scholarly journals The effect of precursor speciation on the growth of scorodite in an atmospheric scorodite synthesis

2020 ◽  
Vol 7 (1) ◽  
pp. 191619
Author(s):  
Zhihao Rong ◽  
Xincun Tang ◽  
Liping Wu ◽  
Xi Chen ◽  
Wei Dang ◽  
...  
Keyword(s):  
Particle Size ◽  
Direct Product ◽  
Arsenic Concentration ◽  
Critical Value ◽  
Transformation Process ◽  
Complex Ions ◽  
Ferric Arsenate ◽  
Growth Pathway ◽  
Positive Force

In this study, we propose a growth pathway of scorodite in an atmospheric scorodite synthesis. Scorodite is a non-direct product, which is derived from the transformation of its precursor. Different precursor speciation leads to different crystallinity and morphology of synthesized scorodite. At 10 and 20 g l −1 initial arsenic concentration, the precursor of scorodite is identified as ferrihydrite. At 10 g l −1 initial arsenic concentration, low arsenic concentration is unfavourable to the complex between arsenate and ferrihydrite, inhibiting the transformation of ferrihydrite into scorodite. The synthesized scorodite is 1–3 µm in size. At 20 g l −1 initial arsenic concentration, higher arsenic concentration favours the complex between arsenate and ferrihydrite. The transformation process is accessible. Large scorodite in the particle size of 5–20 µm with excellent crystallinity is obtained. However, the increasing initial arsenic concentration is not always a positive force for the growth of scorodite. When initial arsenic concentration increases to 30 g l −1 , Fe(O,OH) 6 octahedron preferentially connects to As(O,OH) 4 tetrahedron to form Fe H 2 As O 4 2 + or FeHAs O 4 + ion. Fe–As complex ions accumulate in solution. Once the supersaturation exceeds the critical value, the Fe–As complex ions deprotonate and form poorly crystalline ferric arsenate. Even poorly crystalline ferric arsenate can also transform to crystalline scorodite, its transformation process is much slower than ferrihydrite. Therefore, incomplete developed scorodite with poor crystallinity is obtained.

Production of quicklime from Ashaka limestone through calcination process

2021 ◽  
Vol 1 (2) ◽  
pp. 041-048
Author(s):  
Benson Chinweuba Udeh
Keyword(s):  
Particle Size ◽  
Critical Value ◽  
Operating Conditions ◽  
Quadratic Model ◽  
Particle Sizes ◽  
Calcination Process ◽  
Process Effects ◽  
Effects Of Temperature ◽  
The Difference ◽  
The Relationship

This study is on the production of quicklime from Ashaka limestone through calcination process. Effects of temperature, particle size and time on quicklime yield were determined. The experiment was carried out at temperatures of 800, 900, 1000, 1100 and 1200 0C, particle sizes of 80mm, 90mm, 100mm, 300mm and 425mm and times of 0.5hr, 1hr, 2hrs, 3hrs and 4hrs. Analyses of the results showed that quicklime was successfully produced from Ashaka limestone through the calcination process. Quadratic model adequately described the relationship between quicklime yield and calcination factors of temperature, particle size and time. Recorded model F-value of 134.35 implies that the model is significant. The predicted R² of 0.9597 is in reasonable agreement with the adjusted R² of 0.9844; the difference is less than the critical value of 0.2. Optimum yield of 73.48% was obtained at optima operating conditions; temperature of 1000 0C, particle size of 90 µm and time of 3 hrs.

scholarly journals Effect of Soil Washing Using Oxalic Acid on Arsenic Speciation and Bioaccessibility in Soils

2020 ◽  
Vol 42 (4) ◽  
pp. 218-227
Author(s):  
Yeseul Gwon ◽  
Seong Ryeol Kim ◽  
Eun Jung Kim
Keyword(s):  
Particle Size ◽  
Oxalic Acid ◽  
Contaminated Soil ◽  
Arsenic Speciation ◽  
Arsenic Concentration ◽  
Size Fraction ◽  
Soil Washing ◽  
Large Particle Size ◽  
Amorphous Oxides ◽  
Particle Size Fractions

Objectives : Soil washing process has been widely applied for remediation of contaminated soil with arsenic and heavy metals in Korea. The application of soil washing could change physical and chemical properties of soils and metal speciation in soil, which could affect the risk to the environment and human health. Thus, it is necessary to evaluate metal and arsenic speciation and their mobility in soil after soil remediation in order to evaluate effectiveness of soil remediation process and manage soil quality effectively. The purpose of this study is to evaluate the risk of arsenic in soil after remediation of arsenic contaminated soil via soil washing.Methods : Arsenic contaminated soil collected at the abandoned mine site was washing with oxalic acid. The arsenic contaminated soil was divided into 2,000-500 µm, 500-250 µm, 250-150 µm, 150-75 µm, 75-38 µm, < 38 µm particle size fractions. After soil washing for each soil particle size fraction, arsenic speciation via sequential extraction and bioaccessibility in the soils were evaluated. Results and Discussion : Generally, arsenic and metal concentrations were higher in the soil fractions with smaller particle sizes. But high arsenic concentration was observed at the large particle size fractions (>250 µm), which might be due to the presence of mineral phases containing arsenic such as arsenolite or pyrite in the large particle size fraction soils. Sequential extraction showed that arsenic in mine soils was majorly present as associated with amorphous oxides. After soil washing with oxalic acid, arsenic in soils associated with amorphous oxides was greatly decreased, whereas the arsenic fraction associated sulfide and organic matter was increased. Soil washing decreased the bioaccessible arsenic concentration (mg/kg) in soil, but increased the bioaccessibility (%) depending on the soil characteristics. Conclusions : Soil washing changed arsenic species in soils, which affected mobility and risk of arsenic in soil.

scholarly journals Effects of temperature gradient and particle size on self-ignition temperature of low-rank coal excavated from inner Mongolia, China

2019 ◽  
Vol 6 (9) ◽  
pp. 190374 ◽  
Author(s):  
Yongjun Wang ◽  
Xiaoming Zhang ◽  
Hemeng Zhang ◽  
Kyuro Sasaki
Keyword(s):  
Activation Energy ◽  
Particle Size ◽  
Temperature Gradient ◽  
Ignition Temperature ◽  
Coal Particle ◽  
Critical Value ◽  
Low Rank ◽  
Low Rank Coal ◽  
Coal Particles ◽  
Effects Of Temperature

This study investigates the effects of temperature gradient and coal particle size on the critical self-ignition temperature T CSIT of a coal pile packed with low-rank coal using the wire-mesh basket test to estimate T CSIT based on the Frank–Kamenetskii equation. The values of T CSIT , the temperature gradient and the apparent activation energy of different coal pile volumes packed with coal particles of different sizes are measured. The supercriticality or subcriticality of the coal is assessed using a non-dimensional index I HR based on the temperature gradient at the temperature cross-point between coal and ambient temperatures for coal piles with various volumes and particle sizes. The critical value I HRC at the boundary between supercriticality and subcriticality is determined as a function of pile volume. The coal status of supercritical or subcritical can be separated by critical value of I HR as a function of pile volume. Quantitative effects of coal particle size on T CSIT of coal piles are measured for constant pile volume. It can be concluded that a pile packed with smaller coal particles is more likely to undergo spontaneous combustion, while the chemical activation energy is not sensitive to coal particle size. Finally, the effect of coal particle size on T CSIT is represented by the inclusion of an extra term in the equation giving T CSIT for a coal pile.

Grain Growth of Polycrystalline AZ31 Mg Alloy Containing Second Phase Particles by Phase Field Simulation

2016 ◽  
Vol 850 ◽  
pp. 307-313
Author(s):  
Yan Wu ◽  
Si Xia ◽  
Bernie Ya Ping Zong
Keyword(s):  
Particle Size ◽  
Grain Growth ◽  
Phase Field ◽  
Phase Field Model ◽  
Free Energy Density ◽  
Critical Value ◽  
Spherical Particles ◽  
Second Phase ◽  
Pinning Effect ◽  
Second Phase Particles

A phase field model has been established to simulate the grain growth of AZ31 magnesium alloy containing spherical particles with different sizes and contents under realistic spatial-temporal scales. The expression term of second phase particles are added into the local free energy density equation, and the simulated results show that the pinning effect of particles on the grain growth is increased when the contents of particles is increasing, which is consistent with the law of Zener pinning. There is a critical particle size to affect the grain growth in the microstructure. If the size of particles is higher than the critical value, the pinning effect of particles for grain growth will be increased with further decreasing the particle size; however the effect goes opposite if the particle size is lower than the critical value.

scholarly journals An expression for the angle of repose of dry cohesive granular materials on Earth and in planetary environments

2021 ◽  
Vol 118 (38) ◽  
pp. e2107965118
Author(s):  
Filip Elekes ◽  
Eric J. R. Parteli
Keyword(s):  
Particle Size ◽  
Granular Materials ◽  
Gravitational Force ◽  
Rolling Resistance ◽  
Critical Value ◽  
Angle Of Repose ◽  
Theoretical Expression ◽  
Particle Interactions ◽  
Planetary Environments ◽  
Force Ratio

The angle of repose—i.e., the angle θr between the sloping side of a heap of particles and the horizontal—provides one of the most important observables characterizing the packing and flowability of a granular material. However, this angle is determined by still poorly understood particle-scale processes, as the interactions between particles in the heap cause resistance to roll and slide under the action of gravity. A theoretical expression that predicts θr as a function of particle size and gravity would have impact in the engineering, environmental, and planetary sciences. Here we present such an expression, which we have derived from particle-based numerical simulations that account for both sliding and rolling resistance, as well as for nonbonded attractive particle–particle interactions (van der Waals). Our expression is simple and reproduces the angle of repose of experimental conical heaps as a function of particle size, as well as θr obtained from our simulations with gravity from 0.06 to 100 times that of Earth. Furthermore, we find that heaps undergo a transition from conical to irregular shape when the cohesive to gravitational force ratio exceeds a critical value, thus providing a proxy for particle-scale interactions from heap morphology.

scholarly journals Study on the gas desorption law and indicator influencing factors of fixed-size coal samples

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Lei Li ◽  
Zhongguang Sun ◽  
Fakai Wang ◽  
Kaizhi Zhang
Keyword(s):  
Particle Size ◽  
Diffusion Coefficient ◽  
Coal Particle ◽  
Diffusion Theory ◽  
Mathematical Expression ◽  
Experimental System ◽  
Size Composition ◽  
Critical Value ◽  
Gas Pressure ◽  
Fixed Size

AbstractThe prediction of dangerous hazards in working faces is an important link to prevent coal and gas outbursts. Improving the accuracy of predictive indicators is of great significance for reducing the phenomenon of being prominently below the critical value and ensuring safe production. The fixed-size desorption index K1 is one of the important indicators for coal face and gas outburst prediction. Based on the diffusion theory and the physical meaning of fixed-size coal samples, the mathematical expression of K1 is established by the self-developed high/low temperature pressure swing adsorption-desorption experimental system. According to the equation, the effects of gas pressure, loss time, coal particle size and diffusion coefficient on K1 are studied. The results show that the K1 index is logarithmically related to the gas pressure. Under the same conditions, the longer the loss time is, the smaller the measured K1 is, and the smaller the particle sizes of the drill cuttings are, the more notable the performance is; the diffusion coefficient represents the ability of gas to bypass micropores and the coal matrix. The greater the ability to bypass the matrix is, the larger the diffusion coefficient under the same conditions is, and the larger K1 is; the coal particle size has a greater influence on K1, and the smaller the size is, the more likely it is that the phenomenon of being prominently below the critical value occurs. Therefore, the particle size composition of coal during on-site measurements is crucial for obtaining the true K1 and the exact critical values.

The influence of gypsum particle size on pasture response on a sulphur deficient soil

1968 ◽  
Vol 8 (31) ◽  
pp. 203 ◽  
Author(s):  
KD McLachlan ◽  
Marco DG De
Keyword(s):  
Particle Size ◽  
Soil Surface ◽  
Critical Value ◽  
Sulphur Content ◽  
First Year ◽  
Particle Sizes ◽  
Negative Interaction ◽  
Upper Limits ◽  
Main Effect ◽  
Important Variant

The pasture response to four particle sizes of gypsum fertilizer was measured on a sulphur deficient basaltic soil over a three-year period. At a low rate of application, pasture response was inversely related to particle size ; at a higher rate, only the coarsest fraction differed from the other treatments. The reduction in plant sulphur content and uptake with this fraction suggests that particles >5 mm may be approaching the upper limits of usefulness on this soil. In the first year, the negative interaction between particle size and level of gypsum applied showed that particle size may replace level of application in its effect on response. More efficient use of the sulphur in the fertilizer resulted from application of the finer fractions. Separation of particle size effects into those due to rate of solution of sulphur from the compound, and those due to placement through physical distribution over the soil surface, showed that rate of solution of sulphur was the more important variant. Recognition of its influence could lead to prescribing the correct particle size of gypsum for every sulphur deficient soil. The main effect of the applied sulphur was on the clover component of the pasture. The results suggest that a sulphur content of 0.07 per cent in mature plant tops may be a critical value indicating an adequate sulphur supply, and that 5 lb sulphur an acre in the plant tops may be all that is required for maximum clover production.

scholarly journals The diffusion coefficients of dye solutions and their interpretation

1935 ◽  
Vol 148 (865) ◽  
pp. 681-695 ◽  
Keyword(s):  
Particle Size ◽  
Diffusion Coefficient ◽  
Einstein Equation ◽  
Diffusion Coefficients ◽  
Complex Ions ◽  
Nernst Equation ◽  
Theoretical Paper ◽  
Qualitative Measure ◽  
Dye Solutions

In a previous theoretical paper Hartley and Robinson have pointed out what very misleading results are obtained in calculating the particle size of a dye from the diffusion coefficient if the Stokes-Einstein equation is used and the electrical forces are neglected. The complicating effect of the electrical forces on the diffusion coefficient has, of course, been realized in researches on other colloidal electrolytes. Thus Svedberg, Tizelius, Northrop, McBain and others have taken them into account in the case of proteins, while McBain and Liu pointed out that the diffusion coefficient of soaps is given by an extension of the Nernst equation. But in experiments with dyes, although many diffusion measurements were reported, this aspect of the matter had been entirely overlooked. An investigation of the diffusion coefficients of dyes is, therefore, of particular interest and also because of the light it throws on the more general problem of determination of the particle size of a colloidal electrolyte, where the particle (unlike that of the protein, which appears to be a simple molecule) consists of a number of ions in association. Many dyes are colloidal electrolytes containing multivalent complex ions. Their diffusion coefficient is consequently largely determined by the mobilities of the ions. It was shown that a minimum value for the diffusion coefficient can be calculated from the conductivity. It follows that all dyes that have high conductivities—this seems to include most, if not all, substantive dyes—must have high diffusion coefficients. Consequently, as was shown, it is not possible to obtain even a qualitative measure of the particle size from the diffusion coefficient and the Stokes-Einstein equation.

Influence of Citric Acid on the Formation of Hydroxyapatite Powders by Using Ca(NO3)2-P2O5 Ethanol Solution System

2010 ◽  
Vol 152-153 ◽  
pp. 1248-1252
Author(s):  
Qing Chang ◽  
Hong Qiang Ru ◽  
Liang Yu ◽  
Ji Guang Li
Keyword(s):  
Particle Size ◽  
Citric Acid ◽  
Sol Gel ◽  
Xrd Analysis ◽  
Transformation Process ◽  
Ethanol Solution ◽  
X Ray Diffraction ◽  
Solution System ◽  
Ca Addition ◽  
Xrd Patterns

In this study, nano-hydroxyapatite (HA) powders were synthesized via a simple sol-gel method using Ca(NO3)2•4H2O and P2O5 as starting materials. Two different precursors, with and without citric acid (CA), were prepared. The transformation process of HA from precursors, purity and particle size of the obtained HA powders were evaluated. HA derived from the precursor with CA showed a different transformation process from that without CA. It was observed that the content of CaO as an unavoidable major impurity was reduced due to the addition of CA. In the calcined powders from the CA-free precursor, X-ray diffraction (XRD) patterns revealed an intense CaO peak. For the calcined powders from the CA-addition precursor, XRD analysis showed a very weak CaO peak. It was also found that the synthesized HA powders from precursor with CA were finer than those without CA. The mechanism of the influence of CA on the formation, purity and particle size distribution of HA powders was discussed.

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