الفهرس 
Boron Adsorption/Desorption and Accumulation in a Calcareous Soil Cultivated with Table Grape (Vitis Vinifera L.) and Irrigated with Blended WaterOnly 14 pages are availabe for public view
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Abstract
In the modern chemistry, boron (B) locates in the group IIIA of the periodic table with an atomic number of 5 and atomic mass of 10.81. Its quantum representation is 1s22s22p1
(Lange, 1949). The elemental B in its pure state forms black crystals and it is a brown or yellow amorphous powder in its impure state. Emsley (1991) noted that it is difficult to prepare boron
element in a state of high purity due to its very high melting point (2300°C).
Boron is different from other elements in group IIIA (Aluminum, Al; Gallium, Ga;
Indium, In; and Thallium, Ti), where it is classified as a metalloid having properties between
metals and non-metals elements (Greenwood, 1973). Non-metalic elements have higher ionization energy and electronegativities than the metallic. B with its small size (covalent
radios, 0.8 – 1.01 °A) and high ionization energy (344.2 kJ mol-1
) in contrast to metals in the
group IIIA which form cations B forms anions. Also, B exhibits a characteristic oxidation state
of +3, but because it is much more nonmetallic its acid-forming properties are more pronounced. Moreover, B has high affinity for oxygen that leads to the basis of the extensive
chemistry of borates and related oxo-complexes (Kemp, 1956).
While crystalline boron is chemically inert and resistant to attack even by boiling
hydrofluoric or hydrochloric acid, micron sized amorphous boron reacts easily and sometimes intensely with these acids (Krebs, 2006). Boron salts, on the other, hand are generally very
water soluble, e.g. borax has a water solubility of 25.2 g L-1
(Kemp, 1956).
Boron is widely distributed in the nature but never found free as it occurs in the form of oxide (B2O3) in combination with the oxides of other elements. It is found in rocks and soils, particularly in clay rich marine sediments. According to Krauskopf (1972), the average of B
concentration in the earth’s crust is about 10 mg kg-1, representing 0.001% of the elemental
composition of the earth; ranging from 5.0 mg kg-1 in basalts to 100.0 mg kg-1
in shales (Woods, 1994). Borate mineral deposits are uncommon and often found in arid deserts with a geological
history of volcanic and/or hydrothermal activity (Mellor, 1980). Twelve commercially significant B compounds are found in the earth; the first is sodium tetraboratedecahydrate Na2B4O7 ×10H2O or borax. The other important boron containing minerals are ulexite
(NaCaB5O9. 8H2O), colemanite (Ca2B6O11.5H2O) and kernite (Na2B4O7. 4H2O). Borax, colemanite, ulexite and kernite provide more than 90% of the world’s boron demand (Woods,
1994). In soils, boron content is often low (<10 mg kg-1), while higher B content soils (10 - 100
mg kg-1) are usually associated with volcanic activity.
Boron released from rocks and soils through weathering processes reaches the aqueous environment as inorganic boric acid B(OH)3 or borate ion B(OH)4
. The distribution of these
two forms depends on the first dissociation constant of boric acid (Ka = 5.8×10-10 mol L-1) in
fresh water at 25 °C. Due to a relatively high pKa, boric acid has limited dissociation at neutral
or low pH values. Boric acid is a very weak and it acts as a Lewis acid by accepting a hydroxyl ion to form the borate anion as in the following equation.