Effect Of Solids Concentration Research Articles

Effect of solid content, particle size, and deflocculant on rheological properties of kaolin suspensions

In this research, two different particle sizes of kaolin were selected, and their rheological properties were characterized by steady-state and dynamic rheological tests. Stress relaxation in the flow curves was a novel finding; redefinition and interpretation of flow curves were the focus of our research. Two methods were used and compared for determining the yield stress. The results showed that suspensions with higher solid content and smaller particle size showed more compact inter-particle interactions, exerting multiple stress relaxation and a strong yield and viscoelastic characteristic. The thixotropic properties were also strongly affected by solid content and particle size, and the differences were reflected in the structural recovery capability. Finally, the effects on rheological properties by introducing deflocculant were studied; the stress relaxation disappeared gradually, and storage modulus and yield stress increased.Moreover, kaolin suspensions with smaller particle sizes required more deflocculant for adsorption and electrical neutralization, confirming that more positively charged edges were exposed after fragmentation. This study has provided an excellent approach to control and adjust the rheological properties of kaolin suspensions in industrial applications.

Fabrication of ultralightweight, thermal insulation alumina scaffolds by a hybrid sol–gel/freeze‐casting approach

AbstractFreeze casting is an effective way to fabricate the porous ceramics with anisotropic and interconnected porous structures and can be used in various applications, such as filtration, adsorption, and insulation. However, the ceramic‐based scaffolds fabricated by freeze casting have the upper limit of porosity since excessively low solid content in the slurry will lead to structural instability and cracks formation in scaffolds. This study aims at combining the freeze casting and sol–gel method and developing a hybrid process to overcome the limitation of freeze casting. Besides, the effects of solid content and cooling rates on the microstructure of ultralightweight alumina scaffolds (ULASs) and their mechanical and thermal properties were investigated. Aluminum isopropoxide was selected as the precursor to conduct the hydrolysis reaction in acid environment and condensation process by heat treatment. The successfully synthesized alumina scaffolds have ultrahigh porosity (>90%), low bulk density (0.1240–0.2429 g/cm3), and low relative density (0.0314–0.0615). The anisotropic porous lamellar structure was evaluated by scanning electron microscope, µ‐CT, and mercury porosimeter. A lot of nanoscale pores are observed on the lamellae surfaces, forming the dual‐scale porous structure inside the scaffolds and contributing to higher specific surface area. The unique anisotropic structure, high porosity, and stable mechanical properties enable ULASs to deliver a low thermal conductivity of 0.2 W/m/K and large anisotropy in thermal properties, possessing great potential for thermal insulative materials. This sol–gel/freeze‐casting hybrid approach is believed to be extended to different material systems and provide promising potentials in fabricating the porous materials with various functionalities.

Nano-hydroxyapatite Pickering emulsions as edible mayonnaise-like food sauce templates: A novel approach for food design

Pickering emulsions have the potential to enhance product stability and provide opportunities to create functional solutions that align with labelling requirements. The present work aims to develop Pickering emulsions stabilised by nano-hydroxyapatite (n-HAp) particles to replace traditional mayonnaises. The study addresses the effect of n-HAp solid particle concentration (5–15 wt%) and oil-water ratio (50:50, 60:40, 70:30, and 80:20, v/v) on emulsion stability, rheological properties, and oxidative stability. The results indicate that the produced Pickering emulsions have good stability for the tested period of 90 days, except for the 80:20 o/w emulsion that undergone a prompt quick phase separation. The Pickering emulsions produced with higher n-HAp concentration or oil content have a semi-solid structure, rendering them desirable options for replicating the texture of traditional mayonnaises. Regarding oxidative stability, the Pickering emulsions showed considerably improved stability compared to commercial mayonnaises (∼13 times higher), suggesting higher resistance to peroxidation and a longer shelf-life.

Two-Fluid and Discrete Element Modeling of a Parallel Plate Fluidized Bed Heat Exchanger for Concentrating Solar Power

Abstract A novel high-temperature particle solar receiver is developed using a light trapping planar cavity configuration. As particles fall through the cavity, the concentrated solar radiation warms the boundaries of the receiver and in turn heats the particles. Particles flow through the system, forming a fluidized bed at the lower section, leaving the system from the bottom at a constant flowrate. Air is introduced to the system as the fluidizing medium to improve particle heat transfer and mixing. A laboratory scale cavity receiver is built by collaborators at the Colorado School of Mines and their data are used for model validation. In this experimental setup, near IR quartz lamp is used to provide flux to the vertical wall of the heat exchanger. The system is modeled using the discrete element method and a continuum two-fluid method. The computational model matches the experimental system size and the particle size distribution is assumed monodisperse. A new continuum conduction model that accounts for the effects of solid concentration is implemented, and the heat flux boundary condition matches the experimental setup. Radiative heat transfer is estimated using a widely used correlation during the post-processing step to determine an overall heat transfer coefficient. The model is validated against testing data and achieves less than 30% discrepancy and a heat transfer coefficient greater than 1000 W/m2 K.

Effect of Solid Volume Concentration on the Rheological Properties of Debris Flow: A Case Study of Jiangjiagou Debris Flow in China

The Anton Paar MCR 52 intelligent high-speed rheometer was utilized in this paper to conduct rheological tests on the Jiangjiagou debris flow slurry via linear loading. The relationship curves between shear rate and shear stress at different solid volume concentrations were obtained, and predictive formulas for yield stress and viscosity coefficient variations with the shear rate are proposed. Furthermore, the evolution mechanisms of yield stress and viscosity coefficient with changes in solid volume concentration of the debris flow were thoroughly analyzed. The results indicated that the rheological curves of the Jiangjiagou debris flow conformed to the Bingham fluid model. An increase in solid volume concentration continuously promoted the upward trend of the rheological curves, with significant increments observed only at high volume concentrations. A predictive model for debris flow rheological parameters was established based on the linear relationship between the rheological parameters and the solid volume concentration. The rise in solid volume concentration inhibited turbulence in the debris flow, while clay minerals enhanced the debris flow slurry’s ability to capture pore water. Significant shear-thinning effects were observed within the debris flow, which were particularly more pronounced at lower shear rates. The study outcomes hold crucial engineering significance for a better understanding of debris flow rheological properties, the calculation of debris flow dynamic parameters, and disaster prevention and control.

Preparation of MgAl-LDHs loaded with blast furnace slag and its removal of Cu(II) and methylene blue from aqueous solution

ABSTRACT Blast furnace slag (BFS) is a kind of waste produced in industrial production, as well as a valuable secondary resource. In this paper, layered double hydroxides composites (BFS/LDHs) were prepared by aqueous polymerization, with industrial waste BFS as modifier and magnesium nitrate, aluminium nitrate, and urea as raw materials. BFS/LDHs have been characterized by using scanning electron microscopy (SEM), fourier infrared spectrometer (FT IR), x-ray diffraction (XRD), and the specific surface area analyser (BET). The adsorption of BFS/LDHs on Cu (II) and methylene blue (MB) was investigated by batch experiments. The results showed that the adsorption capacity of BFS/LDHs to Cu (II) is stronger than that of MB. What’s more, the solid concentration effect was found in the process of sorption kinetics and sorption isotherms. The sorption kinetics curves of Cu (II) and MB on BFS/LDHs were well fitted by the quasi-second-order kinetics under different adsorbent concentrations. Langmuir and Freundlich sorption isotherm models were used to analyse the adsorption. It showed that the adsorption conforms to Langmuir and Freundlich’s adsorption isotherm models. The BFS/LDHs composites have good recycling availability in this adsorption process of Cu (II) and MB, the removal capacity of which was reduced by 16.1% and 3.8% after being recycled for six times, respectively. More importantly, BFS/LDHs composites are not only expected to become a sewage treatment agent, but also to solve the problem of industrial waste treatment, which is a win–win strategy.

Experimental investigation of filter cake deposition under cross-flow and static filtration conditions

Effects of cross-flow velocity, filtration pressure, and solid concentration on filter cake properties are studied by using a new filtration setup that allows performing filtration tests under a wide range of operating conditions. The main feature of this setup is that pressure and cross-flow velocity are decoupled, so it was possible to independently investigate the effect of these variables on filter cake properties. Filtration tests have demonstrated that particle invasion into filter media pores occurs initially, leading to the formation of an external filter cake. The increased cross-flow velocity creates an erosive shear stress at the surface of the external cake, which limits cake growth, indirectly maintaining a high filtrate flow rate. This high filtrate rate imparts a considerable drag force onto suspended particles, driving a high count into the porous substrate where these particles could deposit. Increasing pressure amplifies this internal particle deposition, particularly where there is no or limited external filter cake to limit filtrate drag and screen particles at the cake surface. The effect of cross-flow velocity on pore blocking and filter cake structure is observed and demonstrated by CT scanning and scanning electronic microscopy.

Rheological behavior of dehydrated cranberry suspensions: Analysis of the influence of temperature and solid concentration on Casson’s model parameters

Dehydrated cranberries (Vaccinium macrocarpon) are dried fruits known for their high antioxidant potential. Changes in their mechanical and rheological properties occur when cranberries are exposed to certain conditions, such as drying or immersion in a liquid medium (rehydration). To evaluate the rheological behavior of solid suspensions made from dehydrated cranberries, the effects of different temperatures and concentrations of dissolved solids were evaluated using a factorial experimental design (22) with three replications at the center point. Five models were used to investigate the suspensions' flow behavior: Ostwald de Waelle, Newton, Herschel-Bulkley, Casson, and Bingham. The rheometry of the suspensions showed that the fluids presented non-Newtonian behavior, with a satisfactory fit for the Casson model (R² > 0.94) in all evaluated temperature and concentration ranges. Furthermore, the effects of temperature and solid concentration of cranberry suspensions on the rheological parameters of the fitted model, Casson's initial shear stress (K0c), and Casson's plastic viscosity (Kc) were evaluated. From the response and the contour surfaces, it was found that increasing the concentration of the suspension above 20% resulted in higher initial shear stress, which was influenced by temperature, whose increase resulted in a significant reduction in the shear stress at a concentration of 30%. The plastic viscosity (Kc) was highly influenced by the solid’s concentration, and higher temperatures caused a decrease in the value of this parameter. So, the highest value of plastic viscosity was found for concentrations above 20% and at lower temperatures. Therefore, considering the results and for practical purposes, it can be concluded that the flow of the suspensions is facilitated if rehydration is conducted at high temperatures.

Numerical analysis of solid phase hydrodynamics in a continuous precipitator relevant for plutonium reconversion

The extensive application of solid-liquid flow in various industries, has made it important to comprehend the hydrodynamics inside different process equipment and optimize their operation. In the present work, solid phase hydrodynamics in a continuous precipitator relevant for plutonium (Pu) reconversion has been investigated numerically. Euler-Euler two-fluid simulations were performed to analyse the performance by varying the solid concentration (5, 10, 15, and 20 g/l), impeller speed (500 and 700 rpm) and overflow outlet height (0.65, 0.75 and 0.85 m). The solid phase behaviour in precipitator is analysed by comparing the solid volume fraction and pressure distributions along the height. To enable easy handling of precipitator inside glove-box, the solid mass, volume rate and pressure distributions through overflow outlet at different height is thoroughly investigated. Further, the effect of solid concentration and rotating speed of impeller on radial velocity distribution is analysed. The results show that overflow of solid phase is dependent on dispersed phase concentration and rotating speed of the impeller. Further, the increase in overflow outlet height increases the overflow time. However, the volume fraction of solid remains constant during the steady operation. The study will be helpful to design a glove-box adaptable precipitator for continuous plutonium reconversion.

Effect of solid content on the piezoelectric properties of porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 ceramics

The influence of the solid content of porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) ceramics on the pore morphology and mechanical and piezoelectric properties was systematically investigated. The results show that with an increase in solid content, porosity and pore size decreased, and ceramic connectivity increased, leading to an increase in compressive strength. The best ferroelectric performance was achieved with an Ec of 2.40 kV/cm2 and a Pr of 2.01 μC/cm2 at a solid content of 30 vol%. When the solid content increased, the relative dielectric constant and the piezoelectric constant increased, which affected the piezoelectric energy harvesting performance. At a solid content of 20 vol%, g33 and FOM33 reached maxima of 43 × 10−3 Vm/N and 6.7 p.m.2/N, which were 2.40 times and 1.8 times those of the other solid contents, respectively. This work provides new ideas for the design of porous piezoelectric ceramics and the improvement of their piezoelectric properties for future piezoelectric energy harvesting applications.

The synthesis of high-strength monolithic Al2O3-SiO2 aerogels through increased solid content and high-temperature calcination

High-strength Al2O3-SiO2 aerogels were synthesized by simultaneously increasing the solid content and high-temperature calcination. The effects of solid content and high-temperature calcination on mechanical properties, thermal conductivity, and microstructure of Al2O3-SiO2 aerogels were studied. The increase in solid content can improve the mechanical properties of aerogels. High-temperature calcination can further improve mechanical properties and reduce thermal conductivity. Finally, we fabricated a high-strength monolithic Al2O3-SiO2 aerogel with a high Young’s modulus of 127.45 MPa, room temperature thermal conductivity of 29.15 mW·m−1·K−1, and density of 252 mg·cm−3. This work is significant to the adhibition of Al2O3-SiO2 aerogels as high-strength thermal insulation materials.

Characterisation of oscillations in multi-phase unbaffled mixing vessels

Unbaffled mixing systems have several benefits over conventional baffled systems, including significantly lower power required for solids suspension. However, one drawback of unbaffled systems is the possibility of oscillations occurring within the tank. Experimental laboratory-scale experiments have revealed oscillations in settling solids and large variations in the input power, despite the impeller speed remaining constant. These oscillations have been found to be linked through having the same frequency. The frequency and amplitude of these oscillations has been determined across a range of agitator and tank configurations, including variations in impeller size and type, impeller clearance and submerged depth, and the surface boundary conditions. The effect of solids concentration has also been investigated. The oscillations were found to be inherently multi-phase and had a strong concentration dependence. Impeller size and type influenced the amplitude and frequency of the oscillations, as did the impeller clearance. Liquid surface condition did not influence the oscillations. The oscillation frequency appears to be related to the circulation time in the tank. Although these oscillations fall into the definition of previously observed macro-instabilities, several distinguishing features are noted.

Simulation of circular pipe flow of thixotropic cemented tailings pastes

Cemented tailings pastes (CTPs) exhibit complex thixotropic behaviors, which considerably affect the accurate prediction of pressure drop in circular pipe transport. In this work, the thixotropy of CTPs is incorporated into the numerical simulation via a constitutive thixotropic model. The analytical solution of the velocity profile across the pipe based on the equilibrium rheological model is presented. Comparisons indicate that the Bingham model cannot accurately characterize the flow behaviors of CTPs. It also overestimates the pressure drop in the circular pipe. Moreover, the pressure drop predicted by the novel equilibrium model is overestimated because of thixotropy. A peak of the structural parameter can be observed near the edge of the plug region, which highly influences shear rate distribution. The effects of solids content and flow rate on pressure drop are analyzed. In summary, thixotropy should be considered in the circular pipe flow simulation of CTPs.

High gas permeability and directional channels of mullite porous ceramics prepared by pectin‐based freeze‐drying method

AbstractNew gel system for preparing mullite porous ceramics by gel‐casting freeze‐drying was proposed, using pectin as gel source and alumina and silica as raw materials. Directional channels were formed due to sublimation of water during freeze‐drying and decomposition of pectin during high temperature sintering to prepare porous mullite ceramic membranes. Effects of solid content on the properties of mullite ceramics in terms of phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal conductivity, pressure drop, and gas permeability were investigated. It was found that prepared porous mullite possessed high apparent porosity (56.04%–75.34%), low bulk density (.77–1.37 g/cm3), uniform pore size distribution, relatively high compressive strength (.61–3.03 MPa), low thermal conductivity (.224–.329 W/(m·K)), high gas permeability coefficient (1.11 × 10−10–4.73 × 10−11 m2), and gas permeance (2.18 × 10−2–9.32 × 10−3 mol⋅m−2⋅s−1⋅Pa−1). These properties make prepared lightweight mullite ceramic membranes promising for application in high temperature flue gas filtration. Proposed gel system is expected to provide a new route to prepare porous ceramics with high porosity and directional channels.

An Invitation on Characterization of H2-Reduced Bauxite Residue and Recovering Iron through Wet Magnetic Separation Processes

Recovering iron from the bauxite residue (BR) is one of the long-standing challenges in the mining industry. However, there is a substantial lack of information in the literature regarding sample properties and iron extraction by reducing hydrogen. The present study aims at reducing a Greek BR using hydrogen, its characterization, and separating iron by magnetic separation processes. To this end, the reduced sample was characterized using X-ray diffractometry analysis (XRD), X-ray fluorescence spectrometer analysis (XRF), thermomagnetic analysis (TMA), automated mineralogy (AM), and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The effect of particle size (−200 + 100 µm, −100 + 75 µm, and <75 µm) was investigated through a medium-intensity magnetic separation (MIMS, Davis Tube) at 1000–2500 Gauss and a Slon® magnetic separator (1000 G). The effects of solid content (3% and 10% w/w) in a wet low-intensity magnetic separation (WLIMS, 350 G) and a two-stage MIMS followed by WLIMS were investigated. It was revealed that through reduction at 500 °C and 2 h with 20 wt% NaOH under 5 vol.% H2 + 95 vol.% N2, iron oxides and ferric oxyhydroxide (Fe2O3 and FeOOH) were converted into magnetite (Fe3O4), whereas aluminum (oxy)hydroxides (Al(OOH), Al(OH)3) were reacted with Na+ towards sodium aluminates (NaAlO2). The AM observations indicated that only 3% of iron was in the phase of liberated magnetite, and the remaining was associated with Na, Al, and Ti phases with different intensities. The dissemination of iron throughout the matrix of the sample was recognized as the principal challenge in the physical separation processes. It was found that increasing magnetic intensity from 1000 G to 2500 G resulted in improved recovery for all studied particle size fractions in Davis Tube tests. The particle range of −106 + 74 µm was chosen as the most appropriate size to achieve the maximum Fe content of 41%. The results of WLIMS (350 G) showed the maximum Fe grade but revealed less recovery of 52% and 27% at 10% and 3% solid contents, respectively, compared to the Davis Tube trials.

Effect of High Solid Concentration on Friction in a Transitional and Turbulent Flow of Bioliquid Suspension

Some suspensions in nature have a complex structure and demonstrate a yield shear stress and a non-linear relationship between the shear rate and the shear stress. Kaolin clay suspension is such an example in engineering, whereas in nature it is blood. This study represents an innovative approach to simulate bioliquid flow, similar to that of blood when the solid concentration is high. The objective of this study is to examine the influence of high solid concentration of bioliquid, similar to blood, on energy losses and velocity profiles in turbulent and transitional flow in a narrow tube. Using the analogy between the suspension of kaolin clay and blood, the physical model and the mathematical model were formulated. The mathematical model comprises continuity and time-averaged momentum equations, a two-equation turbulence model for low Reynolds numbers, and a specially developed wall damping function, as such suspensions demonstrate the damping of turbulence. Experimental data on blood rheology for solid concentrations equal to 43% and 70% by volume, gathered from the literature, were used to establish a rheological model. The results of the simulations indicated that an increase of solid concentration in bioliquid suspension from 43% to 70% causes an increase in wall shear stress to approximately 10% and 6% for transitional and turbulent flow, respectively, and changes in velocity profiles. Such simulations are important if an inserted stent or a chemical additive to the bioliquid suspension is considered, as they can influence the shear stress. The results of the simulations are presented in graphs, discussed, and conclusions are formulated.

Preparation of hydrogels based on poplar cellulose and their removal efficiency of Cd(II) from aqueous solutions.

Industrial heavy metal-contaminated wastewater is one of the main water pollution problems. Adsorbents are a promising method for the removal of heavy metal contaminants. Herein, polyaspartic acid/carboxymethyl poplar sawdust hydrogels (PASP/CMPP) and ascorbic acid/carboxymethyl poplar sawdust hydrogels (VC/CMPP) were prepared by aqueous polymerization using alkalized poplar sawdust (CMPP) as the substrate and PASP and vitamin C (VC) as modifiers. The effective results, provided by the characterization analysis of SEM and BET, indicate that the surface of the PASP/CMPP hydrogel has a larger number of loose pores and a larger pore volume than the VC/CMPP hydrogel. The treatment effects of the two hydrogels on simulated wastewater containing Cd(II) were investigated by a batch of experiments. The results showed that PASP/CMPP had a better adsorption effect than VC/CMPP under the same adsorption conditions. Interestingly, the solid concentration effect was found in the process of sorption kinetics and sorption isotherms. The sorption kinetic curves of Cd(II) on PASP/CMPP were well-fitted by the quasi-second-order kinetics under different adsorbent concentrations. The adsorption conforms to Langmuir and Freundlich adsorption isotherm models. More importantly, PASP/CMPP composites are expected to be used as a new kind of environmental adsorbent for wastewater treatment.

Effects of Organic Additives on the Properties of Boronsilicate Glass/Al2O3 Composites Tape Casting Slurries and Green Tapes

Tape casting was a new type of low temperature co-fired ceramic (LTCC) forming process, the key to which was the formation of slurry. Suspensions consisting of boronsilicate glass/Al2O3 powders and organic solvent system were studied, in addition, the effect of solid content and mixing time on the property were also investigated. The results indicated that the optimized parameters of the slurry are 55 wt. % boronsilicate glass/Al2O3 composites powders, the three azeotropic solvents (Ethanol/ Dimethylbenzene/ Dimethylcarbinol=30 wt.%: 10 wt.%: 60 wt.%), 3.0 wt.% dispersant, the ratio of plasticizer to binder(R=0.65), and mixing time (20 hours). The green tape had smooth and homogeneous surfaces without cracks, and the sintered sample had a high relative density.

High consistency enzymatic pretreatment of eucalyptus and softwood kraft fibres for regenerated fibre products

Sustainability of regenerated cellulosic fibres could be improved by using paper grade pulp instead of dissolving pulp as a raw material in the fibre spinning process. However, the use of paper grade pulp calls for adjustment of the molar mass distribution (MMD) prior to dissolution to obtain good solubility and spinnability. The objective of this work was to adjust MMD of softwood and eucalyptus kraft pulps by enzymatic treatments at high pulp consistency. The reduction of the MMD of eucalyptus kraft pulp was found to require a nearly 30-fold higher dose of endoglucanase compared to the treatment of softwood pulp. Interestingly, when xylanase was used in combination with endoglucanase to treat eucalyptus kraft pulp, 27% of the xylan was dissolved and the required endoglucanase dose could be decreased from 0.57 to 0.06 mg/g. The endoglucanase dose could be further decreased to 0.028 mg/g when 67% of xylan was removed chemically before the enzymatic treatment. This suggests that xylan hinders endoglucanase action on eucalyptus kraft pulp. For softwood pulp, the addition of xylanase and mannanase had only a minor impact on the treatment efficiency. The different processabilities of softwood and eucalyptus kraft pulps are suggested to originate from the deviating cellulose accessibility which is affected by the fibre structures as well as their hemicellulose composition and localisation. The effect of the treatment consistency was further studied with softwood kraft pulp. Treatment at high consistency clearly enhanced the endoglucanase action whereas the effect of solid content on the hemicellulase action was modest.

Effect of Pressure, Concentration and Sludge Volume on Two-phase Filtrate Volumes Using Bentonite Clay Sludge

The effect of pressure, solids concentration and volume of slurry on total and two-phase filtrate volumes was investigated to establish optimum conditions for routine laboratory filtration. Full factorial design with three levels was utilized to obtain 27 unique experiments. The slurry used was prepared by mixing crushed and sieved bentonite clay of 75 microns with distilled water at different concentrations as obtained from the design of experiment. A filter press was utilized and the results were used to calibrate a two-phase exponential equation for sludge filtration to extract the first and second stage filtrate volumes. The total filtrate volume improved with increasing applied pressure and decreasing solids concentration. A slurry volume of 0.22 litres was found to be ideal. Similar effects were noticed on the first and second stage filtrate volume except that an optimum was discovered at 0.18 litres of slurry. The second stage filtration produced an upward curve with a point of inflection at a range of 0.18 to 0.22 litres of slurry. The second stage filtrate volume is also discovered to be directly proportional to the total filtrate volume. This connection may be considered for use to assess the filterability of other slurries.