Lake clay composition, properties and opportunities for use are little studied in Europe; up to now
there
are no scientific studies in Latvia on lake clay and its use opportunities. According to the data
from
lake
sapropel deposit certificate studies in Rēzekne, Ludza, and Preiļi regions, out of 199 lakes, clay
was
found
in the soil of 109 lakes. 11 Latgale lakes (Zeiļi, Varzova, Šķirpāni, Šķeņova, Notra, Stoļerova,
Kovališķi,
Prezma, Pauguļi, Plusons, Pilcene) were studied, control boreholes were made, and lake deposit
samples –
clay, loam, sapropel - clay – were taken from various depths. Of 11 Latgale lakes studied, clay
deposits
were found in 9.
The remote sensing method - GPR and spectral imaging as a potential method of searching for clay
sediments
was evaluated.
CLAY DETECTION IN LAKES OF LATGALE USING GROUND PENETRATING RADAR
SPECTRAL IMAGING AND CLAY DETECTION IN LATGALE LAKES
The structure and composition studies of the lake clay samples are reflected in the publication
“Investigation of structure and composition of Latgale lakes clay for their practical use”.
INVESTIGATION OF STRUCTURE AND COMPOSITION OF CLAY IN LAKES OF LATGALE FOR PRACTICAL USE
The studies of the lake clay application opportunities are presented in the publication “Lake blue
clay
-
sapropel - flax shive briquettes for water absorption and desorption”.
Lake blue clay - Sapropel - Flax shive briquettes for water absorption and desorption
The biological properties of the lake clay deposit samples were studied. According to the
microbiological
analysis performed, the lake clay meets the requirements of 02.07.2013 Cabinet Regulation No 354
“Procedure
for Meeting the Significant Requirements for Cosmetics” and European Standard EN ISO 17516:2014
Cosmetics -
Microbiology - Microbiological limits. No presence of Candida albicans, Pseudomona aeruginosa,
Staphilococcus aureus, Escherichia coli, Salmonella was found in any of the samples. The yeast,
mold,
Clostridium genus, Bacillus genus microorganism quality and quantity was also determined for the
clay
samples.
The qualitative and quantitative chemical composition of lake clay was determined. In comparison
with
other
commercial clays used in cosmetics, it was found that lake clay contains lesser amount of elements
traditionally considered toxic: As, Ni, Cu, Zn, Sr, Pb. Ba concentrations are significantly lower.
Amounts
of other elements found - Ca, Na, K, Mg, Fe, Mn, Co, Cr, Si, Se, Cd, Hg, Al, N, P, Mo, Ag, Sb, Tl,
Ti,
Li.
pH defined in samples is 5.9 - 7.3.
The odor of unmodified clay samples was determined – typical for clays odor, color – blue-gray,
green-gray, moisture – 30.9 - 49.2 %, consistency – plastic, soft, smooth. Specific heat capacity of
unmodified clay is 949 - 1023 J/(kg x K), thermal conductivity is 0.35 – 0.53 W/(m x K).
Clay was thermally treated in temperatures of 650 - 1150 °C. During the study, the mechanical
properties
(hardness, ultimate compression strength, ultimate strain, Young’s modulus, friction coefficient,
roughness
of surface), electric properties (relative permittivity, specific electrical resistance), structure
and
heat
properties (thermal conductivity, specific heat capacity) of lake clay were defined. The
characteristic
curves of lake clay for relative permittivity, specific electrical resistance (AC) and quality
factor in
the
range from 20Hz to 1MHz were measured at different temperatures (650, 750, 850, 950, 1050, 1150 °C).
It
was
found that the first two characteristics decrease, whereas quality factors increase with the
increase of
the
electric field frequency: relative permittivity - 1189 at 20Hz up to 3.5 at 1MHz, specific
electrical
resistance 1
×10
7Ω×m at 20Hz up to
1
×10
3Ω×m at 1MHz.
Quality factor varies from 0.4 at 20Hz up to 48 at 1MHz.
It was found that specific electrical resistance
ρ (DC) of clay exponentially
grows
with
the increase of
firing temperature. It was found that specific electrical resistance of samples taken from the top
layers of
the bottom of the lake and fired at temperatures 650 - 1050 °C is about 10 times higher than that of
samples
from deeper layers.
The mechanical properties of fired clay were determined. With the increase of clay firing
temperature,
the
ultimate compression strength of clay increases from 5MPa at 650 °C to 35MPa at 1150 °C, the
ultimate
strain
increases from 6 to 11%, hardness increases from 68 to 90 Shored. Young’s modulus is 55 MPa - 551
MPa.
No
correlation was found between firing temperature and roughness of surface, density, friction
coefficient.
Roughness of surface is within the range from 0.1 to 2.1 µm, density - 1.5 to 1.9 g/cm3, friction
coefficient on 304 stainless steel polished plate - 0.32 - 0.56.
Lake Zeiļu Clay Application Induced Changes in Human Skin Hydration, Elasticity, Transepidermal Water Loss and PH in Healthy Individuals
Clay has a great biomedical application potential, however there are just a few instrumental studies
and the impact of lake clay on the skin has not yet been studied. The DermaLab skin analysis system
(Cortex Technology) was used for hydration, elasticity, transepidermal water loss (TEWL) and pH measurements
after lake clay facial applications. Research included short-term tests (measurements 20 and 60 min after clay application)
and long-term tests (application every 4th day for 3 weeks with measurements 20–24 h post-application).
Control measurements and application tests to exclude contact allergy were made beforehand.
No volunteer (n = 30) had positive allergic reaction. The matched-pairs design was applied: the right and left parts of forehead
were used for the test and control groups. The Wilcoxon signed-rank test (significance level p = 0.001) was applied
for statistical analysis. There were statistically significant pH changes demonstrated during the short-term measurements.
The long-term measurements provided data that clay significantly improves skin hydration and elasticity.
