Kinetics of extracting magnesium from mixture of calcined magnesite and calcined dolomite by vacuum aluminothermic reduction

The vacuum aluminothermic reduction of the mixture of calcined magnesite and calcined dolomite was studied. An isothermal reduction method satisfying the vacuum aluminothermic reduction was proposed. The experiments were carried out at 4 Pa. The results indicate that the reduction rate is increased with increasing temperature, content of aluminum and pellet forming pressure. The XRD patterns of pellets at different reduction stages confirm that the reduction process can be roughly classified into three stages：the formation of MgAl2O4, and Ca12Al14O33 phases;the phase transformation from MgAl2O4 and C12A7 to CaAl2O4;the formation of CaAl4O7 phase. The experimental data were divided into three parts according to the kinetic models. The apparent activation energies of the three parts were determined to be 98.2, 133.0 and 223.3 kJ/mol, respectively.

Mechanism of extracting magenesium from mixture of calcined magnesite and calcined dolomite by vacuum aluminothermic reduction

The process of aluminothermic reduction of a mixture of calcined dolomite and calcined magnesite had been developed. The mechanism of the process was studied by SEM and EDS. The reduction process was divided into three stages:0≤ηt/ηf≤0.43±0.06, 0.43±0.06≤ηt/ηf≤0.9±0.02 and 0.9±0.02≤ηt/ηf<1, whereηt andηf are the reduction ratio at time t and the final reduction ratio obtained in the experiment at temperature T, respectively. The first stage included the direct reaction between calcined dolomite or calcined magnesite and Al with 12CaO·7Al2O3 and MgO·Al2O3 as products. The reaction rate depended on the chemical reaction. The CA phase was mainly produced in the second stage and the overall reaction rate was determined by both the diffusion of Ca2+ with molten Al and the chemical reaction. The CA2 phase was mainly produced in the third stage and the reaction process was controlled by the diffusion of Ca2+.

从设备上解决燃烧白云石粘磨问题的探讨

勉县镁厂采取一系列措施，在工艺上尽量减少粘磨，但仍未根绝粘磨现象，后大胆选用河南省新乡市建筑机械厂生产的高效节能振动磨机代替传统的球磨机，效果很好，从根本上解决了粘磨问题，并取得了每年节约资金９万元的较好的经济效益。

Selective flotation of smithsonite from dolomite by using novel mixed collector system

A novel mixed collector (BHOA) was prepared by mixing benzohydroxamic acid (BHA) and sodium oleate (NaOL) and applied to the flotation separation of smithsonite from dolomite. Flotation results showed that NaOL alone had good collecting performance on smithsonite and common gangue mineral dolomite but had poor selectivity. By using a BHA/NaOL mixed system with a molar ratio of 2:1, the recoveries of smithsonite and dolomite reached approximately 90% and 5%, respectively. Surface tension analysis showed that the surface activity of BHOA was a little higher than that of a single NaOL because of synergistic effects. Zeta potential and X-ray photoelectron spectroscopy measurements indicated that surfactants BHA and NaOL co-absorbed on the smithsonite surface and only NaOL was present on the dolomite surface in the presence of BHOA.

Matrix porosity calculation in volcanic and dolomite reservoirs and its application

Matrix porosity calculations of fractured and vuggy reservoirs, such as volcanics and weathered dolomite, are one of the problems urgently needed to solve in well-log evaluation. In this paper, we first compare the an empirical formula for porosity calculation from full diameter rhyolite core experiments with the matrix porosity formulas commonly used. We discuss the applicability of the empirical formula in fractured and vuggy reservoirs, such as intermediate-basic volcanics and weathered dolomite. Based on core analysis data, the error distribution of the calculated porosity of our empirical formula and the other porosity formulas in these reservoirs are given. The statistical error analysis indicates that the our empirical formula provides a higher precision than the other porosity formulas. When the porosity is between 1.5% and 15%, the acoustic experiment formula can be used not only for acidic volcanics but also in other fractured and vuggy reservoirs, such as intermediate-basic volcanics and weathered dolomite. Moreover, the formula can reduce the effects of borehole enlargement and rock alteration on porosity computation.

Effect and mechanism of dolomite with different size fractions on hematite flotation using sodium oleate as collector

The effect of dolomite with different particle size fractions on hematite flotation was studied using sodium oleate as collector at p H of about 9. The effect mechanism of dolomite on hematite flotation was investigated by means of solution chemistry, ultraviolet spectrophotometry(UV), inductively coupled plasma atomic emission spectrometry(ICP-AES) and X-ray photoelectron spectroscopy(XPS). It is observed that dolomite with different size fractions has depressing effect on hematite flotation using sodium oleate as collector, and dolomite could be the "mineral depressant" of hematite using sodium oleate as collector. The reasons for that are concerned with sodium oleate consumption and the adsorption onto hematite of dissolved species of dolomite.

Dolomite apatite separation by amphoteric collector in presence of bacteria

Bioflotation represents one of the growing trends to enhance the selectivity of conventional flotation processes. It utilizes the micro-organisms to replace or to interact with the chemical reagents to increase the gap between surface properties of similar minerals and to enhance the separation selectivity. In this work, dolomite-phosphate separation was investigated using amphoteric collector （dodecyl-N-carboxyethyl-N-hyroxyethyl-imidazoline） in presence of bacteria. Two types of bacteria, Corynebacterium- diphtheriae-intermedius （CDI）, and Pseudomonas aeruginosa （PA）, were used. The collector-bacteria interaction was characterized by Fourier transform infra-red （FTIR）, frothing height and Zeta potential. The results show that the collector-bacteria interaction improves the flotation selectivity. Although, the PA positively affects the separation results, the CDI cannot lower the MgO to less than 1%. A phosphate content of 0.7% MgO and 31.77% P205 with a recovery of 68% at pH 11, 3.0 kg/t amphoteric collector, 4× 10^7 cells of PA is obtained.

Mechanism of separating muscovite and quartz by flotation

Flotation experiments were performed to investigate the separation of muscovite and quartz in the presence of dodecylamine(DDA), tallow amine(TTA) and dodecyltrimethylammonium bromide(DTAC). The adsorption mechanisms of these three kinds of amines on muscovite and quartz were studied by FT-IR spectrum analysis, contact angle measurement and molecular dynamics(MD) simulation. The results reveal that the separation of muscovite from quartz is feasible at strong acid pulp condition using amine collectors. TTA and DTAC show poorer collecting ability for flotation of the two minerals compared with DDA. Physical adsorption is found to be the main adsorption module of amine collectors on muscovite and quartz by FT-IR analysis. MD simulation results show a strong physical adsorption ability of DDA+ cation on muscovite and quartz(muscovite(001):-117.31 kJ/mol, quartz(100):-89.43 kJ/mol), while neutral DDA molecular can hardly absorb onto the surface of these two minerals. These findings provide a novel explanation for the flotation mechanism from the perspective of MD simulation.

Geochronology,geochemistry and geodynamics implications of Middle Triassic garnet-bearing muscovite monzogranite in central Jilin Province

Zircon LA-ICP-MS U-Pb geochronology and geochemical analyses are undertaken for the garnet-bear-ing muscovite monzogranite in Yitong area, central Jilin Province. The formation age and petrogenesis of the granite are determined, and the regional tectonic background is discussed. Zircons from the granite are euhe-dral-subhedral in shape, and display fine-scale oscillatory growth zoning, indicating a magmatie origin. LA- ICP-MS zircon U-Pb dating result indicates that the garnet-bearing muscovite monzogranites formed in the mid-dle Triassic （243 Ma ）. The garnet-bearing muscovite monzogranites have high SiO2 （SiO2 = 74.1%- 76.49% ）, rich aluminum （A1203 = 14.47%-14.68% ） and alkali （ NazO ＋ K20 = 4.31%-7.9% ）, low Fe203T and MgO （MgO =0.1%-0. 13% , Fe203T =0.46%-1.02% ）. The ratio of CaO/Na20 is between 0.17--0. 21. The garnet-bearing muscovite monzogranites in Yitong region are relatively enriched in light rare earth elements （LREEs） and large ion lithophile elements （LILEs） , and depleted of heavy rare earth elements （HREEs） and high field strength elements （HFSEs）. They are characterized by high Sr and Ba, poor Rb and Y, and negative Eu abnormally （δEu =0.48-0.62） , with Rb/Sr 〈 1. The εHf（t） values and TDM2 of zircons range from ＋ 6. 10 to ＋ 8.00 and from 725 Ma to 814 Ma, respectively. The above features indicate that gar- net-bearing muscovite monzogranites in Yitong area were derived from partial melting of metasedimentary rock. These granites have high Sr/Y ratios, which suggest they formed in a thickened continental crust. Combined with the coeval granitic rocks in central Jilin Province, we suggested that a significant eollisional and thickening event took place during the Middle Triassic.

Cementation and diagenetic fluid of algal dolomites in the Sinian Dengying Formation in southeastern Sichuan Basin

The Sinian Dengying Formation in China hosts one of the oldest gas-bearing reservoirs in the world.With a long geological history,it has developed into the reservoir rocks,whose quality depends on chemical dissolution and cementation.Despite presence of cavities and pores in the algal dolomites of the Dengying Formation,they were mostly filled with various forms of dolomite cements.Therefore,the investigation of these dolomites and their evolution is significant for analyzing the mechanism of pore space preservation.There are five types of cements in the Dengying Formation,which were well sampled for lab measurements such as thin section,cathodeluminescence,minor elements,isotope analysis of carbon,oxygen and strontium,in attempt to explore the fillers' geochemical characteristics and the diagenetic fluids.They are characterized as follows:firstly,fibrous rim dolomite cement is a typical product formed at sea bottom,and geochemically very similar to the matrix(micrite and microcrystalline dolomite),which could be a reflection of the geochemical characteristics of water at that time;secondly,the diagenetic fluids of the foliated dolomite cements tend to be inheriting,derived from the shallow burial "imprisoned" seawater;thirdly,fine-to medium-grained dolomite cements with fairly high strontium isotopes and low carbon and oxygen isotopes were precipitated chiefly in freshwater during the period of uplifting caused by Tongwan tectonic movement;fourthly,coarse-grained dolomite cements bear a relatively high percentage of Mn element,but low in Fe and Sr,with carbon and oxygen isotopes remarkably shifted to negative values,which all show that they are related to hydrocarbon maturation and migration,and corresponding Thermochemical Sulfate Reduction;lastly,saddle-shaped dolomite cements are hydrothermally associated,and they were formed in high-temperature brine,which had passed through the areas rich in radioactive strontium isotopes.

Kinetics and rate-limiting mechanisms of dolomite dissolution at various CO_2 partial pressures

Techniques of rotating-disk and catalyst were used in investigating the kinetics of dolomite dissolution in flowing CO2-H2O system. Experiments run in the solutions equilibrated with various CO2 partial pressures (PCO2) from 30 to 100000 Pa. It shows that dissolution rates ofdolomite are related with rotating speeds at conditions far from equilibrium. This was explained by modified diffusion boundary layer (DBL) model. In addition, the dissolution rates increase after addition of carbonic anhydrase (CA) to solutions, where the CA catalyzes CO2 conversion. However, great differences occur among various CO2 partial pressures. The experimental observations give a conclusion that the modified DBL model enables one to predict dissolution rates and their behaviour at various PCO2 with satisfactory precision at least far from equilibrium.

Microbial roles equivalent to geological agents of high temperature and pressure in deep Earth

Microbes not only show sensitive responses to environmental changes but also play important roles in geochemical and geophysical systems. It is well known that microbes have caused major changes in surface environments and biogeochemical cycles through Earth history. Microbial processes can also induce the synthesis of certain minerals under Earth-surface conditions that previously were believed to form only under high temperatures and pressures in the deep Earth. For example, microbes can promote the conversion of smectite to illite, synthesis of authigenic plagioclase, precipitation of dolomite, and biotransformation of geolipids. These effects of microbes are due to their large surface/volume ratios, enzyme production, and abundant functional groups. Microbial catalyzation of chemical reactions proceeds through reaction-specific enzymes, a decrease in Gibbs' s free energy, and/or break through the dynamics reaction thresholds via their metabolisms and physiology. Microbes can lower the surface free energy of mineral nuclei via biophysical adsorption due to their large surface/volume ratios and abundant functional groups. The mineral precipitation and transformation processes induced by microbes are functionally equivalent to geological processes operating at high temperatures and pressures in the deep Earth, suggesting that microbial processes can serve as analogs to deep abiotic processes that are difficult to observe.

Early dolomitisation of the Lower-Middle Ordovician cyclic carbonates in northern Tarim Basin, NW China

High-frequency metre-scale cycles are present within the Lower-Middle Ordovician carbonate successions in northern Tarim Basin, NW China. These metre-scale cycles were variably dolomitised from top to bottom. Three types of replacive dolomites were recognised, including dololaminite(very finely to finely crystalline, planar-s to nonplanar-a dolomite;type-1), patterned dolomite(finely crystalline, planar-s dolomite; type-2), and mottled dolomite(finely to medium crystalline,nonplanar-a(s) dolomite; type-3). Petrographic evidence indicate these dolomites were primarily deposited in supratidal to restricted subtidal environments, and formed in near-surface to shallow burial realms. Geochemically, all types of dolomites have similar δ13C and 87Sr/86 Sr ratios comparable to calcite precipitated in equilibrium with the Early-Middle Ordovician seawater. These geochemical attributes indicate that these dolomites were genetically associated and likely formed from connate seawater-derived brines. Of these, type-1 dolomite has δ18O values(.4.97‰ to.4.04‰ VPDB) slightly higher than those of normal seawater dolomite of the Early-Middle Ordovician age. Considering the absence of associated evaporites within type-1 dolomite, its parental fluids were likely represented by slightly evaporated(i.e., mesosaline to penesaline) seawater with salinity below that of gypsum precipitation. More depleted δ18O values(.7.74‰ to.5.20‰ VPDB) of type-2 dolomite and its stratigraphic position below type-1 dolomite indicate the generation of this dolomite from mesosaline to penesaline brines at higher temperatures in near-surface to shallow burial domains. Type-3 dolomite yields the most depleted δ18O values(–9.30‰to –7.28‰ VPDB), pointing to that it was most likely formed from coeval seawater-derived brines at highest temperatures in a shallow burial setting. There is a downward decreasing trend in δ18O values from type-1 through type-2 to type-3 dolomites, and in abundance of dolomites, indicating that the dolomitising fluids probably migrated downward from above and persisted into shallow burial conditions.

The relationship between extension of lower crust and displacement of the shelf break

With deep sea petroleum explorations become more and more popular,some geological phenomena have emerged:extension of lower crust and upper crust is inhomogeneous;shelf break has been moved rapidly after crustal stretching.These geological phenomena are important to the continental margin evolution.To investigate the thinning of the whole crust and the contribution of the upper crust versus the lower crust to the crustal stretching since the Cenozoic,we calculated the stretching factors of the upper and the lower crust based on the 13 seismic lines in the Baiyun Sag from CNOOC.The results indicated that the whole crustal thickness decreases seaward while the whole crustal stretching factor increases from shelf to slope.Our calculations showed that the lower crustal stretching factor is higher than that of the upper crust in the Baiyun Sag.In the Cenozoic,deformation of the Baiyun Sag is controlled mainly by ductile shearing rather than brittle shearing.Based on the numerical modeling,we can conclude the initial crust in the Baiyun Sag is thermally attenuated.The stretching factor(β)of the lower crust increases from the north to the south of the continental margin,indicating two stretching centers:the Baiyun Sag and the Liwan Sag.The geometry of the shelf break and theβisoline trap have the similar trend in 23.8 and 13.8 Ma,both located in the intense deforming zone of the lower crust,and therefore we conclude the stretching and flowing of the lower crust cause the displacement of the shelf break before and after 23.8 Ma.

Temperatures of dolomitizing fluids in the Feixianguan Formation from the Northeastern Sichuan Basin

The discovery of natural gas reservoirs from the Triassic Feixianguan Formation in the Northeastern Sichuan Basin is an important breakthrough in the field of marine carbonate rocks for Chinese oil and gas exploration in recent years.Because of the dolomite-hosted reservoirs in the Feixianguan Formation,these dolomites and their formation mechanisms have been a research focus for sedimentary geologists and petroleum geologists.Based on the homogenization temperatures of fluid inclusions,oxygen isotopic composition and their calculated temperatures,and the burial and thermal history of the typical well,it is considered that the majority of dolomites are formed by low-temperature dolomitizing fluids in the Triassic Feixianguan Formation,Northeastern Sichuan Basin.Only a minority of dolomites are formed by high-temperature dolomitizing fluids.The ending depth interval of low-temperature dolomitizing fluids was about 1000-2500 m,of which the correspondingly ending timing interval was approximately from early-middle Middle Triassic to early-middle Late Triassic.The main depth interval of high-temperature dolomitizing fluids was about 3200-4500 m,of which the correspondingly main timing interval was approximately early-middle Middle Jurassic.The low-temperature and high-temperature dolomitizing fluids have different meanings to the formation and evolution of the pore volumes of dolomite reservoirs in the Feixianguan Formation,Northeastern Sichuan Basin.