Natural Resources, 2011, 2, 244-249
doi:10.4236/nr.2011.24031 Published Online December 2011 (http://www.SciRP.org/journal/nr)
Recycling of Ornamental Stones Hazardous
Wastes
Abdel Monem Soltan, Zeinab Taman, Baher El-Kaliouby
Geology Department, Faculty of Science, Ain Shams University, Cairo, Egypt.
Received September 11th, 2011; revised October 10th, 2011; accepted October 20th, 2011.
ABSTRACT
Sawing and polishing of the ornamental stones always generate large amount of solid and wet hazardous wastes, which
pollute the environment. In Shak Al-Thoaban area, East Cairo, Egypt, huge amounts of these wastes were accumulated,
during the last years, as rejects “Solid” and wet “Sahala” wastes, representing one of the main sources of environ-
mental pollution. The aim of this work is to characterize and evaluate these wastes for recycling in quicklime produc-
tion. Hence, samples of both wastes were investigated for their chemical and mineral composition applying XRF, XRD,
DTA and TGA methods. Free lime content and reactivity (RDIN) of both samples were also determined after calcination
for differnt soaking times (0.25 - 2.0 h) at 1000˚C. The results were interpreted in relation to composition and micro-
structure of the fired samples as revealed by TLM and SEM methods. The RDIN reactivity of the resulted lime is
changeable along soaking time at 1000˚C because of the microfabric of its crystallites. The lime of the “Solid” sample
is preserving the original limestone microstructure that contributes in its higher RDIN reactivity values at all soaking
times. The relatively higher degree of grain growth of lime crystallites in the “Sahala” sample leads to its lower reactiv-
ity. The optimum soaking times for the highest lime reactivity are 0.25 and 1 h for the “Solid” and “Sahala” samples,
respectively. On increasing soaking time up to 2 h, both samples show minimum RDIN values. The “Solid” sample also
gives higher free lime content than the “Sahala” one at all soaking times. It is gradually increased in the former sample
up to a maximum (96% - 97%) on increasing soaking time up to 1 - 2 h. On the other side, a maximum free lime (~95%)
is detected in “Sahala” sample at 0.25 h soaking time and gradually decreased to (87%) up to 2 h.
Keywords: Recycling, Ornamental Stones, Wastes, Microstructure, Quicklime
1. Introduction
Development of the ornamental stone industry in Egypt
is related to the expansion in the building and construc-
tion sector in the last three decades [1,2]. Most of the or-
namental stone factories are located in Shak Al-Thoaban
area, Katameya, East Cairo, Egypt.
The quarrying, sizing and polishing of the limestone,
granite, marble rocks among others are the main proce-
sses for ornamental stone production. Through these pro-
cesses 20% - 30% of the sawed blocks become fine pow-
der and solid-cutting rejects [3]. The solid-reject wastes
cause dangerous effects on the people working condi-
tions if stacked carelessly, however, the land filling is
costly and has serious drawbacks. Also, the fine powder
can cause serious health problems on inhalation and eco-
logical problems, when mixed with water and poured
into the natural water resources, such as rivers and chan-
nels [4,5].
Recycling of the ornamental stone wastes is the best
way for eliminating their hazardous impact on the people
and environment. This is encouraged by the fact that
these waste materials are mainly rock-derived with high
purity and can be consequently incorporated in different
industries [6].
Many possible applications were suggested to incur-
porate proportions of the wastes in the processing of tiles
[7-12], red ceramics [13-16], building materials [17],
mortars [18], concrete aggregates and mixtures [6,19]
and clay products [20,21].
According to the author’s knowledge, no research
works were directed to recycling of the solid rejects and
wet-powder “Sahala” wastes as a source of quicklime
after calcination. Therefore, this work directly aims at re-
cycling both of these ornamental stone wastes accumu-
lated in Shak Al-Thoaban area for production of reactive
quicklime. Hence, samples of both wastes were investi-
gated for their chemical and mineral composition apply-

Recycling of Ornamental Stones Hazardous Wastes245
ing XRF, XRD, DTA and TGA methods. Free lime con-
tent and reactivity (RDIN) of both samples were also de-
termined after calcination for different soaking times
(0.25 - 2.0 h) at 1000˚C. The results were interpreted in
relation to composition and microstructure of the fired
samples as revealed by TLM and SEM methods.
2. Sampling and Experimental Procedure
In Shak Al-Thoaban area, when the rock fine-powder is
mixed with water during sawing and polishing it trans-
forms into aqueous sludge called “Sahala”, whereas the
rejects of rock-cuttings is called “Solid” wastes and both
are disposed in the surrounding environment (Figures 1
and 2). Representative samples of both wastes were col-
lected and prepared through many field trips to the area.
The “Solid” sample was crushed into grains of 5 - 10
mm in diameter. The average mineral content of the two
samples was determined by conducting X-ray diffraction
analysis (XRD) using a Philips X-ray diffractometer
(Model PW/1840) with a Ni-Filtered, Cu-Kα radiation (λ
= 1.542 Å). The thermal behaviour was revealed by the-
rmal analysis, adopting a simultaneous recording of vari-
ations in heat content and weight by differential-thermal
Figure 1. “Solid” wastes of Shak Al-Thoaban.
Figure 2. “Sahala” wastes of Shak Al-Thoaban.
and thermo-gravimetric analyses (DTA and TGA) meth-
ods, respectively. The thermograms of both analyses are
recorded as a function of temperature, with a rate of heat-
ing of 10˚C/min, using Perkin Elmer, 7 series Thermal
Analysis System. The chemical composition was deter-
mined by X-ray fluorescence (XRF) using a spectrometer
(Model PW/1404) with Rh target and six analyzing crys-
tals. The petrographic characteristics of the “Solid” sam-
ple were examined using transmitted light (TLM) and
scanning electron microscopy (SEM).
Firing of the “Solid” and “Sahala” waste samples was
conducted by loading in alumina boats which calcined in
an electrical muffle furnace at 1000˚C for 0.25, 0.5, 1
and 2 h soaking times. After each firing, the calcined
samples were investigated for their microfabric by SEM
as well as free lime content and reactivity. The lime sam-
ples were dissolved in a sugary solution and titrated agai-
nst standardized HCl solution for determination of free-
lime content [22]. The lime reactivity was measured in
terms of the RDIN values [23], where the lime grains were
mixed with distilled water (1 lime: 4 water) in a calo-
rimeter. The time elapsed to attain a temperature of 60˚C
(T60 sec.) was measured and the RDIN was calculated
from the equation: RDIN = 2400/T60.
3. Results and Discussion
The XRD analysis showed that the main mineral content
of both of the “Solid” and “Sahala” waste samples is the
calcite (CaCO3) together with minor gypsum CaSO4·2H2O
in the “Sahala” sample. The DTA and TG curves (Figure
3) confirm the presence of calcite, where the its decom-
position commences at ~670˚C, 720˚C and ends at
~1000˚C with an average weight loss of 43.63% and
Figure 3. DTA and TGA of the waste samples.

Recycling of Ornamental Stones Hazardous Wastes 246
42.02% in the “Solid” and “Sahala” samples, respec-
tively [24]. The minor amount of gypsum detected by
XRD in the latter sample is confirmed by a small endo-
thermic peak at ~140˚C and a weight loss of ~1.2% due
to its dehydroxylation.
The chemical composition of the two waste samples
(Table 1) indicates highly pure material suitable for the
lime production [25]. The CaO average is 55.23%, where-
as the average of total impurity oxides (sum of silica, alu-
mina, magnesia as well as iron and alkali oxides) is
0.60%. Also, TLM-microstructure of the “Solid” sample
is showing the enrichment of fossils (grain-supported)
with prominent pores as exhibited in (Figure 4).
Figure 5 shows the trends of free lime content and
RDIN-reactivity of both the “Solid” and “Sahala” samples.
In the “Solid” lime samples the free lime content in-
creases with soaking time up to a maximum (~97%) at 1
h. and slightly decreases to (~96%) at 2 h. However, the
“Sahala” free lime is maximized at 0.25 h (~95%), then
gradually decreased to a minimum at 2 h (~87%). The
decrease in lime content is due to the possible belite for-
mation with the longer soaking time [26].
Both the “Solid” and “Sahala” lime samples are highly
reactive at all soaking conditions (RDIN > 30) as shown in
Figure 5. However, the “Solid” lime samples are more
reactive (RDIN = 57 - 97) than the “Sahala” ones (RDIN =
34 - 47). This is attributed to the relatively higher range
of free lime content of the former samples (95% - 97%)
as compared with that of the latter ones (87% - 95%).
Also, preservation of the original ghost pores (OGP) of
the parent limestone of the former samples as shown by
SEM (Figure 6(a)) has contributed in increasing the lime-
particles surface area and hence its reactivity [27].
The RDIN-reactivity values of both the “Solid” and “Sa-
hala” lime show a conspicuous decrease from 97 to 57 in
the former and from 47 to 34 in the latter by increasing
soaking time from 0.25 h to 2 h, respectively. This could
be attributed to the microfabric of the calcined lime as
exhibited in (Figures 6(b)-(d)). The “Solid” lime at 0.25
h is characterized by very small lime crystallites (less
than 2 μm) (Figure 6(b)), however their size is en-
larged to be more than (5 μm) at 2 h (Figure 6(c)). This
is due to the crystallite grain growth at the longer soaking
time [28,29].
On the other side, “Sahala” lime crystallites (Figure 6(d))
show grain growth micopores (GGM), which is the main
cause for its higher reactivity. However, at 2 h, the (GGM)
are closed due to the formation of lime holo- and hemihe-
dral-lime crystallites (HLC and HeLC, respectively) (Fig-
ure 6(e)), leading to lowering the reactivity of lime.
4. Conclusions
The “Solid” and “Sahala” ornamental stone wastes in
Shak Al-Thoaban, Egypt are hazardous materials for the
environment. Firing these wastes will eliminate their
hazardous impact together with production of a useful
Table 1. Chemical composition of the technological waste samples.
Sample CaO MgO SiO2 Al2O3 Fe2O3 TiO2 P2O5 MnO Na2OK
2O SO3 Cl L.O.I
Solid 55.61 0.11 0.160.03 0.11 <0.01 0.04 0.01 0.02 <0.01 < 0.01 0.03 43.70
Sahala 54.85 0.13 0.480.08 0.09 0.02 0.03 0.00 <0.01<0.01 1.05 <0.0143.09
Figure 5. Free lime and hydration behavior of the lime sample s.
Figure 4. Grain-supported limestone enriched with fossils.

Recycling of Ornamental Stones Hazardous Wastes247
Figure 6. SEM micrographs of the lime samples under different conditions (a) The preservation of the original pores of the
“Solid” lime at 0.25 and 2 h; (b) “Solid” lime at 0.25 h with remnant fossil pores; (c) “Solid” lime at 2 h; (d) “Sahala” lime at
1 h with GGM; (e) “Sahala” lime at 2 h with HeLC and HLC.
quick-lime product. The optimum firing conditions for
producing highly reactive lime for the “Solid” and “Sa-
hala” wastes are soaking for 0.25 and 1 h at 1000˚C, re-
spectively.
5. Acknowledgements
The authors are grateful to Ain Shams university, Egypt
for funding the research project: “Recycling of Shak Al-
Thoaban wastes”. The authors are also of deep gratitude
to all the persons working in Shak Al-Thoaban area of-
fered their sincere help, especially Haj Mahdy Abo-Zeid.
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