.4
2
3 0.68
2
3
Although these phases are hydrated, we expect they could be gently dried to produce un-hydrated
materials.
Based on the formation of ZnO and K CO after heating at 500 8C (Fig. 3) and on the obtained
2
3
formula we suggest that this K-containing zinc carbonate hydroxide decomposes according to
ZnðCO3Þ0:61ðOHÞ0:78ꢀ0:233K CO ! ZnO þ 0:233K CO þ 0:61CO " þ 0:39H O "
2
3
2
3
2
2
ZnCO decomposes at a higher temperature than Zn(OH) does [12], so we believe that the
will decrease as x decreases. Fig. 2 shows this to be
3
2
decomposition temperature of Zn(CO ) (OH)
3
x
2À2x
the case, since sample A has x ¼ 1, sample B has x ¼ 0.61 and sample D has x ¼ 0.4. Apparently, the
presence of K CO in the compound salt of sample B does not affect the trend in thermal stability.
2
3
Fig. 4 shows both DSC and TGA curves of sample A (ZnCO ), indicating that the decomposition in
3
air is endothermic with a heat of reaction of about 685 J/g, or 86 kJ/mol. Although we do not present
the DSC data here, the decomposition of samples B and D are also endothermic and the heat of reaction
is about 63 kJ/mol (or 429 J/g) and about 52 kJ/mol (or 468 J/g) for samples B and D, respectively.

1
946
S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
Table 4
Comparison between calculated and tested content for K-containing zinc carbonate hydroxide (sample B)
Calculated
Tested
Test method
Zn content (wt.%)
K content (wt.%)
C content (wt.%)
H content (wt.%)
O content (wt.%)
TGA residual: ZnOþK
44.38
12.31
6.86
44.40
12.32
6.73
AA
AA
CHNO
CHNO
CHNO
TGA
0.53
35.92
77.02
0.59
33.65
77.00
2 3
CO (wt.%)
ꢀ
The calculation was based on the suggested chemical formula: Zn(CO
3
)
0.61(OH)0.78 0.233K
2
CO
3
.
Based on the decomposition behavior of the three compounds studied, we speculate that all compounds
in the Zn(CO ) (OH) family will decompose endothermically.
Three compounds have been identified using XRD, TGA, AA, and CHNO analysis. Table 5
3
x
2À2x
summaries the compositions of the compounds and the methods used to determine them.
3
.4. Stability of K-containing zinc carbonate hydroxide in humidified CO2
Zinc carbonate hydroxides are unlikely to be stable in an acidic environment where the OH group
may react with acid. The combination of CO and moisture, similar to moist air, is an example of such
2
an acidic environment. A study of these compounds in moist CO is important if the zinc carbonate
2
hydroxide compounds are to be used as impregnants on activated carbons for respirator application.
Here we use sample B as an example for focused study.
Fig. 5 shows the XRD profiles collected on sample B when fresh, after 4 months of storage in a
sealed vial, after treatment with dry CO , and after treatment with wet CO . No obvious phase
transition was caused by normal storage or by exposure to dry CO . However, exposure to moist CO
2
2
2
2
Fig. 4. TGA and DSC traces of sample A (ZnCO ). Both were measured using a scan rate of 5 8C/min in air.
3

S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
1947
Table 5
Summary of chemical formulas for three compounds derived from different investigative methods
Sample
XRD
TGA
AA, TGA and CHNO
A
B
D
ZnCO3
ZnCO3
ꢀ
Zn(CO
3
)
0.61(OH)0.78 0.233K
2
CO
3
Zn(CO
3
)0.4(OH)1.2
3
Zn(CO )0.43(OH)1.14
ꢀ
apparently causes the disproportionation of Zn(CO3)0.61(OH)0.78 0.233K CO . Comparing the XRD
2
3
pattern of sample B treated with wet CO to those of ZnCO and heated K CO (500 8C) (Fig. 3d)
2
3
2
3
shows that two separate solid phases, ZnCO3 and K CO , have been produced. Such a
disproportionation is believed to be caused by the reaction of the OH group with H CO and is
2
3
2
3
suggested to take place as follows:
ZnðCO3Þ0:61ðOHÞ0:78ꢀ0:233K CO þ 0:39CO þ 0:39H O ! ZnCO þ 0:233K CO þ 0:78H O
2
3
2
2
3
2
3
2
Based on the XRD results for the sample exposed to dry CO , without water, CO apparently does not
2
2
cause the reaction above to proceed.
2
Fig. 5. XRD profiles collected on: (a) sample B when fresh, (b) stored in a sealed vial for 4 months, (c) treated with dry CO ,
and (d) treated with wet CO . Panel (e) shows the diffraction pattern of ZnCO for comparison with panel (d).
2
3

1
948
S. Zhang et al. / Materials Research Bulletin 39 (2004) 1939–1948
4
. Conclusions
The reaction between zinc acetate and potassium carbonate solutions at room temperature has been
studied. Two phases, hydrozincite and a new K-containing zinc carbonate hydroxide compound salt,
ꢀ
Zn(CO3)0.61(OH)0.78 0.233K CO were identified. ZnCO was synthesized to compare to the other
2
3
3
phases. XRD, TGA/DSC, AA and CHNO have been used to characterize the three compounds with the
focus on the identification of the new phase. The new phase disproportionates to ZnCO and K CO
3
3
2
under the forcing conditions of exposure to humid CO2.
Acknowledgements
The authors acknowledge 3M Canada and NSERC for the funding of this work and G.E. Weagle, S.J.
Smith and J.A. McManus for useful discussions.
References
[
[
[
[
[
[
[
[
[
1] M.J. Abler, US patent 5344626, 1994.
2] International Centre for Diffraction Data (version 2.16). Newtown Square, PA19073, USA. JCPDS card 8-449.
3] International Centre for Diffraction Data (version 2.16). Newtown Square, PA19073, USA. JCPDS card 19-1458.
4] Y. Sawada, M. Murakam, T. Nishide, Thermochim. Acta 273 (1996) 95.
5] N. Ohkum, Y. Funayama, H. Ito, Japn J. Chem. 5 (1987) 802.
6] D.R. Clarke, J. Am. Ceram. Soc. 82 (1999) 485.
7] F.J. Gotor, M. Macias, A. Ortega, J.M. Criado, Int. J. Chem. Kinet. 30 (1998) 647.
8] N. Kanari, D. Mishra, I. Gaballah, B. Dupr e´ , Thermochim. Acta 410 (2004) 93.
9] V.A. Drits, C. Tchoubar, X-ray Diffraction by Disordered Lamellar Structures, Springer-Verlag, 1991.
[10] B.D. Cullity, S.R. Stock, Elements of X-ray Diffraction, Prentice-Hall, 2001.
[
11] R. Ouahes, J. Amiel, A. La ¨ı doudi, Rev. Chim. Min e´ r. 9 (1972) 309.
[12] CRC Handbook of Chemistry and Physics. 70th edition, B-117, 1989–1990.