Content uploaded by Zsigmond J Papp
Author content
All content in this area was uploaded by Zsigmond J Papp on Jul 05, 2016
Content may be subject to copyright.
ACADEMIA ROMÂNĂ
Revue Roumaine de Chimie
http://web.icf.ro/rrch/
Rev. Roum. Chim.,
2016, 61(3), 169-174
MORPHOLOGICAL AND MICROCHEMICAL CHARACTERIZATION
OF HIMALAYAN SALT SAMPLES
Zsigmond PAPP*
Faculty of Biofarming, John Naisbitt University, Maršala Tita 39, 24300 Bačka Topola, Serbia
Received November 19, 2015
Salt represents an important commodity in both ancient and modern times.
Nowadays, numerous unrefined edible salts of different origin are present on
the food market. To some of them, including also the so called Himalayan salt,
unique health benefits are attributed even without thoroughgoing chemical and
medical investigation, which can lead to possibly dangerous misinformation of
the users. Therefore, the main motivation of this work was to broaden the list
of proven information about the characteristics of Himalayan salt. The
research was focused on the applicability of SEM/EDS technique for
micromorphological and microchemical characterization of two Himalayan
salt samples (salt plate and ground salt). Results showed that the samples are
both morphologically and chemically heterogeneous. Besides sodium and
chlorine, nine additional elements were detected. The concentration of the
elements varied in wide ranges and correlated well with the results of
morphological investigation.
INTRODUCTION*
Salt is generally recognised as an important
commodity in both ancient and modern times. It is
well-known that a certain intake of salt is
necessary for human and animal health. It is also
used in different industrial processes and in
traditional societies for food preservation, but also
for its curative properties and for activities such as
tanning. Historically and ethnographically salt has
a simbolic value also.1
Currently, a variety of unrefined edible salts of
many different geographical origins are available
on the food market.2 Lot of uncertain information
is available about these salts, giving them
sometimes unique properties and magic health
effects. The composition of these salts are
frequently under debate. Surely, the chemical
composition of these salts varies with their
geographic origin and production method and it
could be used for their classification. The
knowledge about true composition of these
samples is also important for the elimination of
unreliable and sometimes false information from
online sources.
The Himalayan salt is probably the most well
known type of the currently used unrefined salts. The
Bavarian Health and Food Safety Authority led an
investigation in 2003 about the composition of
15 Himalayan salt samples. The maximal number of
the detected elements per sample was 10, including
sodium and chlorine as main components.3
Nowadays, the nondestructive and minimally
invasive analytical techniques are widely used for the
characterization of solid surfaces. Additionally, the
combination of morphological and microchemical
* Corresponding author: pappzsigmond@yahoo.com; zpap@naisbitt.edu.rs
170 Zsigmond Papp
surface analysis techniques provides deeper insight in
the nature of the investigated object in comparison
with independent techniques.4-6 Currently, very
limited amount of results is available about the use of
such combined techniques for the analysis of
unrefined salt samples.7-9 In this work scanning
electron microscopy/energy dispersive spectrometry
(SEM/EDS) was used for morphological and
microchemical investigation of two Himalayan salt
samples.
EXPERIMENTAL
Samples
A piece of 20×10×2.5 cm Himalayan salt plate and a pack
of fine ground Himalayan salt of the same origin (Pakistan)
were analyzed.
Apparatus
The surface morphology was studied on a Jeol JSM-6460LV
scanning electron microscope (Japan Electron Optics Laboratory,
Japan). The EDS microanalysis was performed on an INCA
microanalysis system (Oxford Instruments, United Kingdom).
Procedures
To obtain fresh, uncontaminated salt surfaces, the salt
plate was broken into several parts and the inner regions were
analyzed. The ground salt was analyzed “as-is”. Before
measurements, all samples were coated with gold using a
BAL-TEC SCD-005 (Bal-Tec AG, Lichtenstein) sputter coater
(working time, 90 s; used current, 30 mA; working distance,
50 mm). As a result of coating, additional peaks related to the
presence of gold appeared in EDS spectra (e.g. at 2.1 and 9.7
keV).
RESULTS AND DISCUSSION
To study the morphological properties of the
investigated salt surfaces several micrographs were
taken from both sample types (Figs. 1, 2).
Two distinct surface types could be identified
even at low magnifications. On the one hand,
mostly broken, but visually homogeneous crystals
of bigger size dominate the surface practically in
all pictures (Fig. 1, A-C). In the ground salt sample
there are more rounded crystals like in the bulk
material (Fig. 1, D), but also the fragmented type
of morphology is dominant (Fig. 1, C).
Fig. 1 – Representative surface micrographs of the Himalayan salt plate (A, B) and ground Himalayan salt (C, D)
taken at different magnifications (A, C, 500×; B, D, 1000×).
Himalayan salt samples 171
Fig. 2 – Representative surface micrograph of an element-rich region of the Himalayan salt plate with complex microstructure.
On the other hand, at some places, regions
with complex microstructure are imbedded
between above mentioned bigger crystals in both
sample types (Fig. 2). In this case, even the
visual inspection suggests possibly different
chemical composition in comparison to the
above mentioned first morphological group.
Areas which can be considered as a mixture
of the above mentioned surface types are also
present in the samples, but they are not frequent.
The elemental analysis using EDS was in
good consistency with the results of the
morphological investigation. In Fig. 3 the
surface characteristics are typical for the above
mentioned first type – broken, but visually
homogeneous composition is shown. The EDS
analysis confirmed that in these regions the only
detectable elements are sodium and chlorine in
ratio characteristic to the pure sodium chloride.
Contrary to this, in regions of second type,
where a complex microstructure was observed
(Fig. 4, Spectrum 2), the EDS analysis showed a
palette of other elements besides to sodium and
chlorine, sometimes in very high concentrations.
In such regions 9 other elements were detected
in addition to the main constituents of the rock
salt: oxygen, magnesium, aluminium, silicon,
sulfur, potassium, calcium, iron and fluorine.
The high concentration of sulfur and oxygen
together with potassium, magnesium and
calcium and their mutual ratio suggest that these
regions are probably composed of polyhalite
type compounds (K2Ca2Mg(SO4)4×2H2O),
together with some other compounds.
Regions which held the characteristics of both
morphological surface types are shown in Fig. 5.
The elemental analysis of these regions also
confirmed the mixed type of these areas, because
more elements are detectable like in pure sodium
chloride composed areas, but they are
significantly less rich in the elements like the
regions with very complex microstructure.
The elemental distribution and the
localization of the complex regions were
completely analogous in both sample types (salt
plate and ground salt), similarly to the results of
the morphological investigation.
172 Zsigmond Papp
Fig. 3 – EDS spectra from of an element-poor region of the ground Himalayan salt.
Fig. 4 – EDS spectra of an element-poor (Spectrum 1) and element-rich (Spectrum 2) regions of the Himalayan salt plate.
Himalayan salt samples 173
Fig. 5 – EDS spectrum of a mixed-morphology region of the Himalayan salt plate.
The concentration (w/w%) of the analyzed
elements was investigated in detail for 11 surface
segments (7 from the salt plate, the rest from the
ground salt), which included all characteristic
regions of both samples types. From the 11
detected elements, sodium and chlorine were
present in all measurements, oxygen in 6,
potassium in 5, sulfur and calcium in 4,
magnesium in 3, aluminium, silicon, iron and
fluoride in just one. The average concentration of
the most important 7 elements was as follows:
chlorine, 47.70±0.87%; sodium, 30.66±0.53%;
oxygen, 10.41±1.26%; sulfur, 4.19±0.20%;
calcium, 2.49±0.15%; potassium, 2.51±0.51%; and
magnesium, 1.06±0.14%. The concentration of the
rest 4 elements, which were detected just in one
measurement are as follows: silicon, ≤0.35%;
aluminium, ≤0.23%; iron, ≤0.17%; and fluorine,
≤0.17%. It must be stated again that these
measurements included also the heterogeneous
parts of the samples, so they cannot be used for the
estimation of the bulk concentration of the
mentioned elements. If we calculate the average
concentration of sodium and chlorine from the
results, which were recorded from the visually
homogeneous crystals in the sample, the
concentration of the main components in the
sample are: chlorine, 59.98±0.65% and sodium,
40.02±0.52%, which represents practically pure
sodium chloride. On the other hand, the
concentration of sodium chloride in measurement
which included the most heterogeneous sample
surface was less than 4.6% (chlorine, 2.61±0.12%
and sodium, 1.63±0.22%). Therefore it is correct
to be said that the samples are both visually and
chemically complex and heterogeneous.
CONCLUSIONS
Morphological and microchemical surface
characterization of a Himalayan salt plate and a
ground Himalayan salt sample was conducted
using SEM/EDS. The eleven elements (Cl, Na, O,
S, Ca, K, Mg, Si, Al, Fe, F) detected in the samples
were present in a wide range of concentration in
different surface areas. At the same time, very
heterogeneous morphological structures were
identified, consisting partly from practically pure
sodium chloride crystals and on the other hand,
from regions with more complex microstructure,
which were in the same time the regions with a
palette of different elements in addition to sodium
and chlorine. Some regions with mixed
characteristics were also identified. The elemental
distribution is really heterogeneous, and in the
dependence from the sample region, very different
results could be obtained.
Acknowledgements: Author would like to thank Miloš
Bokorov for his experimental help.
REFERENCES
1. A. Harding, Geol. Q., 2014, 58, 591-596.
2. G. Park, H. Yoo, Y. Gong, S. Cui, S.-H. Nam, K.-S.
Ham, J. Yoo, S.-H Han and Y. Lee, Bull. Kor. Chem.
Soc., 2015, 36, 189-197.
174 Zsigmond Papp
3. Bavarian Health and Food Safety Authority, Press
Release No. 038/2003, “Alles nur Kochsalz - LGL nimmt
"Himalayasalz" genauer unter die Lupe”, 2003.
4. G. M. Ingo, S. Balbi, T. de Caro, I. Fragilà, E. Angelini
and G. Bultrini, Appl. Phys. A, 2006, 83, 493-497.
5. G. M. Ingo, E. Angelini, T. de Caro and G. Bultrini,
Appl. Phys. A, 2004, 79, 171-176.
6. Z. Papp and I. Kovács, Rev. Roum. Chim., 2013, 58, 65-67.
7. Š.Yalçin and I. H. Mutlu, Acta Phys. Pol. A, 2012, 121,
50-52.
8. S. Kerkar and M. S. Fernandes, Int. Food Res. J., 2013,
20, 2317-2321.
9. S. M. Zelek, K. M. Stadnicka, T. Toboła and L.
Natkaniec-Nowak, Miner. Petrol., 2014, 108, 619-631.
