PHYSICAL-CHEMICAL AND MINERALOGICAL-PETROGRAPHIC EXAMINATIONS OF DIATOMITE FROM DEPOSIT NEAR VILLAGE OF ROŽDEN, REPUBLIC OF MACEDONIA

Abstract

For the characterization of the natural amorphous SiO2 found in a new deposit in Republic of Macedonia, the following examinations were performed: physical-mechanical, chemical, mineralogical, SEM, IR and thermal examinations. Physical-mechanical analyses show that it is a white to grey colored rock, of low hardness, with a low volumetric mass and high porosity. Chemical analyses show that the material dominantly contains SiO2. Mineralogical and XRD analyses show high percentage of isotropic amorphous mass content, with minimal contents of submicroscopic cryptocrystalline mass. Thermal analyses show high thermal stability. Based on the conducted research of the raw material from the new deposit, it can be concluded that it represents SiO2-diatomite of high quality, useful for various purposes.

Key words: amorphous SiO2; diatomite; thermal analysis; chemical analysis; XRD analysis; optical microscopy;
SEM analysis

Full text

278 Geologica Macedonica, Vol. 28, No. 2, pp. 121–126 (2014)
GEOME 2 In print: ISSN 0352 – 1206
Manuscript received: July 17, 2014 On line: ISSN 1857 – 8586
Accepted: September 23, 2014 UDC: 552.581(497.724)
Original scientific paper
PHYSICAL-CHEMICAL AND MINERALOGICAL-PETROGRAPHIC EXAMINATIONS
OF DIATOMITE FROM DEPOSIT NEAR VILLAGE OF ROŽDEN,
REPUBLIC OF MACEDONIA
Arianit A. Reka, Todor Anovski, Slobodan Bogoevski, Blagoj Pavlovski, Boško Boškovski
Faculty of Technology and Metallurgy, “Ss. Cyril and Methodius” University in Skopje,
Karpoš 2 bb, Skopje, Republic of Macedonia
arianit.reka@unite.edu.mk
A b s t r a c t: For the characterization of the natural amorphous SiO2 found in a new deposit in Republic of
Macedonia, the following examinations were performed: physical-mechanical, chemical, mineralogical, SEM, IR and
thermal examinations. Physical-mechanical analyses show that it is a white to grey colored rock, of low hardness,
with a low volumetric mass and high porosity. Chemical analyses show that the material dominantly contains SiO2.
Mineralogical and XRD analyses show high percentage of isotropic amorphous mass content, with minimal contents
of submicroscopic cryptocrystalline mass. Thermal analyses show high thermal stability. Based on the conducted re-
search of the raw material from the new deposit, it can be concluded that it represents SiO2-diatomite of high quality,
useful for various purposes.
Key words: amorphous SiO2; diatomite; thermal analysis; chemical analysis; XRD analysis; optical microscopy;
SEM analysis
INTRODUCTION
Inorganic raw materials are suitable for vari-
ous uses. Silicon dioxide, also known as silica, is
widespread in nature and it occurs in various forms
[1–4]. Macedonia is rich in amorphous SiO2 mate-
rials, and these materials have a wide spectrum of
potential use and application [5, 6]. In this paper
the aim is to characterize in details the raw mate-
rial from Rožden (Kavadarci region) and determine
its application. The exploitation process of the raw
material would be surface-based; this is due to the
fact that the humus thickness is only about 30 to 40
cm over the raw material.
Fig. 1. Geographical map of the deposits

122 A. A. Reka, T. Anovski, S. Bogoevski, B. Pavlovski, B. Boškovski
Geologica Macedonica, 28 (2), 121–126 (2014)
EXPERIMENTAL
Macroscopic examination
The tested sample probe is pretty loose and
soft, weak rock with white to greyish white color.
The sample probe is characterized by a low bulk
density which is less than 1 g/cm3. The probe is
easily disintegrated by applying pressure to it;
however, the fine particles give you the feeling of
scratch.
Fig. 2. Macroscopic sample of the raw material
Physical-mechanical examinations
The characterization of the physical-mechani-
cal properties of the raw material is performed by
analyzing the compressive strength in dry state, as
well as for samples heated at 1000°C for a period
of one hour. The bulk density of the raw material is
determined in dry state as well as for samples heat-
ed at 1000°C for a period of one hour. The values
of these analyses as well as the porosity and the
density of the raw material are shown in Table 1.
Chemical silicate analysis
The chemical composition of the raw material
is determined by classical chemical silicate analy-
sis. The content of SiO2 is determined gravimetri-
cally, while the contents of Al2O3, Fe2O3, TiO2,
CaO, MgO and MnO are determined by volumetric
analysis. The contents of the alkaline oxides K2O
and Na2O are determined while using a flame pho-
tometer. Loss on ignition (LOI) is determined by
thermal treatment of the sample at temperature
1000°C. The results of the chemical analyses are
shown in Table 2.
T a b l e 1
Physical-mechanical properties
of the raw material
Property Value
Compressive strength
In dry state 2.70 MPa
Heated at 1000°C 3.68 MPa
Bulk density in dry state 0.58 g/cm3
Heated at 1000°C 0,60 g/cm3
Porosity
Open porosity 59.55 %
Closed porosity 12.08 %
Total porosity 71.63 %
Density 2,08 g/cm3
T a b l e 2
Chemical composition of the raw material
Oxides Mass (%)
SiO2 92.97
Al2O3 1.52
Fe2O3 0.21
TiO2 0.06
CaO 0.43
MgO 0.19
MnO 0.01
SO3 0.05
P2O5 0.09
K2O 0.26
Na2O 0.08
LOI 3.86
Total 99.73
The chemical analysis confirms the high pu-
rity of the raw material and the dominant presence
of SiO2 with about 93%.
The content of certain trace elements of di-
atomite are determined by ICP-MC analysis, and
the results are shown in Table 3.
According to the presented results of the
physical-mechanical and chemical examinations,
the raw material can be classified as diatomite of
the type 1 (for 70–80% SiO2, according to British
Standard Specification, BS 1795:1976) [7].

Physical-chemical and mineralogical-petrographic examinations of diatomite from deposit near village of Rožden, Republic of Macedonia 123
Geologica Macedonica, 28 (2), 121–126 (2014)
T a b l e 3
Results of ICP-MS analysis of the raw material
Elements ppm
Ag <1
As <5,0
Bi <10
Cd <1,0
Co 1,0
Cr 5,3
Cu 9,3
Fe 1449
Hg <10
Mn 33
Mo <1,0
Ni <1
P <187
Pb 5
Sb <10
Sn <10
Zn 4,5
Mineralogical-petrographic analysis
It is evident from the mineralogical-petrogra-
phic examinations of the raw material, that the ma-
terial dominantly contains isotropic sub-microsco-
pic cryptocrystalline mass, most likely composed
of opal which is the main mineral component. In
the basic mass manifestations of amorphous com-
ponents can be clearly noticed, as well diatomite,
spongolite and other microfossils.
Fig. 3. Transmission optical microscopy – (1) isotropic mass,
(2) diatomite, (3) fine sized quartz, (4) spongolite
Fig. 4. Transmission optical microscopy – relics of snails
with cone shape
Fig. 5. Transmission optical microscopy – (1) amorphous
mass, (2) quartz-slate, (3) quartz, (4) spongolite
In the isotropic mass, besides the various
forms of relicts, there are super fine grains encoun-
tered. These grains can reach sizes up to 20-30 µm,
and they represent alutogenic mineral component.
Scanning electron microscopy analyses
The results of the scanning electron micros-
copy provide the following data: presence of vari-
ous skeletal shapes and their morphological char-
acteristics, skeletons of microorganisms which
have clearly visible pores and canals. In the macro-
level the porosity of the raw materials can be de-
fined as homogenous. The microstructural analysis
also shows that the pores are of various sizes,
shapes and volume. Majority of the pores are open
and do not contain impurities. The dimensions of
the nanopores are in the range 300–600 nm, and
they make this material usable in various fields.
Thus, the raw material can be used as natural filter,
as adsorbent, as clarifier in the food industry [8, 9].

124 A. A. Reka, T. Anovski, S. Bogoevski, B. Pavlovski, B. Boškovski
Geologica Macedonica, 28 (2), 121–126 (2014)
Fig. 6. SEM of the diatomite Fig. 7. SEM of the diatomite
X-ray examinations
The crystalline phases of the diatomite are de-
termined by XRD analysis. XDR analysis was per-
formed on the DRON X-ray diffractometer (Cu Kα
radiation, wavelength λ = 1,54056 mm, testing in-
terval 70°, registration voltage 38 kV, current in-
tensity 18 mA). Results of the examination of the
natural raw material are presented in Figure 8.
Based on the results of the XRD analysis, it
can be concluded that the examined raw material is
amorphous. A small wide peak on the diffracto-
gram in the area 19–25 ° 2θ, is the interval for the
crystalline modifications of SiO2, quartz, cristoba-
lite and tridymite.
Fig. 8. XRD analysis of the diatomite

Physical-chemical and mineralogical-petrographic examinations of diatomite from deposit near village of Rožden, Republic of Macedonia 125
Geologica Macedonica, 28 (2), 121–126 (2014)
DTA/GTA analyses
DTA/TGA analyses of the diatomite were
performed with Stanton Redcroft, England – appa-
ratus, under the following experimental conditions:
temperature range 20 – 1200 °C; speed of heating
10 °C/min; sample mass 11,7 mg; gas environment
– air; material carrier – ceramic pot. Results of the
differential-thermal analysis and the thermo-gravi-
metrical analysis of the diatomite are shown in
Figure 9.
Fig. 9. DTA/TGA of diatomite
Thermo-gravimetrical analysis shows an in-
tensive loss in weight in the temperature interval
30–200 °C and 900–1200 °C. The first phase of the
endothermic peak at 158°C is due to loss of the
absorbed water from the surface and the open
pores, while the intense loss of mass during the
second phase at the temperature range 900–
1200 °C is as result of loss of the hydrated water.
DTA/TGA confirms that the material does not
crystallize even after a thermal treatment at
1000°C, i.e. it remains amorphous material.
FTIR spectroscopy
FTIR spectroscopy was performed in order to
examine the way of connecting hydroxyl groups on
the surface of the diatomite. Figure 10 shows the
results of the IR spectroscopy of the diatomite.
Fig. 10. IR spectroscopy of diatomite

126 A. A. Reka, T. Anovski, S. Bogoevski, B. Pavlovski, B. Boškovski
Geologica Macedonica, 28 (2), 121–126 (2014)
CONCLUSION
Based on the detailed examination of the
natural amorphous SiO2 from the new deposit in
Republic of Macedonia, the following can be con-
cluded that the natural amorphous SiO2 is weakly
bound, soft loose rock with a white to greyish
white color; it has a low bulk mass and high poros-
ity. XRD analyses show that the material is in
amorphous state. DTA and TGA analyes point
characteristic hydroxyl and crystal-hydrate groups,
important parameters especially for application in
processes where surface characteristics are of pri-
mary importance. IR spectroscopy confirms and
deepens the findings for the connected water and
the hydroxyl groups of the DTA/TGA with the
characteristic absorption strips of an amorphous
SiO2. With the microscopic examination the origin
of the material is defined. The material represents
isotropic sub-microscopic cryptocrystalline mass
of diatomite, spongolite and microfossils, with a
small percentage of mineral impurities of optical
anisotropic character. The chemical analysis of the
raw materials shows high percentage of the basic
component SiO2. From chemical as well as minera-
logical point of view, the raw materials represents
a high quality natural amorphous SiO2-diatomite
which can be compared with the other well world
known deposits. Based on the results, the raw ma-
terial from new deposit near Rožden can find usage
in several industrial branches: construction ceram-
ics, refractory ceramics, special oxide ceramics, as
well as widespread use as means for filtering, ad-
sorbent, catalysts, etc.
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Р е з и м е
ФИЗИЧКО-ХЕМИСКИ И МИНЕРАЛОШКО-ПЕТРОГРАФСКИ ИСПИТУВАЊА НА ДИЈАТОМЕИTЕ
ОД НАОЃАЛИШТЕТО ВО БЛИЗИНА НА СЕЛОТО РОЖДЕН,
РЕПУБЛИКА МАКЕДОНИЈА
Арианит А. Река, Тодор Ановски, Слободан Богоевски, Благој Павловски, Бошко Бошковски
Технолошко-металуршки факултет, Универзитет „Св. Кирил и Методиј“ во Скопје,
Карпош 2 бб, Скопје, Републицка Македонија
arianit.reka@unite.edu.mk
Клучни зборови: аморфен SiO2; дијатомеи; термичка анализа; хемиска анализа; XRD-анализа;
оптичка микроскопopија; SEM-анализа
За карактеризација на аморфна SiO2-суровина од но-
во наоѓалиште во Р. Македонија се реализирани физичко-
механички, хемиски, минералошки, SEM, IR и термички
испитувања. Суровината претставува бело-сивкаста карпа
со ниска тврдост, мала волуменска маса и висока пороз-
ност. Хемиската анализа покажува дека материјалот доми-
натно содржи SiO2. Минералошките и XRD анализите по-
кажуваат висок удел на изотропна аморфна маса во соста-
вот со минимални содржини на субмикроскопска крипто-
кристална маса. Термичката анализа покажува висока тер-
мичка стабилност на материјалот. Од реализираните испи-
тувања на SiO2-суровина од новото наоѓачиште, може да
се заклучи дека SiO2-диатомеите се со висок квалитет, со
можност за широка примена.