Ion Diffusion

1997 ◽  
Author(s):  
T. R. Yu ◽  
E. J. Wang
Keyword(s):  
Diffusion Coefficient ◽  
Concentration Gradient ◽  
Time Interval ◽  
Ion Diffusion ◽  
High Concentration ◽  
Low Concentration ◽  
Variable Charge ◽  
Unit Time Interval ◽  
A Site ◽  
Variable Charge Soils

The microregional transport of ions under an externally applied electric field has been discussed previously. When ions are distributed heterogeneously in soil on a macroscopic scale, because of the presence of concentration gradient (i.e., the difference in chemical potential), ions tend to migrate from a site of high concentration to a site of low concentration. Such a phenomenon is called ion diffusion. The diffusion rate of various ions in a soil is related to the nature of the ions and the interaction among them and is also affected by the chemical processes in the soil, such as adsorption, desorption, and repulsion. For variable charge soils carrying both positive and negative surface charges, the factors that affect ion diffusion are rather complex. In the present chapter, after treatment of basic principles of ion diffusion, the characteristic features of ion diffusion in variable charge soils will be discussed, with the emphasis on diffusion of anions because this is one of the important means for elucidating the characteristics of variable charge soils. In a solution, if the ion concentration in point A is higher than that in point B, under static conditions, the number of ions moving from point A to point B will be larger than that moving in the opposite direction due to the random thermal motion of ions. In order to express the net ion flux J within an unit time interval through an unit area, Fick introduced the first diffusion law: . . . J = –D dC/dX . . . (9-1) where dC/dX is the concentration gradient. The negative sign in the equation denotes that the flux is from high concentration to low concentration; that is, the direction of the flux is opposite to that of the concentration gradient. D is called the diffusion coefficient. It can be seen from the equation that the diffusion coefficient is the flux passing through an unit cross-sectional area within a unit time interval under a unit concentration gradient. D is the most important parameter in ion diffusion. Fick’s first diffusion law is applicable to both homogeneous and heterogeneous medium such as soil.

Oxidation-Reduction Reactions

1997 ◽  
Author(s):  
Z. G. Liu ◽  
C. P. Ding
Keyword(s):  
Organic Matter ◽  
Necessary Condition ◽  
Equilibrium System ◽  
High Concentration ◽  
Reduction Reactions ◽  
Variable Charge ◽  
Oxidation Reduction ◽  
High Precipitation ◽  
Reducing Substances ◽  
Variable Charge Soils

Oxidation-reduction reactions are chemical reactions caused by the transfer of electrons between two substances. These reactions occur actively in variable charge soils. This is because that under conditions of high temperature and high precipitation both the accumulation and the decomposition of organic matter proceed rapidly. The decomposition products of organic matter may release electrons, providing the necessary condition for the occurrence of reduction reactions. In particular, because the soil may have a high content of water during seasonal rainy periods, the presence of a strongly reducing condition is possible. Furthermore, large areas of variable charge soils have been cultivated for rice production. For these paddy soils there are always intensive oxidation-reduction reactions proceeding alternately. Variable charge soils have a high content of iron oxides. The content of manganese is also higher than that of constant charge soils. Thus, the soil itself possesses plenty of electron-acceptors. Besides, the high concentration of hydrogen ions in variable charge soils is favorable for the occurrence of reduction reactions. Therefore, as shall be seen in this chapter, contrary to the belief that the significance of oxidation- reduction reactions is confined chiefly to submerged soils, these reactions may play an important role in soil genesis and soil fertility for variable charge soils even under well-aerated conditions. In this chapter, after discussions on factors affecting the intensity of oxidation-reduction and interactions among various oxidation-reduction substances, the oxidation-reduction regimes of variable charge soils under different utilization conditions will be presented. Ferrous and manganous ions, two important inorganic reducing substances in soils, shall be dealt with in the next chapter. The oxidation-reduction intensity of a substance is determined by its ability to liberate or accept electrons. Therefore, electron activity in an equilibrium system may be used as an index for expressing its reduction strength. An electron has a radius of only approximately 1/20,000 of that of a hydrogen atom. Its large charge-to-size ratio prevents it from persisting in free form in aqueous systems. The ephemeral “hydrated electron” has a half-life of less than 1 msec (Bartlett and James, 1993). As a species with a potential of -2.7 V vs. the standard potential of H+/H2, it is a powerful reducing agent.

A contribution to the analysis of grain boundary diffusion measurements

1968 ◽  
Vol 46 (13) ◽  
pp. 1511-1521 ◽  
Author(s):  
Jaroslav Kučera
Keyword(s):  
Diffusion Coefficient ◽  
Grain Boundary ◽  
Penetration Depth ◽  
Boundary Diffusion ◽  
Diffusion Problem ◽  
Grain Boundary Diffusion ◽  
High Concentration ◽  
Low Concentration ◽  
Depth Measurement ◽  
Sectioning Method

The Whipple and Suzuoka exact solutions of the grain boundary diffusion problem have been extended to the Gruzin method. The penetration curves for these two solutions were evaluated numerically using the method of penetration depth measurement, the sectioning method, and the Gruzin method. With the results obtained, relationships are given which make the evaluation of grain boundary diffusion coefficients in the low concentration range (up to 0.005%) comparatively easy. For all three experimental methods the Whipple and Suzuoka solutions have been compared. The comparison for the method of penetration depth measurement was only possible in the low concentration range. When evaluating the data in the low concentration range, using Whipple's or Suzuoka's solutions, approximately the same values of grain boundary coefficient are obtained, irrespective of the experimental method used. A comparison of the solutions using the sectioning and the Gruzin methods in the high concentration range (100%–0.1%) shows that the Gruzin method is not sensitive to the mathematical model used for treating the experimental data. The application of Whipple's solution to the data corresponding to Suzuoka's model gives higher values of the volume diffusion coefficient and slightly higher values of the grain boundary diffusion coefficient in the sectioning method and vice versa.

The Experimental Method Comparison of Concrete Penetration

2011 ◽  
Vol 374-377 ◽  
pp. 1215-1219
Author(s):  
Ruo Dong Ge ◽  
Ai Ping Yu ◽  
Ke Yu Wei
Keyword(s):  
Diffusion Coefficient ◽  
Electric Field ◽  
Concentration Gradient ◽  
Diffusion Mechanism ◽  
Method Comparison ◽  
Chloride Ion ◽  
Ion Diffusion ◽  
The Difference ◽  
Chloride Ion Diffusion

For comparing the difference between Salt ponding test and ASTMC1202 test, the same batch of specimens divided into two groups are tested, and the chloride ion diffusion coefficient was calculated with the corresponding theory. The results indicate that the concentration gradient is larger, the concentration decreased faster and the slope of figure is more steep in salt ponding test, and the chloride ion diffusion is deeper for the role of the electric field in ASTM test. Although the diffusion mechanism is different in two kinds of test, there is little difference between the two groups of test diffusion coefficient.

Study on Switch from High-concentration to Low-concentration Tacalcitol during Concomitant Use of Bath-PUVA Therapy

2007 ◽  
Vol 69 (6) ◽  
pp. 660-664
Author(s):  
Maki IWAKIRI ◽  
Noriko YASAKA ◽  
Kotaro ITO ◽  
Yuichi YOSHIDA ◽  
Yumiko KUBOTA ◽  
...  
Keyword(s):  
Puva Therapy ◽  
High Concentration ◽  
Low Concentration

ASSESSMENT OF HEAVY METAL CONCENTRATION IN COCONUT WATER

1970 ◽  
pp. 07-10
Author(s):  
MdDidarul Islam, Ashiqur Rahaman, Aboni Afrose
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Heavy Metal Concentration ◽  
Coconut Water ◽  
Toxic Heavy Metals ◽  
High Concentration ◽  
Toxic Heavy Metal ◽  
Low Concentration ◽  
Wet Ashing ◽  
Aas Method

This study was based on determining concentration of essential and toxic heavy metal in coconut water available at a local Hazaribagh area in Dhaka, Bangladesh. All essential minerals, if present in the drinking water at high concentration or very low concentration, it has negative actions. In this study, fifteen samples and eight heavy metals were analyzed by Atomic Absorption Spectroscopy (AAS) method which was followed by wet ashing digestion method. The concentration obtained in mg/l were in the range of 0.3 to 1.5, 7.77 to 21.2, 0 to 0.71, 0 to 0.9, 0 to 0.2, 0.9 to 17.3, 0.1 to 0.9, 0 to 0.9 and 0 to 0.7 for Fe, Ni, Cu, Cd, Cr, Zn, Pb and Se respectively. From this data it was concluded that any toxic heavy metals like Cd, Cr, Pb and Ni exceed their toxicity level and some essential nutrients were in low concentration in those samples. 

Assessment of micro and macro nutrients in poultry feeds available in Dhaka city, Bangladesh.

2017 ◽  
Vol 1 ◽  
pp. 264
Author(s):  
Md Didarul Islam ◽  
Ashiqur Rahaman ◽  
Fahmida Jannat
Keyword(s):  
Heavy Metals ◽  
Adverse Effect ◽  
The Other ◽  
Nutrient Level ◽  
Dhaka City ◽  
Toxic Heavy Metals ◽  
High Concentration ◽  
Low Concentration ◽  
Feed Formulation ◽  
Macro Nutrients

This study was based on to determine the concentration of macro and micro nutrients as well as toxic and nontoxic heavy metals present in the chicken feed available in Dhaka city of Bangladesh. All macro nutrients, if present in the feed at high concentration have some adverse effect, at the same time if this nutrient present in the feed at low concentration this have some adverse effect too. So that this nutrient level should be maintained at a marginal level. On the other side toxic heavy metals if present in the feed at very low concentration those can contaminate the total environment of the ecosystem. In this study six brand samples (starter, grower, finisher and layer) which was collected from different renowned chicken feed formulation industry in Bangladesh. Those samples were prepared for analysis by wet ashing and then metals were determined by Atomic Absorption Spectroscopy. It was found that 27.7 to 68.4, 57.3 to 121.9, 0.21 to 4.1, 0.32 to 2.1, 0.11 to 1.58, 0.28 to 2.11 and 0.28 to 1.78 for zinc, iron, copper, mercury, cadmium, nickel and cobalt respectively. It was found that essential macro and micro nutrients were present in the feed in low concentration on the other side mercury was present in high concentration in the feed samples.

Chemistry of Variable Charge Soils

1997 ◽  
Keyword(s):  
Soil Pollution ◽  
Management Practices ◽  
Chemical Properties ◽  
Soil Management ◽  
Soil Productivity ◽  
Basic Difference ◽  
The Past ◽  
Variable Charge ◽  
Constant Charge ◽  
Variable Charge Soils

This book, based on research carried out at the Academia Sinica over the past 30 years, explains the basic difference between the variable charge soils of tropical and subtropical regions, and the constant charge soils of temperate regions. It will focus on the chemical properties of the variable charge soils--properties which have important bearing on soil management practices, including maximizing soil productivity and combating soil pollution.

scholarly journals Start-up Strategies for Anaerobic Ammonia Oxidation (Anammox) in In-Situ Nitrogen Removal from Polluted Groundwater in Rare Earth Mining Areas

2021 ◽  
Vol 13 (8) ◽  
pp. 4591
Author(s):  
Shuanglei Huang ◽  
Daishe Wu
Keyword(s):  
Rare Earth ◽  
Low Temperature ◽  
Removal Efficiency ◽  
Nitrogen Removal ◽  
Ex Situ ◽  
High Concentration ◽  
Low Concentration ◽  
Start Up ◽  
Anammox Activity

The tremendous input of ammonium and rare earth element (REE) ions released by the enormous consumption of (NH4)2SO4 in in situ leaching for ion-adsorption RE mining caused serious ground and surface water contamination. Anaerobic ammonium oxidation (anammox) was a sustainable in situ technology that can reduce this nitrogen pollution. In this research, in situ, semi in situ, and ex situ method of inoculation that included low-concentration (0.02 mg·L−1) and high-concentration (0.10 mg·L−1) lanthanum (La)(III) were adopted to explore effective start-up strategies for starting up anammox reactors seeded with activated sludge and anammox sludge. The reactors were refrigerated for 30 days at 4 °C to investigate the effects of La(III) during a period of low-temperature. The results showed that the in situ and semi in situ enrichment strategies with the addition of La(III) at a low-concentration La(III) addition (0.02 mg·L−1) reduced the length of time required to reactivate the sludge until it reached a state of stable anammox activity and high nitrogen removal efficiency by 60–71 days. The addition of La(III) promoted the formation of sludge floc with a compact structure that enabled it to resist the adverse effects of low temperature and so to maintain a high abundance of AnAOB and microbacterial community diversity of sludge during refrigeration period. The addition of La(III) at a high concentration caused the cellular percentage of AnAOB to decrease from 54.60 ± 6.19% to 17.35 ± 6.69% during the enrichment and reduced nitrogen removal efficiency to an unrecoverable level to post-refrigeration.

scholarly journals Phytoremediation Potential of Vetiver System Technology for Improving the Quality of Palm Oil Mill Effluent

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Negisa Darajeh ◽  
Azni Idris ◽  
Paul Truong ◽  
Astimar Abdul Aziz ◽  
Rosenani Abu Bakar ◽  
...  
Keyword(s):  
Palm Oil ◽  
Oxygen Demand ◽  
Raw Material ◽  
Biofuel Production ◽  
Palm Oil Mill Effluent ◽  
System Technology ◽  
High Concentration ◽  
Low Concentration ◽  
Control Sets ◽  
Palm Oil Mill

Palm oil mill effluent (POME), a pollutant produced by the palm oil industry, was treated by the Vetiver system technology (VST). This technology was applied for the first time to treat POME in order to decrease biochemical oxygen demand (BOD) and chemical oxygen demand (COD). In this study, two different concentrations of POME (low and high) were treated with Vetiver plants for 2 weeks. The results showed that Vetiver was able to reduce the BOD up to 90% in low concentration POME and 60% in high concentration POME, while control sets (without plant) only was able to reduce 15% of BOD. The COD reduction was 94% in low concentration POME and 39% in high concentration POME, while control just shows reduction of 12%. Morphologically, maximum root and shoot lengths were 70 cm, the number of tillers and leaves was 344 and 86, and biomass production was 4.1 kg m−2. These results showed that VST was effective in reducing BOD and COD in POME. The treatment in low concentration was superior to the high concentration. Furthermore, biomass of plant can be considered as a promising raw material for biofuel production while high amount of biomass was generated in low concentration of POME.

Effects of pH and ionic strength on the cation exchange capacity of soils with variable charge

Soil Research ◽  
1981 ◽  
Vol 19 (1) ◽  
pp. 93 ◽  
Author(s):  
GP Gillman
Keyword(s):  
Ionic Strength ◽  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Exchange Capacity ◽  
Surface Soils ◽  
Ph Values ◽  
Variable Charge ◽  
Effects Of Ph ◽  
Variable Charge Soils

The cation exchange capacity of six surface soils from north Queensland and Hawaii has been measured over a range of pH values (4-6) and ionic strength values (0.003-0.05). The results show that for variable charge soils, modest changes in electrolyte ionic strength are as important in their effect on caton exchange capacity as are changes in pH values.

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