Mixture Of Dolomite Research Articles

Antibacterial characteristics of carboncoated CaCO3/Mg0 powder led by the pyrolysis of poly (vinyl alcohol)-dolomite mixture

In order to reduce oral diseases with bacterial growth, carbon-coated CaCO3/MgO powder possessing antibacterial activity was obtained by the pyrolysis of poly (vinyl alcohol)-dolomite mixture at 700°C r in an argon gas. Evaluation of the antibacterial activity was performed by colony count method, using Escherichia coli and Staphylococcus aureus. CaCO3 and MgO were formed at the temperature range from 400 to 700°C. At 800°C, CaO was produced by the calcination of CaCO3. The powders after PVA pyrolysis turned into black, i.e., the formation of carbon on its surface. In the case without PVA, the formation temperature of CaCO3/MgO exceeded 100°C than the mixture of dolomite and PVA. Antibacterial activity of the carbon-coated CaCO3/MgO powder against Staphylococcus aureus was found to be stronger than against Escherichia coli. Comparing with CaCO3/MgO powder without carbon, it was found that the antibacterial action was reduced by forming carbon on its surface.

Performance of pilot-scale vertical-flow constructed wetlands, as affected by season, substrate, hydraulic load and frequency of application of simulated urban sewage

The effects of major operational factors on the performance of vertical-flow pilot-scale constructed wetlands (VFPCWs) were examined in parallel experiments. Experiments were conducted for one year in eight VFPCWs, the main substrate of which consisted of river sand at four of the wetlands, or a mixture of sand and dolomite (10:1 weight ratio) at the other four wetlands. Medium-strength synthetic sewage was applied as influent. A Latin square (balanced for carryover effects) split-plot experimental design was used. The ANOVA statistical model was applied to analyze the relationships between the main operational factors and the effluent COD, NO 2-N, NO 3-N, TN and PO 4-P concentrations. It was found that the effluent concentrations of these parameters were related to the examined factors, as well as to the combined effects of certain influencing factors. The results demonstrated that the VFPCWs operating with relatively small hydraulic load per batch (0.08 m 3 m −2), and applied on the wetlands with low batch frequency (two times per week), could result in high COD removal (more than 92%) and sufficient nitrification (more than 60% of TN was transformed to NO 3-N). However, the addition of dolomite in the substrate did not significantly affect the overall phosphorus removal, which remained in the range of 39–64%.

Thermal behavior of a mineral mixture of sepiolite and dolomite

An industrial raw material taken from Beypazari (Ankara, Turkey) region was heated at different temperatures in the 100–1100°C interval for 2 h. The volumetric percentage of particles having diameter below 2 μm in an aqueous suspension of the material held 24 h were determined as 85% by the particle size distribution analysis. The mineralogical composition of the material was obtained as mass% of 81% sepiolite, 15% dolomite, and 4% interparticle water by using the X-ray diffraction (XRD) and thermal analysis (TG, DTA) data. The temperature ranges were determined for the dehydrations of the interparticle water and the zeolitic water as 25–340°C, for the dehydration of the bound water as 340–580°C, and for the dehydroxylation of the hydroxyls as 800–833°C in the sepiolite. The zig-zag changes in the specific surface area (S/m2 g−1) and specific micro-and mesopore volume (V/cm3 g−1) with the temperature increases were discussed according to the dehydrations and dehydroxylation of the sepiolite.

Biopyribole evolution during tremolite synthesis from dolomite and quartz in CO2-H2O fluid

A series of experiments with and without sample retreatment was performed on a starting mixture of dolomite plus quartz at 0.5 GPa and 600 °C in a CO 2 -H 2 O fluid with a mole fraction of CO 2 of 0.2 for durations up to 582 h. The initial reaction of dolomite and quartz led to rapid formation of talc and calcite instead of tremolite and calcite by the intended reaction: 5 dolomite + 8 quartz + H 2 O = tremolite + 3 calcite + 7 CO 2 . With continued treatment, the talc + calcite + quartz assemblage gradually reacts to form increasing amounts of tremolite and diopside with the eventual loss of quartz and nearly complete loss of talc. The detailed structure of the amphibole and the nature of the Mg enrichment were revealed using AEM analysis of individual amphibole crystals. The most abundant defects are triple-chain chain multiplicity faults (CMFs), which appear as isolated lamellae with single periodicity in short-duration experiments and increasingly as groups of lamellae with variable multiplicity and periodicity in longer duration experiments and especially in a long-duration experiment without retreatment. In this latter experiment, a calcian clinojimthompsonite domain extending 15 unit cells along the b axis was observed. The sample after 582 h and five retreatments shows, on average, 3.5% true solid solution with Mg expressed as the Mg-cummingtonite (MC) component after correction for the presence of CMFs. This sample is thought to most closely approach the equilibrium composition for the amphibole. The sample after 250 h with three retreatments has about 10%, whereas that after 582 h without retreatment has 0.6% MC component, the latter having a relatively high density of CMFs. This study affirms the importance that precursor non-amphibole biopyriboles play in the formation of tremolitic amphibole.

Removal of phosphates by pilot vertical-flow constructed wetlands using a mixture of sand and dolomite as substrate

This study evaluates the performance of a mixture of river sand and dolomite (10:1, w/w) used as substrate in vertical-flow constructed wetlands in removal of phosphates. Two duplicate pilot-scale artificial wetlands (total 4 units) were set up outdoors, planted with Phragmites australis and fed with a synthetic sewage solution, corresponding to medium strength municipal wastewater. The wetlands were fed with two batch (intermittent) operational modes and their effluent was monitored for the presence of soluble phosphates over a period of 3 months. Laboratory (batch) incubation experiments were also carried out separately to ascertain the phosphate adsorption capacity of the two materials (i.e. sand and dolomite). The wetlands were capable to remove more than 45% of initially applied phosphates. Phosphorus accumulation in the wetlands body at the end of the operation period was in the range of 6.5–18%, as compared with the unused media. The Ca Mehlich-III extractable content was also increased, indicating that the removal of phosphates would be mainly attributed to the sorption of orthophosphate ions onto calcium carbonates and/or to the precipitation of orthophosphate ions with calcium ions as the respective insoluble calcium phosphates.

Glass‐ceramic from industrial waste materials

The crystallization behavior of a vitrified sample prepared from a mixture of slag, glass cullet and dolomite was investigated using differential thermal analysis (DTA), X‐ray diffraction and scanning electron microscopy. Differential thermal analyses were performed on the glass at different heating rates up to 1150°C, which showed that the crystallization exotherm occurs in the temperature range 900–1100°C. X‐ray diffraction revealed the presence of diopside Ca(Mg,Al)(Si,Al)2O6 as the major crystalline phase. The microstructure was characterized by the presence of dendritic diopside crystals. The activation energy of crystallization was estimated using Kissinger equation and is equal to 360 kJ/mol. The Avrami parameter was found to be equal to 1.66, which is indicative of three‐dimensional diffusion controlled growth of diopside crystals.

The effect of dissolved magnesium on diffusion creep in calcite

We experimentally tested a series of synthetic calcite marbles with varying amounts of dissolved magnesium in a standard triaxial deformation machine at 300 MPa confining pressure, temperatures between 700 and 850°C, stresses between 2 and 100 MPa, and strain rates between 10 −7 and 10 −3 s −1. The samples were fabricated by hot isostatic pressing of a mixture of calcite and dolomite at 850°C and 300 MPa. The fabrication protocol resulted in a homogeneous, fine-grained high-magnesian calcite aggregate with minimal porosity and with magnesium contents between 0.07 and 0.17 mol% MgCO 3. At stresses below 40 MPa the samples deformed with linear viscosity that depended inversely on grain size to the 3.26±0.51 power, suggesting that the mechanisms of deformation were some combination of grain boundary diffusion and grain boundary sliding. Because small grain sizes tended to occur in the high-magnesium calcite, the strength also appeared to vary inversely with magnesium content. However, the strength at constant grain size does not depend on the amount of dissolved magnesium, and thus, the impurity effect seems to be indirect. At stresses higher than 40 MPa, the aggregates become non-linearly viscous, a regime we interpret to be dislocation creep. The transition between the two regimes depends on grain size, as expected. The activation energy for diffusion creep is 200±30 kJ/mol and is quite similar to previous measurements in natural and synthetic marbles deformed at similar conditions with no added magnesium.

Reactive Synthesis of a Porous Calcium Zirconate/Spinel Composite with Idiomorphic Spinel Grains

Porous CaZrO3/MgAl2O4 composites were synthesized in air by pressureless reactive sintering of an equimolar mixture of dolomite (CaMg(CO3)2), monoclinic zirconia (m‐ZrO2), and α‐alumina powders, with a 0.5 wt% lithium fluoride additive. The reaction behavior of the mixed powders (with/without LiF additive) was studied using high‐temperature X‐ray diffraction. A bulk porous composite resulted from sintering at 1300°C for 2 h (in a nearly closed container, so as to increase the LiF‐doping effect), which consisted of fine grains (CaZrO3 and MgAl2O4, ∼0.5–1 μm) and well‐grown idiomorphic ones (MgAl2O4 octahedra ∼ 2–4 μm). The idiomorphic spinel grains were located around the inner walls of relatively large pores. The composite showed appreciably high bending strength (σf= 110 ± 8 MPa for a porosity of 31%). The porous CaZrO3/MgAl2O4 composites can be applied as high‐temperature filters and lightweight structural components.

Evaluation of Infrared Ignition Furnace for Determination of Asphalt Content

The Troxler Model 4730 infrared ignition furnace was compared with a standard Thermolyne ignition furnace. Comparisons conducted with a single unit of each furnace type were based on the correction factor for aggregate loss during ignition, accuracy, and the variability of the measured asphalt content and aggregate degradation during ignition. Forty-eight samples representing two nominal maximum aggregate sizes (9.5 and 19.0 mm), four aggregate types (granite, crushed gravel, limestone, and dolomite), and two asphalt contents (optimum and optimum plus 0.5% asphalt content) were tested in each furnace. The results indicated that the correction factors for aggregate loss during ignition were significantly different for each type of furnace, thus requiring a separate calibration for each type of furnace. In practical terms, the differences for all but the 9.5-mm nominal maximum aggregate size (NMAS) limestone and both dolomite mixtures were less than 0.1%. The samples with the optimum plus 0.5% asphalt content were tested by using the calibration factors developed for a particular mix–furnace combination. The results were analyzed in terms of accuracy (bias) and variability (standard deviation). Neither the measured biases nor the standard deviations for the two types of furnaces were significantly different. The results obtained with four sieve sizes (NMAS and 4.75, 2.36, and 0.075 mm) were evaluated for aggregate breakdown. A comparison of the aggregate gradations recovered from both furnaces indicated no significant difference in the degree of aggregate degradation. A round-robin investigation should be conducted to confirm that the precision of the infrared furnace is similar to the precision of the standard furnace.

Crop response to the application of special natural amendments based on zeolite tuff

The conception of these investigations is based on the premise that a way should be found to eliminate, or at least mitigate, the harmful effect of excessive soil acidity without resorting to the massive and costly measures of liming. The main issue addressed in this study is how to increase crop yield by increasing nutrient availability rather than how to neutralize the soil. This as well as our earlier investigations, conducted on pseudogley of mesoelevations, indicate that this can be achieved by the application of special natural amendments (SNA) based on zeolite tuff, under the name Agrarvital (AV), in which clinoptilolite prevails while the remaining part is a mixture of soft lithothamnian limestone and dolomite (SLL+D). These amendments enhance ion exchange in the soil and their activation at a considerably lower pH than it is the case after liming. Fertilizing value of Agrarvital (AV) and lime materials (LM) was evaluated according to the yields achieved and some yield components of the crops grown. The results point to the good fertilizing effect of AV upon yields of winter wheat, maize, soybean and winter barley, equal to or better than the effect of conventional LM applied at several times higher rates. 

The influence of special natural amendments based on zeolite tuff and different lime materials on some soil chemical properties

This paper deals with the changes in soil active acidity, mobile aluminium, base saturation, iron and manganese under the influence of quicklime (QL), mixture of soft lithothamnian limestone (SLL) and dolomite (D), and special natural amendments (SNA) based on zeolite tuff. Investigations were carried out on pseudogley of mesoelevations, dystric. The four-year trial was set up according to the Latin rectangle method with 18 trial treatments in four replications. While SNA based on zeolite tuff had little effect on changes of the studied parameters, traditional lime materials (LM), owing also to the fact that they were applied at several times higher rates, had a very positive effect. Soil acidity, iron and manganese were reduced under their influence, mobile aluminium, particularly under their higher rate, was fully blocked or reduced within tolerable limits, and base saturation was raised to a satisfactory level. Effects of SNA depended on the ratio of zeolite tuff and the lime component in them. It could be presupposed that their main efficiency happened in the domain of ion exchange with a positive impact on soil fertility.

Retention of Ca and Mg in the forest floor of a spruce stand after application of various liming materials

In a forest stand lime is commonly applied to the forest floor to neutralize acidity and to improve buffering capacity of soil by the addition of carbonate and other anions of weak acids. This is expected to cause major chemical changes in the forest floor. In this study, different liming materials, equivalent to 60 kmol c Ca 2++Mg 2+ ha −1, were applied to the forest floor of a spruce stand. The limes were dolomite, mixtures of dolomite and calcite or chalk, and silicate industrial slag lime (‘Hüttenkalk’) of varying particle size combinations. Two years after lime application, salt extractable Ca 2+ and Mg 2+ was measured in the forest floor using a sequential percolation method. This method allowed the assessment of Ca 2++Mg 2+ present on exchange sites by distinguishing between the amounts released upon dissolution of residual, undissolved liming material. In all cases there were major changes in exchangeable content of Ca 2+ and Mg 2+ in the L+F layer, whereas changes in the H layer were small. Differences in the effects of liming materials on the litter layer were attributed to their texture, the contents of Ca 2+ and Mg 2+ and the associated anion (carbonate or silicate). High content of exchangeable Ca 2+ and Mg 2+ was observed in the forest floor when liming materials were of high Ca and Mg content and of fine texture. The sum of exchangeable Ca 2++Mg 2+ in the forest floor increased from 7 kmol c ha −1 (control) to 17–26 kmol c ha −1 after liming and accounted for 15.5–31.5% of Ca+Mg applied. This increase in exchangeable Ca 2+ and Mg 2+ of L+F layer indicates large amounts of lime may be required to ameliorate mineral soil at depth, and that the content of these cations will partly determine future lime requirement of the spruce stands.

Agglomerate and particle size effects on reaction sintering of zircon–dolomite mixtures

AbstractThe interdependence of green density and particle size and their influence on the reaction sintering behaviour of zircon–dolomite powder mixtures under constant heating rate conditions, non-isothermal sintering, were investigated. Powder size was controlled by attrition milling for different times and was defined as the average size obtained by laser particle size analysis. Green compact density was shown to be related to the powder particle size distribution for identical consolidation conditions. Both the green density and the degree of powder agglomeration affect the sintering behaviour over the entire process. The experimental results showed that compacts with similar green density and which contained fewer coarse particles had a higher shrinkage rate. By adequate control of processing parameters it is possible to obtain dense or porous materials. The most important controlling parameters are the particle size of the raw materials and sintering temperature.

Reaction sintering of zircon–dolomite mixtures

Abstract Dolomite–zircon mixtures have become interesting for finding alternate sources to improve the production of high magnesia refractories. To asses this option, two minerals, dolomite and zircon were selected, as economically raw materials, to produce MgO–CaZrO 3 –Ca 2 SiO 4 materials. The reaction sintering mechanism of zircon–dolomite mixtures were investigated using finely ground Spanish dolomite and zircon powders as starting materials. During the heat treatment decomposed dolomite (CaO+MgO) reacts with zircon, from 1000 to 1200°C, through a series of reactions before the final stable compounds are formed. From the results obtained the reaction occurs prior to sintering in the presence of an amorphous transitory phase, magnesium calcium silicate phase and the limiting process during the reaction is the formation of Ca 2 SiO 4 . The sintering occurs after the end of the reaction so by controlling the whole process it is possible to obtain materials with controlled porosity. In the present work it is shown that reaction sintering of zircon–dolomite mixtures is a feasible route to obtain MgO–CaZrO 3 –β-Ca 2 SiO 4 porous materials for refractory insulators or as filters applications.

Transformation of echinoid Mg calcite skeletons by heating

Interambularcral plates of echinoid Heterocentrotus trigonarius, composed of Mg calcite 1 (≈14 mol% MgCO 3), were heated in three timed series of experiments at 300°C. Dried plate fragments and fragments with added water were heated separately in pressurized bombs. X-ray powder diffractometry, unit cell dimensions, and phase compositions are used to monitor reaction progress. After 10 h heating in the bombs dolomite (43.5 mol% MgCO 3) and Mg calcite appear (4–7 mol% MgCO 3); by 20 h all Mg calcite 1 is consumed, and at 120 h dolomite composition has evolved to ≈47 mol% MgCO 3 and calcite to ≈2 mol% MgCO 3. Whole plates heated at 300°C in an open muffle furnace develop dolomite (≈42 mol% MgCO 3) and Mg calcite 2 (≈6 mol% MgCO 3) after 10 h and remain compositionally invariant throughout subsequent heating to 620 h. Limited skeletal water catalyzes the early reaction but escapes from the open furnace and consequently reaction ceases after ≈10 h. The experimentally produced dolomite has relative Mg-Ca ordering of 75% to 79%. The stabilization of echinoid Mg calcite by heating at 300°C to a mixture of dolomite and calcite occurs through a dissolution/precipitation reaction. The alteration fabric produced within the stereom consists of irregularly shaped, branched dolomite crystals > 5 μm homoaxially set in a calcite 2 (bomb) or Mg calcite 2 (furnace) matrix. Round and tubular pores 1 to 5 μm are randomly distributed throughout this fabric. The stereom pore system remains intact during furnace heating but is destroyed during heating in bombs. The texture of experimentally stabilized echinoid skeletons is different from that of fossil echinoderms that are composed of microrhomic dolomite homoaxially set in a single calcite crystal.

Aluminous cements containing magnesium aluminate spinel from Egyptian dolomite

Three mixes of calcium aluminate cements containing MA spinel were prepared using appropriate mixtures of Egyptian dolomite (MgO, 20.16% and CaO, 31.32%) with active alumina (99.50% A) 1 1 The following cement notations are used: C, CaO; M, MgO; S, SiO 2; F, Fe 2O 3; A, Al 2O 3; H, H 2O. . The cement mixes were prepared at 1600°C using the sintering method. The products were finely ground and their chemical and mineralogical compositions were investigated using the appropriate techniques. Also, their physicomechanical and refractory properties had been determined. The results indicated that their mineralogical compositions were refractory MA spinel, in addition to CA and/or CA 2 phases depending on the composition of the starting materials. The prepared cements exhibited a compromise between considerable strength and higher refractoriness. When 10% of such cements were added to refractory grade magnesia aggregate, in the presence of 0.1% Li 2CO 3 as a strength modifier, refractory castable bodies with improved hot-strength and thermal shock resistance had been achieved.

ChemInform Abstract: New Uniformly Porous CaZrO3/MgO Composites with Three-Dimensional Network Structure from Natural Dolomite.

Porous CaZrO3/MgO composites with a uniform three-dimensional (3-D) network structure have been successfully synthesized using reactive sintering of highly pure mixtures of natural dolomite (CaMg(CO3)2) and synthesized zirconia powders with LiF additive. Equimolar dolomite and zirconia powders doped with 0.5 wt% LiF were cold isostatically pressed at 200 MPa and sintered at 1100–1400°C for 2 h in air. Through the liquid formation via LiF doping, strong necks were formed between constituent particles before completion of the pyrolysis of dolomite, resulting in the formation of a 3-D network structure. During and after the formation of the network structure, CO2 was given off to form a homogeneous open-pore structure. The pore-size distribution was very narrow (with pore size ∼ 1 μm), and the porosity was controllable (e.g., ∼30%–50%) by changing the sintering temperature. The porous composites can be applied as filter materials with good structural stability at high temperatures.

New Uniformly Porous CaZrO3/MgO Composites with Three‐Dimensional Network Structure from Natural Dolomite

Porous CaZrO3/MgO composites with a uniform three‐dimensional (3‐D) network structure have been successfully synthesized using reactive sintering of highly pure mixtures of natural dolomite (CaMg(CO3)2) and synthesized zirconia powders with LiF additive. Equimolar dolomite and zirconia powders doped with 0.5 wt% LiF were cold isostatically pressed at 200 MPa and sintered at 1100–1400°C for 2 h in air. Through the liquid formation via LiF doping, strong necks were formed between constituent particles before completion of the pyrolysis of dolomite, resulting in the formation of a 3‐D network structure. During and after the formation of the network structure, CO2 was given off to form a homogeneous open‐pore structure. The pore‐size distribution was very narrow (with pore size ∼ 1 μm), and the porosity was controllable (e.g., ∼30%–50%) by changing the sintering temperature. The porous composites can be applied as filter materials with good structural stability at high temperatures.

Biomarkers in a Lower Jurassic concretion from Dorset (UK)

Textural, petrographic and stable isotopic evidence suggest that a zoned concretion (Birchi Bed, Lower Lias, West Dorset, UK), formed under very shallow burial, with carbonate cement passively filling the pore spaces. The calcitic core of the concretion formed initially, whilst the intermediate and outer edge cements, which are dominated by a dolomite and a calcite respectively, precipitated successively. Mixtures of calcite and dolomite occur in the intermediate zone and outer rim, suggesting initial incomplete cementation and later back‐filling. The enveloping fibrous calcite vein (beef) formed later by displacive crystallization. The concretionary carbonates preferentially preserve labile organic compounds (i.e. unsaturated fatty acids) not found in the surrounding shales. Fatty acid distributions in the concretion are distinct and informative. The presence of 10‐methylhexadecanoic acid provides direct evidence for sulphate‐reducing bacteria in the calcitic core whereas the abundance of unsaturated fatty acids in the concretion as a whole is attributed to localized bacterial production and its early formation. The core probably formed in the sulphate reduction zone, whereas dolomite in the intermediate zone was derived largely from methanogenesis and iron reduction, although direct biomarker evidence for methanogenesis was not found. The outer rim and the fibrous calcite vein probably resulted from ‘late’ bacterial processes, probably including renewed sulphate reduction. The complex biogeochemistry of the sedimentary environment is reflected by the concentrations and distributions of biomarkers and by the detailed petrography. Nevertheless, carbonate concretions can provide a ‘snapshot’ of early diagenesis in ancient mudstones.

Effects of Temperature, Pressure, and Carrier Gas on the Cracking of Coal Tar over a Char−Dolomite Mixture and Calcined Dolomite in a Fixed-Bed Reactor

A distillation fraction of a coal-derived liquid (tar) was cracked over a char−dolomite mixture, calcined dolomite, and silicon carbide in a fixed-bed reactor. The char−dolomite mixture (FWC) was produced from Pittsburgh No. 8 coal and dolomite in a Foster Wheeler carbonizer. The experiments were conducted under nitrogen and simulated coal gas (SCG), which was a mixture of CO, CO2, H2S, CH4, N2, and steam, at 1 and 17 atm. The conversion over these materials under nitrogen was much higher at 17 atm than at 1 atm. At higher pressures, tar molecules were trapped in the pores of the bed material and underwent secondary reactions, resulting in the formation of excess char. However, when nitrogen was replaced by SCG, the reactions that induce char formation were suppressed, thus increasing the yield of gaseous products. The analysis of the gaseous products and the spent bed materials for organic and inorganic carbons suggested that the product distribution can be altered by changing the carrier gas, temperature, and pressure.