Structural examinations of natural raw materials pumice and trepel from Republic of Macedonia

Abstract

The aim of this paper is to present the physic-mechanical, chemical and mineralogical-petrographic examinations of the pumice and trepel. The pumice is
from deposit site called Bojanciste, near Kavadarci, and the trepel deposit is from Suvodol near Bitola, Republic of Macedonia. The mineralogical-petrographic
examinations of the pumice and pumicite have shown that the main component of the pumice and pumicite it is the volcanic glass, while in the crystal phase there is
presence of albit, oligoclass, anorthit, microklin and in small quantities presence of quartz, biotit and augit. The examinations of the trepel have shown that it is a
sedimentary rock (of biogenic origin) with greyish-white colour, very light and soft, porous and with fine to superfine grained structure. The trepel is composed mainly of
opal as well as quartz, feldspar, illite and chlorites.

Full text

Proceedings of the XV Balkan Mineral Processing Congress, Sozopol, Bulgaria, June 12 – 16, 2013
73
STRUCTURAL EXAMINATIONS OF NATURAL RAW MATERIALS PUMICE AND TREPEL FROM
REPUBLIC OF MACEDONIA
Blagica Cekova1, Blagoj Pavlovski2 , Darko Spasev1 , Arianit Reka2
1 School of Chemistry and Technology “Maria Curie – Sklodovska”, Treta Makedonska Brigada 63a, 1000 Skopje, Republic of
Macedonia
2 Faculty of Technology and Metallurgy, University Ss. Cyril and Methodius, str Ruger Boskovic 16, 1000 Skopje, Republic of
Macedonia
ABSTRACT. The aim of this paper is to present the physic-mechanical, chemical and mineralogical-petrographic examinations of the pumi ce and trepel. The pumice is
from deposit site called Bojanciste, near Kavadarci , and the trepel deposit is from Suvodol near Bitola, Republic of Macedonia. The mineralogical-petrographic
examinations of the pumice and pumicite have shown th at the main component of the pumice and pumicite it is the volcanic glas s, while in the crystal phase there is
presence of albit, oligoclass, anorthit, microklin and in small quantities presence of quartz, biotit and augit. The examinations of the trepel have shown that it is a
sedimentary rock (of biogenic origin) with greyish-white colour, very light and soft, porous and with fine to superfine grained structure. The trepel is composed mainly of
opal as well as quartz, feldspar, illite and chlorites.
Keywords: raw materials, pumice, trepel, structural analys is
INTRODUCTION
Pumice and pumicite are porous volcanic materials. They are
created with the process of expansion of the volcanic lava that uses
the steam and the gaseous materials dissolved into the lava itself.
The pores of the pumice and pumicite can have size from a wide
range. Namely, the size of the pores can be as large as parts of
micrometre (µm) and more rough pores with sizes up to 2-3 mm. The
main difference between pumice and the pumicite is in the size of the
grains. More specifically, the material with grain size of 2 mm or
larger (up to large blocks) is classified as pumice. On the other hand,
the material with size of grains smaller than 2 mm (including the fine
dispersed material) is classified as pumicite.
The colour of pumice is grey, black and sometimes white; it
consists of silica SiO2 (up to 70%) and alumina Al2O3 (up to 15%).
Pumice occurs in fragments 5 to 50 mm across, ejected to 1400
kg/m3; porosity, 80%; compressive strength, 0.4 to 2.0 MPa;
hardness 6. (1)
Tripoli and Tripolite (diatomite) are sedimentary organogenous
rocks.
Tripoli is lightweight, clay-like rock carrying amorphous silica in the
form of fine opal balls. Its bulk density equals 500-1200 kg/m3, and
porosity 60 to 70%. (1)
Tripolite (diatomite) is a poorly cemented, very porous siliceous
rock, formed of shells of diatom algae and partly of skeletons of living
organisms. Its bulk density lies between 400 and 1000 kg/m3.
Diatomite or diatomaceous earth (also known as tripolite,
kieselguhr, infusorial earth) is a hydrous or opalscent form of silica.
The amount of water of composition seems to be variable, but usually
is between 5 and 10%. In its natural state diatomite also (usually)
contains 25 to 40% of mechanically held water, which is expelled at
100ºC. It usually contains some clay and certain types are high in
lime. Fresh-water deposits often contain organic matter that imparts
a dark-brown or almost black colour to the diatomite.
Tripoli is form of silica (SiO2) derived either from the
decomposition or alterations of chert or as a residual product from
the decomposition of a highly siliceous limestone.
Tripoli is often confused with tripolite, which is another name for
diatomite. The original tripolite from the island of Tripoli in northern
Africa was diatomaceous earth, while the term “tripoli” was first
applied to a material found near Seneca, Missouri, which somewhat
reassembled diatomaceous earth by visual inspection, but contained
no diatmos, was of entirely different origin, and had different physical
and chemical properties. The presence or absence of diatmos, when
examined under a high-power microscope, is the absolutely definite
test. Chemical analyses always show that diatomaceous earth has a
high content of combined water (5-10% or more), while Tripoli has
little or none. (2)
Experimental Section
1. Examination of pumice
The physical characteristics of pumice and pumice-pumicite from
Bojanciste, Kavadarci, Republic of Macedonia are shown in Table 1.
Tabl. 1 Physical characteristics of pumice-pumicite and
pumice
The granulometric composition of pumice-pumicite and pumice are
shown in Table 2.
Tabl. 2 Granulometric composition of pumice-pumicite and
pumice
Fraction (mm) Pumicite-pumice Pumice
- 0, 1 14,8 1,69
0,1 - 0,2 14,5 0,50
0,2 - 0,4 18,7 2,03
0,4 - 0, 8 14,5 6,45
0,8 - 2 12,3 24,14
2 - 4 11,6 19.85
- 8 8,3 25,14
+ 8 5,3 20,20
The chemical composition of the pumice-pumicite and pumice are
made by classical chemical-silicate procedure.
The chemical composition of pumice-pumicite and pumice are given
in Table 3.
Tabl. 3 Chemical composition of pumice-pumicite and pumice
Oxides Pumicite-
pumice Pumice
SiO263,73 62,65
Al2O3 17,48 17,96
F2O33,10 2,85
CaO 2,50 2,26
MgO 0,59 0,49
K2O 4,95 5,20
Na2O 4,45 3,74
SO3 -- 0,34
LOI 3,07 4,43
Total 99,86 99,92
The X-ray powder examinations (DRON, 36 kV, 10 mA, CuKα/Ni) of
pumice are shown in Figure 1.

Proceedings of the XV Balkan Mineral Processing Congress, Sozopol, Bulgaria, June 12 – 16, 2013
74
Fig. 1 X-ray diagram of pumice
From mineralogical point-of-view, pumice is similar with the
pumicite. In the samples found at this location, the main component
of the samples is volcanic glass, while in the crystal phase one can
encounter albit, oligoclass, anorthit, microcline, and in smaller
quantities quartz, biotit and augit. DTA/TG examination of the pumice
are shown in Figure 2.
Fig. 2 DTA/TG of pumice
In the sample, the most intense dehydration occurs at the
temperatures between 180 and 470ºC. With further increase of the
temperature, the dehydration process continues, however, with
decreased intensity.
2. Examination of trepel
Treated trepel deposit was discovered in the Pelagonian
depression, Republic of Macedonia, at Suvodol village near Bitola city.
According to the recent excavation mine works for coal exploitation at
the Suvodol village a peculiar geological profile was opened as
follows:
- the uppermost part is presented by agricultural soils etc. (of
alluvial-deluvial age) the thickness of which is cca 0,5 – 1.0 m;
- the lower part belongs to a biogenetic formation composed of
trepel sediments (the thickness of which is cca 50-70 m) and
coal deposits at the bottom of the abovementioned open profile.
(3)
The physical characteristics of the trepel are shown in table 4.
Tabl. 4 Physical characteristics of trepel from Suvodol, Bitola,
R. of Macedonia
A classical chemical-silicate procedure was performed for the
chemical examination of the trepel. The chemical composition of the
trepel is shown in Table 5.
Tabl. 5 Chemical composition of trepel from Suvodol, Bitola,
Republic of Macedonia
Oxides % (mass)
SiO2 64,95
Al2O3 11,85
F2O3 4,51
CaO 1,49
MgO 1,88
K2O 1,40
Na2O 0,84
SO3 1,74
LOI 11,20
Total 99,86
With X-Ray powder examination (DRON, 36 kV, 18 mA, CuKα/Ni)
in the trepel are determined: quartz, illite, feldspars, chlorites,
kaolinite, and cristobalite. The X-ray diagram of the trepel from
Suvodol, Bitola, Republic of Macedonia is shown in Figure 3.
Fig. 3 X-ray diagram of trepel from Suvodol, Bitola, R. of
Macedonia
The microscopic examinations with the polarizing translucent light
show that treated trepel sample is characterized with a micro-crypto-
crystalline ground mass of optic isotropic nature. This groundmass is
composed of opal inside of which there are very fine to superfine
grained quartz, feldspars, chlorites, illite-hydromica inclusions.
Differential thermal and thermo-gravimetrical analysis of trepel are
shown in Figure 4.
Differential thermal analysis of trepel show two exothermic peaks,
at 340ºC and 910ºC. The first exothermic peak at 340ºC is result of
oxidation of organic matter. The second exothermic peak at 910ºC is
result of crystallization of the amorphous phase in the trepel.
DTA shows also two endothermic peaks at 130ºC and 550ºC. The
first endothermic peak at 130ºC is result of loss of water and
presence of illite in the trepel. The second endothermic peak at
550ºC is result of migration of the OH-groups from the opal phase
and presence of illite in the trepel.
Characteristics Value
Density (g/cm3) 2,39-2,41
Bulk density (g/cm3) 0,64-0,88
Water absorption (%) 85-95
Total porosity (%) 68-75

Proceedings of the XV Balkan Mineral Processing Congress, Sozopol, Bulgaria, June 12 – 16, 2013
75
Fig 4. DTA/TGA of trepel from Suvodol, Bitola, Republic of
Macedonia
CONCLUSION
The examinations of pumice-pumicite and pumice from Bojanciste,
Kavadarci, Republic of Macedonia, showed that the density of
pumice-pumicite is 2,45 g/cm3 and 2,47 g/cm3 by pumice. Bulk
density of pumice-pumicite is 1,34 g/cm3 and 0,89 g/cm3 by pumice.
From the chemical and mineralogical point of view pumice-
pumicite and pumice from the deposit of Bojanciste, Kavadarci, are
similar. The main component of the pumice-pumicite and pumice is
volcanic glass, while in the crystal phase one can encounter albit,
oligoclass, anorthit, microcline, and in smaller quantities quartz, biotit
and augit.
Pumice-pumicite and pumice from deposit of Bojanciste, Kavadarci,
Republic of Macedonia can be used for production of lime-pumicite
brick with a low bulk density and good heat insulating properties.
Lime-pumicite brick are superior to clay brick because they are with a
low bulk density and better heat insulating properties. The pumice-
pumicite and pumice from the deposit of Bojanciste, Kavadarci,
Republic of Macedonia are raw materials which can be used for low
temperature synthesis of zeolite type 4A.(4)
Examined trepel sample from the Suvodol village, Bitola, Republic
of Macedonia actually represents a sedimentary rock (of biogenetic
origin) with greyish to greyish-white colour, very light and soft (1-2
by
Mohs
), fine to superfine grained structure, porous, shell-like break,
tongue sticky etc.
The X-ray and microscopic examinations show that trepel is
characterized with micro-crypto-crystalline ground mass of optic
isotropic nature. This basic mass is opal, inside of which there are
very fine to super fine grained quartz, feldspars, chlorites, illite-
hydromica inclusions.
Mineralogical and chemical composition of the trepel used in our
experiments possesses a possibility to develop a complex inorganic
technological procedure for production of zeolites, light brick,
cements etc.(5)
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Pavlovski, B.
et all
(2011). Trepel – a peculiar sedimentary rock of
biogenetic origin from the Suvodol village, Bitola, Republic of
Macedonia. Geologica Macedonica, Vol 25, No 1, pp 67-72.
Cekova, B.
et all
(2012). Low temperature synthesis of 4A from
natural raw materials “pemza”, XXII Congress of SCTM, Book of
Abstracts, Ohrid 5-9 September 2012, Republic of Macedonia.
Cekova, B.
et all
(2012), Examining the possible use of natural raw
material “trepel” – Bitola for the synthesis of zeolite type 4A.
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