Смягчение воды методом ионного обмена
Thus ions Ca2+ and Mg2+ pass from a solution to cationit, and ions Na+-from cationit in a solution, and rigidity is eliminated. After pauperization of cationit ions of Na+ cationits usually recycle. Them maintain in solution NaCl where there is a return replacement - ions Na+ pass in cationit, and ions Ca2+ and Mg2+ - in a solution:
CaR + 2Na+ = Na2R + Ca 2+
MgR + 2Na + = Na2R + Mg 2+
After that regenerated cationit can be used for mitigation of new portions of hard water. The degree of regeneration is influenced with type of ionits, structure of the sated layer, the nature, concentration and a solution of recycling substance, temperature, time of contact and the charge of reagents. Restoration of exchange capacity at regeneration usually makes 60 - 100 %.
Kinds of rigidity
General rigidity. It is defined by total concentration of ions of calcium and magnesium. Represents the sum of carbonate (time) and uncarbonate (constant) rigidity.
Carbonate rigidity. It is caused by presence in water of hydrocarbonates and carbonates (at рН> 8.3) calcium and magnesium. The given type of rigidity almost completely is eliminated at boiling waters and consequently refers to as time rigidity. At heating water hydrocarbonates break up with formation of a coal acid and settling out of a carbonate of calcium and oxyhydroxide of magnesium.
Uncarbonate rigidity. It is caused by presence calcium and magnesian salts of strong acids (the chamois, nitric, hydrochloric) and at boiling it is not eliminated (constant rigidity).
Origin of rigidity
Ions of calcium (Ca2+) and magnesium (Mg2+), and also others alkali-ground metals causing rigidity, are present at all mineralizeed waters. Their source are natural deposits of limestones, plaster and dolomite. Ions of calcium and magnesium act in water as a result of interaction dissolved dioxide of carbon with minerals and at other processes of dissolution and chemical aeration of rocks. As a source of these ions, the microbiological processes proceeding in soil on the area of a reservoir can serve in ground adjournment, and also sewage of the various enterprises also.
Rigidity of water changes over a wide range and there is a set of types of classifications of water on a degree of its rigidity. Usually in little mineralizeed waters prevails (up to 70%-80 %) the rigidity caused by ions of calcium (though in separate rare cases magnesian rigidity can reach(achieve) 50-60 %). With increase in a degree of a mineralization of water the contents of ions of calcium (Са2+) quickly falls and seldom exceeds 1 g/l. The contents of ions of magnesium (Mg2+) in high mineralizeed waters can reach several grammes, and in salty lakes - tens grammes on one litre of water.As a whole, rigidity of superficial waters, as a rule, is less than rigidity of waters underground. Rigidity of superficial waters is subject to appreciable seasonal fluctuations, reaching usually the greatest value at the end of winter and the least during a high water when it is plentifully diluted soft rain and thawed snow. Sea and ocean water have very high rigidity (tens and hundreds in mg - ecv/l)
Influence of rigidity
From the point of view of application of water for drinking needs, its acceptability on a degree of rigidity can vary essentially depending on local conditions. The threshold of taste for an ion of calcium lays (in recalculation on a mg - equivalent) in a range of 2-6 mg - ecv/l, depending on corresponding of anionits, and a threshold of taste for magnesium and than that is lower. In some cases water is comprehensible to consumers with rigidity above 10 mg-ecv/l. High rigidity worsens organoleptic properties of water, giving to it bitterish taste and having negative an effect on bodies of digestion.
The world Organization of Public health services (CART) does not offer any recommended size of rigidity under indications of influence on health. In materials the CART is spoken that though a number of researches and has revealed statistically inverse relationship between rigidity of potable water and the cardiovascular diseases, the available data are not sufficient for a conclusion about causal character of this communication. Similarly, unequivocally it is not proved, that soft water renders a negative effect on balance of mineral substances of an organism of the person
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