Release of hydroxyl ions during specific adsorption of chloride by variable-charge soils

1998 ◽  
Vol 161 (2) ◽  
pp. 109-113 ◽  
Author(s):  
J. H. Wang ◽  
T. R. Yu
Keyword(s):  
Specific Adsorption ◽  
Variable Charge ◽  
Variable Charge Soils

Coordination Adsorption of Anions

1997 ◽  
Author(s):  
G. Y. Zhang ◽  
T. R. Yu
Keyword(s):  
Functional Groups ◽  
Ligand Exchange ◽  
Specific Adsorption ◽  
Phosphate Adsorption ◽  
Fluoride Ions ◽  
Aluminum Oxides ◽  
Soil Particles ◽  
Variable Charge ◽  
Iron And Aluminum Oxides ◽  
Variable Charge Soils

In Chapter 4, when the electrostatic adsorption of anions by variable charge soils is discussed, another type of adsorption, specific adsorption, has already been mentioned, although it is not very remarkable for chloride ions and nitrate ions. For some other anions, specific adsorption can be very important. Specific adsorption is determined by the nature of the anions and is also related to the kind of functional groups on the surface of soils. In general, this type of adsorption is more pronounced in soils containing large amounts of iron and aluminum oxides. Therefore, specific adsorption of anions is one of the important characteristics of variable charge soils. Specific adsorption is a common term. For anions, the mechanism of specific adsorption is ligand exchange between these ions and some groups that have already been coordinately linked on the surface of soil particles. Therefore, the term coordination adsorption may be more appropriate than the term specific adsorption. For variable charge soils, phosphate is the strongest specifically adsorbed anion species. Phosphate adsorption is also the most intensively studied anion adsorption in soil science. However, the valence status of phosphate ions is apt to change with the change in environmental conditions. In the adsorption of phosphate by soils, in addition to ligand exchange, other mechanisms, such as chemical precipitation, may also be involved. Therefore, the phenomenon of phosphate adsorption is rather complex, and it is often difficult to make definitive interpretations of experimental results. In the present chapter, the coordination adsorption of anions will be discussed, mainly taking sulfate as the example, because sulfate is only secondary to phosphate in importance for agricultural production among anions capable of undergoing coordination adsorption. For the purpose of comparison, the adsorption of fluoride ions will also be mentioned. On the surface of soil particles there are functional groups such as hydroxyl groups (M-OH) and water molecules (M-OH2) that can participate in ligand exchange with anions. Al-OH, Fe-OH, Al-OH2, and Fe-OH2 groups on the surface of soil particles are the important sites for coordination adsorption of anions. Therefore, when a soil contains large amounts of iron and aluminum oxides, the phenomenon of coordination adsorption of anions will be more pronounced.

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.

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.

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

Soil Research ◽  
2007 ◽  
Vol 45 (6) ◽  
pp. 465 ◽  
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.

Effect of tea polyphenols on copper adsorption and manganese release in two variable-charge soils

2018 ◽  
Vol 190 ◽  
pp. 374-380 ◽  
Author(s):  
Ru-hai Wang ◽  
Xiao-fang Zhu ◽  
Wei Qian ◽  
Hao-ye Tang ◽  
Jun Jiang ◽  
...  
Keyword(s):  
Tea Polyphenols ◽  
Copper Adsorption ◽  
Variable Charge ◽  
Manganese Release ◽  
Variable Charge Soils

Acidity

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.

Reactions with Hydrogen Ions

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+.

Electrostatic Adsorption of Anions

1997 ◽  
Author(s):  
G. L. Ji
Keyword(s):  
Electrostatic Force ◽  
Theory And Practice ◽  
Water Molecules ◽  
Specific Force ◽  
Electrostatic Adsorption ◽  
Variable Charge ◽  
Negative Surface ◽  
Repulsive Forces ◽  
Anion Species ◽  
Variable Charge Soils

Electrostatic adsorption of anions is one of the important characteristics of variable charge soils. This is caused by the fundamental feature that these soils carry a large quantity of positive surface charge. However, because these soils carry positive as well as negative surface charges, they may exert both attractive and repulsive forces on anions. Therefore, the situation in the adsorption of anions by these soils may be quite complex. There may also be the occurrence of negative adsorption of anions. Besides, for some anion species both electrostatic force and specific force may be involved during their interactions with variable charge soils. As shall be seen in this chapter, such specific force may be operative even for some anion species such as chloride that are generally considered as solely electrostatic in nature during adsorption. Because of historical reasons, the literature on electrostatic adsorption of anions by soils is very limited. Nevertheless, as shall be seen in this chapter, the topic is of interest in both theory and practice. In the present chapter, adsorption of anions shall be discussed mainly from the viewpoint of electrostatic adsorption. The other type of adsorption, specific adsorption or coordination adsorption, shall be dealt with in Chapter 6. The radius of anions is generally much larger than that of cations. Thus, the charge density on anions would be low. When hydrated, because of the smaller ion-dipole force exerted on water molecules, anions are less hydrated than cations. This can be seen in Table 4.1. The rH/rc ratio for cations ranges from 2.22 to 6.37, while that for anions is smaller than 2 except for F-. The orientation of water molecules around anions, especially in the primary hydration region, is also different from that around cations (Conway, 1981). Because of the small rH/rc ratio, hydration does not induce the change in order of size when anions of the same valency are compared. For example, the crystal radii of Cl-, NO3-, and ClO4- are 0.181, 0.264, and 0.292 nm, respectively, while the hydrated radii of these ions are 0.332, 0.335, and 0.338, respectively.

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