Characterization of Diatomaceous Earth and Halloysite Resources of Poland

Article Characterization of Diatomaceous Earth and Halloysite Resources of Poland

Marcin Luty ´nski 1,* , Piotr Sakiewicz 2 and Sylwia Luty ´nska 3

1 Department of Mining, Faculty of Mining, Safety Engineering and Industrial Automation, Silesian University of Technology, ul. Akademicka 2, 44-100 Gliwice, Poland 2 Division of Nanocrystalline and Functional Materials and Sustainable Proecological Technologies, Institute of Engineering Materials and Biomaterials, Faculty of Mechanical Engineering, Silesian University of Technology, Konarskiego 18a, 44-100 Gliwice, Poland; [email protected] 3 Department of Applied Geology, Faculty of Mining, Safety Engineering and Industrial Automation, Silesian University of Technology, ul. Akademicka 2, 44-100 Gliwice, Poland; [email protected] * Correspondence: [email protected]

Received: 28 August 2019; Accepted: 29 October 2019; Published: 31 October 2019

Abstract: The mining industry of Poland is based mostly on coal and copper ores. Strict carbon emissions and the depletion of deposits will slowly phase out coal. Therefore, metallic ores and other mineral raw materials will dominate the extractive industry of Poland. Current measured resources of the largest deposits of halloysite and diatomaceous earth in Poland are over 0.5 Mt and 10 Mt, respectively. Halloysite and diatomaceous earth samples from halloysite Dunino deposits and Jawornik diatomaceous earth deposits (composed mostly of diatomaceous skeletons (frustules)) were subjected to mineralogical analysis, scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDS) nanostructural, chemical, elemental, and mineral content analysis. Both these minerals have similar properties, i.e., sorption capacity and cation exchange capacity, and are used mostly for the same purposes, e.g., adsorbents, ﬁller material, and ﬁltration. Samples of Dunino halloysite consist of minerals such as halloysite, kaolinite, hematite, magnetite, quartz, magnesioferrite, rutile, ilmenite, geikielite, goyazite, gorceixite, and crandallite, with little impurities in the form of iron oxides. Occasionally, halloysite nanoplates (HNP) nanotubes (HNT) were found. Diatomaceous earth is composed mainly of silica-containing phases (quartz, opal) and clay minerals (illite and kaolinite). The frustules of diatoms are mostly centric (discoid) and have radius values of approximately 50–60 µm. Large resources of these minerals could be used in the future either for manufacturing composite materials or highly advanced adsorbents.

Keywords: halloysite; diatomite; mineral deposit; mineral absorbent

1. Introduction Central Europe has abundant resources of numerous deposits that include metallic ores and fossil fuels [1]. The mining of metallic ores started in the period of the Roman Empire, and advances in mining and processing technology allowed for extensive exploration in the 10th century AD [2]. Most of the easily accessible deposits were already exhausted in the 14th century, yet mining was revived in central Europe in the mid-15th century. This was caused by the increased demand for new kinds of metal ores (e.g., copper), technological innovations such as water pumping from shafts, and hydrometallurgical methods of metal separation [3]. In the 18th century, the Industrial Revolution brought interest in coal mining, and regions such as Ruhr in Germany and Silesia in Poland were the ones in Central Europe where the coal industry played a major role in the development of new mining technologies. Today, Poland still remains a major coal producer in the European Union with over

Minerals 2019, 9, 670; doi:10.3390/min9110670 www.mdpi.com/journal/minerals Minerals 2019, 9, 670 2 of 17

61.436 Gt of hard coal resources, out of which 3.605 Gt are proven reserves. Other important industrial minerals of Poland include metallic ores, which are mostly copper with recoverable reserves of 1.188 Gt. It is worth mentioning that other valuable minerals such as gold, silver, and nickel are extracted from copper ores. In 2018, 1.189 Mt of silver, 523 kg of gold, 1.73 Mt of nickel sulfate, and 66.35 t of selenium were recovered by KGHM Polska Mied´zS.A., making a Polish company one of the world’s largest silver producers [4]. Taking into account current production figures of the most important industrial minerals, we can assume that coal reserves will last for the next 20–30 years, whereas copper ore reserves should suffice for the next 50 years. Taking carbon emission limits into consideration, the coal mining industry will be phasing out in the next 10–15 years. Therefore, metallic ores and other mineral raw materials (except fossil fuels) will dominate the extractive industry of Poland. Other industrial minerals of Poland include chemical raw materials such as barite and fluorspar, clay raw materials for the production of mineral paints, diatomaceous rock, potassium, and magnesium salts, but also siliceous earth and native sulfur [4]. The purpose of this study is a quantitative and qualitative evaluation of two industrial minerals used as effective adsorbents i.e., halloysite and diatomite (diatomaceous earth). These minerals have different origins, structures, and chemical compositions, but exhibit similar properties and are used mostly for the same purposes. Samples from the two largest deposits of these minerals in Poland were acquired and subjected to structural, chemical, and crystal analysis. Resources of deposits were evaluated based on the current geological data and the information acquired from the owners of the deposits.

2. Geological Setting, Resources, and Uses The two materials under investigation, despite being of entirely diﬀerent origin, usually serve the same purposes, i.e., as adsorbents, ﬁller materials, insulation, and lining, and are characterized by similar properties. In Table1, the properties of typical market products of diatomaceous earth and halloysite under investigation are presented. The geological setting of the two deposits and estimated resources are given in the following subsections.

Table 1. Properties of absorbents made of diatomaceous earth from Jawornik deposit and halloysite from the “Dunino” deposit [5,6].

Property Diatomaceous Earth Halloysite Moisture content of adsorbent, % 6 8 Oil sorption, wt.% 45 80–100 Typical sorbent grain size, mm 0.3–3 0.5–2.0 Bulk density, kg/m3 900 800 pH 5.7–8.3 7

2.1. Halloysite Halloysite belongs to the group of phyllosilicates from the kaolinite subgroup. Unlike other minerals in its group, halloysite has a considerably larger specific surface area and greater ion exchange capacity. It is also characterized by good chemical and thermal resistance in low and moderate temperatures [7]. Nowadays, there are only three large-scale active mines of this raw material in the world [8], which are located in the USA, New Zealand, and Poland; the latter features the open pit halloysite mine “Dunino” Sp. z o.o. near Legnica (Lower Silesian Voivodeship). The Dunino deposit, covering an area of 1.99 ha, was documented in 1996 originally as a deposit of halloysite raw material, and now is classified as a kaolinite raw material. Halloysite from this deposit is a product of the weathering of tertiary basalt rocks. It has the form of a horizontal seam, is homogeneous in composition, and was included in the second group of deposit variability in accordance with Baryszew classification (average variability). The thickness of the deposit ranges from 3.5 to 18.8 m (average 12.2 m). The cap Minerals 2019, 9, 670 3 of 17 rock includes: soil, quaternary sandy-loam formations, and weathered basalt with sand with thickness ranging from 1.6 to 7.0 m (average 4.0 m). In the bottom layer, clayey sands and weathered basalt occur [9]. The measured resources of this deposit are 470.63 thousand t, whereas proven reserves account for 374.66 thousand t. The production from this deposit in 2018 amounted to 1350 t [4]. The concession for mining the Dunino deposit is granted to the company until 2029. Currently, the only producer of halloysite in Poland is the Intermark Company, which owns the Dunino deposit. Halloysite may be used for the following purposes:

1. as an adsorbent for the purification of process gases and liquids [10–12]; 2. catalyst in chemical processes (e.g., processing of plastics) [13–15]; 3. additive in the combustion of biomass, Refused-derived fuel (RDF), and coal in boilers (reduces slagging and fouling of boiler heating surfaces and prevents the agglomeration processes in fluidized beds) [16,17]; 4. polymer composites filler (increases mechanical properties and fire resistance) [18–20]; 5. as a slow-release fertilizer and plant protection [21,22]; 6. animal feed additive [23–25]; 7. paint additive (e.g., controlled release of anti-corrosion agents) [26,27]; 8. waste water treatment additive [28,29]; 9. component of geosynthetic clay liners [30]; 10. slow-release drug delivery system [31,32].

The above non-exhaustive list of halloysite uses makes it a valuable resource in modern applications, particularly in medicine and environmental protection.

2.2. Diatomaceous Earth Diatomaceous earth is the naturally occurring fossilized remains of single-celled aquatic algae called diatoms. It belongs to the group of near pure sedimentary silica rock consisting predominantly of opal. The properties that make diatomite industrially valuable include: light weight, low density, high porosity, high surface area, inertness, and high absorption capacity. The only occurrence of diatomite rock in Poland is located in the Eastern Carpathians, within the Menilite series of Krosno strata, in the Leszczawka area. The raw material from the deposit is 3 characterized by a 72% concentration of SiO2, relatively high density (1.42 g/cm ), and relatively low porosity (average 28.5%, maximally 50%). Typical diatomite with silica content above 80% is not found in Poland [4]. Measured resources of diatomite in four deposits in the Leszczawka region (two deposits in Leszczawka and Ku´zminaand Jawornik deposits) amount to a little over 10 Mt (Tables2 and3). The recoverable reserves of diatomite rock for the Leszczawka area are estimated at up to 10 Mt. Much larger prospects for the discovery of diatomite deposits are associated with the Menilite series of Krosno strata in the regions of Bła˙zowa-Pi˛atkowa-Harta-Bachórz and Godów (Rzeszów region) and in the Dydynia-Krzywe region (Krosno region).

Table 2. Diatomaceous earth resources of Poland (Mt) [4].

Measured Resources Amount of Deposits Recoverable Reserves Total Sub-Economic Resources Total resources 4 10.02 2.74 0.2 Deposits with active mining 1 0.64 - 0.2 Deposits with abandoned mining 3 9.38 2.74 - Minerals 2019, 9, 670 4 of 17

Table 3. List of diatomaceous earth deposits in Poland (thousand t) [4].

Measured Resources Recoverable No Deposit Current status Sub-Economic Production Total Reserves Resources 10,015.93 2738 200.10 0.58 1 Jawornik In operation 640.10 2738 200.10 0.58 2 Ku´zmina Abandoned 392.19 - - - Leszczawka-pole 3 Abandoned 3490 - - - Jaworowice-Borownica 4 Leszczawka-pole Ku´zmina Abandoned 5493.64 - - -

At present, the only domestic producer of diatomite materials is the Specjalistyczne Przedsi˛ebiorstwoGórnicze “Górtech” Sp. z o.o., excavating the Jawornik diatomite deposit since 1992 in the Jawornik Ruski mine. The production of diatomaceous earth from this deposit in 2018 amounted to 0.58 thousand t (see Table3). The company supplies raw material in the form of 0.5–3 mm granules (used as a sorbent), powder (used as natural mineral ﬁller), and dusts (for the production of insulation materials). Diatomite uses are as follows:

1. carrier of drug, particularly Nonsteroidal Anti-Inflammatory Drugs (NSAID) [33,34]; 2. production of antibacterial composites [35–38]; 3. filler in cement, asphalt, paint, brick, tile, and ceramics production [39–43]; 4. filtration of impurities [44–47]; 5. sound and heat insulation composites manufacturing [48–50]; 6. thermal storage [51–53].

There are other numerous applications of diatomite, yet the most important property of the deposit should be the purity of resource and lack of organic impurities.

3. Materials and Methods In order to evaluate structure, chemical composition, and properties of halloysite from the Dunino deposit and diatomite from the Jawornik deposit, a detailed study was conducted. Samples from both deposits were subjected to the following set of analyses:

structural–using light microscopy (LM), • microstructural and nanostructural–using scanning electron microscopy (SEM), • elemental–using energy-dispersive X-ray spectroscopy (EDS), • chemical composition–using the X-ray fluorescence method (XRF) and inductively coupled • plasma-optical emission spectrometer (ICP-OES), mineral composition–with the use of the X-ray diffraction (XRD) method. • For the purpose of the study, 30 samples of each mineral were used. First, samples were hand crushed and sieved in order to remove large impurities (>30 mm). Before starting the set of analysis, samples were dried in an oven at 105 ◦C for 2–3 h (until the weight was equilibrated). After drying, samples were placed in a desiccator. SEM-EDS analysis was performed on 20 samples, whereas for LM analysis, 10 samples were used. For the XRD analysis, raw and dry halloysite was used, as well as a dry diatomaceous earth sample. The selection of research areas for metallographic observations was done after previous macroscopic observations by using a light stereoscopic microscope SteREO Discovery ZEISS in a magnification range from 8 to 100 . A Zeiss stereoscopic microscope was equipped with the × × two-channel optical observation system, which allowed the observation of spatial objects with a large depth. The microscope was also equipped with directional and annular lighting and the data acquisition and image analysis system called Axio Vision. Minerals 2019, 9, 670 5 of 17

The surface morphology of the samples prepared from all the supplied pipes was observed Mineralsusing the 2019 high-resolution, 9, x FOR PEER REVIEW scanning electron microscope Zeiss Supra 35, which was equipped with5 of an16 analysis system of the chemical composition with the energy-dispersive X-ray spectroscopy (EDS) TRIDENT XM4XM4 EDAX. EDAX. The The energy-dispersive energy-dispersive X-ray X-ray spectroscopy spectroscopy (EDS) allowed(EDS) allowed studying studying the chemical the chemicalcomposition composition of the samples of the in samples the micro in areasthe micro as well areas as anas analysiswell as an of theanalysis distribution of the distribution of elements of in elementslarge areas. in Inlarge addition, areas. anIn analysisaddition, of an the analysis distribution of the of distribution elements on of the elements surface on of thethe tested surface samples of the testedand the samples topographic and the investigations topographic of investig the surfaceations were of the carried surface out. were carried out. Since minerals from halloysite and diatomite depo depositssits are classifiedclassified as weakly conducting or non-conductive samples to obtain better quality SEM images, their surface was covered with a thin metallic layer of Pd and Au. This prevents disturba disturbancesnces of secondary electron emissions or electron beam emissions. All All samples samples were attached to th thee scanning microscope handlehandle using a conductive carbon tape.tape. ThisThis can can explain explain the the occurrence occurrence on someon some EDS singleEDS single spectrum spectrum of individual of individual peaks derived peaks derivedfrom gold, from palladium, gold, palladium, and carbon. and In carbon. the supplied In the tables,supplied the tables, quantitative the quantitative and qualitative and analysesqualitative of analysesthese elements of these were elements omitted. were omitted. Chemical analysis analysis was was conducted conducted with with the use the of use a Varian of a Varian 710-ES 710-ESinductively inductively coupled coupledplasma- plasma-opticaloptical emission emission spectrometer spectrometer (ICP-OES). (ICP-OES). Prior to Prior the tomeasurements, the measurements, samples samples were weremineralized mineralized in a Magnumin a Magnum II ERTEC II ERTEC mineralizer. mineralizer. A more A more detailed detailed chemical chemical composition composition was was established established by bymeans means of theof the X-ray X-ray fluorescence fluorescence (XRF) (XRF) method method using using the the Epsi Epsilonlon 1 1spectrometer spectrometer manufactured manufactured by by PANalytical. PANalytical. As mentioned above, X-ray diffraction diffraction (XRD) phasephase analysis was conducted for halloysite and diatomaceous earth samples. This This research research was was co conductednducted with with the the use use of an XRD 7 didiffractometerffractometer Seifert-FPM. The applied emission was Co K-alpha with an Fe filter. filter. The X-ray tube parameters were 35 kV/25mA with the scattering angle of 2θ (from 4° for halloysite and 7° for diatomaceous earth) for 35 kV/25mA with the scattering angle of 2θ (from 4◦ for halloysite and 7◦ for diatomaceous earth) for phase analysis up to 70–90°. phase analysis up to 70–90◦.

4. Results Results

4.1. Halloysite Halloysite Since halloysite is a volcanic-derived mineral formed as a result of basalt weathering, in one of the LM photos, a transformationtransformation between basalt and halloysite is visible (Figure1 1).). AreasAreas ofof basaltbasalt rock (black and grey color) weathered into aluminosilicates (yellowish color) and mainly iron oxides inclusions (reddish color) can be observed.observed.

Figure 1. HalloyisteFigure 1. sampleHalloyiste with sample visible with transformation visible transformation from basalt fromrock basalt(LM). rock (LM).

All samplessamples exhibited exhibited the the presence presence of magnetiteof magnetite particles particles surrounded surrounded by aluminosilicate by aluminosilicate crystals. crystals.Magnetite Magnetite particles particles have an have average an average size ofsize 30–60 of 30–60µm μ upm up to to 500 500µ mμm for for the the largestlargest particles. particles. Hematite particles of size not exceeding a few micrometers were also observed. The size of the hematite particles was noticeably smaller than that of the magnetite particles (see Figure 2).

Minerals 2019, 9, 670 6 of 17 Minerals 2019, 9, x FOR PEER REVIEW 6 of 16

Hematite particles of size not exceeding a few micrometers were also observed. The size of the Minerals 2019, 9, x FOR PEER REVIEW 6 of 16 hematite particles was noticeably smaller than that of the magnetite particles (see Figure2).

Figure 2. The structure of mineral from the Dunino deposit (LM). Selected samples from different areasFigureFigure of 2.deposit 2.The The structure structurewith visible of of mineral mineralhematite from from and the the magnetite Dunino Dunino deposit grainsdeposit(LM). of (LM). various Selected Selected sizes samples (redsamples circles). from from di ﬀ differenterent areas ofareas deposit of deposit with visible with visible hematite hematite and magnetite and magnetite grains grains of various of various sizes sizes (red (red circles). circles). Microstructural and nanostructural analysis with the use of SEM showed interesting phenomenonMicrostructuralMicrostructural in some and ofand nanostructuralthe nanostructuralhalloysite samples. analysis analysis withIn several thewith use specimens,the of SEMuse showedof halloysiteSEM interesting showed nanoplates phenomenoninteresting (HNP) (Figureinphenomenon some 3a) of theand halloysitein mixed some halloysiteof samples. the halloysite nanotubes In several samples. specimens,(HNT) In severaland halloysitehalloysite specimens, nanoplatesnanoplates halloysite (HNP) (HNP) nanoplates (Figure occur (HNP) 3(Figurea) and 3b,c).mixed(Figure halloysite 3a) and nanotubesmixed halloysite (HNT) nanotubes and halloysite (HNT) nanoplates and halloysite (HNP) nanoplates occur (Figure (HNP)3b,c). occur (Figure 3b,c).

(a) (b) (a) (b) Figure 3. Cont.

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(c)

Figure 3. SEM images DuninoFigure halloysite3. SEM images samples Dunino with hall (a)oysite halloysiteite samples nanoplates with (a) halloysiteite (HNP) with nanoplates (HNP) with an an occasional intrusion ofoccasional nanotubes intrusion (HNT); of nanotubes (b,c) mixed (HNT); halloysiteite (b,c) mixed nanotubes halloysiteite (HNT) nanotubes and (HNT) and halloysiteite halloysiteite nanoplates. nanoplates.

EDS elemental analysisEDS were elemental conducted analysis for 30 sampleswere conducted of halloysite for 30 from samples the Dunino of halloysite deposit. from the Dunino deposit. The mass-averaged quantitativeThe mass-averaged and qualitative quantitative EDS elemental and analysis qualitative showed EDS that elemental the most important analysis showed that the most elements found are: oxygen,important aluminum, elements silica, found iron, andare: titanium.oxygen, aluminum, The arithmetic silica, mean iron, of and the titanium. analyses The arithmetic mean of is given in the Table4. Thethe di analysesﬀerences is resulting given in from the theTable theoretical 4. The contentdifferences of individual resulting elementsfrom the theoretical content of may result from the heterogeneityindividual elements of composition may result and the from occurrence the hetero of inclusionsgeneity of incomposition the form of and the occurrence of particles and grains as wellinclusions as numerous in the form substitutions of particles of and iron grains and titanium as well as atoms numerous in the halloysitesubstitutions of iron and titanium crystals themselves. atoms in the halloysite crystals themselves.

Table 4. Averaged mass percentageTable 4. Averaged concentrations mass ofpercentage the major concentrations elements in dried of th Duninoe major halloysiteelements in dried Dunino halloysite (energy-dispersive X-ray spectroscopy(energy-dispersive (EDS) analysis). X-ray spectroscopy (EDS) analysis).

Element Mass (%) Element Mass (%) O 43.4 O 43.4 Si 19.4 Si 19.4 Al 18.6 Al 18.6 Fe 12.8 Fe 12.8 Ti 1.41 Ti 1.41

Elemental analysis showedElemental that the analysis Dunino showed deposit that is macroscopically the Dunino depo homogeneous;sit is macroscopically however, homogeneous; however, in micro-areas, there arein local micro-areas, fluctuations there in chemicalare local fluctuations composition in due chemical to the volcaniccomposition origin due of to the the volcanic origin of the mineral. Local differencesmineral. in the Local chemical differences composition in the chemical may be thecomposition result of may individual be the result eruptions, of individual eruptions, and and as a consequence, diasff aerent consequence, compositions different of basalt compositions rock. In of Figures basalt4 rock. and5 In, SEM Figures micrograph 4 and 5, SEM micrograph and EDS and EDS results show diresultsfferences show in thedifferences chemical in composition the chemical of thecomposition samples. of In the Figure samples.5, an iron In Figure 5, an iron oxide oxide impurity is foundimpurity with a high is found content with of a FeK, high whereas content of in FeK, Figure wher4, theeas samein Figure sample 4, the shows same a sample shows a chemical chemical composition thatcomposition is typical forthat halloysite. is typical Thefor halloysite. chemical compositionThe chemical of composition halloysite measured of halloysite measured with ICP- with ICP-OES is shown inOES Table is shown5, and isin consistentTable 5, and with is consistent results obtained with results with EDS. obtained with EDS.

Table 5. Averaged chemicalTable composition 5. Averaged of halloyistechemical composition from Dunino of deposit halloyiste using from an inductivelyDunino deposit using an inductively coupled plasma-optical emissioncoupled spectrometer plasma-optical (ICP-OES). emission spectrometer (ICP-OES).

Compound SiO2 Al2O3 Fe2O3 TiO2 Na2O K2O CaO MgO Loss on Ignition Compound SiO2 Al2O3 Fe2O3 TiO2 Na2OK2O CaO MgO Loss on Ignition (wt.%) 33 28 18 2 0.1 0.1 1.3 0.5 15 (wt.%) 33 28 18 2 0.1 0.1 1.3 0.5 15 Additional XRF analysis (Table 6) show that the chemical composition is consistent with the results obtained with ICP-OES. The dominant trace elements found in halloysite are zirconium, vanadium, and chromium, yet maximum concentrations do not exceed 150 ppm.

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Additional XRF analysis (Table6) show that the chemical composition is consistent with the results obtained with ICP-OES. The dominant trace elements found in halloysite are zirconium, vanadium, Minerals 2019, 9, x FOR PEER REVIEW 8 of 16 and chromium, yet maximum concentrations do not exceed 150 ppm. Table 6. Chemical composition and trace elements of halloysite determined by means of the X-ray Table 6. fluorescenceChemical method. composition and trace elements of halloysite determined by means of the X-ray ﬂuorescence method. Compound wt.% Element Concentration, ppm CompoundSiO2 wt.%33.11 VElement 124.9 Concentration, ppm TiO2 2.23 Cr 103 SiO2 33.11 V 124.9 Al2O3 28.87 Ni 36.1 TiO2 2.23 Cr 103 Al2O3 Fe2O3 28.8717.92 Cu Ni 73.8 36.1 Fe2O3 MnO 17.920.48 Zn Cu 84 73.8 MnOMgO 0.480.14 Ga Zn 16.9 84 MgOCaO 0.140.71 As Ga 8.2 16.9 CaONa2O 0.710 Rb As 131 8.2 Na2OK2O 00.14 Sr Rb 96.3 131 K2OP2O5 0.140.77 Y Sr 28.8 96.3 P2O5 SO3 0.770 Zr Y 180.9 28.8 SO3 Cl 00.05 Nb Zr 10.9 180.9 ClBaO 0.050.08 Mo Nb 4.1 10.9 BaOLOI 0.0815 Sn Mo 37.1 4.1 LOI 15 Sn 37.1 Pb 7 Pb 7

(a) (b)

FigureFigure 4. 4.Example Example ofof SEM micrograph ( a)) and and EDS EDS spectra spectra (b (b) )of of a ahalloysite halloysite sample sample from from the the Dunino Dunino deposit.deposit. TheThe samplesample waswas sputtered by an Au/Pd Au/Pd target.

(a) (b)

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Table 6. Chemical composition and trace elements of halloysite determined by means of the X-ray fluorescence method.

Compound wt.% Element Concentration, ppm SiO2 33.11 V 124.9 TiO2 2.23 Cr 103 Al2O3 28.87 Ni 36.1 Fe2O3 17.92 Cu 73.8 MnO 0.48 Zn 84 MgO 0.14 Ga 16.9 CaO 0.71 As 8.2 Na2O 0 Rb 131 K2O 0.14 Sr 96.3 P2O5 0.77 Y 28.8 SO3 0 Zr 180.9 Cl 0.05 Nb 10.9 BaO 0.08 Mo 4.1 LOI 15 Sn 37.1 Pb 7

(a) (b)

Figure 4. Example of SEM micrograph (a) and EDS spectra (b) of a halloysite sample from the Dunino Mineralsdeposit.2019, 9 ,The 670 sample was sputtered by an Au/Pd target. 9 of 17

Minerals 2019, 9, x FOR PEER REVIEW 9 of 16 (a) (b)

FigureFigure 5.5.Example Example of of SEM SEM micrograph micrograph (a) and(a) and EDS EDS spectra spectra (b) of ( theb) of halloysite the halloysite sample sample from the from Dunino the deposit.Dunino Thedeposit. sample The was sample sputtered was bysputtered the Au/Pd by target. the Au/Pd EDS results target. indicate EDS results impurity, indicate probably impurity, in the formprobably of the in iron the form compound. of the iron compound.

WithWith thethe useuse ofof X-RayX-Ray didiffraction,ffraction, thethe followingfollowing mineralsminerals werewere identifiedidentified (Figure(Figure6 6):): halloysite,halloysite, kaolinite,kaolinite, hematite,hematite, magnetite, magnetite, quartz, quartz, magnesioferrite, magnesioferrite, rutile, ilmenite,rutile, ilmenite, geikielite, geikielite, goyazite, gorceixite,goyazite, andgorceixite, crandallite. and crandallite. TheThe halloysitehalloysite samplesample fromfrom thethe DuninoDunino depositdeposit isis aa typetype ofof aluminasilicatealuminasilicate clayclay wherewhere thethe basicbasic structuralstructural unitunit isis aa singlesingle crystalcrystal surroundedsurrounded byby aa silicasilica tetrahedraltetrahedral sheetsheet andand thethe otherother aluminaalumina octahedraloctahedral sheet.sheet. Between Between these these layers, layers, the the interl interlayerayer water water exists (Figure 77).). AA rawraw samplesample ofof halloyistehalloyiste waswas dehydrateddehydrated duringduring drying,drying, andand thethe 10Å10Å halloysitehalloysite hashas beenbeen irreversiblyirreversibly changedchanged intointo thethe 7Å7Å halloysite.halloysite. In the diffractograms diffractograms of Dunino halloysite samples, the peaks of bothboth thethe rawraw [Al (OH) Si O H O] and dried [Al (OH) Si O ] halloysite are shown (see Figure6). [Al22(OH)4Si22O55∙2·H2 2O]2 and dried [Al2(OH)2 4Si42O25] halloysite5 are shown (see Figure 6).

FigureFigure 6.6.X-ray X-ray di diffractionﬀraction (XRD) (XRD) patterns patterns of raw of raw halloysite halloysite and dried and halloysitedried halloysite from the from Dunino the deposit.Dunino deposit.

Figure 7. Single crystal structure of halloysite from the Dunino deposit.

4.2. Diatomaceous Earth A mineralogical investigation of a diatomaceous earth sample from Jawornik, using light microscopy and SEM analysis, showed that the sample is composed of diatomaceous skeletons (frustules), clay minerals (kaolinite, illite, and smectites), quartz, iron oxides (impurities), a small amount of feldspars, and organic matter (Figures 8 and 9).

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Figure 5. Example of SEM micrograph (a) and EDS spectra (b) of the halloysite sample from the Dunino deposit. The sample was sputtered by the Au/Pd target. EDS results indicate impurity, probably in the form of the iron compound.

With the use of X-Ray diffraction, the following minerals were identified (Figure 6): halloysite, kaolinite, hematite, magnetite, quartz, magnesioferrite, rutile, ilmenite, geikielite, goyazite, gorceixite, and crandallite. The halloysite sample from the Dunino deposit is a type of aluminasilicate clay where the basic structural unit is a single crystal surrounded by a silica tetrahedral sheet and the other alumina octahedral sheet. Between these layers, the interlayer water exists (Figure 7). A raw sample of halloyiste was dehydrated during drying, and the 10Å halloysite has been irreversibly changed into the 7Å halloysite. In the diffractograms of Dunino halloysite samples, the peaks of both the raw [Al2(OH)4Si2O5∙2H2O] and dried [Al2(OH)4Si2O5] halloysite are shown (see Figure 6).

Figure 6. X-ray diffraction (XRD) patterns of raw halloysite and dried halloysite from the Dunino Minerals 2019, 9, 670 10 of 17 deposit.

Figure 7. Single crystal structure of halloysitehalloysite from the Dunino deposit. 4.2. Diatomaceous Earth 4.2. Diatomaceous Earth A mineralogical investigation of a diatomaceous earth sample from Jawornik, using light A mineralogical investigation of a diatomaceous earth sample from Jawornik, using light microscopy and SEM analysis, showed that the sample is composed of diatomaceous skeletons microscopy and SEM analysis, showed that the sample is composed of diatomaceous skeletons (frustules), clay minerals (kaolinite, illite, and smectites), quartz, iron oxides (impurities), a small Minerals(frustules), 2019, 9clay, x FOR minerals PEER REVIEW (kaolinite, illite, and smectites), quartz, iron oxides (impurities), a10 small of 16 amount of feldspars, and organic matter (Figures8 and9). amount of feldspars, and organic matter (Figures 8 and 9).

(a) (b)

Figure 8. TheThe structure structure of of diatomaceous diatomaceous earth earth from from the the Jawornik Jawornik deposit deposit (LM). Dark areas show iron oxide impurities ( a), whereas orange areas show clay minerals,minerals, and whitewhite areare quartzquartz particlesparticles ((bb).).

SEM imagesimages showed showed that that the the frustules frustules are mostly are mo centricstly (discoid)centric (discoid) without anwithout abundant an occurrenceabundant occurrenceof pinnate forms. of pinnate Diatoms forms. have Diatoms a radius ha ofve approximately a radius of approximately 50–60 µm. As 50–60 it can beμm. seen As fromit can Figure be seen9b, fromdiatoms Figure have 9b, ahighly diatoms porous havestructure. a highly porous The pores structure. size on theThe frustule pores si wallsze on rangedthe frustule from 100walls to 200ranged nm. fromPrevious 100 studiesto 200 nm. showed Previous that amorphous studies showed silica ﬁllsthat someamorphous pores of silica a diatom fills some frustule, pores whereas of a diatom others frustule,are partially whereas dissolved others [54 are]; in partially our observations, dissolved we[54] did; in notour encounterobservations, that we phenomenon. did not encounter On some that of phenomenon.the SEM images, On detrital some of grains the SEM are visible images, (Figure detrital9a). Thegrains majority are visible of identiﬁed (Figure frustule9a). The species majority were of identifieddiscoid frustules frustule from species the family wereThalassiosiraceae discoid frustulesand from cylindric the Aulacoseirafamily Thalassiosiraceae islandica (upper and right cylindric corner Aulacoseiraof Figure9a). islandica (upper right corner of Figure 9a).

(a) (b)

Figure 9. SEM images of microstructure and nanostructure of diatomieaus earth from the Jawornik deposit. (a) View of a raw diatomaceous earth sample, (b) close-up of the porous structure of a single frustule.

The elemental analysis made by the energy-dispersive X-ray spectroscopy (EDS) in micro-areas on the surface of diatomieaus earth from the Jawornik deposit show differences in the qualitative and quantitative chemical composition of the minerals. The mass-averaged quantitative and qualitative EDS elemental analysis showed that the most important elements found are: oxygen, silicon, aluminum, and iron. The averaged mass percentage concentrations of the major elements in diatomaceous earth are shown in Table 7.

Minerals 2019, 9, x FOR PEER REVIEW 10 of 16

(a) (b)

Figure 8. The structure of diatomaceous earth from the Jawornik deposit (LM). Dark areas show iron oxide impurities (a), whereas orange areas show clay minerals, and white are quartz particles (b).

SEM images showed that the frustules are mostly centric (discoid) without an abundant occurrence of pinnate forms. Diatoms have a radius of approximately 50–60 μm. As it can be seen from Figure 9b, diatoms have a highly porous structure. The pores size on the frustule walls ranged from 100 to 200 nm. Previous studies showed that amorphous silica fills some pores of a diatom frustule, whereas others are partially dissolved [54]; in our observations, we did not encounter that phenomenon. On some of the SEM images, detrital grains are visible (Figure 9a). The majority of identifiedMinerals 2019 frustule, 9, 670 species were discoid frustules from the family Thalassiosiraceae and cylindric11 of 17 Aulacoseira islandica (upper right corner of Figure 9a).

(a) (b)

FigureFigure 9. 9. SEMSEM images images of of microstructure microstructure and and nanostruct nanostructureure of of diatomieaus diatomieaus earth earth from from the the Jawornik Jawornik deposit.deposit. (a ()a View) View of ofa raw a raw diatomaceous diatomaceous earth earth sample, sample, (b) close-up (b) close-up of the of porous the porous structure structure of a single of a frustule.single frustule.

TheThe elemental elemental analysis analysis made made by by the the energy-disper energy-dispersivesive X-ray X-ray spectroscopy spectroscopy (EDS) (EDS) in in micro-areas micro-areas onon the the surface surface of of diatomieaus diatomieaus eart earthh from from the the Jawornik Jawornik deposit deposit show show differences diﬀerences in in the the qualitative qualitative and and quantitativequantitative chemical chemical composition composition of of the the minerals minerals.. The The mass-averaged mass-averaged quantitative quantitative and and qualitative qualitative EDSEDS elementalelemental analysisanalysis showed showed that that the mostthe most important important elements elements found are: found oxygen, are: silicon,oxygen, aluminum, silicon, aluminum,and iron. The and averaged iron. The mass averaged percentage mass concentrations percentage ofconcentrations the major elements of the in major diatomaceous elements earth in diatomaceousare shown in Tableearth7 are. shown in Table 7.

Table 7. Averaged mass percentage concentrations of the major elements in diatomaceous earth (EDS analysis).

Element Mass (%) O 48.4 Si 45.7 Al 3.2 Fe 2.7

The elemental composition of diatomaceous earth based on the EDS analysis is consistent with chemical composition (Table8).

Table 8. Chemical composition of diatomaceous earth from the Jawornik deposit.

Compound SiO2 Al2O3 Fe2O3 TiO2 Na2OK2O CaO MgO Loss on Ignition (wt.%) 69.2 11.8 4.3 0.5 0.15 1.24 1.2 0.75 10.86

In order to conﬁrm the ICP-OES chemical composition results, additional XRF analyses were also performed for the diatomaceous earth samples (Table9). The chemical composition was consistent with results obtained with ICP-OES and matched the identiﬁed minerals in XRD. The dominant trace elements found in halloysite were chromium, nickel, and vanadium with concentration reaching almost 800 ppm. The concentration of these elements is considerably higher than in halloysite. Minerals 2019, 9, 670 12 of 17

Table 9. Chemical composition and trace elements of diatomaceous earth determined by means of the X-ray ﬂuorescence method.

Compound wt.% Element Concentration, ppm

SiO2 68.16 V 349.8 TiO2 0.51 Cr 776.8 Al2O3 10.95 Bi 8.8 Fe2O3 4.57 Ni 746.8 MnO 0.04 Cu 0 MgO 0.82 Zn 211.7 CaO 0.46 Ga 37.3 Na2O 0.3 Rb 35.4 K2O 2.23 Sr 191.5 P2O5 0.4 Y 131.4 SO3 0.49 Zr 404.7 Cl 0.07 Nb 77.5 BaO 0.02 Mo 7.4 LOI 10.86 Sn 67 Ta 0

An example of the EDS results are shown in Figures 10–12. Figures 10 and 11 show the typical Minerals 2019, 9, x FOR PEER REVIEW 12 of 16 elemental composition of diatom, whereas Figure 12 shows iron oxide impurity.

(a) (b)

FigureFigure 10. 10. ExampleExample of of SEM SEM micrograph micrograph ( (aa)) and and EDS EDS spectra spectra ( (bb)) of of a a diatomaceous diatomaceous earth earth sample sample from from thethe Jawornik Jawornik deposit. deposit. The The sample sample was was sputtered sputtered by by an an Au/Pd Au/Pd target. target.

(a) (b)

Figure 11. Example of SEM micrograph (a) and EDS spectra (b) of a diatomaceous earth sample from the Jawornik deposit. The sample was sputtered by an Au/Pd target.

(a) (b)

Minerals 2019, 9, x FOR PEER REVIEW 12 of 16 Minerals 2019, 9, x FOR PEER REVIEW 12 of 16

(a) (b) (a) (b) Figure 10. Example of SEM micrograph (a) and EDS spectra (b) of a diatomaceous earth sample from Figurethe Jawornik 10. Example deposit. of TheSEM sample micrograph was sputtered (a) and EDS by anspectra Au/Pd (b )target. of a diatomaceous earth sample from Mineralsthe2019 Jawornik, 9, 670 deposit. The sample was sputtered by an Au/Pd target. 13 of 17

(a) (b) (a) (b) Figure 11. Example of SEM micrograph (a) and EDS spectra (b) of a diatomaceous earth sample from FiguretheFigure Jawornik 11. 11. ExampleExample deposit. of of TheSEM SEM sample micrograph micrograph was sputtered ( (aa)) and and EDS EDS by anspectra spectra Au/Pd ( (bb )target.) of of a a diatomaceous diatomaceous earth earth sample sample from from thethe Jawornik Jawornik deposit. deposit. The The sample sample was was sputtered sputtered by by an an Au/Pd Au/Pd target.

(a) (b) (a) (b) Figure 12. Example of SEM micrograph (a) and EDS spectra (b) of a diatomaceous earth sample from the Jawornik deposit.

The XRD of the diatomaceous earth sample (Figure 13) depicted crystalline peaks of silica-containing phases (quartz, opal) and clay minerals (illite and kaolinite). Minerals 2019, 9, x FOR PEER REVIEW 13 of 16

Figure 12. Example of SEM micrograph (a) and EDS spectra (b) of a diatomaceous earth sample from the Jawornik deposit.

MineralsThe2019 XRD, 9, 670 of the diatomaceous earth sample (Figure 13) depicted crystalline peaks of 14silica- of 17 containing phases (quartz, opal) and clay minerals (illite and kaolinite).

FigureFigure 13. 13. X-rayX-ray diffraction diffraction patterns patterns of of a a raw raw diatom diatomiteite sample sample from from the Jawornik deposit. 5. Discussion 5. Discussion The results of the analysis show that both deposits are rather homogeneous; however, impurities The results of the analysis show that both deposits are rather homogeneous; however, impurities in the form of iron oxides or organic matter can be found. This is evident since materials for the tests in the form of iron oxides or organic matter can be found. This is evident since materials for the tests were not subjected to any upgrading method or impurities removal. The most common method of were not subjected to any upgrading method or impurities removal. The most common method of halloysite and diatomaceous earth processing is calcination at 650 C and 900–1000 C, respectively. halloysite and diatomaceous earth processing is calcination at 650 °C◦ and 900–1000 °C,◦ respectively. This process develops the specific surface of these minerals and enhances their sorption capacity [55–58]. This process develops the specific surface of these minerals and enhances their sorption capacity [55– Other methods that could be applied include surface modification or purification, particularly in the case 58]. Other methods that could be applied include surface modification or purification, particularly in of halloysite [59,60]. Both of these minerals have similar properties and could be used interchangeably. the case of halloysite [59,60]. Both of these minerals have similar properties and could be used These two raw materials from deposits located in Poland are abundant and easily accessible. interchangeably. The mining of these minerals is cost-efficient (open-pit mining at shallow depths with the use These two raw materials from deposits located in Poland are abundant and easily accessible. of an excavator), and does not disturb the environment, as in the case of deep open-pit mining. The mining of these minerals is cost-efficient (open-pit mining at shallow depths with the use of an Large resources of these minerals could be used in the future either for manufacturing composite excavator), and does not disturb the environment, as in the case of deep open-pit mining. Large materials or for environmental purposes. This is particularly important given the fact that the mining resources of these minerals could be used in the future either for manufacturing composite materials industry is declining in the European Union, and the share of raw materials imported to the EU or for environmental purposes. This is particularly important given the fact that the mining industry is increasing. The above-mentioned examples show that such deposits could be the future of the is declining in the European Union, and the share of raw materials imported to the EU is increasing. extractive industry in Europe. The above-mentioned examples show that such deposits could be the future of the extractive industry inAuthor Europe. Contributions: As a corresponding author, M.L. conceptualized the work, elaborated the methodology, and wrote the major part of the article along with reviewing and editing. P.S. did the investigation, performed the Authorexperiments Contributions: and analysis, As a along corresponding with the interpretation author, M.L. ofconceptualiz results. S.L.ed did the thework, description elaborated of the geological methodology, setting and wrote resources, the major gathered part and of the interpreted article along data, with and contributedreviewing and to writingediting. and P.S. editing did the the investigation, article. performed the experiments and analysis, along with the interpretation of results. S.L. did the description of geological Acknowledgments: We would like to thank “Dunino” Sp. z o.o. and “Górtech” Sp. z o.o. for manufacturing the settingDIATO and sorbent resources, for access gathered and providing and interpreted the data data, for theand article. contributed to writing and editing the article. Acknowledgments:Conflicts of Interest: WeThe would authors like declare to thank no “Dunino” conflict of Sp. interest. z o.o. and “Górtech” Sp. z o.o. for manufacturing the DIATO sorbent for access and providing the data for the article. References Conflicts of Interest: The authors declare no conflict of interest 1. Cassard, D.; Leistel, J.; Lips, A.L.W.; Stein, G. Metallogenic Map of Central and Southeastern Europe: An Extract from GIS Central Europe; Intermediary Report; BRGM/RP-54703-FR; BRGM: Paris, France, 2008. 2. Martinón-Torres, M.; Rehren, T. Archaeology, History and Science: Integrating Approaches to Ancient Materials; Left Coast Press: Walnut Creek, CA, USA, 2009; ISBN 978-1-59874-350-0. Minerals 2019, 9, 670 15 of 17

3. Pollard, S. Marginal Europe: The Contribution of Marginal Lands since the Middle Ages; Clarendon Press: Oxford, UK; New York, NY, USA, 1997; ISBN 978-0-19-820638-5. 4. Szuflicki, M.; Malon, A.; Tymiński,M. Bilans Zasobów Złó˙zKopalin w Polsce wg Stanu na 31 XII 2018 r; PaństwowyInstytut Geologiczny—PaństwowyInstytut Badawczy: Warszawa, Poland, 2019. 5. Material Safety Data Sheet. “HALOSORB” Universal Mineral Adsorbent; PTH Intermark: Gliwice, Poland, 2016. 6. Material Safety Data Sheet. Diato–Diatomite Sorbent; Specjalistyczne Przedsi˛ebiorstwoGórnicze “Górtech” Sp. z o. o.: Kraków, Poland, 2018. 7. Matusik, J. Minerały z Grupy Kaolinitu Jako Prekursory Nanorurek Mineralnych. Ph.D. Thesis, AGH University of Science and Technology, Krakow, Poland, 2010. 8. Keeling, J.L. The Mineralogy, Geology and Occurrences of Halloysite; Apple Academic Press: Oakville, ON, Canada, 2015. 9. Bogacz, A.; Kawulak, M.; Por˛eba,E.; Lis, J. Obja´snieniado Mapy Geo´srodowiskowej Polski Arkusz Jawor 760; PaństwowyInstytut Geologiczny—PaństwowyInstytut Badawczy: Warszawa, Poland, 2004. 10. Hardy, T.; Kordylewski, W.; Mo´scicki,K. Use of aluminosilicate sorbents to control KCl vapors in biomass combustion gases. J. Power Technol. 2013, 93, 37–43. 11. Cheng, A.-L.; Huang, W.-L. Selective adsorption of hydrocarbon gases on clays and organic matter. Org. Geochem. 2004, 35, 413–423. [CrossRef] 12. Volzone, C.; Thompson, J.G.; Melnitchenko, A.; Ortiga, J.; Palethorpe, S.R. Selective gas adsorption by amorphous clay-mineral derivatives. Clays Clay Miner. 1999, 47, 647–657. [CrossRef] 13. Cho, K.-H.; Jang, B.-S.; Kim, K.-H.; Park, D.-W. Performance of pyrophyllite and halloysite clays in the catalytic degradation of polystyrene. React. Kinet. Catal. Lett. 2006, 88, 43–50. [CrossRef] 14. Shah, J.; Jan, M.R. Polystyrene degradation studies using Cu supported catalysts. J. Anal. Appl. Pyrolysis 2014, 109, 196–204. 15. Tae, J.-W.; Jang, B.-S.; Kim, J.-R.; Kim, I.; Park, D.-W. Catalytic degradation of polystyrene using acid-treated halloysite clays. Solid State Ion. 2004, 172, 129–133. [CrossRef] 16. Selvakumaran, P.; Lawerence, A.; Bakthavatsalam, A.K. Effect of additives on sintering of lignites during CFB combustion. Appl. Therm. Eng. 2014, 67, 480–488. [CrossRef] 17. Mroczek, K.; Kalisz, S.; Pronobis, M.; Sołtys, J. The effect of halloysite additive on operation of boilers firing agricultural biomass. Fuel Process. Technol. 2011, 92, 845–855. [CrossRef] 18. Abdullayev, E.; Lvov, Y. Halloysite clay nanotubes as a ceramic “skeleton” for functional biopolymer composites with sustained drug release. J. Mater. Chem. B 2013, 1, 2894–2903. [CrossRef] 19. De Silva, R.T.; Pasbakhsh, P.; Goh, K.L.; Chai, S.-P.; Ismail, H. Physico-chemical characterisation of chitosan/halloysite composite membranes. Polym. Test. 2013, 32, 265–271. [CrossRef] 20. Cui, Y.; Kumar, S.; Kona, B.R.; van Houcke, D. Gas barrier properties of polymer/clay nanocomposites. RSC Adv. 2015, 5, 63669–63690. [CrossRef] 21. Subramanian, K.S.; Sharmila Rahale, C. Ball milled nanosized zeolite loaded with zinc sulfate: A putative slow release Zn fertilizer. Int. J. Innov. Hortic. 2012, 1, 33–40. 22. Borges, R.; Brunatto, S.F.; Leitão, A.A.; De Carvalho, G.S.; Wypych, F. Solid-state mechanochemical activation of clay minerals and soluble phosphate mixtures to obtain slow-release fertilizers. Clay Miner. 2015, 50, 153–162. [CrossRef] 23. Kulok, M.; Kolacz, R.; Dobrzanski, Z.; Wolska, I. The influence of halloysite on the content of bacteria, fungi and mycotoxins in feed mixtures. In Proceedings of the XIIth International Society for Animal Hygiene Congress, Warsaw, Poland, 4–8 September 2005; Volume 2, pp. 354–357. 24. Korniewicz, D.; Kołacz, R.; Dobrzański,Z.; Korniewicz, A.; Kulok, M. Effect of dietary halloysite on the quality of feed and utilization of nutrients by fatteners. EJPAU Anim. Husb. 2006, 9, 59. 25. Skiba, M.; Kulok, M.; Kołacz, R.; Skiba, T. The influence of halloysite supplementation in laying hens feeding on egg yolk lipid fraction. In World Poultry Science Association, Proceedings of the 19th European Symposium on Quality of Poultry Meat, 13th European Symposium on the Quality of Eggs and Egg Products, Turku, Finland, 21–25 June 2009; World’s Poultry Science Association (WPSA): Beekbergen, The Netherlands, 2009; pp. 1–9. 26. Abdullayev, E.; Price, R.; Shchukin, D.; Lvov, Y. Halloysite tubes as nanocontainers for anticorrosion coating with benzotriazole. ACS Appl. Mater. Interfaces 2009, 1, 1437–1443. [CrossRef][PubMed] Minerals 2019, 9, 670 16 of 17

27. Abdullayev, E.; Abbasov, V.; Tursunbayeva, A.; Portnov, V.; Ibrahimov, H.; Mukhtarova, G.; Lvov, Y. Self-healing coatings based on halloysite clay polymer composites for protection of copper alloys. ACS Appl. Mater. Interfaces 2013, 5, 4464–4471. [CrossRef][PubMed] 28. Shabeer, T.A.; Saha, A.; Gajbhiye, V.T.; Gupta, S.; Manjaiah, K.M.; Varghese, E. Exploitation of nano-bentonite, nano-halloysite and organically modified nano-montmorillonite as an adsorbent and coagulation aid for the removal of multi-pesticides from water: A sorption modelling approach. Water Air Soil Pollut. 2015, 226, 41. [CrossRef] 29. Shabeer, T.A.; Saha, A.; Gajbhiye, V.T.; Gupta, S.; Manjaiah, K.M.; Varghese, E. Removal of poly aromatic hydrocarbons (PAHs) from water: Effect of nano and modified nano-clays as a flocculation aid and adsorbent in coagulation-flocculation process. Polycycl. Aromat. Compd. 2014, 34, 452–467. [CrossRef] 30. Sakiewicz, P.; Nowosielski, R.; Pilarczyk, W.; Gołombek, K.; Lutyński,M. Selected properties of the halloysite as a component of Geosynthetic Clay Liners (GCL). J. Achiev. Mater. Manuf. Eng. 2011, 48, 177–191. 31. Levis, S.R.; Deasy, P.B. Characterisation of halloysite for use as a microtubular drug delivery system. Int. J. Pharm. 2002, 243, 125–134. [CrossRef] 32. Veerabadran, N.G.; Price, R.R.; Lvov, Y.M. Clay nanotubes for encapsulation and sustained release of drugs. Nano 2007, 2, 115–120. [CrossRef] 33. Aw, M.S.; Simovic, S.; Addai-Mensah, J.; Losic, D. Silica microcapsules from diatoms as new carrier for delivery of therapeutics. Nanomedicine 2011, 6, 1159–1173. [CrossRef][PubMed] 34. Janićijević,J.; Milić,J.; Calija,ˇ B.; Micov, A.; Stepanović-Petrović,R.; Tomić,M.; Daković,A.; Dobriˇcić,V.; Vasiljević,B.N.; Krajišnik, D. Potentiation of the ibuprofen antihyperalgesic effect using inorganically functionalized diatomite. J. Mater. Chem. B 2018, 6, 5812–5822. [CrossRef] 35. Gao, L.; Wang, L.; Yang, L.; Zhao, Y.; Shi, N.; An, C.; Sun, Y.; Xie, J.; Wang, H.; Song, Y.; et al. Preparation, characterization and antibacterial activity of silver nanoparticle/graphene oxide/diatomite composite. Appl. Surf. Sci. 2019, 484, 628–636. [CrossRef] 36. Ruíz-Baltazar, Á.J. Green Composite Based on Silver Nanoparticles Supported on Diatomaceous Earth: Kinetic Adsorption Models and Antibacterial Effect. J. Clust. Sci. 2018, 29, 509–519. [CrossRef] 37. Sun, H.; Wen, X.; Zhang, X.; Wei, D.; Yang, H.; Li, C.; Yang, L. Biocompatible silver nanoparticle-modified natural diatomite with anti-infective property. J. Nanomater. 2018, 2018.[CrossRef] 38. Xia, Y.; Jiang, X.; Zhang, J.; Lin, M.; Tang, X.; Zhang, J.; Liu, H. Synthesis and characterization of antimicrobial nanosilver/diatomite nanocomposites and its water treatment application. Appl. Surf. Sci. 2017, 396, 1760–1764. [CrossRef] 39. Degirmenci, N.; Yilmaz, A. Use of diatomite as partial replacement for Portland cement in cement mortars. Constr. Build. Mater. 2009, 23, 284–288. [CrossRef] 40. Ergün, A. Effects of the usage of diatomite and waste marble powder as partial replacement of cement on the mechanical properties of concrete. Constr. Build. Mater. 2011, 25, 806–812. [CrossRef] 41. Ivanov, S.E.; Belyakov, A.V. Diatomite and its applications. Glass Ceram. 2008, 65, 48–51. [CrossRef] 42. Li, X.; Bian, C.; Chen, W.; He, J.; Wang, Z.; Xu, N.; Xue, G. Polyaniline on surface modification of diatomite: A novel way to obtain conducting diatomite fillers. Appl. Surf. Sci. 2003, 207, 378–383. [CrossRef] 43. Kietzman, J.H.; Rodier, C.E. Effect of diatomite filler on performance of asphalt pavements. Transp. Res. Rec. 1984, 968, 8–19. 44. Gómez, J.; Gil, M.L.A.; De La Rosa-Fox, N.; Alguacil, M. Formation of siliceous sediments in brandy after diatomite filtration. Food Chem. 2015, 170, 84–89. [CrossRef][PubMed] 45. Guo, D.; Wang, H.; Fu, P.; Huang, Y.; Liu, Y.; Lv, W.; Wang, F. Diatomite precoat filtration for wastewater treatment: Filtration performance and pollution mechanisms. Chem. Eng. Res. Des. 2018, 137, 403–411. [CrossRef] 46. Zhang, X.; Zhang, B.; Wu, Y.; Wang, T.; Qiu, J. Preparation and characterization of a diatomite hybrid microfiltration carbon membrane for oily wastewater treatment. J. Taiwan Inst. Chem. Eng. 2018, 89, 39–48. [CrossRef] 47. Puszkarewicz, A.; Kaleta, J. Adsorption of chromium (VI) on raw and modified carpathian diatomite. J. Ecol. Eng. 2019, 20, 11–17. 48. Gong, J. Investigation of Sound Absorption Properties of Diatomite/Polypropylene Composite Materials. Jianzhu Cailiao Xuebao/J. Build. Mater. 2018, 21, 678–682. Minerals 2019, 9, 670 17 of 17

49. Lin, J.; Guo, J.; Zhao, Y.; Duan, L.; Jin, S. Microstructure and sound absorption property of diatomite/polyurethane porous composites. Fuhe Cailiao Xuebao/Acta Mater. Compos. Sin. 2014, 31, 1476–1480. 50. Jeong, S.-G.; Jeon, J.; Lee, J.-H.; Kim, S. Optimal preparation of PCM/diatomite composites for enhancing thermal properties. Int. J. Heat Mass Transf. 2013, 62, 711–717. [CrossRef] 51. Sun, Z.; Zhang, Y.; Zheng, S.; Park, Y.; Frost, R.L. Preparation and thermal energy storage properties of paraffin/calcined diatomite composites as form-stable phase change materials. Thermochim. Acta 2013, 558, 16–21. [CrossRef] 52. Xu, B.; Li, Z. Paraffin/diatomite composite phase change material incorporated cement-based composite for thermal energy storage. Appl. Energy 2013, 105, 229–237. [CrossRef] 53. Qian, T.; Li, J.; Min, X.; Guan, W.; Deng, Y.; Ning, L. Enhanced thermal conductivity of PEG/diatomite shape-stabilized phase change materials with Ag nanoparticles for thermal energy storage. J. Mater. Chem. A 2015, 3, 8526–8536. [CrossRef] 54. Figarska-Warchoł, B.; Stańczak,G.; Rembi´s,M.; Toboła, T. Diatomaceous rocks of the Jawornik deposit (the Polish Outer Carpathians): Petrophysical and petrographical evaluation. Geol. Geophys. Environ. 2015, 41, 311–331. [CrossRef] 55. Deng, L.; Yuan, P.; Liu, D.; Du, P.; Zhou, J.; Wei, Y.; Song, Y.; Liu, Y. Effects of calcination and acid treatment on improving benzene adsorption performance of halloysite. Appl. Clay Sci. 2019, 181, 105240. [CrossRef] 56. Yuan, P.; Tan, D.; Annabi-Bergaya, F.; Yan, W.; Fan, M.; Liu, D.; He, H. Changes in structure, morphology, porosity, and surface activity of mesoporous halloysite nanotubes under heating. Clays Clay Miner. 2012, 60, 561–573. [CrossRef] 57. Ediz, N.; Bentli, I.;˙ Tatar, I.˙ Improvement in filtration characteristics of diatomite by calcination. Int. J. Miner. Process. 2010, 94, 129–134. [CrossRef] 58. Yusan, S.; Gok, C.; Erenturk, S.; Aytas, S. Adsorptive removal of thorium (IV) using calcined and flux calcined diatomite from Turkey: Evaluation of equilibrium, kinetic and thermodynamic data. Appl. Clay Sci. 2012, 67, 106–116. [CrossRef] 59. Sakiewicz, P.; Lutynski, M.; Soltys, J.; Pytlinski, A. Purification of halloysite by magnetic separation. Physicochem. Probl. Miner. Process. 2016, 52.[CrossRef] 60. Sakiewicz, P.; Lutynski, M.A. Purification of Dunino halloysite by H2SO4 leaching and magnetic separation. In Proceedings of the E3S Web of Conferences, MEC 2016, Swieradow-Zdroj, Poland, 25–28 September 2016; Volume 8, p. 01032.

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