Chemical improvement of soluble rocks: Foundation of Mosul Dam as case study.

The dissolution of soluble rocks (gypsum/anhydrite) beneath the Mosul Dam by water seepage has been observed upon the initial impoundment; consequently, several sinkholes have been manifested in the vicinity of the dam site. Traditional grouting has been envisaged as a potential remedy; however this measure has not eradicated the problem. The main purpose of this study is to overcome the solubility of the gypsum/anhydrite rocks using chemical grouts. Rock samples were acquired from the Fatha Formation outcrop and problematic layers of brecciated gypsum situated at varying depths beneath the Mosul Dam. Two commercially available liquid polymers, polyurethane (PU) and a mixture of acrylic and cement (ARC) were used to investigate their sealing performance in halting of the solubility of the rocks (gypsum/anhydrite). To simulate the dissolution phenomenon under the influence of artificial hydraulic pressure of the dam and the water flow in its abutments, two distinct laboratory models were devised. The outcomes from the experimental study on both untreated and treated samples revealed that the acrylic-cement composite (ARC) and polyurethane (PU) are influential polymers in halting the solubility of the gypsum rock samples under both factors of water pressure and high-velocity water flow.

Investigation of the Multi-Scale Deterioration Mechanisms of Anhydrite Rock Exposed to Freeze-Thaw Environment.

The deterioration of anhydrite rock exposed to a freeze-thaw environment is a complex process. Therefore, this paper systematically investigated the physical and mechanical evolutions of freeze-thawed anhydrite rock through a series of multi-scale laboratory tests. Meanwhile, the correlation between pore structure and macroscopic mechanical parameters was discussed, and the deterioration mechanisms of anhydrite rock under freeze-thaw cycles were revealed. The results show that with the increase in freeze-thaw processes, the mechanical strength, elastic modulus, cohesion, proportions of micropores (r ≤ 0.1 µm), and PT-Ipore throat (0-0.1 µm) decrease exponentially. In comparison, the mass variation, proportions of mesopores (0.1 µm < r < 1 µm), macropores (r ≥ 1 µm), and PT-II pore throat (0.1-4 µm) increase exponentially. After 120 cycles, the mean porosity increases by 66.27%, and there is a significant honeycomb and pitted surface phenomenon. Meanwhile, as the freeze-thaw cycles increase, the frost resistance coefficient decreases, while the damage variable increases. The correlation analysis between pore structure and macroscopic mechanical parameters shows that macropores play the most significant role in the mechanical characteristic deterioration of freeze-thawed anhydrite rock. Finally, it is revealed that the water-rock expansion and water dissolution effects play a crucial role in the multi-scale damage of anhydrite rock under the freeze-thaw environment.

Analysis of Compressive Strength of Anhydrite Binder Using Full Factorial Design.

Flue gas desulfurization gypsum (FGD gypsum) is obtained from the desulphurization of combustion gases in fossil fuel power plants. FGD gypsum can be used to produce anhydrite binder. This research is devoted to the investigation of the influence of the calcination temperature of FGD gypsum, the activators K2SO4 and Na2SO4, and their amount on the compressive strength of anhydrite binder during hydration. The obtained results showed that as the calcination temperature increased, the compressive strength of anhydrite binder decreased at its early age (up to 3 days) and increased after 28 days. The compressive strength of the anhydrite binder produced at 800 °C and 500 °C differed more than five times after 28 days. The activators K2SO4 and Na2SO4 had a large effect on the hydration of anhydrite binder at its early age (up to 3 days) in comparison with the anhydrite binder without activators. The presence of the activators of either K2SO4 or K2SO4 almost had no influence on the compressive strength after 28 days. To determine which factor, the calcination temperature of FGD gypsum (500-800 °C), the hydration time (3-28 days) or the amount (0-2%) of the activators K2SO4 and Na2SO4, has the greatest influence on the compressive strength, a 23 full factorial design was applied. Multiple linear regression was used to develop a mathematical model and predict the compressive strength of the anhydrite binder. The statistical analysis showed that the hydration time had the strongest impact on the compressive strength of the anhydrite binder using activators K2SO4 and Na2SO4. The activator K2SO4 had a greater influence on the compressive strength than the activator Na2SO4. The obtained mathematical model can be used to forecast the compressive strength of the anhydrite binder produced from FGD gypsum if the considered factors are within the same limiting values as in the suggested model since the coefficient of determination (R2) was close to 1, and the mean absolute percentage error (MAPE) was less than 10%.

Balancing the Strength-Impact Relationship and Other Key Properties in Polypropylene Copolymer-Natural CaSO4 (Anhydrite)-Filled Composites.

To develop novel mineral-filled composites and assess their enhanced properties (stiffness, a good balance between mechanical strength and impact resistance, greater temperature stability), a high-impact polypropylene copolymer (PPc) matrix containing an elastomeric discrete phase was melt mixed with natural CaSO4 ß-anhydrite II (AII) produced from gypsum rocks. First, in a prior investigation, the PPc composites filled with AII (without any modification) displayed enhanced stiffness, which is correlated with the relative content of the filler. The tensile and impact strengths dramatically decreased, especially at high filling (40 wt.%). Therefore, two key methods were considered to tune up their properties: (a) the ionomeric modification of PPc composites by reactive extrusion (REx) with zinc diacrylate (ZA), and (b) the melt mixing of PPc with AII surface modified with ethylenebis(stearamide) (EBS), which is a multifunctional processing/dispersant additive. The properties of composites produced with twin-screw extruders (TSEs) were deeply assessed in terms of morphology, mechanical, and thermal performance, including characterizations under dynamic mechanical solicitations at low and high temperatures. Two categories of products with distinct properties are obtained. The ionomeric modification by Rex (evaluated by FTIR) led to composites characterized by remarkable thermal stability, a higher temperature of crystallization, stronger interfacial interactions, and therefore noticeable mechanical properties (high tensile strength (i.e., 28 MPa), increased stiffness, moderate (3.3 kJ/m2) to good (5.0 kJ/m2) impact resistance) as well as advanced heat deflection temperature (HDT). On the other hand, the surface modification of AII with EBS facilitated the dispersion and debonding of microparticles, leading to composites revealing improved ductility (strain at break from 50% to 260%) and enhanced impact properties (4.3-5.3 kJ/m2), even at high filling. Characterized by notable mechanical and thermal performances, high whiteness, and a good processing ability, these new PPc-AII composites may be tailored to meet the requirements of end-use applications, ranging from packaging to automotive components.

Microbially influenced formation of anhydrite at low temperature.

Calcium sulfate minerals are abundant in nature - on Earth and on Mars - and important in several fields of material sciences. With respect to gypsum and bassanite, anhydrite represents the anhydrous crystalline phase in the CaSO4-H2O system. Despite years of research, the formation of anhydrite in the laboratory at low temperature remains challenging and, in the geological record, this mineral is mostly interpreted as a secondary phase that form through metamorphic dehydration of gypsum. Here, we present the results of laboratory precipitation experiments showing that anhydrite can form at 35 °C from evaporated seawater through a microbially influenced mineralization process. The experiments were conducted in the presence of extracellular polymeric substances (EPS) produced by bacterial strains isolated from a modern evaporitic environment, the Dohat Faishakh sabkha in Qatar. Without organic molecules, only gypsum formed in parallel control experiments. This finding provides a possible explanation for the origin of several natural occurrences of anhydrite that cannot be satisfactorily explained by existing models and reveals a new precipitation pathway that may have industrial applications.

Engineering Polypropylene-Calcium Sulfate (Anhydrite II) Composites: The Key Role of Zinc Ionomers via Reactive Extrusion.

Polypropylene (PP) is one of the most versatile polymers widely used in packaging, textiles, automotive, and electrical applications. Melt blending of PP with micro- and/or nano-fillers is a common approach for obtaining specific end-use characteristics and major enhancements of properties. The study aims to develop high-performance composites by filling PP with CaSO4 ß-anhydrite II (AII) issued from natural gypsum. The effects of the addition of up to 40 wt.% AII into PP matrix have been deeply evaluated in terms of morphology, mechanical and thermal properties. The PP-AII composites (without any modifier) as produced with internal mixers showed enhanced thermal stability and stiffness. At high filler loadings (40% AII), there was a significant decrease in tensile strength and impact resistance; therefore, custom formulations with special reactive modifiers/compatibilizers (PP functionalized/grafted with maleic anhydride (PP-g-MA) and zinc diacrylate (ZnDA)) were developed. The study revealed that the addition of only 2% ZnDA (able to induce ionomeric character) leads to PP-AII composites characterized by improved kinetics of crystallization, remarkable thermal stability, and enhanced mechanical properties, i.e., high tensile strength, rigidity, and even rise in impact resistance. The formation of Zn ionomers and dynamic ionic crosslinks, finer dispersion of AII microparticles, and better compatibility within the polyolefinic matrix allow us to explain the recorded increase in properties. Interestingly, the PP-AII composites also exhibited significant improvements in the elastic behavior under dynamic mechanical stress and of the heat deflection temperature (HDT), thus paving the way for engineering applications. Larger experimental trials have been conducted to produce the most promising composite materials by reactive extrusion (REx) on twin-screw extruders, while evaluating their performances through various methods of analysis and processing.

Tailoring and Long-Term Preservation of the Properties of PLA Composites with "Green" Plasticizers.

Concerning new polylactide (PLA) applications, the study investigates the toughening of PLA-CaSO4 ß-anhydrite II (AII) composites with bio-sourced tributyl citrate (TBC). The effects of 5-20 wt.% TBC were evaluated in terms of morphology, mechanical and thermal properties, focusing on the enhancement of PLA crystallization and modification of glass transition temperature (Tg). Due to the strong plasticizing effects of TBC (even at 10%), the plasticized composites are characterized by significant decrease of Tg and rigidity, increase of ductility and impact resistance. Correlated with the amounts of plasticizer, a dramatic drop in melt viscosity is also revealed. Therefore, for applications requiring increased viscosity and enhanced melt strength (extrusion, thermoforming), the reactive modification, with up to 1% epoxy functional styrene-acrylic oligomers, was explored to enhance their rheology. Moreover, larger quantities of products were obtained by reactive extrusion (REX) and characterized to evidence their lower stiffness, enhanced ductility, and toughness. In current prospects, selected samples were tested for the extrusion of tubes (straws) and films. The migration of plasticizer was not noted (at 10% TBC), whereas the mechanical and thermal characterizations of films after two years of aging evidenced a surprising preservation of properties.

Influence of Anhydrite on the Properties and Microstructure of Aluminophosphate Cement.

Aluminophosphate cement (APC) is a new type of hydraulic cementitious material with many potential functions. Microscopic analysis techniques were used to study the effect of anhydrite on the performance and hydration process of APC under standard curing conditions. The results show that adding an appropriate amount of anhydrite promotes the hydration of APC. The highest compressive strength is reached at an anhydrite content of 15 wt.%. As the anhydrite content increases, the APC's compressive strength decreases. The microscopic analysis of the hydration product morphology shows that the incorporation of anhydrite produces ettringite and other hydration products, improving the microstructure of the cement paste. The mercury intrusion porosimetry results show that the total porosity of the hardened APC paste decreases, and the microstructure becomes denser with an increase in the curing age, resulting in an increase in the compressive strength over time.

Recent Advances in Production of Ecofriendly Polylactide (PLA)-Calcium Sulfate (Anhydrite II) Composites: From the Evidence of Filler Stability to the Effects of PLA Matrix and Filling on Key Properties.

The melt-mixing of polylactide (PLA) with micro- and/or nanofillers is a key method used to obtain specific end-use characteristics and improvements of properties. So-called "insoluble" CaSO4 (CS) ß-anhydrite II (AII) is a mineral filler recently considered for the industry of polymer composites. First, the study proves that AII made from natural gypsum by a specifically thermal treatment is highly stable compared to other CS forms. Then, PLAs of different isomer purity and molecular weights (for injection molding (IM) and extrusion), have been used to produce "green" composites filled with 20-40 wt.% AII. The composites show good thermal and mechanical properties, accounting for the excellent filler dispersion and stability. The stiffness of composites increases with the amount of filler, whereas their tensile strength is found to be dependent on PLA molecular weights. Interestingly, the impact resistance is improved by adding 20% AII into all investigated PLAs. Due to advanced kinetics of crystallization ascribed to the effects of AII and use of a PLA grade of high L-lactic acid isomer purity, the composites show after IM an impressive degree of crystallinity (DC), i.e., as high as 50%, while their Vicat softening temperature is remarkably increased to 160 °C, which are thermal properties of great interest for applications requiring elevated rigidity and heat resistance.

Material characteristics of historic scagliola interiors in Vienna: A view through the microscope.

Composition and microstructure of four Viennese scagliola samples, originating from the early 18th to early 20th centuries, were analysed by different methods of microscopy. Results indicate a similar composition in all samples; only minor differences could be observed in the porosity and grain-size-distribution. While, the calcium sulphate raw material was fired at low temperatures (<200°C), the presumable presence of anhydrite II in two samples may indicate hot spots (200-300°C) during the calcination. To achieve 'marble-like' patterns mineral pigments were used to dye the ground mass. The first results show that scagliola surfaces of this study were produced by using the same or very similar technology between the 18th and early 20th centuries. The present study focuses on scagliola interiors in Vienna, Austria from different stylistic periods between the early 18th and early 20th centuries. Scagliola, also called stucco marble, imitates natural stone. It is produced by a mixture of gypsum (CaSO4 ·2H2 O), different pigments, animal glue and water. In the history of interior design, the material played an important role in the 18th and 19th centuries in Central Europe. The aim of the research was a detailed investigation of four selected samples in order to identify the raw materials and manufacturing technology of the stucco marbles used over time in Vienna. As a first step thin sections (i.e. polished, transparent samples with a thickness of 0.03 mm) were prepared from the samples and analysed by different microscopic techniques. All samples showed similarities in their bulk properties, but detailed investigations revealed also some differences in their mineralogical composition. The gypsum binders contained typical air voids and so-called secondary pores which were formed by dissolving larger binder-related particles during the preparation of the mixture. The macroporosity (i.e. the amount of the pores in the samples which are larger than 0.01 mm) measured on microscopic images varied in a narrow range between 14.1% and 19.3%. The raw materials of all samples were fired at relatively low temperatures (i.e. below 200°C), but in two samples we could also determine a few anhydrite (CaSO4 ) crystals that normally form at higher temperatures in the kiln. This indicates that the distribution of temperature in the kiln was heterogeneous during the firing process. The amount and appearance of some minor mineral constituents such as dolomite (CaMg[CO3 ]2 ) and celestine (SrSO4 ) suggest that they were naturally occurred in the raw material and not deliberately added to the binder as a filling material. To achieve different colour hues and imitate natural stone surfaces, fine-grained mineral pigments and charcoal powder were used. Although we have no distinct information about the gypsum sources of these stucco marbles, several small historical gypsum quarries existed southwest of Vienna. Some of them were already in operation in the 16th century, thus a local gypsum occurrence used as a raw material is very probable. Due to the fact that the main features of the analysed samples were very similar, we assume that the scagliola surfaces of this study were produced by using the same or very similar technology between the 18th and early 20th centuries.

Seeds of imperfection rule the mesocrystalline disorder in natural anhydrite single crystals.

In recent years, we have come to appreciate the astounding intricacies associated with the formation of minerals from ions in aqueous solutions. In this context, a number of studies have revealed that the nucleation of calcium sulfate systems occurs nonclassically, involving the aggregation and reorganization of nanosized prenucleation species. In recent work, we have shown that this particle-mediated nucleation pathway is actually imprinted in the resultant micrometer-sized CaSO4 crystals. This property of CaSO4 minerals provides us with the unique opportunity to search for evidence of nonclassical nucleation pathways in geological environments. In particular, we focused on large anhydrite crystals extracted from the Naica Mine in Mexico. We were able to shed light on this mineral's growth history by mapping defects at different length scales. Based on this, we argue that the nanoscale misalignment of the structural subunits, observed in the initial calcium sulfate crystal seeds, propagates through different length scales both in morphological, as well as in strictly crystallographic aspects, eventually causing the formation of large mesostructured single crystals of anhydrite. Hence, the nonclassical nucleation mechanism introduces a "seed of imperfection," which leads to a macroscopic "single" crystal whose fragments do not fit together at different length scales in a self-similar manner. Consequently, anisotropic voids of various sizes are formed with very well-defined walls/edges. However, at the same time, the material retains in part its single crystal nature.

Factors Influencing the Hydration, Dimensional Stability, and Strength Development of the OPC-CSA-Anhydrite Ternary System.

Due to the advantages of high early strength and rapid setting, ternary systems consisting of ordinary Portland clinker (OPC), calcium sulphoaluminate (CSA) clinker, and anhydrite have broad application prospects. However, further studies need to be undertaken to find a more optimal mixing proportion of this ternary binder in order to meet basic performance requirements. In this paper, isothermal calorimetric tests, chemical shrinkage tests, drying shrinkage tests, and compressive strength tests were carried out to systematically identify the effect of the OPC/CSA ratio and anhydrite dosage on the hydration, mechanical property development, and dimensional stability of ternary binders. It was found that a higher CSA content leads to a higher cumulative hydration heat, a shorter acceleration period, and a delayed induction period, which can be ascribed to the retardation of C3S at a high aluminate concentration. However, a higher addition of anhydrite can retard the main peak of hydration despite promoting the intermediate peak and improving the hydration reaction rate. The drying shrinkage of blends decreases first along with the CSA proportion and then increases. Moreover, a higher anhydrite content mitigates the drying shrinkage and hinders the strength development. Finally, considering the properties of both the fresh and hardened binder, the ternary blends with 5% anhydrite and OPC/CSA ratios ranging from 3/7 to 2/8 were identified as most suitable for applications that require a high early strength, stable late strength, and small level of shrinkage.

Verification of Gardner's equation and derivation of an empirical equation for anhydrite rocks in Sirte basin, Libya: case study.

Bulk density is a physical property of rocks measured in the laboratory on rock samples or obtained from oil field logging tools. When bulk density is not measured, a synthetic bulk density log can be calculated, for which Gardner's equation is the most widely used. However, Gardner's equation might not be appropriate for regions in which the density-velocity relationship does not conform to Gardner's curves. Here, we verified the applicability of Gardner's equation to calculation of synthetic bulk density of anhydrite rocks in the Sirte Basin (Libya) and compared the results to those obtained from an equation derived from the available measured bulk density and sonic logs. We used fifteen wells to calibrate Gardner's equation and three wells to derive an equation for the anhydrite rocks. The anhydrite rocks were 10-510 feet thick. The bulk density calculated by Gardner's equation differed only slightly from the measured log values, with the exception of the eastern part of the Sirte Basin. The average of the differences in bulk density between the measured values and Gardner's equation results were 0.022-0.040 g/cm3, and between the measured values and the derived equation results 0.002-0.045 g/cm3, both with a standard error of about 0.01 of the bulk density estimated results. We conclude that while Gardner's equation is more appropriate for estimating the bulk density of anhydrite rocks in the eastern part of the basin, the derived equation could be more appropriate for the western region.

Mechanism of water extraction from gypsum rock by desert colonizing microorganisms.

Microorganisms, in the most hyperarid deserts around the world, inhabit the inside of rocks as a survival strategy. Water is essential for life, and the ability of a rock substrate to retain water is essential for its habitability. Here we report the mechanism by which gypsum rocks from the Atacama Desert, Chile, provide water for its colonizing microorganisms. We show that the microorganisms can extract water of crystallization (i.e., structurally ordered) from the rock, inducing a phase transformation from gypsum (CaSO4·2H2O) to anhydrite (CaSO4). To investigate and validate the water extraction and phase transformation mechanisms found in the natural geological environment, we cultivated a cyanobacterium isolate on gypsum rock samples under controlled conditions. We found that the cyanobacteria attached onto high surface energy crystal planes ({011}) of gypsum samples generate a thin biofilm that induced mineral dissolution accompanied by water extraction. This process led to a phase transformation to an anhydrous calcium sulfate, anhydrite, which was formed via reprecipitation and subsequent attachment and alignment of nanocrystals. Results in this work not only shed light on how microorganisms can obtain water under severe xeric conditions but also provide insights into potential life in even more extreme environments, such as Mars, as well as offering strategies for advanced water storage methods.

In situ S-isotope compositions of sulfate and sulfide from the 3.2 Ga Moodies Group, South Africa: A record of oxidative sulfur cycling.

Sulfate minerals are rare in the Archean rock record and largely restricted to the occurrence of barite (BaSO4 ). The origin of this barite remains controversially debated. The mass-independent fractionation of sulfur isotopes in these and other Archean sedimentary rocks suggests that photolysis of volcanic aerosols in an oxygen-poor atmosphere played an important role in their formation. Here, we report on the multiple sulfur isotopic composition of sedimentary anhydrite in the ca. 3.22 Ga Moodies Group of the Barberton Greenstone Belt, southern Africa. Anhydrite occurs, together with barite and pyrite, in regionally traceable beds that formed in fluvial settings. Variable abundances of barite versus anhydrite reflect changes in sulfate enrichment by evaporitic concentration across orders of magnitude in an arid, nearshore terrestrial environment, periodically replenished by influxes of seawater. The multiple S-isotope compositions of anhydrite and pyrite are consistent with microbial sulfate reduction. S-isotope signatures in barite suggest an additional oxidative sulfate source probably derived from continental weathering of sulfide possibly enhanced by microbial sulfur oxidation. Although depositional environments of Moodies sulfate minerals differ strongly from marine barite deposits, their sulfur isotopic composition is similar and most likely reflects a primary isotopic signature. The data indicate that a constant input of small portions of oxidized sulfur from the continents into the ocean may have contributed to the observed long-term increase in Δ33 Ssulfate values through the Paleoarchean.

Detoxification and reclamation of hydrometallurgical arsenic- and trace metals-bearing gypsum via hydrothermal recrystallization in acid solution.

Arsenic- and trace metals-bearing gypsum (As-gypsum) is one of the major hazardous solid wastes produced from metallurgical industry that poses a serious threat to the environment. However, the method for effective extraction of As and trace metals from As-gypsum is still lacking. In this study, simultaneous extraction of As and trace metals from a hydrometallurgical As-gypsum via hydrothermal recrystallization in acid solution was investigated. The effects of the type (H2SO4 vs HCl) and concentration of acid, and temperature on extraction efficiency were assessed. The results showed that 99% As, >92% Cu and >96% Zn could be extracted from the As-gypsum during hydrothermal treatment in 6 mol L-1 H2SO4 at 90 and 120 °C, but Pb and Cd could not be extracted efficiently. The results of hydrothermal treatment in HCl solutions demonstrated that higher HCl concentration and temperature significantly enhanced the extraction efficiency and 100% As, Cu2+, Zn2+, Pb2+ and >90% Cd were removed from the As-gypsum after treatment in 6 mol L-1 HCl, at 120 °C, for 12 h. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy results revealed that dissolution-recrystallization of gypsum is the key process for the removal of the incorporated As and trace metals. Thermodynamic modelling indicated that the released HAsO42-/Me2+ transformed into H3AsO4/MeCln(2-n) (1 ≤ n ≤ 4) species in HCl solution, hence inhibiting their reincorporation into the recrystallization products via isomorphic substitution for SO42-/Ca2+. This work provides a simple and effective method for detoxification and reclamation of As-gypsum.

Analytical characterization of the palette and painting techniques of Jorge Afonso, the great 16th century Master of Lisbon painting workshop.

In this work, a study on a set of paintings from the most significant altarpiece assigned to Master Jorge Afonso (c. 1470-1540) painting workshop is presented. This altarpiece is composed by fourteen paintings made to the church of Convento de Jesus, in Setúbal, Portugal, and was made circa 1517-19/1530, according to art-history. This set of paintings is compared to one of the other most important Portuguese altarpieces from the 16th century: the panels of the Round Church of the Convento de Cristo, in Tomar, made circa 1510-1515. The aim of this study is to characterize the wooden support, pigments, ground layers materials and technique used in Jorge Afonso workshop by means of complementary analyses. A dendrochronological approach was made in order to corroborate (or not) the historical date initially assigned. Infrared photography (IRP) and reflectography (IRR) allowed the study of the underdrawing technique and macro photography (MP) was used to recognize overlapping layers technique. Cross-sections from the paintings were examined by optical microscopy (OM), and analyzed by µ-X-ray diffraction (µ-XRD), Energy Dispersive X-ray Fluorescence spectroscopy (EDXRF), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), micro-Raman spectroscopy (µ-Raman), micro-Fourier Transform Infrared spectroscopy (µ-FTIR), Pyrolysis Gas Chromatography Mass Spectrometry (py-GC/MS). The characterization of the palette and ground layers and the study of the overlapping of paint layers brought a new insight of the adopted painting techniques by the most important group of painters working in Portugal in the 16th century - the Lisbon workshop, leaded by Master Jorge Afonso.

Extraction and Separation of Boron in Anhydrite and Gypsum Minerals and Its Isotopic Measurement by Thermal Ionization Mass Spectrometry / 分析化学

The anhydrite and gypsum are the main sulfate minerals during evaporation of seawater or lake.They record the information about relative hydrogeology and the composition of mother liquor.Boron is diffluent element, and often occurs in all kinds of evaporites.Presently, the boron isotope has been applied widely in mineral deposits forming, geochemistry and palaeoenvironment.However, there is little research about characteristic of boron isotope in anhydrite and gypsum minerals, because of the low content of boron and micro-solubility in water and hydrochloric acid.This study developed a method of extracting and purifying boron in anhydrite and gypsum by phase transformation and ion-exchange.Firstly, the samples were mixed with ammonium hydrogen carbonate to transform the calcium sulfate to calcium carbonate.And diluted hydrochloric acid (1 mol/L) was added to resolve calcium carbonate.The percent conversion was about 85%in the first stage, and up to complete resolution by repeating this process.Secondly, boron specific ion-exchange resin ( Amberlite IRA 743 ) was used to gather the boron ions fully and further refined the samples with more than 1 μg of boron by anionic and cationic resin mixed by Ion Exchange Ⅱ and Dowex 50 W × 8.Finally, according to the modified method by He, the values of boron isotope were determined by TIMS.The boron content is analytically pure gypsum was 3.501 ± 0.128 μg/g ( n=12 , RSD=3.6%) and the average recovery was 100.47%.Besides, the δ11B value of analytically pure gypsum added with NIST SRM 951 was 17.98‰±0.21‰ (n=3, RSD=1.2%).This method has good repeatability and can meet the requirements of boron isotopic measurement of anhydrite and gypsum.

Production of Synthetic Phosphoanhydrite and Its Use as a Binder in Self-Leveling Underlayments (SLU).

An experimental study was conducted to investigate the potential use of phosphogypsum (PG) to produce self-leveling underlayments. The study was designed in two stages. Initially a phosphoanhydrite (PA) was produced by heating phosphogypsum at temperatures of 350 °C, 450 °C, 550 °C, and 650 °C. Two periods of heating were applied (2 and 4 h). The formation of anhydrite was determined by thermogravimetric analysis (DTA-TG) and confirmed by X-ray diffraction (XRD). The results show that anhydrite II was obtained at temperatures above 450 °C, and at higher calcination temperatures the PA solubility was lower. In the second stage of this research, the PA was used in self-leveling underlayments as the main binder in the ternary system comprised of calcium sulfate, calcium aluminate cement, and Portland cement. Self-leveling mortar screeds produced using PA (550 °C/4 h) and PA (650 °C/4 h) showed the best performance in terms of mechanical strength and no degradation was observed after immersion and immersion-drying tests. The formation of ettringite, identified by scanning electron microscopy (SEM), may have contributed to these results. Morphological changes were studied using the scanning electron microscopy (SEM) technique.

Adsorção de Cd 2+, Ni 2+ e Zn 2+ em soluções aquosas usando anidrita e lama vermelha / Adsorption of Cd2+, Ni2+ and Zn2+ in aqueous solutions using anhydrite and red mud

RESUMO Vários minerais e resíduos industriais têm sido estudados para uso como adsorvente, entre eles a lama vermelha e a anidrita. A lama vermelha é um resíduo insolúvel gerado em grande quantidade durante o processamento da bauxita. A anidrita é um sulfato de cálcio (CaSO4) cristalizado sob a forma rômbica e usada como matéria-prima na indústria. Nesta investigação, a capacidade de adsorção de Cd2+, Ni2+ e Zn2+ pela anidrita e pela lama vermelha foi avaliada usando isotermas de adsorção de Langmuir e Freundlich. Os materiais empregados apresentaram adsorção ≥75±1% para todos os metais em soluções aquosas com concentração de 0,5 mmol.25 mL-1. As isotermas baseadas no modelo de Langmuir foram as mais apropriadas para descrever o fenômeno de remoção de Cd2+, Ni2+ e Zn2+ para a anidrita e a lama vermelha, com valores de capacidade máxima de adsorção de 0,47 e 0,51 mmol.g-1 para o Cd2+, 1,18 e 1,56 mmol.g-1 para o Ni2+ e 0,84 e 1,47 mmol.g-1 para o Zn2+, respectivamente. Esses valores foram superiores a outros valores exibidos por materiais empregados como adsorventes descritos em estudos prévios.

ABSTRACT Various minerals and industrial waste have been studied for use as an adsorbent, in particular the anhydrite and the red mud. The red mud is an insoluble residue that is generated in large quantities during the processing of bauxite. The anhydrite is a calcium sulfate (CaSO4), crystallized as a rhombic way, and used as raw material in the industry. In this study, the Cd2+, Ni2+ and Zn2+adsorption capacity by anhydrite and by red mud was evaluated using adsorption isotherms obtained by the Langmuir and Freundlich models. The materials used showed adsorption ≥75±1% for all metals in aqueous solutions with a concentration of 0.5 mmol.25 mL-1. The Langmuir isotherm was more appropriate to describe the phenomenon of Cd2+, Ni2+ and Zn2+ removal, with highest adsorption capacity at 0.47 and 0.51 mmol.g-1 for Cd2+, 1.18 and 1.56 mmol.g-1 for Ni2+, and 0.84 and 1.47 mmol.g-1 for Zn2+, respectively. These values were higher than those ones obtained for other materials described in previous studies.