Physicochemical properties of amorphous silicon dioxide produced from nepheline

Article abstract of DOI:10.1134/S0036023611030144

The properties of silicon dioxide precipitates produced by acid processing of nepheline have been investigated. Regardless of the production method, silicon dioxide takes an intermediate position between commercial silica gel and white soot in terms of the structure and some physicochemical properties, this position determining possible applications of this product. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611030144

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 3, pp. 338–340. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © V.A. Matveev, V.I. Zakharov, D.B. Mayorov, T.V. Kondratenko, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 3, pp. 380–382.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Physicochemical Properties of Amorphous Silicon Dioxide
Produced from Nepheline
V. A. Matveev, V. I. Zakharov, D. B. Mayorov, and T. V. Kondratenko
Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials,
Kola Scientific Center, Russian Academy of Sciences, ul. Fersmana 14, Apatity, Murmansk oblast, 184200 Russia
eꢀmail: zotov@chemy.kolasc.net.ru
Received October 15, 2009
Abstract—The properties of silicon dioxide precipitates produced by acid processing of nepheline have been
investigated. Regardless of the production method, silicon dioxide takes an intermediate position between
commercial silica gel and white soot in terms of the structure and some physicochemical properties, this posiꢀ
tion determining possible applications of this product.
DOI: 10.1134/S0036023611030144
At the Institute of Chemistry of Kola Scientific
(4) KSKG silica gel produced according to the
Center, Russian Academy of Science, a process has Russian State Standard (GOST) 3956ꢀ76;
been developed for acid digestion of nepheline to proꢀ
duce easily filtered suspensions [1]. The underlying
idea of the method consists of stepwise dosed addition
of nepheline to preheated acid. In this process, silicon
dioxide is first transferred into solution and then preꢀ
cipitates from it after having experienced a number of
transformations which can be significantly intensified
in the presence of a seed. As a result, acidꢀinsoluble
precipitate is a mechanical mixture of amorphous siliꢀ
con dioxide and acidꢀresistant admixture minerals.
The investigations have shown that a significant differꢀ
entiation of particles in the specific weight allows wellꢀ
known gravitation procedures to be used to recover
amorphous silica containing 95–98% SiO2 (based on
dry weight) with product yields of 45–55%.
(
5) BSꢀ120 white soot produced according to the
Russian State Standard.
One essential parameter of a powder is the value of its
specific surface. In acid technologies of nepheline, this
parameter to a considerable extent controls the waterꢀ
retaining ability and filtration properties of silicaꢀconꢀ
taining precipitates. The BET specific surface of samples
1–5 determined using nitrogen as the adsorbate gas is
03. 5, 92.4, 74.6, 428.2, and 125.7 m /g, respectively.
These values prove that, in this parameter, our silꢀ
icaꢀcontaining powders approach to white soot, some
kinds of which (BSꢀ50 and BSꢀ100) are known to conꢀ
2
1
2
tain particles with specific surfaces of 50 and 100 m /g.
According to crystallooptic analysis data, samples
1
and
habit. The surface of the particles is not smooth and in
some cases looks like a sponge. Refractive indexes
are 1.432 and 1.450. The material of sample also repꢀ
resents grains of uncertain shape but with smoother
surfaces than samples and . These samples contain
a significant amount of admixtures as a set of anisotroꢀ
pic crystals: needleꢀshaped, greenishꢀcolored, transꢀ
parent, and some others (N = 1.441). Sample 4 conꢀ
tains an isotropic glasslike transparent material; its
refractive index is 1.446. Spot birefringence is observed.
Sample
metric (round) shape, namely, hollow spheres. The
refractive index is 1.445, however, having a different
value for for the shells of the spheres. At the same time,
the shells are not continuous and are not observed for all
grains. The surfaces of the particles are porous. The
2 are matt, nontrasparent grains with uncertain
EXPERIMENTAL AND RESULTS
N
3
Two main types of precipitated silicas are produced
on the large scale: highly dispersed silica (white soot)
and silica gels of different types and sorts. For this reaꢀ
son it appeared interesting to classify silicon dioxide
recovered from the precipitates of acid decomposition
of nepheline with certain types of commercial silicas.
The following samples of silicaꢀcontaining precipiꢀ
tates were chosen to be studied:
1
2
5 consists of optically isotropic entities of isoꢀ
(
1) a light fraction of the precipitate obtained by
dozed addition of nepheline to 35% nitric acid for 5 h;
2) a light fraction of the precipitate obtained by
(
dozed addition of nepheline to 35% sulfuric acid in the
presence of 20% silica seed for 3 h;
(
3) a precipitate obtained by a single addition of results of crystallooptic analysis do not allow the amorꢀ
nepheline to 75% sulfuric acid followed by water phous silicas obtained from nepheline to be unambiguꢀ
leaching [2, 3]; ously classified as white soot or silica gel.
338

PHYSICOCHEMICAL PROPERTIES OF AMORPHOUS SILICON DIOXIDE
DTG, %/min
339
DTG, %/min
(а)
(c)
TG, %
00
DSC,
µ
V/mg
0.2
.1
TG, %
100
DSC,
µ
V/mg
0.4
1
0
1
0
3
1
3
0
0
0
0
0
.3 –0.1
.2 –0.2
.1 –0.3
–0.4
98
96
94
92
90
88
–0.2
0
9
8
6
–
–
0.1
0.2
–
–
–
–
0.4
0.6
0.8
1.0
9
–0.3
0.4
0.5
–0.6
0.7
–
–0.1 –0.5
0.2 –0.6
–0.3
–0.7
94
92
–
–
2
2
–
1
00 200 300 400 500 600 700 800 900
100 200 300 400 500 600 700 800 900
T, °C
T
,
°
C
DTG, %/min
V/mg
DTG, %/min
(
b)
(d)
DSC,
µ
TG, %
00
TG, %
100
DSC, µV/mg
1
0
0
0
.3
1
9
9
9
8
6
4
–
0.1
0.6
0.4
0.2
0
0.2
1
–
–
–
0.1
0.2
0.3
98
96
94
92
90
3
0
.1 –0.2
0
–
–
–
0.3 92
0.1
0.2
90
3
–0.4
2
88
86
–0.4
–
0.5
–0.3
0.4 –0.6 84
–
0.5
0.6
2
–
–0.2
–
100 200 300 400 500 600 700 800 900
T, °C
1
00 200 300 400 500 600 700 800 900
T
, °C
Fig. 1.
(1
) DSC, (2) TG, and (
3) DTG curves for samples (a)
1, (b)
2, (c)
3
and
4, and (d)
5
.
Heating curves and weight losses for the test samples decomposition of nepheline in the dozed loading mode
recorded on NETZSCH STA 409 PC/PG are preꢀ is closer to the structure of silica gel rather that the
sented in Fig. 1 (both curves for samples and look
completely alike). All DSC curves feature characteristic
endotherm in the temperature range 108–120 which
3
4
structure of white soot.
°С
is associated with the removal of adsorbed water and
water loosely bound to the silica surface though hydroꢀ
gen bonds. The absence of endotherms at higher temꢀ
peratures evidences the almost complete absence of
interlayer and subsurface water. The run of the weight
loss curves also evidences for this assumption. For samꢀ
4
0
.7
0.6
3
0.5
1
2
ples
weight loss occurs in three steps: 3.3, 1.9, and 2.4% of
the weight are lost as a result of heating to 100–110
when the temperature increases to 210–220 , 4.2,
.4, and 3.3% are additionally lost, while further heatꢀ
ing to 950 leads to a 4.2, 4.0, and 3.2% decrease in
weight, respectively. A fundamentally different TG
curve is observed for sample (BSꢀ120). The weight loss
1, 2, and 4 the TG curves have similar runs. The
0
.4
.3
°С;
°С
0
2
°С
0.2
5
occurs in four steps, 66% of the total weight loss occurꢀ
ring while the sample is heated in the temperature range
0.1
220–580°С. This is evidence of the presence of a conꢀ
siderable amount of subsurface silanol groups
≡
SiOH
0
10
20
30
40
50
60
70
and arises from the fact that white soot particles are
simultaneously finely dispersed and porous. The results
of the analysis show that the structure of the amorphous
silica samples recovered from the residues of acid
Time, days
Fig. 2. Measurement of waterꢀretention capacity of samꢀ
ples ( ) of silicaꢀcontaining precipitates in the sorption
process.
1–4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

340
MATVEEV et al.
In order to determine the waterꢀretaining capacity foundry production, production of special sorts of
of silicaꢀcontaining products, weighted portions ~5 g concrete, and in other applications.
in weight were dried at 105 and placed into an desꢀ
iccator with water and kept at 20 until they were
completely saturated with water. Since white soot is
not usually used as a water adsorbent, sample was not
tested for the waterꢀretention capacity. The results are
given in Fig. 2. It follows that sample has an intermeꢀ
diate position between the commercial silica gel samꢀ
ple (sample ) and amorphous silica obtained by
dozed addition of nepheline to a 35% nitric and sulfuꢀ
ric acids (samples and ).
°С
°С
ACKNOWLEDGMENTS
The study was financially supported by the Russian
Foundation for Fundamental Research (project
no. 07ꢀ03ꢀ97621).
5
3
4
REFERENCES
1
. V. I. Zakharov, V. T. Kalinnikov, V. A. Matveev, and
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and Development of New Lines of Complex Processing
and Use of Alkali Aluminosilicates (Izd–vo KNTs RAN,
Apatity, 1995), Pt 1 [in Russian].
1
2
Therefore, as regards physicochemical properties
and structure, amorphous silica obtained from
nepheline has an intermediate position between white
soot and silica gel. It has been established that amorꢀ
phous silica prepared by acid treatment of nepheline
can be used for the production of catalysts, as fillers for
rubber and polymer materials, protective composiꢀ
tions for plants, for the production of liquid glass, in
2
. K. V. Tkachev, A. K. Zapol’skii, and Yu. K. Kisil’, The
Coagulant Technology (Khimiya, Leningrad, 1978) [in
Russian].
3
. Yu. A. Lainer, Complex Processing of AluminumꢀConꢀ
taining Raw Materials by Acid Processes (Nauka, Mosꢀ
cow, 1982) [in Russian].
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011