Saturation , Langelier

Calcium—In general, calcium (as CaCOs) below 800 ppm should not result in calcium sulfate scale. In arid climates, however, the critical level may be much lower. For calcium carbonate scaling tendencies, calculate the Langelier Saturation Index or the Ryznar Stability Index. 

Langelier Saturation Index—Ideally, maintain between -0.5 and +0.5 A negative LSI indicates corrosion tendencies. A positive LSI indicates CaCOs scaling tendencies. 

LSI (Langelier Saturation Index) an indication of the corrosive (negative) or scale-forming (positive) tendencies of the water. Hardness the total dissolved calcium and magnesium salts in water. Compounds of these two elements are responsible for most scale deposits. Units are mg/l as CaCOs. 

Fig. 2.15 Langelier saturation index chart (after the American Chemical Society).

Domestic heating coil internal corrosion. Where naturally soft or lean city water is supplied and the Langelier Saturation Index (LSI) is below -1.0, acid corrosion takes place as a result of the acidic nature of the water. This water often has a high dissolved gas content, which additionally leads to pinhole corrosion. Where water velocities are too high (say, over 6 ft/s 1.8 m/s) the protective oxide layer is stripped off and erosion corrosion takes place. 

Water hardness in milligrams per liter of total Ca and Mg is considered soft at 0 to 17 mg/L, moderately hard at 60 to 120 mg/L, and very hard at > 180 mg/L. The Langelier saturation index, a measure of CaCOs solubility, should be < 0 in the retentate to prevent precipitation Pure Water Handbook, Osmonics, 1997). 

Procedure, for reducing sugars, 23 475 Laneth-5, cosmetic surfactant, 7 834t Langbeinite, 5 785t 20 627, 628 in chemical fertilizer, 20 629 screen analyses of, 20 629t Langelier saturation index (LSI), 26 142— 143... 

An early standard treatment method, used up to the mid 1950s and based on first identifying the precise cooling water CaCC>3 solubility equilibrium point for any system, then using sulfuric acid to control the Langelier Saturation Index (LSI) to approx. +0.6 (M alkalinity of approx. 80 ppm CaCC>3). Primarily employed for cooling systems with makeup water of a... 

Are the calculations for Langelier Saturation Index (LSI) or Ryznar Stability Index (SI) regularly undertaken and interpreted ... 

The Langelier Saturation Index (LSI) is a method for quantifying the scaling or corrosion tendency of water. It was originally applied to cooling water. The LSI is based on the pH and temperature of the water in question as well as the concentrations of TDS, calcium hardness, and alkalinity. 

Langelier Saturation Index is calculated using equation 3.10 ... 

Langelier Saturation Index is valid up to about 4,000 ppm TDS. At higher TDS concentrations, the Stiff-Davis Saturation Index (SDSI) is used, Equation 3.12 ... 

Solution The saturation pH is given as pHj = 10. The actual pH is 8.7, so the system is not saturated with calcium carbonate and no carbonate will precipitate the precipitation potential is therefore zero. At equilibrium at the Langelier saturation pH, the calcium ion concentration will remain the same at [Ca ] = 10 gmol/L. Ans... 

In recarbonation, the available calcium ion in solution is prevented from precipitation. Therefore, it remains to determine at what pH will the equilibrium condition be, given this calcium concentration. This determination is, in fact, the basis of the Langelier saturation pH. Adding carbonic acid will increase the acidity of the solution after it has neutralized any existing alkalinity. 

I I Water treatment engineers use the Langelier saturation index (LI) and Ryznar stability index (Rl) [7,2] to evaluate the scaling and corroding tendencies of water. Here is a graphical method for determining these pa-... 

Ryznar suggested an empirical expression similar to the Langelier saturation indices. The term 2pHj - pH which assumes only positive values was called the stability index. If the stability index ranges from 7.5-8.5 water is aggressive. If the index values are lower than 6 it means that the water will probably cause incrustations. If the stability index is approximately 7 the water is in equilibrium. 

LANGELIER SATURATION INDEX - An index (SI) based upon the pH of saturation of calcium carbonate used to determine the tendencies of a water supply toward corrosion or scaling. A positive index indicates scaling tendencies a negative one means corrosion tendencies. (Langlier Index = pH - pHs, where pH = actual pH of water and pHs = pH at which water having the same alkalinity and calcium content is just saturated with calcium carbonate. 

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