Surface Charge

Chemistry of Variable Charge Soils ◽

10.1093/oso/9780195097450.003.0005 ◽

1997 ◽

Author(s):

X. N. Zhang ◽

A. Z. Zhao

Keyword(s):

Charge Density ◽

Surface Charge ◽

Clay Minerals ◽

Chemical Properties ◽

Surface Charges ◽

Variable Charge ◽

Surface Materials ◽

Two Factors ◽

Constant Charge ◽

Variable Charge Soils

The surface of soil colloids carries electric charges, and these surface charges are the basic cause for soil to possess a series of surface properties. Soil surface charges affect the chemical properties of the soil through varying the quantity of electric charge and the surface charge density. For example, adsorptions of cations and anions are caused by negative and positive surface charges of the soil, respectively. The amount of ions adsorbed is determined by the quantity of surface charge, whereas the tightness of adsorption is related to charge density. In addition, the migration of ions in soil, the formation of organo-mineral complexes,and the dispersion, flocculation, swelling, and shrinkage are all affected by surface charge properties of the soil. Therefore, surface charge properties have an important bearing on soil structure and plant nutrition. Variable charge soils are characterized by the high content of iron and aluminum oxides. The clay mineralogical composition is dominated by 1:1-type minerals, such as kaolinite. These two factors make the surface charge properties of variable charge soils distinctly different from those of constant charge soils of temperate regions which chiefly containin 2:1-type clay minerals. However, unlike the case for pure variable charge minerals, in variable charge soils there is generally the presence of a certain amount of 2:1-type clay minerals. Therefore, as a mixture of variable charge minerals and constant charge minerals, the surface charge properties of variable charge soils is more complicated. In this chapter, the origin and factors affecting surface charges of the soil as well as the relationship between these charges and soil type will be discussed. Despite the complexity in composition, a soil may be regarded as a mixed system consisting of constant charge surface materials and constant potential surface materials in different ratios (Anderson and Sposito, 1992; Gillman and Uehara, 1980). Examples of the former type such as montmorillonite and vermiculite carry permanent negative charges, while those of the latter type such as iron oxide and aluminum oxide carry variable charges. Commonly found constant charge clay minerals in soils include those layer silicates such as hydrous mica, vermiculite, montmorillonite, and chlorite.

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Chemistry of Variable Charge Soils

10.1093/oso/9780195097450.001.0001 ◽

1997 ◽

Cited By ~ 2

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.

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Acidity

Chemistry of Variable Charge Soils ◽

10.1093/oso/9780195097450.003.0014 ◽

1997 ◽

Author(s):

X. L. Kong ◽

X. N. Zhang

Keyword(s):

Surface Charge ◽

Soil Acidity ◽

Solid Phase ◽

Hydrogen Ions ◽

Variable Charge ◽

Aluminum Ions ◽

Acid Reaction ◽

The Relationship ◽

Constant Charge ◽

Variable Charge Soils

For variable charge soils, acidity is a property that is of equal importance as the surface charge. These two properties may affect each other, with the effect of the former on the latter more remarkable than the reverse. In the previous chapters it was shown that pH affects many other properties of the soil by affecting the surface charge. Therefore, soil acidity is more significant than surface charge in some aspects. Owing to a similar reason, the importance of acidity for variable charge soils may exceed that for constant charge soils. Soil acidity generally manifests itself in the form of hydrogen ions. Actually, these hydrogen ions are chiefly the product of the hydrolysis of aluminum ions. Therefore, when examining soil acidity it is necessary to examine the properties of aluminum ions. In the previous chapter the transformation of hydrogen ions into aluminum ions has already been mentioned. In this chapter the relationship between aluminum ions and hydrogen ions will be discussed in greater detail. Another difference between variable charge soils and constant charge soils with respect to acidity is that, not only hydrogen ions, but also hydroxyl ions can participate in chemical reactions between the solid phase and the liquid phase. In constant charge soils the quantity of hydroxyl ions is an induced variable and is determined by the quantity of hydrogen ions in the solution and the ionic product of water. In variable charge soils, on the other hand, the quantity is also determined by the chemical equilibrium of that ion species itself at the solid-solution interface. Thus, hydroxyl ions can, in turn, affect the quantity of hydrogen ions in solution. In this chapter the nature of acidity of variable charge soils will be discussed mainly from these characteristics. In the field of soil chemistry, there has been an interesting history with regard to the nature of soil acidity. Soon after the recognition of the relationship between acid reaction and hydrogen ions in chemistry, this concept of the nature of acidity was introduced into soil science, and the significance of hydrogen ions was invariably associated with it whenever soil acidity was considered.

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The role of clay minerals and the effect of H+ ions on removal of heavy metal (Pb2+) from contaminated soils

Canadian Geotechnical Journal ◽

10.1139/t99-106 ◽

2000 ◽

Vol 37 (2) ◽

pp. 296-307 ◽

Cited By ~ 31

Author(s):

Loretta Y Li ◽

Raymond S Li

Keyword(s):

Heavy Metals ◽

Heavy Metal ◽

Surface Charge ◽

Clay Minerals ◽

Contaminated Soils ◽

Surface Charges ◽

Buffer Solution ◽

Soil System ◽

Variable Charge ◽

Acid Leach

The importance of the surface charge of clay minerals (fixed or variable) and the effect of H+ ions on the adsorption and removal of Pb2+ ions from contaminated soil are investigated using kaolinite (variable charge) and two illitic (fixed charge) soils with pH 3.9 and 9.2. The adsorption-desorption characteristics of Pb2+ ions were determined using batch equilibrium tests and acid leach tests with various acids used to leach the soils. Under the same adsorption conditions, illitic soil adsorbed much more Pb2+ ions than kaolinite. The difference is largely due to the surface charges on the clay minerals. Removal of Pb2+ ions from variable-charge minerals (e.g., kaolinite) requires much less effort than removal of Pb2+ ions from constant-charge minerals (e.g., illite). The surface charge of a clay mineral has an important effect. By increasing the number of H+ ions available in the soil system with a buffer solution such as NaOAc-HOAc, heavy metals adsorbed on the clay surface are expelled to pore water. The increase in H+ ions in the soil system also assists in dissolving any metal carbonates, thereby increasing the solubility of heavy metals in illitic soil. The more H+ ions available in the pore fluid, the more Pb2+ ions can be released from the system.Key words: clay minerals, sorption, desorption, heavy metal, hydrogen ion, electrokinetic, acid leach.

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Charge Characteristics and Cation Exchanges Properties of Hilly Dryland Soils Aceh Besar, Indonesia

Aceh International Journal of Science and Technology ◽

10.13170/aijst.9.2.17565 ◽

2020 ◽

Vol 9 (2) ◽

pp. 90-101

Author(s):

Sufardi Sufardi ◽

Teti Arabia ◽

Khairullah Khairullah ◽

Karnilawati Karnilawati ◽

Sahbudin Sahbudin ◽

...

Keyword(s):

Cation Exchange ◽

Surface Charge ◽

Organic Amendments ◽

Chemical Properties ◽

Soil Surface ◽

Tropical Soils ◽

Exchange Capacity ◽

Surface Charges ◽

Variable Charge ◽

Negative Surface

Soil surface charge and cation exchange are important parameters of soil fertility in tropical soils. This study was conducted to investigate characteristics of surface charges and cation exchanges on four soil orders of the dryland in Aceh Besar district. The soil order includes Entisols Jantho (05o16’58.41” N; 95o37’51.82” E), Andisols Saree (05o27'15.6" N; 95o44'09,1" E), Inceptisols Cucum (05º18’18,37” N; 95º32’48,04” E), dan Oxisols Lembah Seulawah (05o27’19,4” N; 95o46’19,2” E). The charge characteristics of surface charge are evaluated from the parameter of DpH (pHH2O-pHKCl), variable charge (Vc), permanent charge (Pc), and point of zero charges (PZC). In contrast, cation exchange properties are evaluated from several soil chemical properties, such as soil organic matter (SOM), base saturation (BS), cation exchange capacity (CEC), and effective CEC (ECEC). The results show that the four pedons of soil in the hilly dryland of Aceh Besar include a variable charge because it has a PZC, which is characterized by a negative surface charge with a PZC of pHH2O and has CEC dependent soil pH. PZC value varies from 3.21 – 5.26 and sequentially PZC Andisols Oxisols Entisols Inceptisols. The total CEC value differs considerably from ECEC and the sum of cations. CEC total of the soils varies from 12.8 – 34.4 cmol kg-1, whereas the ECEC values vary from 2.72 – 8.66 cmol kg-1. The highest variable charge percentage is found in Andisols Saree. In contrast, the highest permanent charge is found in Inceptisols Cucum and is positively correlated with pHH20, PZC, CEC, and sums of cations or ECEC. Improving soil quality in hilly dryland soils in Aceh Besar District can be done by decreasing the PZC status of soils with organic amendments and fertilizers or increasing the pH by using liming.

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Effect of arsenate on adsorption of Zn(II) by three variable charge soils

Soil Research ◽

10.1071/sr06181 ◽

2007 ◽

Vol 45 (6) ◽

pp. 465 ◽

Cited By ~ 5

Author(s):

Jing Liang ◽

Ren-kou Xu ◽

Diwakar Tiwari ◽

An-zhen Zhao

Keyword(s):

Zeta Potential ◽

Surface Charge ◽

Iron Oxides ◽

Initial Concentration ◽

Variable Charge ◽

Study Results ◽

Negative Surface ◽

Negative Surface Charge ◽

Enhanced Adsorption ◽

Variable Charge Soils

The effect of arsenate on adsorption of Zn(II) in 3 variable charge soils (Hyper-Rhodic Ferralsol, Rhodic Ferralsol, and Haplic Acrisol) and the desorption of pre-adsorbed Zn(II) in the presence of arsenate were investigated in this study. Results showed that the presence of arsenate led to an increase in both the adsorption and desorption of Zn(II) in these variable charge soils. It was also suggested that the enhanced Zn(II) adsorption by arsenate was mainly due to the increase in negative surface charge of the soils induced by the specific adsorption of arsenate, and the increase in electrostatically adsorbed Zn(II) was responsible for the increase in the desorption of Zn(II). The effect of arsenate on Zn(II) adsorption primarily depends on the initial concentration of arsenate and Zn(II), the system pH, and the nature of soils. The enhanced adsorption of Zn(II) increased with the increase in the initial concentration of arsenate and the amount of arsenate adsorbed by the soils. The presence of arsenate decreased the zeta potential of soil suspensions and soil IEP and thus shifted the adsorption edge of Zn(II) to a lower pH region. The effect of arsenate on Zn(II) adsorption in these 3 soils followed the order Hyper-Rhodic Ferralsol > Rhodic Ferralsol > Haplic Acrisol, which was consistent to the contents of iron oxides in these soils and the amount of arsenate adsorbed by the soils.

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Reactions with Hydrogen Ions

Chemistry of Variable Charge Soils ◽

10.1093/oso/9780195097450.003.0013 ◽

1997 ◽

Author(s):

F. S. Zhang ◽

T. R. Yu

Keyword(s):

Ionization Energy ◽

Alkali Metals ◽

Chemical Properties ◽

Hydrogen Ion ◽

Hydrogen Ions ◽

Soil Particles ◽

Variable Charge ◽

Hydrated Proton ◽

Characteristic Features ◽

Variable Charge Soils

Hydrogen ion is one kind of cation which possesses many properties common to all cations. Hydrogen ion also has its own characteristic features which are of particular significance for variable charge soils. The interactions between hydrogen ions and the surface of soil particles is the basic cause of the variability of both positive and negative surface charges of variable charge soils. The quantity of hydrogen ions in soils determines the acidity of the soil while the acidity of variable charge soils is among the strongest in all the soils. This strong acidity of variable charge soils affects many other chemical properties of the soil. In this chapter, the basic properties of hydrogen ions will be briefly discussed. Then, the products and the kinetics of the interaction between hydrogen ions and variable charge soils will be treated. The dissociation of hydrogen ions from the surface of soil particles has already been mentioned in Chapter 2. After the dissociation of an electron, a hydrogen atom becomes a proton (H+ ion). The ionization energy of hydrogen atoms is 1310 kj mol-1, whereas those of alkali metals, Li, Na, K, and Cs, are 519, 494, 419 and 377 kj mol-1, respectively. This difference in the ionization energy between hydrogen and alkali metals indicates that protons have a particularly strong affinity for electrons. Therefore, protons are apt to form a covalent bond with other atoms by sharing a pair of electrons, or to form a hydrogen bond. Because of the absence of an electronic shell, a proton has a diameter of the order of 10-13 cm, while other ions with electronic shells generally have a diameter of the order of 10-8 cm. Because a proton is so small, it is quite accessible to its neighboring ions and molecules. Therefore, there is very little steric hindrance when protons participate in chemical reactions. The above-mentioned features of proton are the basis for its particular properties. Free proton in solution is extremely unstable because it is very active. In an aqueous solution it will react with water molecules to form a hydrated proton, H3O+.

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Interactions BetweenEscherchia coliand the Colloids of Three Variable Charge Soils and Their Effects on Soil Surface Charge Properties

Geomicrobiology Journal ◽

10.1080/01490451.2014.967419 ◽

2014 ◽

Vol 32 (6) ◽

pp. 511-520 ◽

Cited By ~ 11

Author(s):

Zhao-Dong Liu ◽

Zhi-Neng Hong ◽

Jiu-Yu Li ◽

Jun Jiang ◽

Ren-Kou Xu

Keyword(s):

Surface Charge ◽

Soil Surface ◽

Variable Charge ◽

Variable Charge Soils

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Effects of surface charge on the electrostatic energy of an ionic crystal

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1982.0068 ◽

1982 ◽

Vol 381 (1780) ◽

pp. 241-247 ◽

Cited By ~ 16

Keyword(s):

Charge Density ◽

Surface Charge ◽

Ionic Crystal ◽

Surface Charge Density ◽

Electrostatic Energy ◽

Excess Charge ◽

Surface Charges

An earlier paper discussed the influence of the shape of a macroscopic piece of ionic crystal on the electrostatic energy of the whole piece of crystal. Some of the considerations of that paper are extended to include the effects on the bulk term in the energy of distributing excess charge on the surface of the piece of crystal. The bulk term in the electrostatic energy of the piece of crystal plus surface charges depends on the shape of the piece and the surface charge density. The minimum of this bulk term with respect to surface charge density occurs at a well defined surface charge density and is the usual (shape-independent) Madelung crystal energy.

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Effect of Fe/Al oxides on desorption of Cd2+ from soils and minerals as related to diffuse layer overlapping

Soil Research ◽

10.1071/sr10148 ◽

2011 ◽

Vol 49 (3) ◽

pp. 231 ◽

Cited By ~ 11

Author(s):

Yan-ping Wang ◽

Ren-kou Xu ◽

Jiu-yu Li

Keyword(s):

Charge Density ◽

Surface Charge ◽

Surface Charge Density ◽

Charged Particles ◽

Double Layers ◽

Mineral Particles ◽

Variable Charge ◽

Electrical Double Layers ◽

Oppositely Charged ◽

Positively Charged

Cadmium is a toxic metal with high reactivity in acid variable charge soils. Adsorption and desorption of Cd2+ in soil and mineral particles can be affected by the interaction between the electrical double layers on oppositely charged particles, because the interaction can decrease the surface-charge density of the particles. We studied the effect of Fe/Al oxides on desorption of Cd2+ from soils and minerals and proposed the desorption mechanisms based on the overlapping of diffuse layers between negatively charged soils and mineral particles and positively charged Fe/Al oxide particles. Our results indicate that the overlapping of diffuse layers of electrical double layers between positively charged Fe/Al oxides [crystalline and amorphous Al(OH)3 and amorphous Fe(OH)3] and negatively charged Ultisol, Alfisol, kaolinite, and bentonite caused the effective negative surface-charge density on the soils and minerals to become less negative, and thus the adsorption affinity of these negatively charged surfaces for Cd2+ declined as a result of the incorporation of the Fe/Al oxides. Consequently, the release of exchangeable Cd2+ from the surfaces of the soils and minerals increased with the amount of Fe/Al oxides added. The more positive the charge on the surfaces of the Fe/Al oxides, the stronger the interaction of the electrical double layers between the oxides and soils and minerals, and thus the greater the release of Cd2+ from the soils and minerals. A decrease in pH led to an increase in the positive surface charge on the Fe/Al oxides and enhancement of the interaction of the electrical double layers between the oxides and soils and minerals. As a result, more Cd2+ was desorbed from the soils and minerals. This study suggests that the interaction between oppositely charged particles of variable charge soils can enhance the mobility of cadmium in the soils and thus increase its environmental risk.

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Supporting the surface charging mechanism of seismic-electromagnetic phenomena by the direct measurements of the electron and hole trapping centers

10.5194/egusphere-egu21-14204 ◽

2021 ◽

Author(s):

Kiriha Tanaka ◽

Hiroyuki Nagahama ◽

Jun Muto ◽

Toshitaka Oka ◽

Yasuo Yabe

Keyword(s):

Charge Density ◽

Surface Charge ◽

Surface Charge Density ◽

Rock Fracture ◽

Surface Charges ◽

Low Velocity ◽

Hole Trapping ◽

Surface Charging ◽

Charging Mechanism ◽

Trapping Centers

The mechanisms of the seismic-electromagnetic phenomena (SEP) attracted as precursors of short-term earthquake forecast have been suggested, however, it is still incompletely understood. Among the possible mechanisms of the SEP is the surface charging mechanism related to the electron and hole trapping centers in quartz. Previous studies evaluated the plausibility of the mechanism from the surface charge density by the measurement of current or potential changes. On the other hand, only a few studies have evaluated the plausibility from the direct measurements of the trapping centers&#8217; concentration.We have performed low-velocity friction experiments mimicking the fracture with low-frictional heating for simulated fault gouges (commercial natural quartz sands) at a normal stress of 1.0 MPa with displacements up to 1.4 m. In order to measure the concentration of the trapping centers in the simulated-fault gouges, we conducted electron spin resonance for the standard sample, TEMPOL (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl), and the gouges before and after friction. In recent decades, researchers also have obtained the concentrations of the trapping centers in the quartz damaged in the rock fracture experiments using ESR and a radical scavenger. From those concentrations with the measured or assumed surface areas, we calculated the surface charge density of the quartz and discussed the plausibility of the surface charging mechanism of the SEP.In our friction experiments, the E&#8217; type centers were detected at g2 = 2.001 (e.g., E1&#8217; center; &#8801;Si&#65381;, ES&#8217; center; &#8801;Si&#65381;, E&#945;&#8217; center; =Si:, where &#8722; is an electron pair, : is a lone pair, and &#65381; is an unpaired electron) in the ESR spectra of the simulated-quartz gouges and the trapping center increased by the fracture of low-velocity friction. Assuming that the trapping centers were produced on the grain surfaces by the fracture, the range of the increase in the surface charge density was (0.21&#8211;8.0) &#215;10-4 C/m2. The rock fracture experiments found the E1&#8217; center, non-bridging oxygen hole center (NBOHC; &#8801;Si&#8722;O&#65381;), and peroxy center (&#8801;Si&#8722;O&#8722;O&#65381;) in quartz. On the same assumption, the total surface charge density of those trapping centers and the density of the E1&#8217; center or NBOHC were estimated as 2.7&#215;10-1 and 5.0&#215;10-2&#8211;3.94 C/m2, respectively.The surface charge density required for a corona discharge that can cause the SEP in the air over a flat plane is reported over 5.0&#215;10-5 C/m2. The quantities calculated above are almost enough to induce a corona discharge. The surface charges can form the electric dipoles on the fault plane, inducing the electric and magnetic fields. Our experiment showed that the fracture by fault motions could produce the surface charges on the fault. It proves that the electromagnetic abnormalities by the fault motions may also be observed through the surface charging mechanism. Therefore, our study supports that the surface charging mechanism is plausible.

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