Coagulation Of Fine Particles Research Articles

Identification of conditions for ultrasonic effect on gas-dispersed medium and creation of radiators to increase the efficiency of coagulation in devices with swirling flow

Relevance. The presence and uncontrolled distribution of aerosols of various substances in the air, which have a negative impact on humans, flora and fauna. This problem is especially acute in the extraction, processing and combustion of georesources. The most effective way to solve the problem is the use of high-intensity ultrasonic vibrations, the effect of which on aerosols causes convergence and agglomeration of small particles into large ones. However, at low concentrations, the particle coagulation efficiency is not sufficient to increase the recovery rate of gas treatment equipment. Therefore, there is a need to find new ways to optimize ultrasonic equipment for coagulation of fine particles in order to increase its efficiency. Aim. To determine the optimal conditions for ultrasonic influence on a swirling gas-dispersed flow, ensuring maximum efficiency of agglomeration of highly dispersed particles. Carrying out comparative studies of coagulation of particles when exposed to ultrasonic fields generated by different types of radiators and their combined effects will make it possible to determine the effectiveness of ultrasonic coagulation and the optimal design scheme of ultrasonic exposure. Objects. Coagulation of particles under ultrasonic impact, formed by various types of radiators. Methods. Computer modeling of the generated ultrasonic field using the finite element method using harmonic acoustic analysis. Finite element modeling and design of disk radiators using modal analysis. To determine the characteristics of the aerosol, a Malvern Spraytec Particle Analyzer was used. Results. The results of calculations and experiments have shown that the use of an extended ultrasonic tubular radiator operating on a bending-diametric mode of vibration and forming a ring standing wave with a sound pressure level of 162–165 dB as the main source of ultrasonic impact for devices with swirling flows may be the most energy efficient. Further increase in the efficiency of coagulation can only be achieved by the combined action of a tubular radiator and a longitudinally oscillating radiator. This significantly modifies the field structure and provides not only an increase in the sound pressure level (up to 167 dB), but also in the number of formed nodal surfaces (up to 44).

Organic Matter, Agricultural Use, and Dispersion of Ferralsols for Grain Size Analysis

ABSTRACT Ferralsols are a class of highly weathered, oxidic and often acidic and low fertility soils ubiquitous of the tropical environments. Ferralsols can present anomalous behavior when dispersion is performed for grain size analysis using settling methods. This study evaluates the effect of total dispersion and dispersed solution stability of two Ferralsols from Brazil, under cultivated areas and native savannah vegetation with or without organic matter removal using hydrogen peroxide (H2O2), on percent clay, silt, and sand estimation. Samples of a Rhodic Ferralsol and an Orthic Ferralsol were dispersed using a reciprocating shaker for 16 h at 120 rpm in sodium hydroxide (NaOH) solutions. Results show that chemical modifications associated with agriculture alter the dispersion behavior of the two Ferralsols. Removal of organic matter in cultivated areas caused coagulation of fine particles. For native vegetation sites, removal of organic matter increased soil dispersion increasing clay content and decreasing sand content. NaOH was not an effective dispersant agent in all conditions and thus there is a need for investigating better chemical compounds or combinations of thereof for the dispersion of Ferralsols. Standardization of grain size analysis of Ferralsols is needed for comparisons between different studies and laboratories to be possible.

Influence of H2O and SO3 on fine particles coagulation for sintering flue gas after desulfurization in an alternating electric field.

Electric coagulation of fine particles has been studied in the simulated sintering flue gas after semi-dry desulfurization to quantify the influence of H2O and SO3. The electric coagulation platform has a DC charging zone and an AC coagulation zone. Fine particles were divided into different diameter intervals to deeply explore the impact of H2O and SO3, including less than 0.15μm (PM0.15), 0.15-0.5μm (PM0.15-0.5) and 0.5-1μm (PM0.5-1). The particle charge, mass fractions of fine particles, and the mean diameter are measured and compared under water and SO3 atmosphere. The experiments showed that the increasing AC voltage helps particles larger than 0.5μm to coagulate but has little effect on the rest particles without H2O or SO3. Both H2O and SO3 enhance the PM1.0 AC coagulation. When flue gas relative humidity went up from 20 to 80%, the charge per particle maximally increased by 120%, as well as the mass fraction of PM0.5-1, PM0.15-0.5, and PM0.15 decreased by 83.2%, 64.5%, and 66.6%, respectively. When the SO3 concentration rose up from 0ppm to 12.3ppm, the charge per particle maximally increased by 100%, as well as the mass fractions of PM0.5-1, PM0.15-0.5, and PM0.15 decreased by 54.5%, 28.6%, and 33.3%, respectively. The impact of water and sulfuric mist on the particle intervals was sequenced as: PM0.5-1 > PM0.15 > PM0.15-0.5. The influence on PM1.0 AC coagulation was sequenced as H2O > sulfuric mist > AC voltage. Through data regression, H2O had approximate linear correlation with the particle mass fractions while the impact of sulfuric mist was non-linear. The interparticle forces were calculated to analyze the dominant force of particle AC coagulation with water: liquid bridge force > Coulomb force > > van der Waals force. The liquid bridge force indicated that liquid film was form on the surface of fine particles when water or sulfuric mist was added into the system which was the main reason enhancing the AC coagulation.

Acoustic waste water clarification practices

The article covers the problems of reagent-free clarification of circulating and waste waters of enterprises with their production sites located in valleys of spawning rivers in the environmentally-sensitive northern territories. It is shown that horizontal sumps, widely used at mining enterprises due to their low construction and operation costs, fail to ensure the production and environmental indicators required in the current conditions. The article analyses the results of 20 years of application in the Russian Federation and the countries of the Asia-Pacific region of the complex acoustic method (CAM), based on the mechanisms of coagulation of fine particles, forced sedimentation of initial and coagulated particles, as well as sludge thickening and dewatering. The advantages and limitations are shown for the CAM method, developed by the author of the article and based on the principles of: complexity, with the use of the laws of linear and nonlinear acoustics; acoustic impact on the water system for the purpose of acoustic degassing of water; acoustic coagulation of fine suspended solids (and subsequent gravity sedimentation of the newly formed aggregates); acoustic (forced) sedimentation of the original and previously acoustically coagulated suspended solids; acoustic thickening of sludge in sumps and acoustic dewater ing of sludge at depositing sites with drainage systems; the cascade (boundary) nature of acoustic impacts on the water system in the main water catchers, sumps, etc. The specific behavior of processes under a complex acoustic impact ensures their high productivity and low power consumption values (unattainable by any other methods) and the required environmental safety in the special conditions of the Far North and the Far East.

Turbulent coagulation of micron and submicron particles in swirling flow

Coagulation of fine particles in turbulent swirling flow is investigated experimentally and numerically. First, different swirl producers are compared and helical blade is adopted due to its enhanced diffusion and convection in the radial direction. Then, study on structural parameters of helical blade is carried out, the result shows that smaller diameter of inner blades or shorter axial spacing between inner and outer blades can create better performance. Finally, research on the effect of operating parameters is conducted. The result implies that lower velocity or higher particle concentration helps improve coagulation performance, since diffusion and particle interaction are strongly affected by the turbulent two-phase flow field. The patterns of coagulation for micron and submicron particles are slightly different due to varied particle dynamics, specifically, breakup is an important factor for larger particles. Rising temperature has positive effect on coagulation of submicron particles because of enhanced thermal motions. Comparatively, the thermal effect is negligible for the micron particles. The study analyzed the mechanism behind turbulent coagulation in swirling flow, from which directions for optimal design are provided.

Emission characteristics of parent and halogenated PAHs in simulated municipal solid waste incineration

With a self-designed small-scale waste incinerator, emission behaviors of parent and halogenated polycyclic aromatic hydrocarbons (PAHs and HPAHs) were simulated and visualized. According to our results, the 2–3 ring PAHs have higher emission factors (EFs) than those of the 4–6 ring PAHs during waste incineration. The EFs of individual HPAHs are comparable in all incineration products. Overall, the EFs of Ʃ16PAH and Ʃ3ClPAH decreased in the order of gas > bottom ash > particle > fine particle while the EF order for Ʃ6BrPAH is bottom ash > particle > gas > fine particle. Based on qualitative observation, the size distributions of Σ16PAH, Σ3ClPAH, and Σ6BrPAH were characterized by trimodal peaks. Coagulation of fine particles in air may lead to enrichment of target compounds in the coarse particle fraction. The gas-particle partition did not reach theoretical equilibrium and most PAHs and HPAHs were absorbed inside the organic carbon. Estimated mass emission of target compounds in Shenzhen suggests that the gaseous phase from MSW incineration is the major contributor to the urban environment. However, automotive emissions contribute more to urban air pollution than MSW incineration in Shenzhen. Generally, compared with other real waste treatment, waste incineration is a more efficient method for waste-to-energy recovery and produces fewer pollutants, although the resultant carcinogenic substances are never truly harmless.

A particle size distribution analysis method to quantitatively evaluate coagulation of fine particles in aqueous solutions

ABSTRACTA laser particle size analysis method was proposed to quantitatively evaluate the fine particles coagulation. Laser particle size analyzer was used to measure the particle size distribution of coal slime at different stirring rates and different concentrations of Ca2+ or Na+. The value of d10, d50, and d90 can be used to quantitatively evaluate the coagulation performance of fine particles, the greater value of d10, d50, and d90 they are, and the better coagulation performance it is. It was found that the addition of Ca2+ could promote easier coagulation for fine particles than the addition of Na+, and the best coagulation performance, in which d90 was greater than 700 µm, occurred at the conditions of 1000 rpm stirring speed and Ca2+ concentration above 5 mmol/L. It is because that the electronegativity of coal and clay particles would be weakened in the presence of Ca2+, and the electrostatic repulsive force of fine particles would be reduced, resulting in the fine particles becoming easy to coagulate. Moderate stirring speed could provide kinetic energy for particle to cross the energy barrier of two colloidal particles. On the contray, coagulated particles broke up when the stirring speed reached a high level.

FLOCCULATION/DISPERSION OF HEMATITE WITH CAUSTIC DIGESTED STARCH

Selective flocculation of hematite with starch is a process well-known in practice. However, the separation of hematite from other minerals depends strongly on the methods of starch digestion performed either as heating-digestion or alkali-digestion (different type and dosage of alkali). The purpose of this study is to identify possible influence of the alkali-digested starch on flocculation of ultra- fine hematite when the starch was digested at different concentrations of sodium hydroxide at room temperature. Adsorption of starch digested with sodium hydroxide at different concentration on hematite was investigated by abstraction and co-precipitation tests. Turbidities tests, settling rates, flocculation/dispersion measurement and Fourier transform infrared spectroscopic analysis (FTIR) have also been conducted. Based on the results of the above mentioned tests it is suggested that the flocculating power of caustic digested starch towards fine particles may be significantly weakened, while its dispersing ability starts to play a role instead, if the concentration of sodium hydroxide is high enough in starch digestion. When the weight ratio of NaOH /starch is lower than 2, incomplete gelatinization of starch granules may lead to coagulation of fine particles of hematite mostly due to non-selective electrostatic attraction. The weight ratio of NaOH /starch from 2 to 4 helps to flocculate mineral surfaces selectively and efficiently, assuring a complete digestion of starch granules and a small amount of acidic functional products on the starch chain. However, much smaller and homogenous short-chain granules resulting from higher concentration of sodium hydroxide (the weight ratio of NaOH /starch is more than 4) used to digest starch may weaken the flocculating capacity of the caustized starch for hematite and lead to its dispersion.

Acoustic Coagulation of Fine Particles from WFGD

The objective of this study is employing acoustic coagulation to induce agglomeration of fine and ultrafine particles after wet flue gas desulfurization (WFGD) and analyzing its effectiveness and characteristic based on numerical simulation. Matters such as calcium sulfate and calcium sulfite in WFGD can form very fine particles. Smoluchoski’s equation is employed as the simulating model. Orthokinetic coagulation, hydrodynamic coagulation and Brownian coagulation are taken into account to form the agglomeration kernel. An improved sectional arithmetic is introduced to achieve sectional size adjusting automatically according to the mass concentration of particles, so that section size is fine where the mass concentration is large to guarantee computational accuracy, but coarse where the mass concentration is small to save computation time. Besides, mass conservation rate is introduced to estimate the calculation error in the compute of mass concentration. Simulation results show that the overall number concentration decreased more than 40% after acoustic wave acting on the flue gas for 2 second; Increasing sound intensity level (SIL) is more effective to coagulation than increasing frequency; There exists an optimal acoustic wave frequency within 1500~2000Hz; Coarse particles are more sensitive to acoustic wave frequency than fine particles.

Method of Taylor Expansion Moment Incorporating Fractal Theories for Brownian Coagulation of Fine Particles

Abstract Fine particles aggregating into larger units or flocculation body is a random combination process. Increasing the size and density of flocculation body is the main approach to rapid particle removal or sedimentation in water. Aiming at the Brownian coagulation of fine particles, a new method of Taylor expansion moment construction of fractal flocs has been developed in this paper, incorporating the Taylor expansion approach based on the moment method and the fractal dimension of the floc structure originated from fractal theories. This method successfully overcomes the limit of previous moment methods that require pre-assumed particle size distribution. Results of the zero and second order moments of Brownian flocs from the proposed method are compared with those from the Laguerre method, integral moment method and finite element method. It is found that the higher accuracy and efficiency of computation have been achieved by the new method, compared to the previous ones. Effects of the fractal dimension on the zero and second order moments, geometric average volume and standard deviation are also analyzed using this method. The self-conservation characteristics of particle distribution is observed without presumption of initial distributions.

The mechanism of improving the dehydration and viscosity of municipal activated sludge (MAS) with calcined magnesia

To deal with the problems of water content and high viscosity in municipal activated sludge, which lead to a restriction in resource utilisation, we used calcined magnesia to treat the sludge. As shown in the X-ray diffraction analysis, compared with untreated municipal activated sludge, the mineral composition, including kaolin [Al 2Si 2O 5(OH) 4] and chloritoid [(Fe, Mg)Al 2Si 2O 5(OH) 2], in the municipal sludge treated with calcined magnesia dramatically changed. Because its intramolecular water disappears and a portion of the water content is evaporated during the reaction between the calcined magnesia and water, the dehydration rate of the municipal waste activated sludge increased, the drying time was shortened to 5.30 min and the dried coat thickness increases at least 3-fold. Using a scanning electron microscope, we determined that using calcined magnesia to treat municipal activated sludge leads to a coagulation of fine particles and an increase in rough particles, along with a reduction in soil particles of less than 0.01 mm by up to 69%. Using calcined magnesia to treat the municipal activated sludge can improve its dehydration properties and lower the viscosity and cost in a simple operation. Additionally, it provides magnesium to plants for thermophilic fermentation, creating favourable conditions for aerobic composting.

Water Coagulation Using Electrostatic Patch Coagulation (EPC) Mechanism

Coagulation of fine particles to form large flocs is an essential step to reach efficient dewatering of wet materials. The electrostatic patch coagulation (EPC) mechanism was applied in this study to remove turbidity and natural organic matters in water using four different dosing-mixing schemes. Sufficient rapid mixing and slow mixing or applying two-stage coagulation benefit removal of turbidity. The EPC mechanism could only efficiently remove organic matters of molecular weight of 7500–10,000 Da. Only sufficient rapid mixing is relevant to organic matter removal. The mechanisms for natural organic matters (NOM) removal are proposed to be complexation of ions and NOM to form insoluble aggregates to be separated by membrane filtration.

A model for the particulate matter enrichment with toxic metals in solid fuel flames

A mathematical model for predicting the fate of toxic heavy metals during combustion is presented. The model accounts for the formation of new particles through nucleation and the growth of existing particles through the combined effects of condensation and coagulation. A key simplification enabling the development of a usable methodology is the subdivision of the particle size distribution into just two modes, one comprising fine particles and the other coarse particles. The toxic heavy metal calculations are embodied in a post-processor appended to a parent code for the prediction of the aerodynamics and combustion. Three flames are studied for a coal fuel, sewage sludge fuel and a blend of these two fuels. The partitioning and emissions of the semi-volatile metals, lead and cadmium, are predicted and compared with data collected in a large-scale laboratory combustor. The predicted metal enrichments on the small particles are remarkably well-predicted. However, it is concluded that heterogeneous condensation of the metal vapours alone is insufficient to explain fully the fate of metal vapours. Surface reaction and gas phase chemical reaction should also be considered, but the necessary chemical kinetic data are currently lacking. The results indicated that ash mineral matter, such as kaolinite, is an effective sorbent for lead, but not for cadmium. As expected, the coagulation of fine particles is influenced more by the particles number density than by combustion variables. It is also found that the scavenging of fine particles by coarse particles has little effect on the metal partitioning.

Crystal Growth of γ‐Lithium Aluminate in Molten Li/K Carbonates

The electrolyte tile of molten carbonate fuel cells consists of a matrix prepared from lithium aluminate powders impregnated with molten alkaline metal carbonate. The increase in lithium aluminate particle size in the molten carbonate accelerates degradation of the electrolyte tile. We investigated the mechanism of lithium aluminate particle growth. Results indicate that, although the particles basically grow through a dissolution‐precipitation mechanism, with lithium aluminate passing through the molten carbonate, growth tends to occur readily in the interior of agglomerates resulting from the coagulation of fine particles. As fine pores fill fully with lithium aluminate precipitate in the interior of the agglomerates, and then are amalgamated into other surrounding particles, the particles can grow at higher rates than individual particles, which grow by the dissolution‐precipitation mechanism.

微粒子の分散と凝集 基礎と応用

微粒子の分散と凝集 基礎と応用

Optimum Design of a Solid-Liquid Stirred System by Taking into Account the Propagation of Turbulent Energy

Abstract The mixing behavior of material in a stirred vessel is generally governed by macromixing due to circulating convective flow and micromixing due to turbulent fluctuating flow. The mixing energy is consumed more in micromixing than in macromixing, and hence the propagation of turbulent energy has to be evaluated explicity for the optimum design and scale-up formulation. The energy spectrum function of turbulence in a stirred vessel was derived from the Eulerian time correlation function of fluctuation velocities, and then the decay of turbulent energy was evaluated by the spectrum function. The stochastic mean of the fluctuating velocities, the integral space scale of turbulence, and the energy dissipation rate were correlated with the operating variables of the stirred vessel, and the spatial distributions of these characteristics were calculated in the macromixing and/or micromixing flow fields. Particle behavior in a solid-liquid two-phase system was numerically analyzed by using an axial diffusion equation with a space variant diffusion coefficient. Finally, as a mass transfer model the turbulent diffusive coagulation of fine particles was evaluated in reference to the optimum design of the stirred vessel.

Géologie et géochimie du fleuve, de l'estuaire et du golfe Saint-Laurent (Canada)

This article provides an outline of conditions of particulate material and sediments in the river, estuarine, and gulf sections of the St. Lawrence (Québec, Canada). The concentration of solids in the river above lac St. Pierre varies between 4 and 10 mg/L, whereas downstream towards Québec the concentrations rise to 30–50 mg/L. With the exception of the Sorel delta, this section of the river does not constitute a major sink of sedimentary materials, but the surface sediments of the river are enriched with phosphorus, polychlorinated biphenyls, copper, and lead. The portion immediately upstream from Île d'Orléans is the interface of riverine water and salt water from the Gulf of St. Lawrence and at this point is a region of high concentrations of suspended solids (up to 300 mg/L). The process of sedimentation in the estuary is complicated by the coagulation of fine particles after contact with salt water. As a result, there is a zone of high sedimentation rates of fine participates enriched in phosphorus, organic matter, and polychlorinated biphenyls in the area of Île d'Orléans, making constant dredging necessary. Downstream from Île d'Orléans is a decrease from 40–80 mg/L suspended solids to 1–2 mg/L in the Gulf of St. Lawrence.

Mojave Playa Crusts: Physical Properties and Mineral Content

ABSTRACT Field observation suggests five distinct crustal types among the playas of the Mojave Desert, southern California, as follows: (1) Hard, dry, smooth, compact and impermeable crusts, generally with low water tables, ordinarily contain in excess of 50 percent clay-size particles, average about 7.0 percent carbonate, and contain about 5.0 percent or less soluble salines. (2) Soft, porous and moderately permeable surfaces ordinarily contain less that 35 percent clay-size particles, average about 2.0 percent carbonate, and contain more than 5.0 percent soluble salines. When clay is covered, introduction of moisture to the surface produces a self-rising ground or surface. High water tables are common to these surfaces and vehicular traffic is poorly supported. (3) Salt pavements, (4) calcareous crusts, and (5) permanently wet crusts constitute three additional types recognized in the field. Combinations of two or more types may also occur in one playa. Salt pavements and wet crusts are often found in the same playa basin with puffy crustal types. These playas, although not distinct crustal types, have been referred to as compound surfaces. Contacts between surface types are gradational and appear to follow definite trends suggesting mineralogic control. Some crusts contain 35-49 percent clay-size particles and moderate amounts of carbonate and soluble salts. Although these surfaces are megascopically indiscernible from clay crusts, they are more susceptible to physical change when exposed to precipitation. These surfaces are considered as a variation of the clay crustal type. Laboratory examination indicates that type depends in a large measure upon the nature, proportions, and particle-sizes of the mineral constituents combined with the presence or absence of moisture. Strength, compaction, and permeability are shown to be interrelated with mineral content. The mineral content of crusts depends in a large measure on lacustrine conditions of sedimentation, largely Pleistocene. The high-carbonate clay crusts as now found appear to demonstrate slow flocculation of clay particles in relatively low alkali-chloride basins. Carbonate or possibly bicarbonate phases may have acted as peptizers which inhibited clay flocculation and led ultimately to a wide, homogeneous, distribution of clay particles. Slow settling of clays resulted in a dense, compact clay mass with a high degree of particle alignment. Mutual clay-carbonate precipitation may have resulted in a surface interaction between the phases. Basin water of high alkali-chlorinity electrostatically induced rapid coagulation of fine particles. The resulting sediment texture was heterogenous, with clay particles aligned in a haphazard manner. Salt, clay, and silts were intermixed. These factors facilitate brine percolation and result in a mineral complex producing puffy, saliniferous, wet, and compound crusts. Local geologic factors may influence ground water and brine movement in crusts so that secondary mineralization may alter original assemblages. These altered areas are generally of minor aerial extent as compared to the playa as a whole, and are easily recognized.