BET Measurements: Outgassing of Minerals

Outgassing minerals at elevated temperatures prior to BET measurements can lead to phase changes, especially in the case of amorphous and poorly crystalline materials. In order to evaluate the applicability of the BET method when low outgassing temperatures are required, selected aquifer minerals were outgassed at different temperatures and for different times. The studied minerals are 2-line ferrihydrite, goethite, lepidocrocite, quartz, calcite, alpha-alumina, and kaolinite. The results demonstrate that measured specific surface areas of iron oxides are strongly dependent on outgassing conditions because the surface area increased by 170% with increasing temperature. In the poorly crystalline minerals, phase changes caused by heating were observed at temperatures lower than 100 degrees C. Therefore low outgassing temperatures are preferable for minimizing phase changes. As demonstrated in this study, stable BET values can be obtained by increasing the outgassing time without heating iron oxides. For quartz, calcite, alpha-alumina, and kaolinite, stable BET values were obtained after outgassing the minerals at 100 to 250 degrees C for 2 h. However, outgassing these minerals at room temperature (20 degrees C) only resulted in minor errors, implying that aquifer sediments containing poorly crystalline materials can be outgassed at low temperatures if the outgassing time is increased. Scanning electron microscopy of the studied minerals demonstrated that the particle size as calculated from BET data compares well with particle size observed by scanning electron microscopy images. Copyright 2000 Academic Press.     

Adsorption of polyvinylimidazole onto kaolinite

The adsorption of polyvinylimidazole (PVI) onto kaolinite from aqueous solutions has been investigated systematically as a function of parameters such as calcination temperature of kaolinite, pH, ionic strength, and temperature. According to the experimental results, the adsorption of PVI increases with pH from 8.50 to 11.50, temperature from 25 to 55 degrees C, and ionic strength from 0 to 0.1 mol L(-1). The kaolinite sample calcined at 600 degrees C has a maximum adsorption capacity. Adsorption isotherms of PVI onto kaolinite have been determined and correlated with common isotherm equations such as Langmuir and Freundlich isotherm models. The Langmuir isotherm model appeared to fit the isotherm data better than the Freundlich isotherm model. The physical properties of this adsorbent are consistent with the parameters obtained from the isotherm equations. Furthermore, the zeta potentials of kaolinite suspensions have been measured in aqueous solutions of different PVI concentrations and pH. From the experimental results, (i) pH strongly alters the zeta potential of kaolinite; (ii) kaolinite has an isoelectric point at about pH 2.35 in water and about pH 8.75 in 249.9 ppm PVI concentration; (iii) PVI changes the interface charge from negative to positive for kaolinite. The study of temperature effect has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy, and entropy changes. The dimensionless separation factor (RL) has shown that kaolinite can be used for adsorption of PVI from aqueous solutions.     

Thermal behaviour of some minerals

Thermal behaviour of some minerals (kaolinite, halloysite, two montmorillonites, quartz and calcite) for different sample amounts and heating rates has been investigated using differential thermal analysis. On the basis of the DTA analysis carried out, the PA curves of each mineral have been obtained for different heating rates. These diagrams can be employed in the semiquantitative evaluation of identical substances contained in uncharacterized polymineral samples.     

Thermophysical properties of oil shale minerals

The thermal diffusivity values of eight minerals that are commonly associated with oil shales of the Green River formation have been measured by the laser flash technique. Data are presented in the temperature range 25–500°C for quartz, dolomite, calcite, plagioclase, analcite, pyrite, potassium feldspar and low albite. A comparison of the thermal conductivities of some of these minerals, calculated from experimentally measured thermal diffusivity and density, with the experimental values reported in the literature reveals good agreement. Trends in the variation of thermal diffusivity with temperature and anisotropic effects in thermophysical parameters are discussed from the point of view of grain boundary effects in these polycrystalline mineral aggregates.     

Temperature influence of nonionic polyethylene oxide and anionic polyacrylamide on flocculation and dewatering behavior of kaolinite dispersions

Nonionic polyethylene oxide (PEO) and anionic polyacrylamide (PAM) flocculation of kaolinite dispersions has been investigated at pH 7.5 in the temperature range 20-60 degrees C. The surface chemistry (zeta potential), particle interactions (shear yield stress), and dewatering behavior were also examined. An increase in the magnitude of zeta potential of kaolinite particles, in the absence of flocculant and at a fixed PEO and PAM concentration, with increasing temperature was observed. The zeta potential behavior of the flocculated particles indicated a decrease in the adsorbed polymer layer thickness, while at the same time, however, the adsorbed polymer density showed a significant increase with increasing temperature. These results suggest that polymer adsorption was accompanied by temperature-influenced conformation changes. The hydrodynamic diameter and supernatant solution viscosity of both polymers decreased with increasing temperature, consistent with a change in polymer-solvent interactions and conformation, prior to adsorption. The analysis of the free energy (DeltaG(ads)) of adsorption showed a strong temperature dependence and the adsorption process to be more entropically than enthalpically driven. The polymer conformation change and increased negative charge at the kaolinite particle surface with increasing temperature resulted in decreased polymer bridging and flocculation performance. Consequently, the shear yield stress and the rate and the extent of dewatering (consolidation) of the pulp decreased significantly at higher temperatures (>40 degrees C). The temperature effect was more pronounced in the presence of PEO than PAM, with 40 and 20 degrees C indicated as the optima for enhanced performance of the latter and former flocculants, respectively. The results demonstrate that a temperature-induced conformation change, together with polymer structure type, plays an important role in flocculation and dewatering behavior of kaolinite dispersions.     

Dispersion stability of a ceramic glaze achieved through ionic surfactant adsorption

The adsorption of cetylpyridinium chloride (CPC) and sodium dodecylbenzenesulfonate (SDBS) onto a ceramic glaze mixture composed of limestone, feldspar, quartz, and kaolin has been investigated. Both adsorption isotherms and the average particle zeta potential have been studied in order to understand the suspension stability as a function of pH, ionic strength, and surfactant concentration. The adsorption of small amounts of cationic CPC onto the primarily negatively charged surfaces of the particles at pH 7 and 9 results in strong attraction and flocculation due to hydrophobic interactions. At higher surfactant concentrations a zeta potential of more than +60 mV results from the bilayered adsorbed surfactant, providing stability at salt concentrations < or = 0.01 M. At 0.1 M salt poor stability results despite substantial zeta potential values. Three mechanisms for SDBS adsorption have been identified. When anionic SDBS monomers either adsorb by electrostatic interactions with the few positive surface sites at high pH or adsorb onto like charged negative surface sites due to dispersion or hydrophobic interactions, the magnitude of the negative zeta potential increases slightly. At pH 9 this increase is enough to promote stability with an average zeta potential of more than -55 mV, whereas at pH 7 the zeta potential is lower at about -45 mV. The stability of suspensions at pH 7 is additionally due to steric repulsion caused by the adsorption of thick layers of neutrally charged Ca(DBS)2 complexes created when the surfactant interacts with dissolved calcium ions from the calcium carbonate component.     

新疆高碱煤分选组分中碱性矿物赋存及差异演化研究

以新疆五彩湾高碱煤为原料,通过有机重液浮选和理化分析及热力学模拟解析活性矿物质热演化特性。结果表明,五彩湾煤以密度在1.40-1.50 g/cm~3的组分为主(质量分数超过70%)。可溶性Na和K等主要存在于较低密度组分(-1.40 g/cm~3)中;在高密度(+1.50 g/cm~3)组分中发现了以硅铝酸盐形式存在的碱及碱土金属(AAEMs)。Ca主要以方解石形式存在,伴随高岭土和石英富集在高密度组分中。在低温(500℃)灰化时少量Na释放,大量可溶钠盐的残留导致各分选组分中Na的扩散量相差不大。在815℃热处理温度下,低密度组分中大部分Na挥发到气相中;高密度组分中的部分碱金属可被黏土(高岭土)和石英等矿物质捕获,抑制其释放。Fact Sage热力学模拟发现,温度低于550℃时Na盐仍稳定存在于灰中;温度高于550℃时Na盐开始挥发,同时部分Na向NaAlSiO_4转化;在约620℃时,Na盐消失,同时NaAlSiO_4的含量逐渐趋于稳定。SiO_2含量的差异显著影响含Na等矿物质的演变行为。在500-815℃,Ca以CaSO_4和硅铝酸钙的形式稳定存在,而M g则在不同形式的硅酸盐之间发生转变。     

Raman microspectroscopy of organic inclusions in spodumenes from Nilaw (Nuristan, Afghanistan)

The color varieties of spodumene (green spodumene, kunzite) from Nilaw mine (Nuristan, Afghanistan) have been investigated by microthermometry and Raman spectroscopy analyses. These minerals are rich in primary and secondary fluid inclusions. Measured values of temperature homogenization (T(h)) and pressure (P) for selected fluid-inclusion assemblages (I-IV) FIA in green spodumene and (I-II) FIA in kunzite ranges from 370 to 430°C, 1.16 to 1.44 kbar and 300 to 334°C, 0.81 to 1.12 kbar, respectively. The brine content and concentration varies from 4.3 to 6.6 wt.% eq. NaCl. Numerous and diverse mineral phases (quartz, feldspars, mica, beryl, zirconium, apatite, calcite, gypsum) present in this mineral as solid inclusions were studied by Raman microspectroscopy. Raman spectra of selected fluid, organic and solid inclusions were collected as line or rectangular maps and also depth profiles to study their size and contents. There appeared very interesting calcite (156, 283, 711 and 1085 cm(-1)), beryl (324, 397, 686, 1068 and 3610 cm(-1)), topaz (231, 285, 707, 780 and 910 cm(-1)) and spodumene (355, 707 and 1073 cm(-1)) inclusions accompanied by fluid and/or organic inclusions (liquid and gas hydrocarbons) with bands at 2350 cm(-1) (CO(2), N(2)), 2550 cm(-1) (H(2)S) and 2900 cm(-1) (C(2)H(6)-CH(3)). Some solid inclusions contain carbonaceous matter (D-band at ca. 1320 cm(-1) and/or G-band at ca. 1600 cm(-1)).     

煤中矿物质对灰熔融和燃烧特性的影响

采用化学分步萃取、XRD和SEM-EDS、煤灰灰成分分析等测试方法对五彩湾煤中矿物质的赋存形态进行了研究,并对逐级萃取前后煤样的燃烧特性和灰熔融特性进行了分析和比较.结果表明,五彩湾煤中原始矿物质主要有方解石、硫酸钙、高岭石、石英、黄铁矿等;煤中钠含量很高,主要以水合离子的形态溶于煤的内水中;有机形态的钠、镁和钙提高了煤的燃烧特性;五彩湾煤的煤灰熔融性主要受铁钙物质的量比(F₂O₃/CaO)影响,灰熔融特性温度随铁钙物质的量比(F₂O₃/CaO)的增大而降低.     

高温气化条件下煤直接液化残渣中矿物质演化行为的研究

利用XRD和FT-IR分析了高温(1 100~1 500 ℃)气化条件下液化残渣中矿物质的演变行为,并利用穆斯堡尔谱仪对残渣灰中的含铁相及铁的价态铁进行了定量分析。结果表明,煤直接液化残渣中的主要矿物质为石英、硫酸钙、紫铝铁矾、磁黄铁矿、高岭石和方解石。高温气化条件下残渣灰中主要矿物质为钙长石、钙黄长石、磁赤铁矿和磁铁矿。由于钙长石、钙黄长石等含钙化合物低温共熔作用,使得残渣灰具有较低的熔融温度。残渣灰中的含铁相主要为磁赤铁矿、磁铁矿、铁橄榄石和玻璃体,并且随温度的升高,玻璃体中的铁含量逐渐增加。同时,残渣灰中Fe²⁺/Fe³⁺出现先增加后降低再增加的变化趋势。当温度由1 100 ℃升高至1 200 ℃时,由于磁赤铁矿的还原,Fe²⁺/Fe³⁺由1.08升高至2.39;1 200 ℃以上Fe²⁺/Fe³⁺的变化不明显。另外,玻璃体中铁含量的增加是引起残渣灰液相含量随温度升高而增加的重要原因,铁含量高是导致残渣灰熔融温度低的主要原因。     

Effect of temperature on n-tetradecane emulsion in the presence of phospholipid DPPC and enzyme lipase or phospholipase A2

Zeta potentials and effective diameters of n-tetradecane emulsions in 1 M ethanol were investigated in the presence of 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC) (1 mg/100 mL), Candida cylindracea lipase (CCL), and phospholipase PLA2 (1 mg/100 mL) at 20, 37, and 45 degrees C. The enzyme was added at the beginning of mechanical emulsion homogenization or 1 min before the end of stirring for 10 min at 10,000 rpm. It was found that DPPC decreases the negative zeta potentials at all three temperatures. The decrease was largest at 20 degrees C and smallest at 45 degrees C. The influence of the enzymes on the zeta potentials depended on the enzyme kind, time of its injection, and temperature. More negative values of the zeta potentials relative to n-C14H30/DPPC droplets were obtained if the lipase was present. Generally, the effective diameters correlate with the zeta potentials, i.e., lower zeta potential corresponds with bigger effective diameter. Possible reasons for the observed changes of the measured parameters are discussed.     

CH_4和CO_2在油页岩中矿物质结构内部吸附的分子模拟

利用Materials Studio2017模拟软件构建了蒙脱石、高岭石、方解石和生石膏四种矿物质分子模型。采用巨正则蒙特卡洛(GCMC)方法和分子动力学(MD)方法对四种模型的吸附量和吸附热进行了模拟计算。研究表明,相同温度和压力条件下四种矿物质对CH_4和CO_2分子吸附量大小为:蒙脱石高岭石生石膏方解石;CH_4和CO_2分子的单组分吸附量随压力的增大而增大,两种气体吸附均符合Langmuir吸附规律;四种矿物质对CH_4和CO_2分子的等量吸附热均小于42 k J/mol,即为物理吸附;随着温度的升高,CH_4和CO_2分子的吸附量和吸附热均减小,且CH_4和CO_2分子的等量吸附热和等温吸附量之间呈良好的正相关。     

Zeta potential study of the oxidation of copper sulfide minerals

The zeta potential of the copper sulfide minerals, chalcocite, covellite, chalcopyrite, bornite, enargite and tennantite was measured as a function of pH and oxidising conditions. The changes in zeta potential observed in this study are consistent with the presence of a copper hydroxide layer covering a metal-deficient sulfur-rich surface and with the extent of this copper hydroxide coverage increasing with oxidation conditions. The existence of these surface species and their percentage were also confirmed by X-ray photoelectron spectroscopy. Analysis of the zeta potential data revealed that during the acid titration of the minerals, dissolution of the surface copper hydroxide layer occurs at pH values less than 8 while during the base titration, precipitation of copper hydroxide on the mineral surface is observed at pH values higher than 6. Hysteresis between the zeta potential acid and base titration curves was only observed in oxidising conditions and is attributed to the dissolution of the minerals at acidic pH values. The following ranking for the oxidation of these minerals is obtained: chalcocite>tennantite>enargite>bornite>covellite>chalcopyrite.     

Constrained synthesis of cobalt oxide nanomaterials in the 12-subunit protein cage from Listeria innocua

The protein cage of the 12-subunit ferritin-like protein from Listeria innocua has been utilized as a size and shape constrained reaction environment for the synthesis of two cobalt oxide minerals, Co(3)O(4) and Co(O)OH. Reaction of Co(II) with H(2)O(2) at pH 8.5 under either elevated temperature (65 degrees C) or ambient temperature (23 degrees C) resulted in the formation of cobalt oxide nanoparticles encapsulated within the protein cage. At elevated temperatures, Co(3)O(4) was formed while at lower temperature the oxyhydroxide Co(O)OH was found. Mineral particles, commensurate in size with the internal dimensions of the protein (5 nm), were imaged by transmission electron microscopy and shown to be surrounded by the intact protein cage. The minerals were investigated by electron diffraction and revealed a crystalline Co(3)O(4) phase and an amorphous Co(O)OH phase. Further investigation of these composite materials using size exclusion chromatography, gel electrophoresis, dynamic light scattering, and zeta potential measurements indicated that the mineral was encapsulated within the protein cage giving rise to properties of both the mineral and protein components.     

Determination of the critical surface tension of wetting of minerals treated with surfactants by shear flocculation approach

This paper contributes the shear flocculation method as a new approach to determine the critical surface tension of wetting of minerals treated with surfactants. This newly developed approach is based on the decrease of the shear flocculation of the mineral suspension, with decreasing of the surface tension of the liquids used. The solution surface tension value at which shear flocculation does not occur can be defined as the critical surface tension of wetting (gamma c) of the mineral. By using the shear flocculation method, the critical surface tensions of wetting (gamma c) for calcite and barite minerals, treated with surfactants, were obtained as 30.9 and 35.0 mN/m, respectively. These values are in good agreement with data reported previously on the same minerals obtained by the contact angle measurement and flotation methods. The chemical agents used for the treatment of calcite and barite particles were sodium oleate and sodium dodecyl sulfate, respectively.     

准东煤灰化过程中的矿物演变及矿物添加剂对其灰熔融特性的影响

利用低温灰化、高温灰化和X射线衍射物相分析相结合的方法对准东煤中矿物质在加热过程中的演变规律进行了研究。结果表明,准东煤中原始矿物质以方解石、高岭石为主,随着燃烧温度的升高,煤灰中矿物质最终生成了铁橄榄石、硅酸钙等。此外,向准东煤中掺加不同比例的高岭土和刚玉混合添加剂,发现随着SiO₂/Al₂O₃比值的降低,煤中生成了钙矾石、钙铝榴石等高熔点物质,准东煤的灰熔点逐步升高。     

Spectroscopic study of phase transitions in natural calcite mineral

The process and the formation of new minerals upon heating the carbonate rocks containing clay minerals, together with calcite are determined with thermal analysis, X-ray diffraction, infrared and Raman spectroscopy. The calcite-calcium oxide phase transition sequence was followed up to 947 degrees C in naturally occurring limestone samples. The spectral variations of the internal modes of the carbonate trigonal (nu(1), nu(2), nu(3) and nu(4)) were used to probe the structural phase transitions. The calcium oxide phase (which on reaction with atmospheric water forms portlandite) with an onset temperature of around 950 degrees C was also characterized by the appearance of the infrared mode around 450 cm(-1). The minerals, which were formed upon heating the calcite, were calcium oxide and wollastonite.     

Effects of acid treatments on Moroccan Tarfaya oil shale and pyrolysis of oil shale and their kerogen

In this study, the kerogen of oil shale from Moroccan Tarfaya deposits was isolated and the changes in the initial organic matter during the removal of the mineral matrix were examined. Chloroform extraction of the oil shale increases the intensity of the peaks in the X-ray diffractograms. Infrared spectra and X-ray diffractograms reveal the presence of mineral, calcite, quartz, kaolinite, and pyrite in the mineral matrix of the oil shale. Hydrochloric and hydrofluoric acids dissolution do not alter the organic matter. The nonisothermal weight loss measurements indicate that thermal decomposition of the isolated kerogen can be described by firstorder reaction. A single kinetic expression is valid over the temperature range of kerogen pyrolysis between 433K and 873K. Furthermore, the results indicate that the removal of mineral matter causes a decrease in the activation energies of the pyrolysis reactions of oil shale.     

Adsorption of UO2 2+ on natural composite materials

The prediction of the adsorption behavior of natural composite materials was studied by a single mineral approach. The adsorption of U(VI) on single minerals such as goethite, hematite, kaolinite and quartz was fully modeled using the diffuse-layer model in various experimental conditions. A quasi-thermodynamic database of surface complexation constants for single minerals was established in a consistent manner. In a preliminary work, the adsorption of a synthetic mixture of goethite and kaolinite was simulated using the model established for a single mineral system. The competitive adsorption of U(VI) between goethite and kaolinite can be well explained by the model. The adsorption behavior of natural composite materials taken from the Koongarra uranium deposit (Australia) was predicted in a similar manner. In comparison with the synthetic mixture, the prediction was less successful in the acidic pH range. However, the model predicted well the adsorption behavior in the neutral to alkaline pH range. Furthermore, the model reasonably explained the role of iron oxide minerals in the adsorption of U(VI) on natural composite materials.     

Sorption of Cypermethrin Diastereoisomers to Quartz,Corundum, Goethite,Kaolinite and Montmorillonite

Differential sorption and degradation of different pesticide stereoisomers in soil may result in accumulation of the most strongly sorbed and the slowest degradable isomers. In this work the pyrethroid cypermethrin (8 isomers) has been used for test of stereochemical interactions with surfaces of the minerals quartz, corundum, goethite, kaolinite and montmorillonite. The sorption of three diastereoisomeric fractions denoted Cis A, Trans C and Cis B + Trans D were quantified by use of GC-ECD in batch experiments with initial cypermethrin concentrations in the range 1-9 µg/L. Correction for cypermethrin sorbed to surfaces of the shaking flasks were accomplished to obtain net sorption isotherms for the minerals, all of which were well fitted by the Freundlich equation. Bonding affinities per unit surface area decreased in the order: corundum > quartz > kaolinite > montmorillonite > goethite. The isotherms for sorption of all diastereoisomeric fractions to quartz, corundum and goethite were all linear, whereas non-linear isotherms were found for sorption of Cis A and Trans C fractions to kaolinite and montmorillonite. Corundum, quartz and goethite showed a significantly stronger sorption of Cis A than the other fractions, while kaolinite sorbed Cis B + Trans D most strongly. The observed differences predict less leaching and slower degradation of the Cis A fraction in subsoils low in organic carbon.