Orthorhombic Sulfur Research Articles

Insights into the Superior Bioavailability of Biogenic Sulfur from the View of Its Unique Properties: The Key Role of Trace Organic Substances.

Elemental sulfur (S0) is widely utilized in environmental pollution control, while its low bioavailability has become a bottleneck for S0-based biotechnologies. Biogenic sulfur (bio-S0) has been demonstrated to have superior bioavailability, while little is known about its mechanisms thus far. This study investigated the bioavailability and relevant properties of bio-S0 based on the denitrifying activity of Thiobacillus denitrificans with chemical sulfur (chem-S0) as the control. It was found that the conversion rate and removal efficiency of nitrate in the bio-S0 system were 2.23 and 2.04 times those of the chem-S0 system. Bio-S0 was not pure orthorhombic sulfur [S: 96.88 ± 0.25% (w/w)]. Trace organic substances detected on the bio-S0 surface were revealed to contribute to its hydrophilicity, resulting in better dispersibility in the aqueous liquid. In addition, the adhesion force of T. denitrificans on bio-S0 was 1.54 times that of chem-S0, endowing a higher bacterial adhesion efficiency on the sulfur particle. The weaker intermolecular binding force due to the low crystallinity of bio-S0 led to enhanced cellular uptake by attached bacteria. The mechanisms for the superior bioavailability of bio-S0 were further proposed. This study provides a comprehensive view of the superior bioavailability of bio-S0 and is beneficial to developing high-quality sulfur resources.

Phase transition process of sulfur in bitumen and its effect on rheological properties of bitumen

Partial substitution of sulfur for bitumen helps reduce bitumen consumption while promoting recycling of the sulfur in waste residues. The properties of sulfur-extended bitumen (SEB) are closely related to the chemical reaction process and the phase transition process of sulfur in bitumen, and these two processes are influenced by sulfur dosage and curing time. Therefore, SEB samples with sulfur dosages of 1 %, 5 %, 10 %, 15 %, 20 %, 25 % and 30 % were prepared and cured for 0, 15, 30, or 60 days. Differential scanning calorimetry was conducted to understand the sulfur recrystallization process in bitumen, and a dynamic shear rheometer was used to analyze the rheological properties of SEB samples. Results show that molten sulfur can turn to monoclinic sulfur immediately after cooling; the monoclinic sulfur gradually turns to orthorhombic sulfur, and the ratio between the two forms stabilizes after curing for 15 days. The recrystallization of sulfur in bitumen needs sufficient curing time, and the sulfur states in bitumen vary depending on the sulfur dosage. When the sulfur dosage is lower than 15 %, sulfur dissolves into bitumen. The dissolved sulfur softens the bitumen and increases its low-temperature properties and resistance to fatigue cracking. When the sulfur dosage is 10 %, 15 %, 20 %, 25 %, or 30 %, surplus sulfur is recrystallized to orthorhombic sulfur. When the sulfur dosage is 35 % or more (the dosages evaluated in the former study), surplus sulfur is recrystallized to monoclinic sulfur. The chemically crosslinked sulfur and recrystallization sulfur help increase the elastic component in bitumen and improve the rutting resistance and fatigue life of bitumen. However, when the sulfur dosage exceeds 20 %, the effect of stress concentration stands out due to bulk gathering of recrystallized sulfur, and this effect stops further improvement in the fatigue life of SEB samples. The effects of recrystallization sulfur on bitumen are mainly concentrated in the first 15 days of curing time, even though much more recrystallized sulfur is detected after more curing time, even at 60 days (the longest curing time evaluated in this study). Therefore, a curing time of 15 days is sufficient for accurate evaluation of SEB properties.

Positron lifetime spectroscopy applied to pure sulphur and selenium

High purity crystalline orthorhombic Sulphur and hexagonal Selenium have been investigated using Positron Lifetime Spectroscopy technique. Annealed for 3 h at 120 °C Selenium lifetime (308(1) ps) has been compared with previous Positron Lifetime Spectroscopy knowledge in order to validate the measurements and the analysis procedure, and also compared with theoretical calculations available in literature, including different methods and parametrizations, resulting on the best match of LMTO-ASA method with GGA parametrization. Annealed for 3 h at 80 °C Sulphur samples were studied by the same means providing a single lifetime component with value 300(1) ps that has been assigned to the positron annihilation in the bulk that is not present in the current literature.

Электронная зонная структура, распределение зарядовой плотности и химическая связь в молекулярных кристаллах халькогенов

The electronic band structure and the charge density distribution are theoretically studied in rhombohedral and monoclinic selenium, rhombohedral and orthorhombic sulphur with the aim to classify types of chemical bonding in molecular crystals of chalcogens. It is found that valence s- and lower in energy p-electrons contribute mainly in covalent bonds between nearest neighboring atoms in ring-shaped molecules, while all types of valence p-electrons provide bonding between rings of atoms in crystals. Parameters of critical points and the character of the charge density distribution in their vicinity point to coexistence of a number of types of chemical bonding in molecular crystals of Se and S: covalent, semimetallic and one more type, characterizing by the charge density fluctuations. Van der Waals forces, being important for finding equilibrium lattice parameters, have little impact on the charge density distribution and on the chemical bonding in crystals of chalcogens.

Electronic band structure, charge density distribution and chemical bonding in molecular crystals of chalcogens

The electronic band structure and the charge density distribution are theoretically studied in rhombohedral and monoclinic selenium, rhombohedral and orthorhombic sulphur with the aim to classify types of chemical bonding in molecular crystals of chalcogens. It is found that valence s- and lower in energy p-electrons contribute mainly in covalent bonds between nearest neighboring atoms in ring-shaped molecules, while all types of valence p-electrons provide bonding between rings of atoms in crystals. Parameters of critical points and the character of the charge density distribution in their vicinity point to coexistence of a number of types of chemical bonding in molecular crystals of Se and S: covalent, semimetallic and one more type, characterizing by the charge density fluctuations. Van der Waals forces, being important for finding equilibrium lattice parameters, have little impact on the charge density distribution and on the chemical bonding in crystals of chalcogens. Keywords: chalcogens, molecular crystals, electronic band structure, types of chemical bonding.

Near-far IR photoconductivity damping in hyperdoped Si at low temperatures

Silicon p-n junction photoelement fabricated on a p-doped wafer by sulfur-based n-doping of its sub-micron thick surface layer, exhibits at liquid-helium temperatures impurity-based near-far IR (2–21 μ m) photoconductivity spectra in the form of well-resolved separate bands of neutral and ionized atomic-like and cluster-like sulfur centers. Temperature variation in the range of 5–105 K demonstrates first at lower temperatures < 35 K strong damping of IR photoconductivity related to cluster-like sulfur centers with ultralow activation energy ≈ 4 meV, corresponding to excitation of the lowest energy of Raman-active phonon in orthorhombic crystalline sulfur lattice. Further increase in temperature results in the next damping step above 85 K for all spectral bands above 1800 cm-1 with higher activation energy ≈ 20 meV, representing the lowest energy of Raman-active vibration of octagon molecules in the crystalline sulfur. Broad near-far IR photosensitivity of the hyperdoped material, provided by the concentration-driven sulfur aggregation and quantum-level temperature control of its photoconductivity, paves the way for silicon photonics in far-IR and, possibly in the future, even THz spectral regions.

Influence of Component Ratio on Thermal and Mechanical Properties of Terpenoid-Sulfur Composites

Terpenoids are potentially sustainable replacements for petrochemical olefins. Sulfur is a waste product produced in large quantities from fossil fuel refining. Several composites with attractive properties have recently been made from terpenoids and sulfur. This report details the extent to which the ratio of sulfur to terpenoid and the terpenoid olefin content influences the thermal and mechanical properties of such terpenoid-sulfur composites. The terpenoids selected were diunsaturated geraniol and triunsaturated farnesol that, upon their inverse vulcanization with elemental sulfur, yield composites GerSx and FarSx, respectively (x = wt % sulfur). The wt % sulfur in the monomer feed was varied from 30–95 for this study, providing twelve materials. Mechanical analysis of these materials was undertaken by compressive and tensile strength techniques. Differential scanning calorimetric analysis revealed both polymeric and orthorhombic sulfur present in the materials with glass transition temperatures (Tg) of −37 °C to −13 °C and melt temperatures (Tm) of 119 to 104 °C. The crystallinity of composites decreases as the weight fraction of sulfur decreases and composites having the highest olefin content exhibit no detectable crystalline microstructures. The compressive strength of the materials showed increasing strength for higher olefin-content materials for both GerSx (with compressive strength of up to 32 MPa) and FarSx (with compressive strength of up to 43 MPa). The improved strength with increasing olefin content levels off at around 80–85% of terpenoid, after which point both tensile and compressive strength diminish.

A Study of the chemical nature of sulfur-containing rocks and Frasch sulfur in the Al-Mishraq Sulfur field

The economic evaluation of the exploration sulfur well depends mainly on the elemental sulfur content and its association other factors, so a sample of sulfur rocks extracted by a special excavator for one of the exploratory wells was studied and in the form of a bore hole rock. The elemental sulfur ratio reached 12.8% an important ratio in estimating the explored sulfur reserves and through XRD, the predominant crystalline composition is calcite mineral with hexagonal crystalline form and with a lesser percentage in orthorhombic crystal sulfur this supports one of the theories that explained the formation of sulfur. Also, the mine Mishraq sulfur extracted by the underground melting method (known as the Frasch process) was studied chemically, and the elemental sulfur ratio reached 98.58% and the bituminous material 1.157%. Also, the SEM scanning electron microscope showed the presence of nanotubes of size (20-44 nm) belonging to the carb-sulfur compounds in the SEM, which are observed for the first time in this form.

Fe3O4-seated rGO–sulfur complex as a potential cathode material for lithium–sulfur batteries

Lithium–sulfur battery has been proposed as a futuristic energy storage system owing to its positive aspects such as high theoretical specific energy density, less expensive, large availability of elemental sulfur, and better safety. Nevertheless, Li–S batteries have not come to the market for commercialization which is mainly attributed to the limitations such as the insulating nature of orthorhombic sulfur, undesirable polysulfide crossover between the electrodes, and poor interfacial properties between lithium anode and electrolytes. In order to solve these issues, several attempts have been made by researchers around the world. In the present work, in order to restrict polysulfide crossover and to promote the conductivity of elemental sulfur, Fe3O4-seated rGO–sulfur complex is prepared and used as cathode. The Li–S cell delivers a discharge capacity of 1400 mAh g−1 at 0.1 C-rate on its first cycle and a steady discharge capacity is attained at 0.5 C-rate. In the composite cathode, every element works for a particular reason: the added rGO enhances the conductivity of cathode, while Fe3O4 confines polysulfides appreciably as evidenced by TEM and XPS analyses. The self-discharge of the cell is also reduced. The variations of electrolyte resistance (Rs), interfacial resistance (Ri), and charge transfer resistance (Rct) for various depth of discharge (DOD) and state of charge (SOC) are systematically analyzed by electrochemical impedance spectroscopy.

Unit cell parameters of 32S8 – 34S8 solid mixtures and their extremal behavior

The behavior of isotopic mixtures of polyatomic molecular compounds can have a critical character. Orthorhombic sulfur α-S8 is a typical representative of polyatomic molecular compounds among simple substances. Samples comprised of orthorhombic sulfur of different 32S and 34S ratio have been prepared and examined with powder X-Ray diffractometry in the temperature region from −100 to +90 °С. Unit cell parameters of sulfur samples with intermolecular isotopic substitution, containing 0.4 to 0.5 parts of 34S8 molecules, differ radically from the samples of the isotopic composition close to pure α-32S8 and α-34S8. Maximal deviation of unit cell volume −0.17% at −100.0 °C is observed for the sample with a part of 34S8 molecules being 0.45. Such a behavior could well be attributed to the ordering between 32S8 and 34S8 molecules in the crystal that can be triggered by lowering temperature.

Orthorhombic sulfur from Cap Garonne, Mine du Pradet

Abstract Natural orthorhombic sulfur (α-S8), grown on galena crystals from Cap Garonne, Mine du Pradet, France, were studied by single crystal X-ray diffraction at 150 K: Fddd, a=1036.75(5), b=1273.54(7), c=2437.85(13) pm, wR=0.0380, 1433 F 2 values (all data) and 37 variables. Refinements of the occupancy parameters along with EDX data indicate pure sulfur.

Biokinetics of microbial consortia using biogenic sulfur as a novel electron donor for sustainable denitrification

In this study, the biokinetics of autotrophic denitrification with biogenic S0 (ADBIOS) for the treatment of nitrogen pollution in wastewaters were investigated. The used biogenic S0, a by-product of gas desulfurization, was an elemental microcrystalline orthorhombic sulfur with a median size of 4.69 µm and a specific surface area of 3.38 m2/g, which made S0 particularly reactive and bioavailable. During denitritation, the biomass enriched on nitrite (NO2–) was capable of degrading up to 240 mg/l NO2–-N with a denitritation activity of 339.5 mg NO2–-N/g VSS·d. The use of biogenic S0 induced a low NO2–-N accumulation, hindering the NO2–-N negative impact on the denitrifying consortia and resulting in a specific denitrification activity of 223.0 mg NO3–-N/g VSS·d. Besides Thiobacillus being the most abundant genus, Moheibacter and Thermomonas were predominantly selected for denitrification and denitritation, respectively.

Sandwich-like graphene-mesoporous carbon as sulfur host for enhanced lithium–sulfur batteries

Graphene-mesoporous carbon/sulfur composites (G-MPC/S) were constructed by melt-infiltration of sulfur into graphene-mesoporous carbon which was synthesized by soft template method. The SEM and BET results of the graphene-mesoporous carbon show that the as-prepared sandwich-like G-MPC composites with a unique microporous-mesoporous structure had a high specific surface area of 554.164 m2 · g−1 and an average pore size of about 13 nm. The XRD analysis presents the existence of orthorhombic sulfur in the G-MPC/S composite, which indicates the complete infiltration of sulfur into the pores of the G-MPC. When the graphene-mesoporous carbon/surfur composites (G-MPC/S) with 53.9 wt.% sulfur loading were used as the cathode for lithium–sulfur (Li–S) batteries, it exhibited an outstanding electrochemical performance including excellent initial discharge specific capacity of 1393 mAh · g−1 at 0.1 °C, high cycle stability (731 mAh · g−1 at 200 cycles) and good rate performance (1038 mAh · g−1, 770 mAh · g−1, 518 mAh · g−1 and 377 mAh · g−1 at 0.1 °C, 0.2 °C, 0.5 °C and 1 °C, respectively), which suggested the important role of the G-MPC composite in providing more electrons and ions channels, in addition, the shuttle effect caused by the dissolved polysulfide was also suppressed.

Preparation and physicochemical characterization of ingredients of Indian traditional medicine, Mahamrutyunjaya Rasa

BackgroundMahamrutyunjaya rasa is an ayurvedic formulation used in the treatment of cardiac disorders. It contains the purified roots of Visa (Aconitum ferox), Brihati (Solanum indicum), fruits of Pippali Kana (Piper longum), Marica (Piper nigrum), Gandhaka (Sulfur), Hingula (Cinnabar) and Tankana (Sodium metaborate) as per Bhaishajya Ratnavali. The purification (shodhana) process changes the physiochemical properties of the raw materials which need to be studied and understood. ObjectiveThe present work aims to perform a comprehensive physicochemical characterization of raw materials, intermediates and the final product obtained during purification, using modern analytical techniques. Materials and methodsThe standard methods as per traditional text were followed and the physicochemical changes were also investigated by collecting samples at different steps of purification. The samples were analysed using various techniques, viz. Fourier transform infra-red spectroscopic (FTIR), X-ray diffraction (XRD), Differential Scanning Calorimeter (DSC) and High Performance thin Layer chromatography (HPTLC). ResultsThe FTIR and HPTLC analysis of the alkaloidal extracts of Visa showed loss of an ester group with shift in the peaks from 1720 cm−1 (CO stretching of esters) to 1676 cm−1 (CO stretching of Ketone) which signifies the conversion of alkaloid Aconitine (LD50 – 0.08 mg/kg) to Benzoylaconine (LD50 – 24 mg/kg) improving its safety. The analysis of gandhaka by XRD and DSC showed that purification brought about transformation of orthorhombic sulphur into monoclinic sulphur and it reverted back to original form with higher purity. The treatments given to gandhaka and hingula with organic compounds made them homologous to the body tissues. Analysis of purified tankana showed that the processing led to loss of water and slight change in the crystal structure with the shift in the endothermic peak from 110.6 °C to 104.2 °C. ConclusionThus, the present study provides a scientific backing to the methodologies used by Ayurvedic practitioners. The study also provides physicochemical fingerprints for the standardization as well as characterization of raw materials and forms a technical platform for manufacturers to develop quality control standards.

Addition of Sulphur to Graphene Nanoflakes Using Thermal Plasma for Oxygen Reduction Reaction in Alkaline Medium

A batch process is developed to generate sulphur functionalized graphene nanoflakes (S-GNFs), corresponding to nanoparticles of stacked graphene. The growth and functionalization of the catalysts are done in a single thermal plasma reactor. The GNFs are first grown through the decomposition of methane in the thermal plasma volume followed by homogeneous nucleation of the nanoparticles in the well-controlled recombining plasma stream allowing the 2-dimensional evolution of the nanoparticle morphology. The precursor feeding conditions are then changed to liquid carbon disulphide in order to generate sulphur-based functional groups on the nanoparticles. The plasma conditions and carbon disulphide injection are varied, and samples with tuneable amount of sulphur between 4 and 28 at% are obtained. The functional groups generated include polythiophene polymer partly covering the GNFs, sulphur functionalities implemented directly on the graphitic structure, and traces of orthorhombic sulphur. The S-GNFs exhibit higher electrocatalytic activity toward the oxygen reduction reaction in alkaline medium for the samples containing the highest amounts of sulphur.

Monoclinic sulfur cathode utilizing carbon for high-performance lithium–sulfur batteries

Abstract Sulfur cathodes for lithium–sulfur batteries have been designed to be combined with conductive carbon because the insulating nature of sulfur causes low active material utilization and poor rate capability. This paper is the first to report that carbon can induce a phase transition in a sulfur cathode. The stable form of a sulfur crystal at ambient temperature is orthorhombic sulfur. We found that monoclinic sulfur becomes more stable than orthorhombic sulfur if carbon atoms penetrate into the sulfur at elevated temperatures and the carbon density exceeds a threshold of C 0.3 S 8 . The high stability of the carbon-containing monoclinic sulfur persists during lithiation and is attributed to locally formed linear SC 3 S chains with marked stability. This study provides a novel perspective on the role of carbon in the sulfur cathode and suggests control of the crystal phase of electrodes by composite elements as a new way of designing efficient electrode materials.

Electrochemical Properties of Mo Doped High Voltage Cathode for Lithium-Ion Battery

Lithium-ion batteries play an important role in portable electronic devices and e-mobility due to their high gravimetric energy density. However they are not able to meet the growing demand for higher capacity batteries for extended range electric vehicles. Alternatively, lithium-sulfur batteries based on multi-step redox conversion reaction provide a theoretical specific capacity of 1675 mAh/g. However LiS batteries also suffer from many problems, such as severe volumetric expansion/contraction during lithiation/de-lithiation, polysulfide (PS) dissolution and shuttling dendritic lithium growth on the anode, corrosion of aluminum current collector, low sulfur utilization and low current efficiency (CE). In this manuscript, we demonstrate that specific types of sulfur allotropes react differently from standard orthorhombic sulfur used in state of art LiS batteries. Significant improvements are achieved by using sulfur allotropes as both cathode active mass and 3D structural additive. Dissolution of polysulfides is confined within the cathode by the use of a bi-functional additive capable of controlling cathode reaction and the first discharge plateau is extended to deliver a capacity of 408 mAh/g at 0.2C which is close to theoretical limit of 418 mAh/g for long chain PS (Fig.1). Instead of using various methods for controlling PS dissolution and migration which are mostly based on PS binding and interaction with host-catalyst structures, we used a bi-functional additive capable to control both reaction proceeding as well as its kinetics. This method allows PS dissolution but reactions are strictly limited into cathode compartment and cannot proceed outside the cathode. An important aspect of this approach is significantly reduced side-reaction between PS and electrolyte. Fig.1: Comparison of discharge curves of standard electrode and electrode with bi-functional additive 0.7M LiTFSI + 0.25M LiNO3 , DOL/DME 2:1 v/v, active mass S loading bi-additive 1.95 mg/cm2, standard 1.65 mg/cm2 This research has been carried by Graphene Batteries AS in close cooperation with the Centre for Research and Utilization of Renewable Energy (CVVOZE) as a part of collaboration project NPU I programme (project No. LO1210), (project No. FEKT-S-14-2293) Figure 1

Mechanochemical Synthesis of Lithium Sulfide for Li-S Batteries

Lithium–sulfur (Li–S) batteries are receiving intense interest because their promise for low-cost and high-energy electrochemical storage [1]. Sulfur has a high theoretical specific capacity (1675 mAh g−1) and energy density (2600 Wh kg−1). In addition, it is abundant, inexpensive and nontoxic. Despite these advantages Li-S batteries have not been commercially produced. Major drawbacks are the insulating nature of orthorhombic sulfur and its discharge product (Li2S), the dissolution of lithium polysulfide formed during the electrochemical process in organic liquid electrolyte, and the large volumetric expansion of sulfur during lithiation. These factors result in a low utilization of active material and poor cycle life [2]. Furthermore this kind of battery must use lithium metal as the anode. Fully-lithiated lithium sulfide (Li2S) is more desirable than sulfur as a high capacity cathode material because it allows the use of a variety of lithium-free anode materials. Recently, a number of studies on Li2S with promising results have emerged. Some authors ball-milled commercial Li2S to get different particle sizes, and the resulting particles are mostly micrometer-sized [3-4]. Furthermore, high-energy ball milling was also used for the preparation of compounds with improved chemical properties. Iio et al. [5] have synthesized lithium ion conducting materials in the system Li3N-SiS2 by mechanical milling at room temperature using Li3N as a lithium source. In the present study we synthesized Li2S by high energy ball milling using elemental sulfur and Li3N. To identify crystalline phases of samples, X-ray diffraction measurements (Rigaku Miniflex diffractometer) were performed for powdered samples after mechanical milling for a given period of time. In the figure below is showed the X-ray diffraction patterns of the sample obtained after 1 h of ball milling. It is possible to observe that the sulfur was completely converted into Li2S. The Scherrer's formula was used to evaluate the crystal size of the crystallite: d = k*λ/B*cosθ where d is the size of the crystallites, k is a constant that depends on the shape of the crystallites, λ is the wavelength of the radiation used, B is the peak width at half height and θ is the angle of diffraction of the peak. The value of the crystallite size calculated with the Sherrer’s formula was about 17-18 nm. The so obtained material was used to produce an electrode and the electrochemical properties were evaluated in a two electrodes lithium cell. LiClO4 dissolved in a mixture of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether 50:50 was used as the electrolyte. We found that lithium can be electrochemically extracted and reversible reinserted into the material. The capacity was limited to about 180 mAh g-1 with a good capacity retention with cyclation . Further study will be addressed to increase the specific capacity of the material and to couple the electrode with suitable anode materials to obtain a full lithium-ion cell. A. Manthiram, S.H. Chung, C.X. Zu. Advanc. Mat. 2015, 27,1980-2006.M. Helen, M. Anji Reddy, T. Diemant, U. Golla-Schindler, R. J. Behm, U. Kaiser, and M. Fichtner. Scient. Rep. 20015, 5, 12146.K. Cai, M. Song, E. J. Cairns, Y. Zhang. Nano Lett. 2012, 12, 6474−6479.A. Manthiram, Y. Fu, Y. Su. Acc. Chem. Res. 2012, 46, 1125− 1134.K. Iio, A. Hayashi, H. Morimoto, M. Tatsumisago, and T. Minami, Chem. Mater. 2002, 14, 2444-2449. Figure 1

Methodology of Nanomodified Binder Examination: Experimental and Numerical <i>Ab Initio</i> Studies

Feasibility of the sulfur-based construction materials is caused by properties, availability and low cost of sulfur. There exist numerous ways to improve the operational properties, including the ways that are based on nanotechnology, and ab initio (quantum chemistry) studies. Unfortunately, both application and verification of numerical simulation within the same research are quite complex. In the present case study we present typical scheme of survey involving both experimental and numerical studies. As a test subject we have selected orthorhombic sulfur crystals grown from the solution in toluene. It was clearly shown that good correspondence between experimental and numerical results can be achieved for offered methodology; Raman shifts for isolated S8 molecule mostly correspond to the shifts of sulfur crystal. Computed frequencies for all primary modes are close to the experimental data. Similar correspondences can serve as proofs of conformity between unknown molecular structures in nanomodified sulfur-based material and selected structural models

Lattice deformation of blue halite from Zechstein evaporite basin: Kłodawa Salt Mine, Central Poland

Outcrops of natural blue and purple halite crystals have been found in Klodawa (Poland) salt deposit originating from the Permian (Zechstein) salt formation within tectonic zones. Field works carried out on various levels of Klodawa Salt Mine indicated differences both in intensity of the hue and in the size of the outcrops. Their occurrence was connected with the presence of epigenetic sediments rich in potassium. For the samples of blue halite, an optical anisotropy (birefringence) was observed for both standard mineralogical thin sections and thick plates, indicating a deviation from cubic symmetry. The blue colouration of the halites, described by ultraviolet–visible spectroscopy, is due to the presence of colour centres. The colour centres have been recently identified as: F, R1 (F3), R2 (F3), M and plasmons (Weselucha-Birczynska et al., Vib Spectrosc 60:124–128, 2012). The trace amount of impurities detected in the blue halites by means of scanning electron microscopy–energy dispersive X-ray spectroscopy and micro-X-ray fluorescence techniques were connected mainly with solid inclusions such as K x Na(1 − x)Cl, KMgCl3·6H2O, KCl, orthorhombic sulphur, quartz and some other phases like pyrite. Crystallographic data obtained by X-ray diffraction experiments for the single crystals of the halite from Klodawa with different saturation of blue or purple colours, as well as for natural colourless halite, revealed lowering of space-group symmetry to monoclinic, orthorhombic, trigonal, tetragonal or even triclinic systems while the space group typical for pure NaCl is Fm-3m.