Addition Of Dolomite Research Articles

Steam Gasification for Biomass Tar with Natural Ores of Limonite and Dolomite

Light gases were produced from biomass tar gasification using limonite and dolomite as catalysts. Experiments were performed in a fixed bed reactor with the gasification temperatures of 600–800 °C. Limonite gave the obvious effect on the tar gasification, and the light gases of hydrogen and carbon oxides were mainly obtained. Also, the gas yields depended on the catalytic temperature. Hydrogen yields tend to increasing with temperatures from 650 to 800 °C. The reaction equilibrium was changed by dolomite addition in the reactor system; hydrogen gas was doubled with the limonite and dolomite mixture compared to limonite only.

Foaming in Electric Arc Furnace—Part II: Foaming Visualization and Comparison with Plant Trials

The kinetics of slag foaming by limestone particles was studied at 1773 K (1500 °C) with the aid of an X-ray imaging system. Two models were implemented to describe the decrease in foam height with the time on the basis of the lowering of the average temperature and CaO shell formation during decomposition reaction. The energy impact of carbonate additions was studied on an industrial scale in a 100-ton electric arc furnace (EAF). It was found that, in the case of the addition of carbonates after the scrap is completely molten, the heat effects for limestone and dolomite (2255 and 2264 kJ/kg, respectively) were only 70 pct from theoretical values. Comparing these values with similar additions during the scrap melting stage shows that the energy requirements in the case of carbonate additions to steel bath are much smaller. It was found from the trial heats with dolomite addition to the steel bath that the partial substitution of lime by raw dolomite can be made without an increase in energy consumption.

Calcined Dolomite: Alternative to Lime for Minimizing Undesirable Element Leachability from Fly Ash

A comparison of the effectiveness of totally and partially calcined dolomite additives (TCD and PCD) on the leachability of elemental constituents from three fly ashes was performed. Both additives were found effective in reducing the concentrations of several undesirable oxyanion constituents in fly ash leachates, although enhanced leaching of fly ashes was also detected as a result of calcined dolomite treatment. As compared to the straight water/ash runs, the extra leached fraction of fly ashes range approximately from 4 to 13% for the PCD-added runs and 25 to 31% for the TCD-added runs, respectively. The principal mechanism for oxyanion removal is through the formation of hydrocalumite and hydrotalcite. Although PCD is not quite as efficient as TCD in reducing oxyanion concentrations, it produces a less caustic leachate composition characterized by lower pHs, alkalinities, and calcium concentrations. PCD is a viable alternative to lime as fly ash additive.

백운석 첨가가 응집에 의한 하수 처리수의 인 제거에 미치는 영향

Wastewater treatment plants need to reduce phosphorus in order to meet increasingly stringent regulations on phosphorus. This study evaluated the feasibility of dolomite as a coagulation aid to enhance phosphorus removal from secondary treated wastewater by chemical coagulation. Standard jar tests were conducted to evaluate the effect of dolomite addition on a coagulation process for phosphorus removal and to determine the optimum doses of coagulants and dolomite. Coagulants used with dolomite yielded a significant improvement in phosphorus removal and reduced total phosphorus concentrations below 0.02 mg/L in wastewater effluent. Dolomite has played an important role in enhancing phosphate adsorption and increasing pH, as a coagulation aid. The maximum removal efficiency of phosphorus in this study was yielded at 25 mg/l of dolomite and 20 mg Al/L of PAC dose. However, considering economic aspects, the optimum doses of dolomite and PAC were 10 mg/L and 15mg Al/L, respectively. Consequently, dolomite, a coagulation aid, can be used in coagulation processes to enhance the removal of phosphorus.

Optimizing the MgO content of the charge in sintering and blast-furnace smelting

A study is made of the effect of the addition of dolomite to the charge used in sintering a mixture of Mikhailovskii and Lebedinskii concentrates and Bakal and Mikhailovskii ores. The size of the dolomite addition is optimized from the standpoint of ensuring efficient operation of the blast furnace and avoiding any reduction in the strength of the sinter.

Effect of sintering process and additives on the properties of cordierite based ceramics

Cordierite is largely known for its low coefficient of thermal expansion and other valuable properties leading to its wide use in severe thermal and chemical conditions. Cordierite ceramics for technical use have been synthetically created using various starting materials and synthesis techniques, most commonly - solid-state reaction. Cordierite crystalline phase containing ceramics have been attempted to produce from oxides and natural raw materials using traditional sintering and faster alternative – spark plasma sintering (SPS) methods in this paper. Starting powders were prepared from magnesium, aluminium and silicon oxides using clay and 3 different dolomite additives in attempt to replace part of required amount of magnesium oxide. Two different milling times were used to homogenise green powders. X-ray diffraction analysis and compressive strength testing, as well as measurments of ceramic properties have been carried out and evaluated for obtained samples.

Thermodynamics of reduction of sintered dolomite

The thermodynamic data are determined, and the variations in the standard values of the Gibbs energy (ΔG0) are evaluated for three groups of reactions (selected among 32) of the silicothermic reduction of roasted dolomite, which differ in oxygen content in the reduction products and in the characteristics of the processes with a limited oxygen access (retort method), and of the vacuum silicothermic reduction both with the addition of dolomite and without it. It is established that the reduction reactions of roasted dolomite to Fe2SiO4, Ca2SiO4, and CaMg(SiO3)2 in the retort method, which are presented in classic works, have a positive or close-to-zero negative value of ΔG0 and, consequently, are low-probable in practice. The reactions with the formation of a complex calcium-magnesium silicate Ca3Mg(SiO4) are more preferable thermodynamically. For the vacuum silicothermic reduction with the introduction of carbon and without it with the formation of Ca2SiO4 at 1200–1350 K, the negative value of ΔG0 is larger by a factor of 4–8 by the absolute magnitude. The optimal temperature and kinetic parameters of these processes are found experimentally. It is shown that the use of carbon as an additional reducing agent stably increases the yield of Mg by 20–30%. In this case, the FeSi consumption decreases by a factor of 3 compared with the retort method and by a factor of 2 compared with the vacuum process without carbon. Our data served as the basis for the project task of designing an installation for the vacuum-silicothermic reduction of magnesium from roasted dolomites.

Synthesis and Characterization of Fe2MoO4 as a Precursor Material for Mo Alloying in Steel

The objective of the present thesis is to optimize the electric arc furnace (EAF) practice from an environmental view point. Two aspects that meet the requirements of the secondary steelmaking industries today, viz. Mo alloying with maximum retainment of the alloying element in molten steel and optimization of foaming by carbonate addition with a view to optimize the energy need of the process. Both these aspects would also have a significant impact on the process economy. Iron molybdate (Fe2MoO4) has been synthesized from commercial grade materials and proposed as a new potential precursor for steel alloying with Mo. The thermal stabilities of different molybdates, viz. Fe2MoO4, CaMoO4 and MgMoO4, were studied using thermogravimetry analysis (TGA). It was found that Fe2MoO4 is the most stable one and doesn’t evaporate in Ar atmosphere when heating up to 1573 K. The synthesis of Fe2MoO4 requires high temperature (1373 K) and long holding time (up to 16 hours). In a view of this, the possibilities for in-situ formation of Fe2MoO4 and CaMoO4 from their precursor mixtures were studied with the aid of high-temperature X-ray diffraction (XRD) and TGA analysis. Laboratory and industrial trials on steel alloying with Mo were conducted using precursor mixtures as sources of Mo. It was found that the mixture, which contains FeOx, MoO3 and C (Fe2MoO4 precursor), can provide the Mo yield up to 98 % at both the laboratory as well as industrial trials. The Mo yields even in the case of C+MoO3 and C+MoO3+CaO mixtures were around 93 % in these trials. The higher yield for the MoO3+C+FeOx mixture was attributed to the stabilization of Mo in the precursor (marked by the decrease in the Gibbs energy of Mo) and the readiness to dissolve in the steel bath. The heat effect of the slag foaming with carbonates addition was studied at 1623 and 1673 K with the aid of thermal analysis technique with a new crucible design. Experiments were conducted by adding limestone and dolomite pieces of defined shapes (together with iron sinkers) in molten slag and monitoring the temperature changes accompanying the decomposition of carbonates. It was found that the decomposition energies for dolomite and limestone for the studied slag composition are in the range 56-79 % of theoretical values, which is linked to the energy saving effect of slag foaming. No influence of sample shape on decomposition energy was found both for limestone and dolomite. The kinetics of slag foaming by limestone particles was studied at 1773 K with the aid of X-ray imaging system. A model was proposed to describe the decrease in foam height with time on the basis of CaO shell formation during decomposition reaction. The energy impact of limestone and raw dolomite addition was examined in a 100-ton EAF. It was found that, in the case of addition of carbonates after the scrap is completely molten; the endothermic heat effects for limestone and dolomite (2255 and 2264 kJ/kg respectively) were only 70 % from theoretical values. This is indicative of the resistance to heat transfer due to increased foaming.

Influence of magnesia on iron ore sinter properties and productivity

Dolomite and other MgO bearing materials are being increasingly used as basic flux constituents for production of fluxed sinters. Addition of flux materials in sinter influences the resultant sinter microstructure and chemical properties. The physical and metallurgical properties of sinter mainly depend on mineralogy of the sinter. Dolomite is the source of double carbonate of calcium and magnesium. Recent studies reveal that, apart from the additional fuel needed, the addition of dolomite and MgO bearing material greatly influences the magnetite content and the properties of the sinter produced. The increasing use of MgO bearing fluxes in the blast furnace burden, and the trend to incorporate a major part of fluxes in the sinter mix led to an investigation of the influence of MgO on sinter properties and productivity. In this study, the systematic investigation has been made on the influence of MgO% (1·4 to 2·6) on sinter mineralogy and sinter properties with dolomite. Microstructural examination of dolomite sinter revealed that hematite and calcium ferrite phases decreased whereas magnetite phase increased with increase in MgO percentage in sinter. From the laboratory pot grate sintering results it was found that sinter reduction degradation index improved whereas tumbler index and reducibility decreased with increase in MgO%.

Heating rate effect on the thermal behavior of ammonium nitrate and its blends with limestone and dolomite

The effect of heating rate on the thermal behavior of ammonium nitrate (AN) and on the kinetic parameters of decomposition of AN and its blends with limestone and dolomite was studied on the basis of commercial fertilizer-grade AN and several Estonian limestone and dolomite samples. Experiments were carried out under dynamic heating conditions up to 900 °C at heating rates of 2, 5, 10 and 20 °C min−1 in a stream of dry air using Setaram Labsys 2000 equipment. For calculation of kinetic parameters, the TG data were processed by differential isoconversional method of Friedman. The variation of the value of activation energy E along the reaction progress α showed a complex character of decomposition of AN—interaction of AN with limestone and dolomite additives with the formation of nitrates as well as decomposition of these nitrates at higher temperatures.

ドロマイト化作用と貯留岩性状

Dolomite (dolostone) is a common carbonate rock in the geological records and is also a very important carbonate reservoir rock, which stock about 40% of global oil reserves. Most of the dolomites in the geological record are considered to be of replacement origin, although some were precipitated directly from pore-fluids. A variety of dolomitization models in different diagenetic environments are currently proposed for interpreting ancient dolomites: (1) evaporative dolomitization including sabkha and seepage-reflux models, (2) mixed-water dolomitization, (3) marine dolomitization, (4) burial dolomitization, (5) hydrothermal dolomitization. The dolomites formed by each dolomitization model have different geological, petrographical, mineralogical and geochemical features. Based on these features, we can, therefore, identify dolomitization models and diagenetic environments of ancient dolomites. A dolomite reservoir is often of as good quality as a limestone reservoir. Dolomitization affects carbonate reservoir characteristics, such as porosity and permeability, and, as a result, reservoir characteristics are significantly changed from those of primary carbonate rocks. The important factors associated with dolomitization and controlling the characteristics of carbonate reservoir rocks are: (1) increasing crystal size (2) decreasing porosity due to a net addition of dolomite, (3) developing moldic pores, (4) increasing resistance to compaction, and (5) increasing fractures. Dolomitization and diagenetic history of individual carbonate reservoirs differ from each other and result in the complexity of reservoir characteristics. It is, therefore, indispensable to understand the processes that formed each dolomite reservoir.

Study on the combustion kinetic characteristics of biomass tar under catalysts

TG and DTA experiments were performed to investigate the biomass tar combustion behavior in coexistence of dolomite and mayenite at two different heating rates as 5 and 15°C min−1. Different reaction kinetic mechanisms with the classical Arrhenius model were used to treat TG data, and showed that the first-order combustion model fitted the data well. Three stages combustion model was proposed and applied for the calculation of kinetics parameters successfully. The starting temperature of high temperature combustion stage moved up near 100°C because of the coexistence catalysts, and the combustion amount of biomass of the stage also improved nearly 10 mass%. By calculation a uniform trend of decreasing activation energies was observed with the addition of dolomite and mayenite, and also greatly improved the amount and speed of tar combustion process.

Hot bending strength and creep behaviour at 1000–1400 °C of high alumina refractory castables with spinel, periclase and dolomite additions

The modulus of rupture and creep behaviour of refractory castables at high temperature (1000–1400 °C) with additions of spinel, periclase and dolomite has been studied. Three processing routes for obtaining refractory concretes within the alumina-rich zone of the Al 2O 3–MgO–CaO ternary system were employed. To achieve high temperature mechanical properties special attention was paid to the processing route (synthetic spinel, periclase and dolomite additions), and the composition (effect of synthetic or self-forming spinel and CaO contents). The results demonstrate that these refractory castables show a highly viscoplasticity behaviour at temperatures >1100 °C and a hot bending strength depending on the loading rate. Refractory castables made with synthetic spinel have lower high temperature bending strength values than castables made with periclase additions owing to their less viscoplastic behaviour. In this work neither the amount of spinel nor processing route chosen were found to have any significant influence on the hot bending tests between 1100 and 1400 °C. The creep tests show that in the temperature range of 1100–1300 °C the main reaction governing deformation is the interaction between the alumina and the calcium aluminate cement phases. Above 1300 °C, castables made first with dolomite, then with periclase and finally with synthetic spinel are more prone to deformation in that order.

Room temperature mechanical properties of high alumina refractory castables with spinel, periclase and dolomite additions

The mechanical properties of refractory castables at room temperature are critical parameters for selecting suitable operating conditions for the structural design of refractory components. In this work, high alumina refractory castables based on the alumina-rich zone of the Al 2O 3–MgO–CaO ternary phase equilibrium diagram were prepared by adding synthetic spinel, periclase and dolomite via three processing routes. Bending strength studies at room temperature under several thermal treatments and the analysis of the elastic modulus of the refractories and their matrices point to two different mechanical behaviours. From room temperature to 1000 °C the refractory castables present a pronounced non-linear stress–strain behaviour both in the uniaxial tensile and compressive modes, as a result of damage to the microcrack network. Above 1000 °C the refractory castables begin to sinter owing to a transitory liquid phase, the crystallization of calcium aluminate cement phases (such as CA 2 and CA 6, for example) and the self-forming spinel phase (refractory castables with periclase or dolomite additions). At higher firing temperatures the sintering process leads a strengthening of the mechanical properties.

Effect of Domestic Dolomite Additives Used in the Refractory Production

Abstract In this study, the effect of alumina addition on dolomite refractory (extracted from Konya/Turkey) which has been planned to use in refractory industry was investigated. The aim of the study is to increase the brownmillerite phase which aids the sintering process of dolomite. For that purpose, 0.5 wt-% alumina powder (including 99,5% Al2O3) was added to 3 to 6 mm fraction dolomite, and a sintering operation was carried out at a temperature of 1600, 1650 and 1700°C for 3 different soaking times (2, 4 and 6 h). The resultant phases occured at dolomas (sintered dolomite) were investigated and evaluated by X-Ray diffraction pattern (XRD) and analized by scanning electron microscopy (SEM). It turned out that periclase, lime also portlandite, alite, forsterite, tricalcium aluminate, brownmillerite, merwinite were created. The densities of dolomas were measured. Temperature and increase in time were investigated but convenience in density could not be established.

Limestone assimilation and the origin of CO 2 emissions at the Alban Hills (Central Italy): Constraints from experimental petrology

The Alban Hills volcanic region (20 km south of Rome, in the Roman Province) emitted a large volume of potassic magmas (> 280 km 3) during the Quaternary. Chemical interactions between ascending magmas and the ∼ 7000–8000-m-thick sedimentary carbonate basement are documented by abundant high temperature skarn xenoliths in the eruptive products and have been frequently corroborated by geochemical surveys. In this paper we characterize the effect of carbonate assimilation on phase relationships at 200 MPa and 1150–1050 °C by experimental petrology. Calcite and dolomite addition promotes the crystallization of Ca-rich pyroxene and Mg-rich olivine respectively, and addition of both carbonates results in the desilication of the melt. Furthermore, carbonate assimilation liberates a large quantity of CO 2-rich fluid. A comparison of experimental versus natural mineral, glass and bulk rock compositions suggests large variations in the degree of carbonate assimilation for the different Alban Hills eruptions. A maximum of 15 wt.% assimilation is suggested by some melt inclusion and clinopyroxene compositions; however, most of the natural data indicate assimilation of between 3 and 12 wt.% carbonate. Current high CO 2 emissions in this area most likely indicate that such an assimilation process still occurs at depth. We calculate that a magma intruding into the carbonate basement with a rate of ∼ 1 – 2 · 10 6 m 3/year, estimated by geophysical studies, and assimilating 3–12 wt.% of host rocks would release an amount of CO 2 matching the current yearly emissions at the Alban Hills. Our results strongly suggest that current CO 2 emissions in this region are the shallow manifestation of hot mafic magma intrusion in the carbonate-hosted reservoir at 5–6 km depth, with important consequences for the present-day volcanic hazard evaluation in this densely populated and historical area.

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%.

Effect of natural dolomites on the in vitro fermentation and rumen protozoan population using rumen fluid and fresh faeces inoculum from sheep

The objective of the study was to determine the effect of dolomites from five different sources upon the end products of in vitro fermentation (total gas, methane, total and individual fatty acids, hydrogen recovery) and protozoan population. Dolomites as natural products in the dose of 0.1 g were added to the fermentation bottles containing inoculum from sheep and substrates. Both rumen fluid (RF) and fresh faeces (FF) from sheep as the sources of inocula for in vitro fermentation were used. Meadow hay (MH) and barley grain (BG) were used as fermentation substrates and incubated with the buffered rumen fluid using an in vitro gas measuring technique in separate incubation during 72 h. Both inocula (RF and FF) and dolomites impact in vitro fermentation characteristics. The gas volume was significantly increased with dolomites with RF or FF, respectively, by 20% or 20–40% (MH) and by 10% or 10–30% (BG). The methane production was significantly decreased with dolomite additives with RF inocula by 15–32% (MH) and by 50–70% (BG). A significant effect of the dolomite additives on the rumen protozoan population was observed during fermentation of MH; the total protozoan concentration and the number of Entodinium spp. was decreased ( P < 0.05). Populations of Isotrichids and large Entodiniomorphids were not influenced by experimental incubations. More studies are needed to optimize the combination of different diets with dolomite additives for practical feeding conditions.

Effect of Dolomite Addition on the Densification of Fly Ash Based Ceramics

Fly ash from Tapada do Outeiro, a coal power plant in the north of Portugal, has been processed by a powder technology route in order to obtain durable and mechanical resistant ceramics. Dolomite (CaCO3.MgCO3) was added in different proportions to the waste material, from zero up to 10 wt%, and the effect of this addition on the densification behaviour of the fired samples was investigated by measuring the apparent density, the open porosity and the linear shrinkage. The powder mixtures were uniaxially dry pressed in a steel die and fired at temperatures ranging from 950 to 1150°C. XRD and SEM were used to identify the phases present in the sintered materials and the degree of densification. The results revealed that added dolomite was responsible for the appearance of anorthite, an extra phase besides mullite and quartz, for an increase in the amount of liquid phase and for the swelling of closed pores at the highest firing temperatures. Significant morphological changes and phase transformations occurred during sintering and their effects on the physical-mechanical and leaching characteristics of the sintered materials were analyzed.

Green metallurgical processing of chromite

A new green metallurgical process for chromite ore has been proposed and developed to solve the serious environmental problem in the traditional production process of chromate. In the new process, the oxidation of chromite ore is carried out in sub-molten potassium hydroxide at 300 °C. Compared with the traditional roasting process in a rotary kiln at 1200 °C, the oxidation and mass transfer are greatly intensified in the new process. Chemical conversion of chromium is above 99% and the recovery of chromium is raised by more than 20% while the reaction temperature is dropped by 900 °C. Thus the energy consumption is decreased. Furthermore, as no limestone or dolomite additives are required, the amount of chromium-containing residue is decreased from 2.5 tonnes to 0.5 tonnes with the production of 1.0 tonne of product in the new process. As all reactions and separating operations are performed in liquid media, pollution due to toxic dust is prevented. With the change of reaction medium, the new process achieves higher resource and energy utilization efficiency. At the same time, the new process also changes the physical and chemical properties of other components co-existing in the chromite ore. The process provides the possibility for virtually complete utilization of chromite and zero emission of residue. Thus, the clean production of chromate can be realized.