Feldspar Particles Research Articles

New insights into the oleate flotation response of feldspar particles of different sizes: Anisotropic adsorption model

The anisotropic adsorption of sodium oleate (NaOL) on feldspar surfaces was investigated to elucidate the different flotation properties of feldspar particles of four different size ranges. Microflotation experiments showed that the feldspar flotation recovery of particles with sizes spanning different ranges decreased in the order 0–19>19–38>45–75>38–45μm. Zeta potential and FTIR measurements showed that NaOL was chemically adsorbed on the Al sites of the feldspar surface. The anisotropic surface energies and broken bond densities estimated by density functional theory calculations showed that, although feldspar mostly exposed (010) and (001) surfaces, only the (001) surfaces contained the Al sites needed for NaOL adsorption. The interaction energies calculated by molecular dynamics simulations confirmed the more favorable NaOL adsorption on (001) than (010) surfaces, which may represent the main cause for the anisotropic NaOL adsorption on feldspar particles of different sizes. SEM measurements showed that the main exposed surfaces on coarse and fine feldspar particles were the side (010) and basal (001) ones, respectively. A higher fraction of Al-rich (001) surfaces is exposed on fine feldspar particles, resulting in better floatability compared with coarse particles. XPS and adsorption measurements confirmed that the Al content on the feldspar surface varied with the particle size, explaining the different NaOL flotation of feldspar particles of different sizes. Therefore, the present results suggest that coarsely ground ore should be used for the separation of feldspar gangue minerals. Further improvements in the flotation separation of feldspar from associated valuable minerals can be achieved through selective comminution or grinding processes favoring the exposure of (010) surfaces.

Alkali-Feldspar as a Catalyst for Biomass Gasification in a 2-MW Indirect Gasifier

The aim of this work was to investigate the potential of alkali-feldspar ore [(K, Na)AlSi3O8] as an alternative bed material for indirect gasification of biomass. Experiments conducted in the Chalmers 2-MW gasifier confirmed that alkali-feldspar could withstand stringent fluidizing conditions. Moreover, this material showed strong promise for promoting the water–gas shift reaction and reforming higher hydrocarbons, in particular tars. This activity was enhanced by time-on-stream in the indirect gasifier, and the gas and tar yields were higher than for activated olivine or bauxite used in the same unit. SEM-EDX analysis revealed that the observed activity of alkali-feldspar was due to the formation of active ash layers on the feldspar particles (consisting principally of Ca, Mg, K, and Na) that originated from the woody fuel. At some point, the feldspar showed capacity to transport oxygen from the boiler to the gasifier. Thus, an optimal level of bed regeneration would benefit the reforming reactions in th...

A comparative study of K-rich and Na/Ca-rich feldspar ice-nucleating particles in a nanoliter droplet freezing assay

Abstract. A recently designed droplet freezing assay was used to study the freezing of up to 1500 identical 0.2 nL water droplets containing suspensions of one Na/Ca-rich feldspar and three K-rich and one Na/Ca-rich feldspar particles. Three types of experiments have been conducted: cooling ramp, isothermal freezing at a constant temperature, and freeze–thaw cycles. The observed freezing behavior has been interpreted with the help of a model based on the classical nucleation theory (soccer ball model (SBM); Niedermeier et al., 2015). By applying the model to the different freezing experiments conducted with the same ice-nucleating material, the unique sets of model parameters for specific feldspar suspensions could be derived. The SBM was shown to adequately describe the observed cooling rate dependence, the ice-nucleating active sites (INAS) surface density ns(T) in a wide temperature range, and the shift of the freezing curves towards lower temperature with dilution. Moreover, the SBM was capable of reproducing the variation of INAS surface density ns(T) with concentration of ice-nucleating particles in the suspension droplets and correctly predicting the leveling-off of ns(T) at low temperature. The freeze–thaw experiments have clearly shown that the heterogeneous freezing induced even by very active ice-nucleating species still possesses a stochastic nature, with the degree of randomness increasing towards homogeneous nucleation. A population of the high-temperature INAS has been identified in one of the K-rich feldspar samples. The freezing of 0.8 wt % suspension droplets of this particular feldspar was observed already at −5 °C. These high-temperature active sites could be deactivated by treating the sample with hydrogen peroxide but survived heating up to 90 °C. Given a high mass concentration of these high-temperature active sites (2.9 × 108 g−1) and a very low value of contact angle (0.56 rad) the possibility of biological contamination of the sample was concluded to be unlikely but could not be completely ruled out. The freezing efficacy of all feldspar samples has been shown to reduce only slightly after suspension in water for over 5 months.

Flotation of quartz from quartz-feldspar mixtures by the HF method

Flotation experiments performed on a quartz-feldspar mixture demonstrate that quartz can be floated selectively from feldspars in diluted solutions of hydrofluoric acid (HF) simply by the aid of a frother. High grades and good recoveries were obtained for both quartz and feldspars. A feldspar concentrate of 99.9% at a recovery of 95.6% was produced. No further cleaning of the quartz concentrate (95.4% quartz at a recovery of 88.6%) was attempted. Feldspar impurities in the quartz concentrate is believed to be particles entrained in the froth, non-liberated quartz-feldspar particles, in addition to feldspar particles with sufficient hydrogen terminated silicon sites.

Mineralogical and morphological properties of individual dust particles in ice cores from the Tibetan Plateau

ABSTRACTUsing a field emission scanning electron microscope and energy-dispersive X-ray spectrometer (FESEM−EDS), individual insoluble dust particles in ice cores recovered from the northern (Dunde), western (Muztagata) and south-eastern (Palong-Zangbo) Tibetan Plateau were analysed in order to reveal the mineralogical and morphological characteristics of the analogue of long-range transported Asian dust. The results reveal that the dust particles are mainly composed of quartz (17–36%, number abundance), clay (37–48%) and feldspar (12–18%). Illite and chlorite are the dominant clay species, while kaolinite is rarely observed. For the three sites, regional differences in the mineral assemblages are significant, in particular the abundance of quartz, chlorite and muscovite species, reflecting the regional provenance of these dust particles and the climatic regime in their source areas. Oxide ratios in clays indicate different weathering strengths of the particles in their source regions, with a higher K2O/(SiO2 + Al2O3) in the western and northern Tibetan Plateau. The individual particles have modes of 1.48 and 1.53 in the aspect ratio and circularity distribution respectively. No significant relationship between aspect ratio and circularity was found. Quartz and feldspar particles have a narrow aspect ratio distribution. Muscovite particles have the coarsest grain size, while chlorite particles have the finest.

Influence of the AC voltage frequency on the oscillation trajectory and path length of particles inside a planar–type electric curtain

Experimental investigations of the average path length of oscillating dust particles inside a planar –type electric curtain (PTEC) are presented as a function of the frequency of the AC voltage. The frequency was adjusted within the range of 10–300 Hz. The oscillation paths of feldspar particles of diameter 40–60 μm inside a small cloud were recorded photographically. The main purpose of this investigation was to study the changes in average path length as a function of the supply voltage frequency. These results can be used to improve the precipitation and separation processes for charged dust particles inside a PTEC.

Can we define an asymptotic value for the ice active surface site density for heterogeneous ice nucleation?

AbstractThe immersion freezing behavior of droplets containing size‐segregated, monodisperse feldspar particles was investigated. For all particle sizes investigated, a leveling off of the frozen droplet fraction was observed reaching a plateau within the heterogeneous freezing temperature regime (T >− 38°C). The frozen fraction in the plateau region was proportional to the particle surface area. Based on these findings, an asymptotic value for ice active surface site density ns, which we named , could be determined for the investigated feldspar sample. The comparison of these results with those of other studies not only elucidates the general feasibility of determining such an asymptotic value but also shows that the value of strongly depends on the method of the particle surface area determination. However, such an asymptotic value might be an important input parameter for atmospheric modeling applications. At least it shows that care should be taken when ns is extrapolated to lower or higher temperature.

Dust-aerosol optical modeling with Gaussian spheres: Combined invariant-imbedding T-matrix and geometric-optics approach

The Gaussian sphere has been widely used as a model to study light scattering by irregular particles; and, despite extensive numerical studies, the optical properties are not thoroughly understood. Based on Gaussian spheres and using a combination of the invariant imbedding T-matrix method and an improved geometric-optics method, the single-scattering properties (namely, the 4×4 phase matrix, extinction cross section, single-scattering albedo, and asymmetry factor) are computed in the Rayleigh to geometric optics regimes. The simulations are performed with various degrees of irregularity, and the effects of particle irregularities are investigated over a wide range of particle sizes. Furthermore, the theoretical simulations based on Gaussian spheres are used to fit the measured optical properties of feldspar particles from the well-known Amsterdam–Granada light scattering database. A mixture of several shapes is shown to closely reproduce the measured phase matrices. The results may be potentially useful for remote-sensing and radiative-transfer applications involving dust aerosol.

Fe-Si-Mn-oxyhydroxide encrustations on basalts at east pacific rise near 13°N: An SEM-EDS study

Fe-Si-Mn-oxyhydroxide encrustations at the East Pacific Rise (EPR) near 13°N were analyzed using the scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS). These encrustations are mainly composed of amorphous Fe-Si-Mn-oxyhydroxides forming laminated, spherical, porous aggregates with some biodetritus, anhydrite, nontronite, and feldspar particles. Anhydrite particles and nontronite crystals in the Fe-Si-Mn-oxyhydroxide encrustations imply that the Fe-Si-Mn-oxyhydroxide may have formed under relatively low- to high-temperature hydrothermal conditions. The Fe-Si-Mn-oxyhydroxide encrustations on pillow basalts are 1–2 mm thick. The growth rate of ferromanganese crusts in the survey area suggests that these encrustations are an unlikely result of hydrogenic deposition alone having a hydrothermal and (Fe/Mn ratio up to 7.7 and Fe/(Fe+Mn+Al) ratio exceeding 0.78) hydrogenic origin (0.22 Fe/Mn ratio close to the mean value of 0.7 for open-ocean seamount crusts). The varying Fe/Mn ratios indicate that the Fe-Si-Mn-oxyhydroxide encrustations have formed through several stages of seafloor hydrothermalism. It is suggested that, at the initial formation stage, dense Fe-Si-oxyhydroxides with low Mn content deposit from a relatively reducing hydrothermal fluid, and then the loose Fe-Si-Mn-oxyhydroxides deposit on the Fe-Si-oxyhydroxides. As the oxidation degree of hydrothermal fluid increases and Si-oxide is inhibited, Mn-oxide will precipitate with Fe-oxyhydroxides.

Characterization of Reactor Ash Deposits from Pilot-Scale Pressurized Entrained-Flow Gasification of Woody Biomass

Pressurized entrained-flow gasification of renewable forest residues has the potential to produce high-quality syngas suitable for the synthesis of transport fuels and chemicals. The ash transformation behavior during gasification is critical to the overall production process and necessitates a level of understanding to implement appropriate control measures. Toward this end, ash deposits were collected from inside the reactor of a pilot-scale O2-blown pressurized entrained-flow gasifier firing stem wood, bark, and pulp mill debarking residue (PMDR) in separate campaigns. These deposits were characterized with environmental scanning electron microscopy equipped with energy-dispersive X-ray spectrometry and X-ray diffractometry. The stem wood deposit contained high levels of calcium and was comparatively insubstantial. The bark and PMDR fuels contained contaminant sand and feldspar particles that were subsequently evident in each respective deposit. The bark deposit consisted of lightly sintered ash aggregates comprising presumably a silicate melt that enveloped particles of quartz and, to a lesser degree, feldspars. Discontinuous layers likely to be composed of alkaline-earth metal silicates were found upon the aggregate peripheries. The PMDR deposit consisted of a continuous slag that contained quartz and feldspar particles dispersed within a silicate melt. Significant levels of alkaline-earth and alkali metals constituted the silicate melts of both the bark and PMDR deposits. Overall, the results suggest that fuel contaminants (i.e., quartz and feldspars) play a significant role in the slag formation process during pressurized entrained-flow gasification of these woody biomasses.

The importance of feldspar for ice nucleation by mineral dust in mixed-phase clouds

The amount of ice present in mixed-phase clouds, which contain both supercooled liquid water droplets and ice particles, affects cloud extent, lifetime, particle size and radiative properties. The freezing of cloud droplets can be catalysed by the presence of aerosol particles known as ice nuclei. One of the most important ice nuclei is thought to be mineral dust aerosol from arid regions. It is generally assumed that clay minerals, which contribute approximately two-thirds of the dust mass, dominate ice nucleation by mineral dust, and many experimental studies have therefore focused on these materials. Here we use an established droplet-freezing technique to show that feldspar minerals dominate ice nucleation by mineral dusts under mixed-phase cloud conditions, despite feldspar being a minor component of dust emitted from arid regions. We also find that clay minerals are relatively unimportant ice nuclei. Our results from a global aerosol model study suggest that feldspar ice nuclei are globally distributed and that feldspar particles may account for a large proportion of the ice nuclei in Earth's atmosphere that contribute to freezing at temperatures below about -15 °C.

The seeds of ice in clouds

An investigation of droplet freezing in clouds suggests that a minor component of mineral dust in the atmosphere is the main catalyst for this process. Two experts discuss the ramifications of this finding for those investigating cloud-droplet freezing, and for scientists studying atmospheric aerosols. See Letter p.355 Mineral dust aerosols arising in arid regions trigger ice formation in supercooled clouds, which can influence cloud radiative properties and therefore climate. It is thought that clay minerals, the major component of these dusts, are also the most potent ice-nucleating particles. But Ben Murray and colleagues show here that feldspar minerals dominate ice nucleation by mineral dust, despite being a minor dust component. They also suggest that feldspar particles may account for a large proportion of ice nuclei in the Earth's atmosphere at certain temperatures, and as feldspar content can vary, changes in the location of dust sources may alter the concentration of ice nuclei in the atmosphere and the associated climate effects.

Light scattering by feldspar particles: Comparison of model agglomerate debris particles with laboratory samples

We present comparisons of the non-zero light-scattering Mueller-matrix elements of agglomerated debris particles with those of well-characterized experimentally measured feldspar samples at blue and red wavelengths. The only completely free parameter in our comparisons is the small-size cut-off of the sample, which was not known. The significance is that both the light scattering and the measured properties of model and real particles agree very well. While some tweaking of the particle parameters could achieve some improvement, the fits are remarkably good, with significant deviations (∼5%) occurring in portions of the polarization elements, e.g. S34. We suggest that the reason for the good fits is not that the model particles exactly represent those of the sample particles, but rather that both sets of particles belong to a class of highly irregular particles, whose high degree of irregularity dominates the resulting scattering behavior, suppressing the effect of any characteristic morphological features.

Variation of Compressive Strength of Quartz, Feldspar Particles in Granite by Weathering

Variation of Compressive Strength of Quartz, Feldspar Particles in Granite by Weathering

AN INVESTIGATION INTO THE RELATIONSHIP BETWEEN THE RAW MATERIALS USED IN THE PRODUCTION OF CHINESE PORCELAIN AND STONEWARE BODIES AND THE RESULTING MICROSTRUCTURES*

The microstructures of porcelain and stoneware bodies from north and south China, spanning the period from the Tang to the Ming dynasty (7th–17th centuries ad), were examined in polished sections in a scanning electron microscope (SEM) after etching the sections with hydrofluoric acid (HF). Mullite, present as fine, mainly elongated crystals, is the dominant crystalline phase observed. The bulk chemical compositions of the bodies are determined by energy‐dispersive spectrometry in the SEM, and the relative amounts of mullite and quartz present in the different ceramics are estimated from X‐ray diffraction measurements. Mullite formed from areas of kaolinitic clay, mica particles and feldspar particles is distinguished through a combination of the arrangement of the mullite crystals, and the associated SiO2/Al2O3 wt% concentration ratios. It is shown that very different microstructures are observed in ceramic bodies produced using kaolinitic clay from north China (Ding porcelain and Jun stoneware), porcelain stone from south China (qingbai and underglaze blue porcelain and Longquan stoneware), and stoneware clays from south China (Yue and Guan stonewares). Therefore, SEM examination of HF‐etched, polished sections of the bodies of high‐refractory ceramics has considerable potential for investigating the raw materials used in their production.

Synthesis and characterization of new electrorheological fluids by carboxymethyl starch nanocomposites

Electrorheological fluids are new materials with good properties such as dielectric constant, dielectric loss or conductivity. These materials find practical applications in various industries. In this paper have been studied a ternary nanocomposite as rheological fluid based on Carboxymethyl starch and dimethylsulfoxide with feldspar particles. These nano composite was prepared by the two-step composite method. Firstly, the polar DMSO compound was directly intercalated into the interlayer of nano ferric oxide and then the intercalated complex was composite with CMS by the solution method. The composites, thus synthesized have been characterized by Fourier transfer infrared (FT-IR) spectrophotometer and X-ray diffraction. The morphology of these composites was studied by scanning electron microscopy.

Morphological evolution of dissolving feldspar particles with anisotropic surface kinetics and implications for dissolution rate normalization and grain size dependence: A kinetic modeling study

With previous two-dimensional (2D) simulations based on surface-specific feldspar dissolution succeeding in relating the macroscopic feldspar kinetics to the molecular-scale surface reactions of Si and Al atoms ( Zhang and Lüttge, 2008, 2009), we extended our modeling effort to three-dimensional (3D) feldspar particle dissolution simulations. Bearing on the same theoretical basis, the 3D feldspar particle dissolution simulations have verified the anisotropic surface kinetics observed in the 2D surface-specific simulations. The combined effect of saturation state, pH, and temperature on the surface kinetics anisotropy has been subsequently evaluated, found offering diverse options for morphological evolution of dissolving feldspar nanoparticles with varying grain sizes and starting shapes. Among the three primary faces on the simulated feldspar surface, the (1 0 0) face has the biggest dissolution rate across an extensively wide saturation state range and thus acquires a higher percentage of the surface area upon dissolution. The slowest dissolution occurs to either (0 0 1) or (0 1 0) faces depending on the bond energies of Si–(O)–Si ( Φ Si–O–Si/ kT) and Al–(O)–Si ( Φ Al–O–Si/ kT). When the ratio of Φ Si–O–Si/ kT to Φ Al–O–Si/ kT changes from 6:3 to 7:5, the dissolution rates of three primary faces change from the trend of (1 0 0) > (0 1 0) > (0 0 1) to the trend of (1 0 0) > (0 0 1) > (0 1 0). The rate difference between faces becomes more distinct and accordingly edge rounding becomes more significant. Feldspar nanoparticles also experience an increasing degree of edge rounding from far-from-equilibrium to close-to-equilibrium. Furthermore, we assessed the connection between the continuous morphological modification and the variation in the bulk dissolution rate during the dissolution of a single feldspar particle. Different normalization treatments equivalent to the commonly used mass, cube assumption, sphere assumption, geometric surface area, and reactive surface area normalizations have been used to normalize the bulk dissolution rate. For each of the treatments, time consistence and grain size dependence of the normalized dissolution rate have been evaluated and the results revealed significant dependences on the magnitude of surface kinetic anisotropy under differing environmental conditions. In general, the normalized dissolution rates are strongly dependent on grain size. Time-consistent normalization treatment varies with the investigated condition. The modeling results suggest that the sphere-, cube-, and BET-normalized dissolution rates are appropriate under the far-from-equilibrium conditions at low pH where these normalizations are time-consistent and are slightly dependent on grain size.

A NEW CORRELATION FOR TWO-PHASE PRESSURE DROPS IN FULLY DEVELOPED DILUTE SLURRY UP-FLOWS THROUGH AN ANNULUS

The prediction of two-phase pressure drops is important in the design of fluidized beds, heat exchangers, slurry transport lines, annular risers in reactors, driers, and other applications of particulate flows. Experimental data for liquid-solid up-flows through annuli are very limited. In this study, a correlation was developed for predicting two-phase pressure drops via Euler number (Eu tp ) for liquid-solid suspension up-flows in the fully developed flow region of an annulus in terms of mixture Reynolds number (Re m ), solid particle Froude number (Fr p ), ratio of particle diameter to hydraulic diameter, and ratio of area-averaged solids density in the tested cross-sectional flow area of the annulus to the average density of the feed slurry entering the annulus. The proposed correlation, having an accuracy of almost ±25%, was obtained for water-feldspar dilute suspension up-flows in an annulus with a hydraulic diameter of 79.8 mm and with feldspar particles (2400 kg/m3 in material density and 0.072–0.138 mm in average diameter) at low concentrations.

Single particle analysis reveals that bacterial community structures are semi-specific to the type of soil particle

With the aim of understanding how diverse bacteria are distributed within a heterogeneous soil, we compared local bacterial communities on individual soil particles. We picked up 11 coarse sand-sized particles (quartz, whitish feldspar, yellow feldspar or unidentified brown particles) from a sandy soil, extracted DNA from each particle, and carried out partial 16S rDNA polymerase chain reaction denaturing gradient gel electrophoresis analysis. Bacterial communities located on soil particles of the same type were more similar in composition than communities located on particles of the other types. Thus, the local structure of a bacterial community is related to the type of soil particle, which suggests that a high diversity of soil bacteria emerges through a combination of local bacterial communities on different types of soil particles.

Evaluation of Wear Behavior of Feldspar Particles Reinforced Copper Alloy Composite Materials

The wear behavior of unreinforced as well as feldspar particles reinforced copper alloy (phosphor-bronze) composites was studied as a function of sliding speed and applied loads under unlubricated conditions. The content of feldspar particles in the composites was varied from 1- 5% by weight in steps of 2%. A pin-on-disc wear tester was used to evaluate the wear rate. Loads of 20-160 N in steps of 20 N and speeds of 1.25, 1.56, and 1.87 m/s were employed. The results indicated that the wear rate of both the composites and the alloy increased with increase in load and sliding speed. However, the composites exhibited lower wear rate than the alloy. It was found that above a critical applied load, there exists a transition from mild to severe wear both in the unreinforced alloy and in the composites. But the transition loads for the composites were much higher than that of the alloy. The transition loads increase with the increase in weight % of feldspar particles, but decreases with the increase in sliding speeds.