CHARACTERIZATION OF GRANITE WASTE FOR INCORPORATION IN
RED CERAMIC
C. M. F. Vieira, S. N. Monteiro
State University of North Fluminense, UENF
Advanced Materials Laboratory, LAMAV
Av. Alberto Lamego, 2000. Zip code: 28015-620 - Campos dos Goytacazes-RJ, Brazil.
[email protected]
ABSTRACT
This work had as its objective the characterization of a granite powder waste from
sawing operations with a view to its incorporation in red ceramic. The granite waste came
from the municipal area of Santo Antônio de Pádua, State of Rio de Janeiro, Brazil. The
characterization was performed in terms of chemical composition, particles size distribution,
X-ray diffraction and thermal analysis (DTA/TG). The results indicate that the granite waste
presents favorable characteristics for incorporation in red ceramic compositions due to its fine
granulometry as well as a considerable fluxing potential related to its high amount of alkaline
oxides.
Keywords: Characterization, granite, red ceramic, powder, waste.
1. INTRODUCTION
Granite is a rock with worldwide applications, especially in the manufacture of
ornamental stones for civil construction. Brazil is a large producer of ornamental stones such
as granite and marble [1]. In particular, the county of Santo Antônio de Pádua located in the
northwest of the State of Rio de Janeiro, has ornamental stone extraction as its main economic
activity. The fundamental type of rocks found in the region consists of gnaisses and
migmatites with interspersed quartzite [1,2]. Miracema Stone, a commercial name of the
grayish gnaisse, is the regions most exploited stone, with many varieties such as “dove’s eye”,
“fine granite” and “rose spotted granite” [1,2]. These rocks are processed as flat pieces or tiles
to be used, for example, in walls and floors.
After mining, the granite blocks are submitted to primary dressing, which consist of
sawing, to obtain semi finished pieces of various sizes. In some cases, this is followed by
secondary dressing in which the sectioned pieces undergo polishing and surface finishing.
During primary dressing, an estimated loss of up to 35% of the stone occur in the form of
sludge, composed of granite powder and water. A monthly 400 tons of granite waste is
estimated to be produced at Santo Antônio de Pádua. The final disposal of this waste has
brought serious environmental problems. Since most industries do not have an adequate
sludge treatment, the granite waste is nowadays responsible for contaminating the soil and
polluting underground waters as well as obstructing rivers and lakes.
One alternative for recycling this type of granite waste is by its incorporation in
industrial materials that use clay based ceramic bodies such as red ceramic and ceramic tiles
[3-5]. The chemical-mineralogical composition of the waste and its powder particle size can
be favorable characteristics. In addition, the application of granite waste in red ceramic can
improve the process eficency and the product quality. This work aims to determine the granite
waste characteristics for the Santo Antônio de Pádua material that could have direct influence
in red ceramic processing.
2. MATERIAL AND METHODS
The material used in this work was a granite waste, from “dove’s eye” stone, obtained in
the form of a sludge collected from the primary dressing sector of a stone sawing industry
located in Santo Antônio de Pádua, State of Rio de Janeiro, Brazil.
After drying at 110oC until constant weight was achieved, the granite waste was
submitted to the following characterization techniques: X-ray diffraction (XRD), chemical
composition, particle size distribution and thermal analysis (DTA/TG).
The XRD, used to determine the mineralogical constituents, was carried out in a Sheifert
Model URD 65, X-ray diffractometer operating with Cu-Kα radiation for a 2θ variation from
5º to 65º. The chemical composition was obtained by X-ray fluorescence. The particle size
distribution of the granite waste was obtained by both wet sieving and sedimentation
techniques, according to the Brazilian standards [6]. The thermal behavior was investigated
by means of simultaneous thermodifferential (DTA) and thermogravimetric analysis (TGA) in
static air, with as thermal gradient of 5oC/min and maximum firing temperature of 1000oC
(TA model SDT 2960 equipment).
3. RESULTS AND DISCUSSION
3.1. Mineralogical composition
The XRD pattern of the granite waste, shown in Fig. 1., exhibits a mineralogical
composition comprising micaceous mineral (biotite), amphibolic mineral (hornblend),
feldspars (microcline, albite and anortite) and quartz.
In a possible mixture with clays, in the pre-firing stages, the granite waste could act as a
non-plastic material, decreasing the plasticity of the ceramic body. In the firing stages the
activity of the various mineral constituents of the granite waste will depend on many factors,
such as the other constituents, the particle size and the firing conditions such as heating rate,
maximum temperature and holding time at maximum temperature. For practical proposes, it
can be established that at firing temperatures around 1000oC, normally used for roofing tiles,
biotite and microcline will act as fluxes, forming a liquid phase. The microcline, for example,
forms an eutectic with silica at around 1000oC [7,8]. The other constituents will remain inert
due to their high melting point. At temperatures lower than 1000oC, liquid phase is also
formed, in small amounts and with high viscosity, making the sintering by the liquid phase
associated with the vitrification process difficult. At temperatures above 1000oC, the amount
of liquid phase is increased and the viscosity becomes lower. In this case, albite will also act
as flux and fine quartz could be dissolved in the liquid phase.
4000
Q
Intensity (Counts)
3000
2000
B
Mi
An
Al
1000
Q
An
Al
Ho
Mi
0
B
10
Al
An
20
Al
B
Mi
B Mi
Mi
Q
30
Q
40
Q
Q
Q
50
2θ
Figure 1. X-ray pattern of the granite waste. B – Biotite; Al = Albite; Na = Anortite; Ho =
Hornblend; Q = Quartz.
3.2. Chemical composition
The chemical composition of the granite waste is presented in Table 1. The two most
abundant oxides are SiO2 and Al2O3. These oxides are the main constituents of most minerals
present in this granite, such as hornblend, biotite and feldspars, shown in Fig. 1. In addition,
the XRD pattern, Fig. 1, also presents quartz, composed of SiO2. Table 1 also shows a
relatively large presence of alkaline oxides, K2O and Na2O. These oxides form eutectics with
SiO2 and Al2O3 at temperatures above approximately 700oC. This confirms the idea that the
granites could produce a fluxing action if added to clay ceramic bodies. The 1.91% CaO in
Table 1 came from the anortite and possibly plagioclases feldspars, which were not identified
in the XRD pattern. The amount of Fe2O3, associated with most of the biotite, contributes to a
reddish color after firing in the case of an possible mixture of this granite waste with clays.
The MgO is probably an impurity of the alumino-silicate phases. The low percentage of loss
on ignition indicates that the firing reactions present an insignificant weight loss. This will be
discussed in more details in the item 3.4.
Table 1. Chemical composition and loss ignition (LoI) of the granite waste (Wt. %)
SiO2 Al2O3 Fe2O3 TiO2 K2O Na2O CaO MgO LoI
67.14 14.92
4.40
0.73 5.18 2.93
1.91 0.73 0.50
3.3. Particle size distribution
Figure 2 shows the particle size distribution of the granite waste. It can be observed
that the particles size varies approximately from 1 to 300 µm, with a frequency maximum
corresponding to 8-10 µm. The granulometry of the granite waste can thus be considered as a
fine powder with only 0.8% in weight of the particles retained in the 230 mesh. This fine
granulometry is very important to the red ceramic processing, since it facilitates the sintering
reactions. Moreover it eliminates the necessity of grinding, which could be a problem for the
common equipment used in red ceramic, especially the laminators that are not appropriate for
crushing hard materials such as granite.
14
12
80
10
60
8
6
40
Frequency (%)
Cumulative mass percent finer
100
4
20
2
0
0
1
10
100
1000
Diameter (µm)
Figure 2. Particle size distribution curve and frequency bars of the granite waste.
3.4. Thermal behavior
Figure 3 shows the thermogravimetric and thermodifferential curves of the granite
waste. The fundamental aspects of the thermal behavior of the granite waste are:
(i) endothermic peak at 97.3oC due to the loss of physically adsorbed water. The weight of
loss associated with this reaction is 0.54%;
(ii) sharp gain in weight between 125oC and 327oC. This is probably due to the oxidation of
iron oxide;
(iii) loss of weight of 0.49% between 327oC and 588oC due to the oxidation of possible
organic matter and structural water;
(iv) endothermic peak at 565.9oC associated with the allotropic transformation of quartz-α to
quartz-β;
(v) loss of structural water between 588oC and 676oC of the micaceous mineral (biotite). The
loss of weight is 0.18%;
(vi) loss of weight of 0.16% between 676oC and 903oC, probably due to the decomposition of
calcite traces;
Figure 3 shows that the thermal processing of the granite waste should not cause any
problem with respect to atmospheric pollution. The thermal reactions that occur in association
with firing generate basically water vapor and, possibly, a low amount of carbon oxides.
100,0
25
-0.54%
20
o
565.9 C
+0.12
99,0
10
-0.18%
TGA (%)
-0.49%
15
DTA (uV)
99,5
-0.16%
5
98,5
o
97.3 C
0
98,0
Exo Up
0
200
400
600
800
1000
o
Temperature ( C)
Figure 3. Thermoanalysis curves of granite waste.
4. CONCLUSIONS
The characterization of granite waste from the sawing operation of ornamental stone
industrial plants showed that this material presents the following favorable aspects for
incorporation in red ceramic compositions.
• Fine granulometry, which favors the sintering reactions among the various mineral
constituents in an eventual mixture with clays. This contributes to reduce the porosity of the
ceramic pieces. Another important advantage of a fine granulometry is that it precludes the
need of grinding.
• A considerable fluxing potential due to the high amount of alkaline oxides, K2O and Na2O,
from the feldspars and micaceous mineral;
• Thermal stability with low loss of ignition.
ACKNOWLEDGMENTS
The authors would like to thank the financial support for this investigation provided by
FAPERJ, process number: E-26/151.544/2001
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