Langelier saturation index ...

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Langelier saturation index (LSI) is the most widely used index in water treatment and distribution field. The index is based on the effect of pH on the equilibrium of calcium carbonate, CaCO3. LSI is the difference between the measured (actual) pH of water and the hypothetical value when water is in equilibrium with solid calcium carbonate. This value is known as pHs. LSI is defined by the following equation:
LSI = pH - pHs
At saturation, calcium carbonate is neither deposited nor dissolved. So LSI=0 and water believed to be stable. At super-saturation, LSI >0 , and water tends to precipitate calcium carbonate . It is called protective or precipitated and non-corrosive water. When pH is less than pHs then LSI

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May i know detail how can we control PH by Controlling & measuring LSI.....

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Very clear water, like RO permeate, has high tendency for dilluting anything is in contact with. So, if pipes are made from concrete, is very likely to dissolve carbonates consistently its pH raising.

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pH measurement of low TDS water has to be performed immediatelly after sampling and using a low impedance glass electrode. Otherwise sample's pH is tending to neutral, measurement takes long time to stabilized and electrode is destroyed.

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