Surface Of Ash Particles Research Articles

Sulfur in Tephra of Opala Volcano Eruption ca. 1500 years ago, Kamchatka

Sulfur-bearing compounds of Plinian-type volcanic eruptions can be transferred with ash particles of distal tephra over considerable distances. Average sulfur content in tephra of Opala volcano (Kamchatka, eruption ca. 1500 years ago) comprises 310 ppm with maximum concentration up to 800 ppm. Connection detected between sulfur content in bulk samples and the particle size distribution – sulfur is predominantly contained in the fraction 0.25‒0.50 mm represented by elongated ash particles with elongated gas pores 1.0‒10.0 mkm in diameter. The most likely reason for the dependence of sulfur content on the texture of ash particles is preservation of sulfur compounds of the water-soluble complex inside gas pores. Sulfur-containing compounds deposited on the surface of ash particles were removed by precipitation in the process of existing tephra in continental environment. Ingress of ash particles into bottom sediments containing sulfur compounds on the inner surface of gas pores during plinian type eruptions similar to the eruption of Opala volcano ca. 1500 years ago, may influence the geochemistry of lithogenesis and lead to redistribution of elements sensitive to the presence of acid-forming agents in the sediment at the stage of diagenesis.

Influence of ball materials on the surface activation behavior of coal ash particles during a mechanochemical process

In this study, the surfaces of coal ash particles were activated via a planetary ball mill-assisted mechanochemical process by utilizing balls that were made from different materials such as zirconia, alumina, and iron. The influence of ball materials on particle morphology, crystallinity, chemical structure, and elution of Si and Al ions in alkali solvents were systematically investigated for the first time, during when the impact energy and friction force induced on the coal ash surface was also clarified in details via the assistance of a self-constructed system. It was found that the mechanochemical process performed with zirconia and iron balls featured a preferred “grinding effect” with decreasing particle size and increasing specific surface area. This was due to the efficiently impact energy induced. In contrast, alumina balls featured an “activation effect” by inducing crystal distortion on the surface and thereby, promoting the ion elution within the alkaline solvents.

Lowering efflorescence potential of fly ash-based geopolymers by incorporating butyl stearate

This paper reports the incorporation of butyl stearate into fly ash-based geopolymers to lower the efflorescence potential. Three incorporation ways are comparatively studied, i.e., matrix distribution: fly ash particle surface modification (PM), lamination: inserting layered butyl stearate sheet in the binder (LS), and coating: surface treatment of hardened bulk samples (ST). Results show that the use of butyl stearate does not change the amorphous feature of activation products but increases the contact angle of the surface. It hinders the capillary water absorption and ion transportation, effectively slows down the formation of efflorescence. Compared with PM and LS samples, the surface treated ST samples have the lowest accumulative leaching of Na+ (76 mg), the lowest water absorption (0.07%), the lowest porosity (7.5%), and the highest compressive strength (14.08 MPa) after accelerated efflorescence. The microstructure analysis results obtained in this study provides a useful insight for the efflorescence control for fly ash-based geopolymers, and suggest that for this particular type of very porous geopolymer, surface treatment of a bulk product may be the best choice.

Insight into the mechanism of gasification fine slag enhanced flotation with selective dispersion flocculation

Coal gasification fine slag (CGFS) produced in the coal chemical industry has caused severe environmental pollution and resource waste. To realize the utilization of CGFS, we have to efficiently separate unburned carbon (UC) in CGFS. In this work, based on the discovery of the covering between CGFS particles, the selective dispersion flocculation flotation method is proposed to improve the efficient separation of UC from CGFS. The mechanism of selective dispersion flocculation is revealed through adsorption mode, interaction force between particles, and the particle size distribution of floc under different reagent conditions. Results show that a hydrophilic layer is formed on the surface of ash particles, which hinders the adsorption of PAM and ash particles due to the chemical adsorption of SHMP with ash particles. However, carbon particles are not affected by SHMP and can be directly adsorbed with PAM. This selective adsorption dominates the interaction force of adsorbed particles, and then controls the agglomeration of particles. After selective dispersion flocculation, the original carbon-ash selective agglomeration state is changed to the carbon–carbon selective agglomeration state. D90 of fine carbon particles changed from 110.21 μm to 356.84 μm. Compared with the traditional flotation process, the combustible recovery rate of foam products is increased by 10.4 % and loss on ignition (LOI) is increased by approximately 5 %. This work is conducive to fundamentally understanding the mechanism of selective dispersion flocculation. It is helpful to guide the separation of carbon and ash from gasification slag in industry.

Clear and Present Dangers: The Multiple Health Hazards of Volcanic Eruptions.

Clear and Present Dangers: The Multiple Health Hazards of Volcanic Eruptions.

PHYSICAL-MECHANICAL PROPERTIES OF COMPOSITES BASEDON LOW DENSITY POLYETHYLENE AND THERMALASH OF HOUSEHOLD WASTE

The article presents the results of a study of the influence of the concentration and disper-sion of household waste thermal ash on the physical-mechanical properties of composites based on low-density polyethylene. Thermal ash was obtained in a thermal furnace at the Balakhani enter-prise in Baku city at a temperature of 1200°C. We studied such properties of composites as tensile yield strength, ultimate tensile stress, elongation at break, and flexural strength. To study the effect of thermal ash dispersity on the properties, three grindings with a particle size were obtained: 80-110nm, 300-500nm and 1200-2000nm. It was found that low-density polyethylene nanocompo-sites with a particle size of 80–110 nm have relatively high strength properties (ultimate tensile stress, tensile yield strength, flexural modulus). It has been shown that, regardless of the dispersion of the particles, the maximum value of the tensile yield strength and ultimate tensile stress is achieved for samples containing 10 wt % of thermal ash. The maximum value of the flexural strength was established for samples with 20 wt % thermal ash content. In order to improve the compatibility of the components in the polymer-filler mixture, a compatibilizer of the Exxelor PO1040 brand was used, which is a graft copolymer of polyethylene with maleic anhydride (content of maleic anhydride 5.6 wt %). According to the data obtained, loading of the compatibilizer con-tributed to a significant improvement in the compatibility of the filler with the polymer, which was expressed in an increase in the strength properties of the composites. A theoretical substantiation is given for the regularities found in the change in the physical-mechanical properties of compo-sites depending on the dispersion and concentration of thermal ash. IR spectral analysis of the composites showed characteristic absorption bands of thermal ash alone and as part of low density polyethylene. The shift of absorption bands in the composition of the polymer matrix made it pos-sible to assert the probability of physical interaction of macrochains with the surface of thermal ash particles. The results of the study of the melt flow index of composites are presented. It has been established that loading of thermal ash in some cases leads to an increase in the fluidity of the melt of polymer composites.

Differences between the composition of surface and inner layers of fly ash particles

By studying samples from Czech power plants burning brown coal using X-ray photoelectron spectrometry (XPS) have demonstrated differences in the composition of the ashes in their surface and subsurface layers. The main components of the samples were compounds of aluminum, silicon and oxygen - aluminosilicates. Other elements included sulphur, fluorine and in some cases demonstrably calcium, sodium, magnesium, fluorine and iron. The largest part of the carbon compounds present is the so-called "adventitious carbon", contaminating carbon, i.e. hydrocarbons adsorbed on the surface from the atmosphere. Others come from technology including a small amount of carbides. Distribution of sulphur and iron compounds detected using a short time ion etching is in most cases following: sulphur compounds are concentrated on the surface of ash particles while iron compounds are typically concentrated inside. Differences in composition of surface layers were found to be significant as in the surface composition as in theirs depth profiles. Gas evolution was detected in an ash-water reaction test in which the analysis of the gas has shown that it is mainly about hydrogen and carbon dioxide. Another test with water showed the formation of an incrustation and documented the evolution of gases by the formation of bubbles. The released gases can form explosive mixtures with air, which must be taken into account when removing deposits with a water jet.

Catalytic function of ferric oxide and effect of water on the formation of sulfur trioxide

Sulfur trioxide (SO3) is not only environmentally harmful but also highly corrosive, taking a great threat to the safe operation of coal-fired power plants. A dominant pathway of SO3 formation in coal-fired power plant is through the catalytic oxidation of SO2 (SO2+1/2O2→SO3) on the surfaces of ash particles containing Fe2O3. The catalytic formation of SO3 could be affected by complex atmosphere, where the effect from H2O is still debatable. In this paper, density functional theory (DFT) is employed to explore the reaction pathway of SO3 formation catalyzed by α-Fe2O3 in complex atmosphere containing O, O2, SO2 and H2O. In order to get the stable adsorption sites of these species, the adsorption energy of potential adsorption configurations on the α-Fe2O3 (001) surface is calculated. The dissociations of O2 molecule on complete and defect α-Fe2O3 (001) surfaces with O vacancy are calculated, and the Langmuir-Hinshelwood and Eley-Rideal mechanisms for the O(ads) reaction with SO2(ads) or SO2 are compared. The effect of H2O besides of SO2 and O2 on the formation of SO3 is especially discussed. The DFT calculation results show that for the formation of SO3 in gas phase, the energy barrier of ‘SO2+1/2O2→SO3’ is 436.75 kJ mol−1, in contrast, for the catalytic formation of SO3 on α-Fe2O3 surfaces, this energy barrier becomes an order of magnitude smaller, 24.82 kJ mol−1. O2 molecules can dissociate on the defect α-Fe2O3 (001) surface with O vacancy spontaneously, indicating that the defect α-Fe2O3 is favorable for the dissociation of O2, thereby promotes the formation of SO3. The energy barrier of ‘SO2(ads)+O(ads)→SO3(ads)’ through Langmuir-Hinshelwood mechanism is much higher than that of ‘SO2+O(ads)→SO3(ads)’ through Eley-Rideal mechanism. The adsorption energy on the α-Fe2O3 (001) surface of H2O is much smaller than that of SO2 and O2, indicating that H2O has little effect on the adsorption of O, O2, SO2 and eventually the heterogeneous formation of SO3. The DFT analysis results in this study provide a deep understanding on the reaction pathway of SO3 catalytic formation by Fe2O3.

Electroless silver plating on modified fly ash particle surface

Ag-plated fly ash (FA) powders were prepared through modified electroless plating, which could be utilized for manufacturing conductive polymers for Electromagnetic interference (EMI) shielding applications. In order to improve the FA surface activity, alkali cleaning and coupling modification were employed. Extensive characterizations of Ag-plated FA particles were carried out by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. The mechanism of electroless Ag plating was mainly studied by using XPS. The XPS results showed that the diammonia functional group from the coupling agent adsorbed silver ions to form the N-Ag coordination bond and produce pure Ag film. In addition, electrical conductivity and electromagnetic properties were studied by Four-probe resistance tester and vector network analyzer, respectively. The results indicated that uniform and compact Ag films were formed on FA particle surface strongly after alkali cleaning and coupling modification. The electrical conductivity of the as-prepared 0.6-FA-S-Ag particles with a coated thickness of 200 nm was about 8.2 × 10−5 Ω·cm. The electromagnetic parameters and calculated reflection loss indicate that Ag-plated FA powders have no magnetic conductivity and the main contribution of electromagnetic loss comes from dielectric loss.

Study on Modification Technology of High Calcium Ash Steel Slag Composite Based on Microstructure Characteristics

By means of physicochemical modification technology, mineral admixture particles adhere to the surface of high calcium ash particles. On the one hand, mineral admixtures play a role of grinding aids, on the other hand, mineral admixtures are uniformly dispersed and closely contacted with high calcium ash particles. It is conducive to the hydration reaction of high calcium ash particles and reduces the most probable pore distribution and porosity. Active calcium oxide has a high content and contains a certain amount of self-hardening minerals. The single modification method of chemical admixtures can not effectively exert the chemical excitation effect of chemical admixtures on the activity of high calcium ash. High calcium ash and steel slag have great potential for utilization in cement concrete, and their full utilization is beneficial to environmental protection, energy saving and obtaining certain economic benefits. High calcium ash and steel slag admixture technology have achieved certain results. However, it is necessary to further study the activity of high calcium ash and steel slag in the fluctuation range of raw materials. And applied to the preparation of high durability gelation blending amount.

Intra- and inter-particle heterogeneity of municipal solid waste incineration fly ash particles

This study firstly investigated elemental heterogeneity of municipal solid waste incineration (MSWI) fly ash particles. Two types of heterogeneities were measured quantitatively focusing on three structural components of fly ash particles. They are internal heterogeneity of individual fly ash particles (intra-particle heterogeneity) and inter-particle heterogeneities among fly ash particles. On the surface of fly ash particles, Cl, K, and Na have 0–82% larger intra-particle heterogeneities than Al, Ca, and Si owing to KCl/NaCl-based aggregates. Smaller intra-particle heterogeneity of Ca in semi-soluble component than those of Al and Si suggest that semi-soluble Al/Ca/Si-based matrices around insoluble cores are Ca-based materials including aluminosilicate domains. Inter-particle heterogeneities of Al, Ca, and Si in semi-soluble and insoluble components are 9–40% and 49–352% higher than those of fly ash particle surface, respectively. Inter-particle heterogeneity analysis also suggests that insoluble components mainly consists of Si-, Al-, or Ca-rich cores. MSWI fly ash particles have both internal heterogeneities inside their bodies and also are heterogeneous in inter-particle level. When MSWI fly ash becomes wet during chelate treatment, it changed intra-particle heterogeneity as well as inter-particle heterogeneity. Their variations were contrast depending on element and site (fly ash particle component).

Treatment of Lignite Mine Water with Lignite Fly Ash and Its Zeolite

As expected, a zeolite formed from lignite fly ash proved to be far more effective in treating the water from the Neyvelli lignite mines than the fly ash itself. Treatment of mine water at different doses with both materials revealed that the zeolite increased the pH from 2.73 to 8.58 and removed most of the hardness, including the Ca and Mg hardness, as well as the acidity from the mine water. In contrast, the fly ash increased the hardness, Ca, Mg, and sulphate in the mine water. The fly ash was partially effective in removing metals like Mn, Ni, Zn, and Cr. In contrast, increased dosing of lignite fly ash zeolite removed 98.6% of the Mn, 99.94% of the Fe, 96.35% of the Ni, 99.30% of the Cu, 19.15% of the Cd, and 100% of the Zn, Pb, and Cr from lignite mine water. The surface of the lignite fly ash particles were initially covered with loosely attached metals that were released in the acidic water, though due to its alkaline nature, it did partially remove the metals from the mine water.

Monochlorinated to Octachlorinated Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Emissions in Sintering Fly Ash from Multiple-Field Electrostatic Precipitators.

Polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) emissions in fly ash from multiple-field electrostatic precipitators in different sized sintering plants were studied. The monochlorinated-trichlorinated and tetrachlorinated-octachlorinated PCDD/F concentrations were higher for small plants (90 m2) than for medium (91-180 m2) and large (>180 m2) plants. The PCDD/F concentrations and less-chlorinated PCDD/F contributions to the total PCDD/F concentrations increased as the fly ash particle size decreased moving through the precipitator stages; the abundance of monochlorinated-trichlorinated PCDD/F congeners and homologues also increased. The ash particle size and surface area can be directly used to indicate monochlorinated-trichlorinated PCDD/Fs and toxic equivalents (TEQs). Previously ignored PCDD/F emissions in discarded fly ash were identified. Estimated total monochlorinated-trichlorinated PCDD/F and TEQ emissions in discarded fly ash were 155 and 1.979 kg TEQ, respectively, in 2003-2014, and the ratio between annual PCDD/F emissions in discarded fly ash and flue gases has gradually increased. Reductions in monochlorinated-trichlorinated PCDD/F emitted in flue gas and fly ash in 2003-2014 were 28 and 40 kg, respectively, because of the phasing out of small-scale plants. Reductions in TEQs emitted in flue gas and fly ash in 2003-2014 were 7476 and 180 g TEQ, respectively.

Behavior of radioactive cesium during incineration of radioactively contaminated wastes from decontamination activities in Fukushima

Large volumes of decontamination wastes (DW) generated by off-site decontamination activities in Fukushima Prefecture have been incinerated since 2015. The behavior of radioactive cesium during incineration of DW was investigated at a working incineration plant. The incineration discharged bottom ash (BA) and fly ash (FA) with similar levels of radiocesium, and the leachability of the radiocesium from both types of ash was very low (<1%). These results are significantly different from those obtained for the incineration of contaminated municipal solid waste (CMSW) reported in earlier studies. The source of radiocesium in DW-FA is chiefly small particles derived from DW and DW-BA blown into the flue gas, not the deposition of gaseous synthesized radiocesium compounds on the surfaces of ash particles in the flue gas as observed in CMSW incineration. This source difference causes the behavior of radiocesium during waste incineration to differ between DW and CMSW.

How does aluminium foaming agent impact the geopolymer formation mechanism?

Aluminium is widely used as a foaming agent in lightweight geopolymer concretes. The impact of aluminium reaction on the phase evolution of fly-ash based geopolymers is investigated. In-situ Fourier transform infrared spectroscopy (FTIR) is used to track the changes in the nanostructure of geopolymers. By combining the FTIR functional group analysis with Atomic-force microscopy (AFM) results, it is possible to evaluate the phase development during the early hours of reaction. At the initial stages of geopolymerization, aluminium reaction induces the formation of aluminium hydroxide gel which precipitates on fly ash and conceals the reactive surface of ash particles. Therefore, the dissolution rate of fly ash declines and the strength development is delayed. The high release rate of alumina into the solution, as a result of the aluminium metal reaction, leads to a better connectivity of unreacted particles and better microstructural development as shown in SEM images. Also, by consuming part of the sodium hydroxide catalyst at the beginning of the reaction, aluminium powder protects some of the alkali content of geopolymer matrix from carbonation.

Comparative Analysis of the Physical and Chemical Properties of Different Biomass Ashes Produced from Various Combustion Conditions

The ash yield, composition, mineral phases, and other physical and chemical properties of various biomass ashes are dependent on ashing temperature. To fully understand the impacts of biomass species and ashing temperature on the characterization of biomass ashes, three kinds of biomass fuels were treated at different ashing temperatures to produce biomass ashes. Their properties were analyzed by a series of qualitative and quantitative methods, including X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), thermal gravimetric, and differential thermal analyzer (TG-DTA). The experimental results indicated that as the ashing temperature was raised, the ash slagging tendency could be enhanced. The fused layer on the surface of ash particles was coated with potassium chloride, which was the key reason for the development of severe agglomeration and slagging. Due to the high carbon content and large number of pores in the lower temperature ashes, a low-cost adsorbent could be developed effectively from these carbon materials. The thermal decomposition of all ashes showed a stepwise mechanism. The total weight loss of the same biomass ash decreased with increased ashing temperature, which corresponded well with the phase transitions and thermal reaction sequences.

Porous Structure of Municipal Solid Waste Incineration Bottom Ash in Initial Stage of Landfill

For quantitative estimation of the intra-layer porous structure in the initial stage of landfill formation with municipal solid waste incineration (MSWI) bottom ash, the water absorption of individual MSWI bottom ash particles was measured under still-water, degassed, and agitated conditions. The ratio of the water absorption rate found for the still-water procedure to the effective absorption capacity which was the one under degassing was 35.2%. In the water flow experiment of a column filled with MSWI bottom ash, the true density of the bottom ash was higher after water flow than before, which indicated that dissolution of the soluble components of the bottom ash particle surfaces resulted in a loss of apparent particle volume that more than offset the accompanying weight loss. The volume-based water absorption rate found for the bottom ash particles following 50 mL/h water flow through the column, as a ratio to the effective absorption capacity was about 51.8% of the effective absorption capacity. In a landfill layer comprised of MSWI bottom ash, it was suggested that some regions of the ash particle interiors underwent almost no contact with water.

Effects of wall temperature on slagging and ash deposition of Zhundong coal during circulating fluidized bed gasification

Zhundong coal with a large reserve is faced severe ash-related problems including slagging and fouling during pulverized-coal boiler combustion. The gasification in circulating fluidized bed is a good way to use Zhundong coal due to the low reaction temperature, while it is unknown for the slagging and ash deposition mechanism of Zhundong coal during circulating fluidized bed gasification. In this paper, the gasification of Zhundong coal was tested in a 0.4t/d CFB test rig simulating the real industrial device. Ash deposition probes were installed along the gas flow direction to characterize its slagging and ash deposition at different wall temperatures. These probes were treated with three cooling methods (no cooling, air cooling or water cooling) to reach different wall temperatures (882–737, 665–429 and 81–45°C). The results reveal that deposition was affected greatly by wall temperature. Mineral elements including Na, Ca, Fe, Al and Si were likely to accumulate in deposits on high-temperature surfaces, and existed in the forms of silicates and sulfates at wall temperature above 882°C, resulting in slagging. Although the contents of most mineral elements in the deposits on cooled surfaces were always low, a large gas-wall temperature gradient triggered the condensation of gaseous species, such as Na, Cl and K. The CaSO4 and CaO in gases were condensed and restructured in an ordered crystalline array on the surfaces of ash particles, forming a coating layer that made the ash particles stickier. Chemical composition and crystallographic analyses show that the properties of deposits on the probes and gas-borne ashes were different. More mineral phases as well as sodium were present in deposits. Additionally, due to the Cl enrichment on air-cooled surfaces, the corrosion of the metal surfaces should be focused.

Prediction of sulfuric acid dew point temperature on heat transfer fin surface

Sulfuric acid dew point temperature is an important parameter denoting the dew point corrosion. The sulfuric acid dew point temperature is calculated by considering both the vapor–liquid equilibrium effect and multi-component diffusion effect. In addition, the local distribution of acid dew point temperature on fin surface is numerically predicted for the first time. The influences of fuel type (sulfur content, water content and ash content), wall temperature, excess air ratio, flue gas inlet velocity, fly ash particle (size and quantity) and heat transfer fin structure on the sulfuric acid dew point temperature are discussed. The results show that different types of fuels (which differ in gas composition and combustion temperature) have a great impact on the sulfuric acid dew point temperature. The sulfuric acid dew point temperature decreases with the reduction of excess air ratio, the increasing of wall temperature, and the condensation of sulfuric acid vapor on ash particle surface. The sulfuric acid vapor condensates more seriously on the tube windward than on the leeward. The novel types of heat transfer fins with high heat transfer performance can also reduce the local sulfuric acid dew point temperature, and the maximum reduction of sulfuric acid dew point is 4.1 K between the novel fin surface and the original H-type fin surface.

Nanoscale surface modification of Mt. Etna volcanic ashes

Ashes emitted during volcanic explosive activity present peculiar surface chemical and mineralogical features related in literature to the interaction in the plume of solid particles with gases and aerosols. The compositional differences of magmas and gases, the magnitude, intensity and duration of the emission and the physical condition during the eruption, strongly influence the results of the modification processes. Here we report the characterization of the products emitted during the 2013 paroxysmal activity of Mt. Etna. The surface features of the ash particles were investigated through X-ray photoelectron spectroscopy (XPS) and Transmission electron microscopy (TEM) allowing the analysis at nanometer scale. TEM images showed on the surface the presence of composite structures formed by Ca, Mg and Na sulphates and halides and of droplets and crystals of chlorides; nanometric magnesioferrite and metallic iron dendrites are observable directly below the surface. From the chemical point of view, the most external layer of the volcanic glassy particles (<5nm), analysed by XPS, presents depletion in Si, Mg, Ca, Na and K and strong enrichment in volatile elements especially F and S, with respect to the inner zone, which represents the unaltered counterpart. Below this external layer, a transition glassy shell (thick 50–100nm) is characterized by Fe, Mg and Ca enrichments with respect to the inner zone. We propose that the ash particle surface composition is the result of a sequence of events which start at shallow depth, above the exsolution surface, where gas bubbles nucleate and the interfaces between bubbles and melt represent proto-surfaces of future ash particles. Enrichment of Ca, Mg and Fe and halides may be due to the early partition of F and Cl in the gas phase and their interaction with the melt layer located close to the bubbles. Furthermore the formation of volatile SiF4 and KF explain the observed depletion of Si and K. The F enrichment in the external ∼50nm thick layer of the glassy particles suggests the resorption of this element during the rise from depth less than 400m below the summit vent. During the eruption, the gas/ash interaction persists inside the plume where further changes on the particle surface occurs. Gaseous S, Cl and F react causing the formation of solid Ca, Mg, Na and K compounds, while SiF4 was released as volatile phase and HF was physisorbed. Finally, in the low temperature plume zone, halides previously formed continuously react with gases producing sulfates.