Effect of the size of variable charge soil particles on cadmium accumulation and adsorption

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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Impact of pre-existing sulphate on retention of imported chloride and nitrate in variable charge soil profiles

Geoderma ◽

10.1016/j.geoderma.2004.02.001 ◽

2004 ◽

Vol 123 (3-4) ◽

pp. 205-218 ◽

Cited By ~ 9

Author(s):

V. Rasiah ◽

J.D. Armour ◽

N.W. Menzies ◽

D.H. Heiner ◽

M.J. Donn

Keyword(s):

Soil Profiles ◽

Variable Charge ◽

Variable Charge Soil

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Electric Conductance

Chemistry of Variable Charge Soils ◽

10.1093/oso/9780195097450.003.0011 ◽

1997 ◽

Author(s):

C. B. Li

Keyword(s):

Electric Field ◽

Electric Fields ◽

Colloidal Particles ◽

Free Solution ◽

Soil Particles ◽

Electric Conductance ◽

Variable Charge ◽

Ac Electric Fields ◽

The Difference ◽

Variable Charge Soils

The migration of colloidal soil particles in an applied electric field has been discussed in Chapter 7. Soil particles carrying electric charges invariably adsorb equivalent amounts of ions of the opposite charge. Generally there is a certain amount of free ions present in soil solution. When an electric field is applied to a soil system, a phenomenon known as electric conductance occurs. As in the case for electrolyte solutions, soil particles and various ions interact with one another during their migration, and these interactions can affect the electric conductance of the system. Variable charge soils carry both positive and negative surface charges, and it can be expected that their interactions with various ions would be rather complicated during conductance. On the other hand, this makes the measurement of electric conductance an effective means in elucidating the mechanisms of interactions between variable charge soils and ions. Both direct-current (DC) electric fields and alternating-current (AC) electric fields can induce the migration of charged particles. In the latter case, the migration of these particles should be related to the frequency of the applied AC electric field. Therefore, in this chapter, after describing the principles of electric conductance of ions and colloids and the factors that affect the conductance of a soil, emphasis shall be placed on the interaction between variable charge soils and various ions as reflected by the frequency effect in electric conductance. For a colloidal suspension, the electric conductance may be regarded as the contribution of conductances of both charged colloidal particles and ions. These two parts may be called the electric conductance of colloidal panicles and the electric conductance of ions, respectively. However, in actual cases it is difficult to distinguish between these two parts. Therefore, it is a general practice to distinguish the electric conductance as that caused by colloidal particles plus their counterions from that caused by ions of the free solution. These may be called electric conductance of the colloid and electric conductance of the free solution. The former conductance is the difference between the electric conductance of the suspension and that of the free solution.

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Effect of pH, Ionic Strength and Heavy Metal Ions on p-Nitrophenol Adsorption by Variable Charge Soil of South China

Asian Journal of Chemistry ◽

10.14233/ajchem.2014.15788 ◽

2014 ◽

Vol 26 (9) ◽

pp. 2655-2660 ◽

Cited By ~ 2

Author(s):

J.Y. Zhang ◽

C.D. Wu ◽

Z.L. Zhang

Keyword(s):

Heavy Metal ◽

Ionic Strength ◽

Metal Ions ◽

South China ◽

Heavy Metal Ions ◽

Effect Of Ph ◽

Variable Charge ◽

Variable Charge Soil

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Sulfate adsorption on a variable charge soil and on reference minerals

Agriculture Ecosystems & Environment ◽

10.1016/0167-8809(93)90104-w ◽

1993 ◽

Vol 47 (2) ◽

pp. 87-102 ◽

Cited By ~ 26

Author(s):

Laurent Charlet ◽

Nancy Dise ◽

Werner Stumm

Keyword(s):

Sulfate Adsorption ◽

Variable Charge ◽

Variable Charge Soil

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The performance of enhanced coagulation for treating slightly polluted raw water combining polyaluminum chloride with variable charge soil

Water Science & Technology ◽

10.2166/wst.2014.423 ◽

2014 ◽

Vol 70 (12) ◽

pp. 1907-1912 ◽

Cited By ~ 2

Author(s):

Z. L. Zhang ◽

C. D. Wu ◽

Y. J. Wang ◽

J. C. Tang ◽

Y. P. Liu

Keyword(s):

Heavy Metals ◽

Main Mechanism ◽

Raw Water ◽

Polyaluminum Chloride ◽

Enhanced Coagulation ◽

Charge Neutralization ◽

Variable Charge ◽

Coagulation Performance ◽

Removal Efficiencies ◽

Variable Charge Soil

The feasibility and effectiveness of treating pollutants in slightly polluted raw water by variable charge soil and polyaluminum chloride (PAC) was investigated. Removal efficiencies of turbidity, phenol, aniline, algae and heavy metals (Cu2+, Zn2+ and Pb2+) were used to evaluate the coagulation performance. The results indicated that the addition of variable charge soil as a coagulant aid is advantageous due to the improvement of removal efficiencies. The tests also demonstrated that the presence of variable charge soil increased the removal of turbidity rather than adding residuary turbidity. The use of variable charge soil produced settleable flocs of greater density and bigger size. The main mechanism involved in the PAC coagulation was supposed to be sweep flocculation as well as charge-neutralization. Variable charge soil played a promoted aid role by adsorption in the enhanced coagulation process. It is concluded that the enhanced coagulation by PAC and variable charge soil, as coagulant and adsorbent, is more effective and efficient than traditional coagulation.

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Phosphate adsorption at variable charge soil/water interfaces as influenced by ionic strength

Soil Research ◽

10.1071/sr08181 ◽

2009 ◽

Vol 47 (5) ◽

pp. 529 ◽

Cited By ~ 8

Author(s):

Yong Wang ◽

Jun Jiang ◽

Ren-kou Xu ◽

Diwakar Tiwari

Keyword(s):

Ionic Strength ◽

Zeta Potential ◽

Salt Effect ◽

Phosphate Adsorption ◽

Adsorption Model ◽

Net Charge ◽

Variable Charge ◽

Opposite Trend ◽

Variable Charge Soil ◽

Soil Colloids

The effect of phosphate adsorption on zeta potential of the colloids of variable charge soils and the effect of ionic strength on phosphate adsorption by the soils were investigated using batch experimental method. The presence of phosphate resulted in the decrease in zeta potential and isoelectric point (IEP) of the colloids of the soils, which further suggested that the phosphate was adsorbed specifically by these soils. The effect of phosphate adsorption on zeta potential was correlated with the content of free Fe/Al oxides in the soils; the higher the content of Fe/Al oxides in a soil the greater was the decrease in zeta potential and IEP of the soil colloids. The intersection of phosphate adsorption–pH curves at different ionic strengths (a characteristic pH) was obtained for 2 Oxisols. Above this pH, the adsorption of phosphate increased with increasing ionic strength, whereas below it the reverse trend occurred. The intersect pH was 4.60 for the Oxisol from Guangdong and 4.55 for the Oxisol from Yunnan, which was lower than the values of PZSE (point of zero salt effect) of these soils, but near the PZNC (point of zero net charge) of the soils. The effects of ionic strength and pH on phosphate adsorption by these soils were interpreted with the help of an adsorption model developed previously by Bowden et al. The results of zeta potential suggested that the potential in an adsorption plane became less negative with increasing ionic strength above the soil PZNC and decreased with increasing ionic strength below the soil PZNC. These results support the hypothesis of the adsorption model that the potential in the adsorption plane changed with ionic strength with an opposite trend to the surface charge of these soils. The phosphate adsorption by these soils was related not only to the ionic strength but also to the types of electrolytes present. K+ induced a greater increase in phosphate adsorption than Na+ due to the greater affinity of the soils to K+ than Na+.

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