Preparation of Zeolite F as Slow Release Fertilizers from K-Feldspar Powder

Abstract

Influence of KOH concentration and reaction time on the synthesis of zeolite F from K-feldspar, and the kinetics of potassium slow release from the product were studied. X-ray diffraction (XRD), Fourier transformation infrared spectrometry (FTIR), and scanning electron microscopy (SEM) were applied to characterize the as-synthesized samples. The XRD results indicate that there exist K−G zeolite (K2Al2SiO6⋅H2O) with hexagonal structure at the KOH concentration of 2 mol⋅kg⁻¹ and zeolite F (KAlSiO4⋅1.5H2O) with tetragonal structure at 4–5 mol⋅kg⁻¹. In terms of synthesis efficiency, crystallization time of 12 h was chosen as optimal condition. The surface area and pore diameter of zeolite F sample synthesized in 4 mol⋅kg⁻¹ at 95 °C for 12 h were investigated by surface area analyzer, the values of which are 27 m²/g and 0.513 nm, respectively. Slow-release testing results suggest that the potassium cumulative release fraction of zeolite F in water for 42 d is up to 68.97% and can be fitted well with Elovich equation.

Full text

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
zInorganic Chemistry
Preparation of Zeolite F as Slow Release Fertilizers from
K-Feldspar Powder
Jiangyan Yuan, Jing Yang, Hongwen Ma,* and Qianqian Chang[a]
Influence of KOH concentration and reaction time on the
synthesis of zeolite F from K-feldspar, and the kinetics of
potassium slow release from the product were studied. X-ray
diffraction (XRD), Fourier transformation infrared spectrometry
(FTIR), and scanning electron microscopy (SEM) were applied to
characterize the as-synthesized samples. The XRD results
indicate that there exist KG zeolite (K2Al2SiO6·H2O) with
hexagonal structure at the KOH concentration of 2 mol·kg1
and zeolite F (KAlSiO4·1.5H2O) with tetragonal structure at 4–
5 mol·kg1. In terms of synthesis efficiency, crystallization time
of 12 h was chosen as optimal condition. The surface area and
pore diameter of zeolite F sample synthesized in 4 mol·kg1at
958C for 12 h were investigated by surface area analyzer, the
values of which are 27 m2/g and 0.513 nm, respectively. Slow-
release testing results suggest that the potassium cumulative
release fraction of zeolite F in water for 42 d is up to 68.97%
and can be fitted well with Elovich equation.
1. Introduction
The 30–50% of crop yields rely on the commercial chemical
fertilizers according to conservative estimation.[1,2] Abuse of
chemical fertilizers causes serious environmental contamination
and only a little nutrition is really absorbed by the plant. The
excess chemical fertilizer will pollute groundwater when
washed off in the form of high concentrations of elements such
as nitrogen, phosphorus, and potassium.[3] Moreover, the faster
dissolution rate of fertilizer in soil than the absorption rate by
plants will result in the loss of fertilizer and contamination of
surrounding watershed.[4–6] What’s more, the rapidly increasing
world population requires correspondingly higher agricultural
productivity.[7] The utilization of slow release fertilizer (SRF) can
slow down the migration rate of nutritional elements, which is
beneficial to the improvement of fertilizer use efficiency and
production, as well as the decrease of soil contamination.[8] It is
promising for the sustainable development of ecological
environment to use slow release fertilizer.[9]
The global demand of potash has exceeded 32 million
metric tons of K2O in current time and will have a continuous
increase in the coming decade.[10,11] The United Nations Food
and Agriculture Organization (FAO) have emphasized that
global potash will appear a temporary shortage in the near
future.[12] Potassium-bearing framework aluminosilicate miner-
als are widely distributed in China, mainly consisting of K-
feldspar and illite, although the water-insolute potassium
minerals are rare.[13] Also, potassium-bearing framework alumi-
nosilicate minerals have been proposed as a substitute source
of potassium.[14–16]
Zeolites is a whole class of hydrated and crystalline
aluminosilicate minerals with three-dimensional framework
structure built by [AlO4] and [SiO4], along with secondary
cations for charge balancing.[17] Due to the particular structure,
zeolites have a wide range of applications, such as water
adsorption, gas separations, petroleum industries and agricul-
ture.[18,19] Natural zeolites help to maintain nutrients and water,
promote the migration of nutrient elements and water, and
improve long-term soil quality owe to the channel and pore
structure.[20] As a kind of K-zeolite, zeolite F still can provide K
element necessary to the growth of plants and amend soil
besides the functions of retaining water and nutritions.
Synthesis of zeolites F is one of promising applications for
K-feldspar. The present study focuses on the synthesis of
Zeolite F using K-feldspar from Rongcheng county of Shandong
Province in China, which is very significant for the application
of K-feldspar in fertilizers, which not only can supply the
potassium element needed by plants, but also decrease the
loss of nutrition and water. Moreover, K-feldspar (K: Al: Si=
1:1:3) can provide theoretically sufficient and necessary potas-
sium, aluminum, and silicon sources for zeolite F (K: Al: Si =
1:1:1). Because the K/Al in zeolite F (KAlSiO4·1.5H2O) is same as
that in K-feldspar, KOH was not consumed in whole process
theoretically. So it is necessary to investigate the structure and
slow-release property of zeolite F. In this paper, preparation in
different conditions, crystal structure, specific surface area, the
slow release property and kinetics analysis of zeolite F were
discussed in detail.
[a] Dr. J. Yuan, J. Yang, Prof. H. Ma, Q. Chang
Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and
Solid Wastes, School of Materials Science and Technology, China University
of Geosciences, Beijing, 100083, P. R. China
Tel. /Fax: +86 10 82323374
E-mail: mahw@cugb.edu.cn
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/slct.201702120
Full Papers
DOI: 10.1002/slct.201702120
10722
ChemistrySelect 2017,2, 10722 –10726  2017 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim
Wiley VCH Dienstag, 21.11.2017
1733 / 102669 [S. 10722/10726] 1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
2. Result and discussion
2.1. Synthesis of Zeolite F
The X-ray diffraction patterns of zeolite F obtained at various
KOH concentration for 48 h are displayed in Figure 1, and all of
the diffraction peaks can be indexed to the tetragonal phases
of zeolite F (JCPDS file 38–0216) and hexagonal phase of KG
zeolite (JCPDS file 12–0194), suggesting that the decrease of
KOH concentration makes the crystal structure and category of
products different. The strongest peak of zeolite F at 30.178is
assigned to its (114) crystal plane, and that of KG zeolite found
at 12.758corresponds to the (110) diffraction plane. As shown
in Figure 1, the main phase is KG zeolite (K2Al2SiO6·H2O) when
the concentration of KOH is 2 mol·kg1(F-2), and there exist
two phases (KG zeolite and zeolite F) when concentration of
KOH is 3 mol·kg1(F-3). The phase of KG zeolite disappears
completely until 4 mol·kg1(F-4) at 95 8C. It turns out that
zeolite F is the stable phase in higher concentration of KOH
and KG zeolite is more stable in lower concentration of KOH.
The results reveal that K+and OHare the dominant influence
factors controlling the formation of different product struc-
tures.[21]
The chemical compositions of products obtained at various
concentrations of KOH at 958C for 48 h are given in Table 2.
When the concentration of KOH is in the range of 2 to
3 mol·kg1, the mass fraction of SiO2in the products is between
36.65%–39.05%, Al2O3is between 22.88%–25.31%, and K2Ois
between 19.65%-21.50%. According to the chemical composi-
tions of F-4 and F-2 calculated by the least square method,[22]
the mass fractions of KG zeolite and zeolite F in sample of F-3
are 65.5% and 34.5%, respectively. With the concentration of
KOH increased, the contents of SiO2and Al2O3change from
35.89 to 34.32% and 26.82 to 27.87%, respectively. The content
of K2O increases from 23.46 to 24.73%, which is beneficial to
the supplement of K+ion for crops when zeolite F is added to
soil as fertilizer. The raw K-feldspar powder has K2O/Al2O3ratio
of 0.957 according to Table S1, we can obtain that the ratio
K2O/Al2O3of F-2~F-5 are 0.930, 0.921, 0.949, 0.957, respectively,
by the calculation of contents in Table 1. Therefore, no extra
potassium, aluminum, and silicon sources are needed owe to
the same K/Al ratio of K-feldspar and Zeolite F (KAlSiO4·1.5H2O)
in the synthetic process.
The FTIR spectra of product samples at various KOH
concentrations of 2, 3, 4, 5 mol·kg1for 48 h were given in
Figure 2. There exist adsorption bands at 3586 and 1643 cm1
attributing to the existence of -OH in all samples. The
vibrational band at 1137 cm1disappears as the increase of
hydrothermal concentration owe to the transformation of
octahedral Al to tetrahedral Al and the formation of Si-OAl
from the combination of Al with Si-OSi.[23] The strong
absorption band at around 956 cm1moves to higher wave-
Figure 1. XRD patterns of product samples synthesized from K-feldspar at
various KOH concentrations of 2, 3, 4, 5 mol·kg1(from bottom to top) for
48 h.
Table 1. chemical compositions of zeolite F obtained in various KOH concentrations for 48 h
Samples Concentration of KOH SiO2Al2O3K2OH
2Ophase
mol·kg1wt% wt% wt% wt%
F-2 2.0 39.05 22.88 19.65 18.42 KG zeolite
F-3 3.0 36.65 25.31 21.50 16.54 KG zeolite +zeolite F
F-4 4.0 35.89 26.82 23.46 13.83 K0.892Al0.942Si1.070O4·1.375H2O
F-5 5.0 36.14 26.71 23.56 13.59 K0.894Al0.936Si1.075O4·1.348H2O
Figure 2. FTIR spectra of product samples synthesized at various KOH
concentration of 2, 3, 4, 5 mol·kg1(from bottom to top) for 48 h.
Full Papers
10723
ChemistrySelect 2017,2, 10722 –10726  2017 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim
Wiley VCH Dienstag, 21.11.2017
1733 / 102669 [S. 10723/10726] 1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
length and becomes narrow as the concentration increases,
indicating the polymerization degree of SiO2increases and the
sample of F-4 has the largest polymerization. The band at
736 cm1belongs to the stretching vibration of SiSi and
SiAl(Si).[24] And the bands at 673 and 513 cm1gradually
disappear along with the increase of KOH solution concen-
trations due to the major secondary building of zeolite F when
the concentration of KOH reaches to 3 mol·kg1.
Figure 3 presents the SEM images of product samples
prepared at various KOH concentrations of 2, 3, 4, 5 mol·kg1,
respectively. The shape of sample F-2 (Figure 3a) in KOH
concentration of 2 mol·kg1presents hexagon pieces with the
side length of around 1.5 mm, and there are two orthogo-
nal planes crossing the disk, indicating the zeolite KG has a
higher crystallization. The cross-shape (Figure 3c) of F-4 in the
concentration of 4 mol·kg1is composed of many rectangle
rods, the center of which are many square sections. The
morphology of sample F-3 (Figure 3b) consists of many
tetragonal rods embedding in the disks, indicating there exist
two phases of zeolite F and KG zeolite in F-3 corresponding to
XRD results. Compared with the shapeless of F-5 (Figure 3d),
the sample F-4 (Figure 3c) has better crystallization. Combining
the analysis of SEM and FTIR, 4 mol·kg1was chosen the most
suitable concentration.
The experiments of the crystallization times on the
formation of zeolite F and KG zeolite were carried out as well
as the XRD results and crystallinity were shown in Figure 4.
Comparing the XRD results of KG zeolite (Figure S3) and
zeolite F (Figure 4a) in different time, the synthesis time of KG
zeolite is far longer than that of zeolite F. By the calculation of
relative crystallinity (RC), RC of KG zeolite obtained in 36 h and
48 h just are 9.58% and 56.60%, respectively, but that of zeolite
F has been up to 96.83% in 16 h, so zeolite F was chosen to
continue the next experiments. The synthesis of zeolite F is
determined by the dissolution rate of gel, number and
distribution of nuclei in the initial stage, and crystal growth rate
during hydrothermal treatment.[25] When reaction time is less
than 8 h, crystallinity of zeolite F has a slow increase. The RC of
zeolite F increases dramatically from 1.945 to 95.14% when
reaction time is between 8 h and 12 h. RC of zeolite F reaches
the optimal yield of around 96.83% at 16 h and RC of zeolite F
starts to decline slowly after 16 h. Combining the XRD results,
we can see that the solid samples obtained still maintain
amorphous shapes when reaction time is 4–8 h. The products
prepared from the obtained AS change to a crystalline structure
when they were subjected to hydrothermal treatment for 8–
12 h and purer zeolite F phase was formed when reaction time
is 12 h. In terms of composition and FTIR spectra of solid
samples obtained in different hydrothermal reaction time
(Table S2 and Figure S4), 12 h was chosen as optimal reaction
time owe to the higher polymerization degree of SiO2and K/Al.
In order to have a more clear understanding, the crystal
structures of zeolite F was displayed in Figure 5a and b. zeolite
Figure 3. The SEM images of samples at various KOH concentration of 2, 3, 4,
5 mol·kg1(a-d).
Figure 4. (a) XRD patterns of product samples under hydrothermal conditions with KOH concentration of 4 mol·kg1( 4, 8, 12, 16, 24, 36 h, from bottom to
top); (b) Relative crystallinity of zeolite F and KG zeolite for different reaction time.
Full Papers
10724
ChemistrySelect 2017,2, 10722 –10726  2017 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim
Wiley VCH Dienstag, 21.11.2017
1733 / 102669 [S. 10724/10726] 1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
F is assigned to the orthorhombic system with space group
I222 (No. 23). Crystal structure of zeolite F is composed of three
dimensional framework consisting of [AlO4] and [SiO4] con-
nected and sharing their corners and edges to form 8-
membered rings. Different potassium atoms (K1, K2, K2, K1,
from top to bottom) are arranged along caxis. There are three
types K atoms (K3, K5, K4) located the sites off-center. From the
plane (001), open tunnels are formed along c-axis, the center of
which was occupied by a series potassium atoms (K2, K1, K1,
K2 from outside to inside.[26] The N2adsorption-desorption
isotherms of the as-prepared zeolite F samples are displayed in
Figure 6. The zeolite F sample exhibits type II isotherms with a
surface area of 27 m2/g and pore diameter of 5.13 A
˚, which is
larger than the diameters of Pb2+(1.98 A
˚), Cd2+(1.92 A
˚), Cr3+
(1.26 A
˚) and Cr6+(1.04 A
˚), indicating the pore of zeolite F is
enough to adsorb those toxic ions.[27] For example, El-Kamash
et al using synthetic zeolite A as an efficient sorbent media to
remove Cd2+and Zn2+from aqueous solutions and waste-
water.[28] Sprynskyy et al investigated the adsorption of Pb2+,
Cu2+,Ni
2+, and Cd2+ions from aqueous solution onto
clinoptilolite.[29] So, zeolite F not only can be used as slow-
release fertilizer but soil amelioration.
2.2. Slow-release behavior of zeolite F
The release behavior of potassium ions from zeolite F was
investigated in distilled water and is shown in Figure 7. The
following formula was used to calculate the cumulative release
of K2O:
hið%Þ¼ciV=mw ð1Þ
Ft¼h1þ::: þhtð2Þ
Where irepresents release days; ciis the concentration of
Figure 5. (a) and(b) Crystal structure of the zeolite F.
Figure 6. N2adsorption-desorption isotherm of sample obtained in optimal
conditions and (inset) the corresponding pore size distribution.
Figure 7. Release rate of potassium ions from zeolite F in distilled water.
Full Papers
10725
ChemistrySelect 2017,2, 10722 –10726  2017 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim
Wiley VCH Dienstag, 21.11.2017
1733 / 102669 [S. 10725/10726] 1

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
K+in aqueous extracts for different days; V =100 mL; m =5g;
and w=23.96%; t represent the release days; Ftis the
cumulative release fraction at time t; The dramatical increase of
release fraction in the initial time and the stable change in the
rest time indicate that zeolite F is situated in nutrient release
period in the beginning stage and can be used as soil amend-
ments ( the absorption of Cd2+,Cr
3+,Pb
2+) in the late stage
when added to soil. As we all know, water-soluble NPK
compound fertilizer is so easily dissolved in water, and quickly
runs out as well as causes damage to soil after being added to
the soil.[6] Here, the K ions were located in the cage structure
and rather difficult to be dissolved in cool water and soil.
According to the test of water solubility, accumulative release
of K2O can be fitted by the equation as follows:
y¼0:6349 þ0:0157ln ðx0:994Þð3Þ
Where y represents accumulative release of K2O (%) and x is
days; and the correlation coefficient R2=0.991. which indicates
the release of zeolite F belongs to Elovich equation.[30] By the
observation and prediction of Figure 7, the accumulative
release of K2O reaches 68.97% after water solubility testing for
42 days, 72.09% for 240 days, and 72.75% for 365 days,
respectively, indicating the sample could be used as a long-
term soil amendment media besides a slow-release potassium
fertilizer with nutrient K2O release.
3. Conclusion
In summary, effects of KOH concentration and crystallization
time on the synthesis of zeolite F, and slow-release behavior as
slow-fertilizer were studied in this paper. KG zeolite
(K2Al2SiO6·H2O) is formed in the lower KOH concentration of 1~
2 mol·kg1and zeolite F (KAlSiO4·1.5H2O) is stable in the higher
KOH concentration of 4 ~5 mol·kg1at 95 8C. Considering the
crystallization time and synthesis efficiency, 12 h was chosen as
the optimal condition. Zeolite F sample synthesized in
4 mol·kg1at 958C for 12 h exhibits type II isotherms with a
surface area of 27 m2/g and pore diameter of 0.513 nm. The
water solute release tests indicate that the accumulative release
of K2O belongs to Elovich equation and zeolite F can be used
as soil amendments in the late stage besides a slow-release
fertilizer.
Supporting Information Summary
Details of experimental section and additional information
(FTIR spectra and a table of chemical compositions of product
samples obtained in KOH concentration of 4 mol·kg1for 4–
36 h, XRD patterns of KG for different reaction times) are
given in the supporting information.
Acknowledgements
The present work was supported by Fundamental Research Funds
for the Central Universities (292016058, 2952016059).
Conflict of Interest
The authors declare no conflict of interest.
Keywords: K-feldspar ·slow-release ·Zeolite F
[1] M. Zhang, B. Gao, J. Chen, Y. Li, A. E. Creamer, H. Chen, Chem. Eng. J.
2014,255, 107–113.
[2] W. M. Stewart, D. W. Dibb, A. E. Johnston, T. J. Smyth, Agron. J. 2005,97,
1–6.
[3] A. K. Bansiwal, S. S. Rayalu, N. K. Labhasetwar, A. A. Juwarkar, S. Devotta,
J. Agric. Food. Chem. 2006,54, 4773–4779.
[4] E. A. Guertal, Agron. J. 2000,2, 388–393.
[5] U. Shavit, A. Shaviv, G. Shalit, D. Zaslavsky, J. Control. Release. 1997,2,
131–138.
[6] G Z. Zhao, Y. Q. Liu, Y. Tian, Y. Y. Sun, Y. Cao, J. polym. Res. 2010,1, 119–
125.
[7] B. Ni, M. Liu, S. L, L. Xie, Y. Wang, J. Agr. Food. Chem. 2011,18, 10169–
10175.
[8] R. Hidayat, G. Fadillah, U. Chasanah, S. Wahyuningsih, A. H. Ramelan, Afr.
J. Agr. Res. 2015,14, 1785–1788.
[9] L. Xie, M. Liu, B. Ni, Y. Wang, Ind. Eng. Chem. Res. 2012,10, 3855–3862.
[10] D. A. C. Manning, Agron. Sustain. Dev. 2010,2, 281–294.
[11] T. Skorina, A. Allanore, Green. Chem. 2015,4, 2123–2136.
[12] “Current world fertilizer trends and outlook” to be found under ftp://
ftp.fao.org/ag/agp/docs/cwfto16.pdf. 2016.
[13] H. W. Ma, Potassic rocks in China: resourse and clean utilization
techniques (in Chinese), Chemical Industry Press, 2010, pp. 3–13.
[14] H. W. Ma, J. Yang, S. Q. Su, M. T. Liu, H. Zheng, Y. B. Wang, H. B. Qi, P.
Zhang, Earth Sci Front. 2014,5, 236–254.
[15] H. W. Ma, S. Q. Su, J. Yang, B. Y. Cai, M. T. Liu, W. G. Yao, H. Peng (2014),
CIESC J 6: 2363–2371.
[16] H. W Ma, J. Yang, S. Q. Su, M. T. Liu, H. Zheng, et al, Acta. Geol. Sin-Eng.
2015,6, 2058–2071.
[17] J. Y. Yuan, J. Yang, H. W. Ma, C. J. Liu, Micropor. Mesopor. Mat. 2016,222,
202–208.
[18] X. Ma, J. Yang, H. W. Ma, C. J. Liu, P. Zhang, Micropor. Mesopor. Mat.
2015,201, 134–140.
[19] J. N. Hao, B. Yan, Dalton. T. 2014,43, 2810–2818.
[20] E. Polat, M. Karaca, H. Demir, A. Naci-Onus, J. Fruit. Ornam. Plant. Res.
2004,1, 183–189.
[21] B. M. Skofteland, O. H. Ellestad, K. P. Lillerud, Micropor. Mesopor. Mat.
2001,1, 61–71.
[22] H. W. Ma, Thermodynamic software of crystalline rock (In Chinese).
Geological Publishing House, 1999, pp. 1–38.
[23] Q. X. Pan, H. H. Pan, H. B. Lu, J. F. Su, D. Y. Chen, J. Mat. Sci. Eng. 2009,4,
553–557.
[24] K. S. Hui, C. Y. H. Chao, J. Hazard. Mater. 2006,137, 1401–409.
[25] A. A. AMEI-Kamash, J Hazard Mater. 2005,127,211.
[26] C. Baerlocher, R. M. Barker, Zeitschrift. Fr. Kristallographie. 1974,140, 10–
26.
[27] Y. Danian, A. Desheng, R. S. Zeng, Science (in China). 2004,29, 303–310.
[28] M. Sprynskyy, B. Buszewski, A. P. Terzyk, J. Colloid. Interf. Sci. 2006,304,
21–28.
[29] R. M. Barrer, D. E. Mainwaring, J. Chem. Soc. Dalton. T. 1972, 1254–1259.
[30] S. Bedrossian, B. Singh, 3rd Australian New Zealand Soils Conference,
(University of Sydney, Australia), 2004, pp. 1–7.
Submitted: September 11, 2017
Revised: November 2, 2017
Accepted: November 6, 2017
Full Papers
10726
ChemistrySelect 2017,2, 10722 –10726  2017 Wiley-VCH Verlag GmbH &Co. KGaA, Weinheim
Wiley VCH Dienstag, 21.11.2017
1733 / 102669 [S. 10726/10726] 1