Calcium hardness

100 ml of the water sample is pipetted into a flask and 1 ml of 4N-sodium hydroxide and one tablet of calcium hardness indicator (BDH) is added. The content is titrated with 0.02 N-EDTA solution until the solution becomes violet (0.1 ml causes no further colour change). 

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Noncarbonate or permanent calcium hardness, if present, is not affected by treatment with lime alone. If noncarbonate magnesium hardness is present in an amount greater than 70 ppm and an excess hydroxyl alkalinity of about 5 ppm is maintained, the magnesium will be reduced to about 70 ppm, but the calcium will increase in proportion to the magnesium reduction. 

To improve magnesium reduction, which also improves siHca reduction in cold process softening, sodium aluminate may be used. The sodium aluminate provides hydroxyl ion (OH ) needed for improved magnesium reduction, without increasing calcium hardness in the treated water. In addition, the hydrolysis of sodium aluminate results in the formation of aluminum hydroxide, which aids in floe formation, sludge blanket conditioning, and siHca reduction. 

A negative attribute of orthophosphate is its tendency to precipitate with calcium hardness found ia natural waters. In recent years, deposit control agents that prevent this deposition have been developed. Owiag to its relatively low cost, orthophosphate is widely used as an iadustrial corrosion inhibitor. 

Environment Internal pH 8.2-7.8, phosphate-zinc, chlorine, 65-100°F (18-38°C), calcium, hardness 300-600 ppm, total alkalinity 45-60 ppm... 

Hardness leakage is also dependent on the raw water characteristics. If the Na/Ca ratio and calcium hardness are very high in the raw water, leakage of the hardness ions will be higher. 

Concentrations of individual constituents, such as calcium, hardness or alkalinity should be brought to mg/1 as CaC03 for any comparisons or calculations. 

Of the dissolved gases occurring in water, oxygen occupies a special position as it stimulates the corrosion reaction. Carbon dioxide is scarcely less important this constituent must, however, be considered in relation to other constituents, especially calcium hardness. 

NOTE The reporting of calcium hardness, total hardness, and alkalinity as CaC03 is simply a convenience because the molecular weight for this compound is an easy-to-use 100 ... 

Total hardness is equal to the sum of the calcium hardness and the magnesium hardness. 

Calcium hardness precipitates as calcium carbonate sludge... 

FWCaH — FW calcium hardness, in mg/1 (ppm) CaC03 FWMgH = FW magnesium hardness, in mg/1 CaC03 FWMA = FW methyl orange/total alkalinity, in mg/1 CaC03 RBWPA — Required BW phenolphthalein alkalinity, in mg/1 CaC03 COC = Cycles of FW concentration required in the BW... 

Nitrilotriacetic acid (NTA) and especially its trisodium, monohydrate salt, N(CHC00Na)3,H20. NTA is primarily manufactured by Monsanto Chemical Company, Inc. and Hampshire Chemical. Anhydrous NTA has a MW of 257. It is generally supplied for incorporation into formulations as 40% NTA (42.8% NTA Na3 H20), (Hampene 150). Its chelating activity at a pH level of 11 is 156 mg CaC03 per gram of chelant. That is, 10 ppm of chelant will sequester 1.56 ppm of calcium hardness. 

SS/MA may be structured in different ratios of sulfonated styrene to maleic anhydride. Typically, it is 3 1 (20,000 MW) or 1 1 (15,000 MW). The application rates of all calcium phosphate scale/sludge inhibitors or stabilizers vary, based on the amount of calcium present in the cooling system, with increased calcium hardness leading to higher levels of polymer required. 

M = the magnesium hardness expressed as CaC03 in the FW C = the calcium hardness expressed as CaC03 in the FW S = the silica expressed as Si02 in the FW... 

How would the calculations be changed if 20 mg kg-1 CaCOs equivalent of the permanent hardness were actually due to noncarbonate calcium hardness ... 

Scaling and corrosion are related phenomena. The properties of water influencing both are the calcium hardness, alkalinity, total dissolved solids, pH and temperature. Theoretically, the above conditions can be controlled so that the water is in equilibrium and neither corrosion nor scaling results. In practice, however, this equilibrium is difficult to achieve since it is a border condition, and a delicate balance must be maintained. 

C = calcium hardness, expressed as ppm CaC03 D = alkalinity, expressed as ppm CaC03... 

The amounts of each dissolved mineral present can be measured as calcium hardness, total hardness, alkalinity, etc., and often recorded in terms of ppm (mg/1) calcium carbonate (CaC03), simply because the molecular weight for this compound is an easy-to-use 100 (40 + 12 + 16 + 16 + 16 = 100). 

Total hardness is the sum of calcium hardness and magnesium hardness. 

Similarly, cooling water that is fully softened tends to lack sufficient buffering capacity and creates the potential for significant corrosion within the cooling system, so care and attention to design detail are needed if future corrosion problems are to be avoided. Also, most chemical treatments incorporate polymers or phosphonates of some sort to provide a measure of corrosion inhibition. These products usually require the presence of at least 25 to 35 ppm of calcium hardness to provide satisfactory inhibition. 

A useful rule for the prevention or minimization of magnesium silicate deposition within the typical pH range of a cooling system (which therefore tends to limit the calcium hardness component in the cooling water as well) is as follows ... 

This program formulation will tend to be dosed continuously to achieve a total phosphate reserve in the recirculating cooling water based on calcium hardness (as ppm CaCC>3), as shown here. 

The maximum calcium hardness that can be tolerated before bleed is mandatory is typically 1000 to 1200 ppm CaCC>3. 

Traditionally, recommendations for maximum calcium hardness have suggested levels of 800 ppm Ca hardness as CaCC>3. This is an oversimplification and depends greatly on a number of factors (see Critical Factors for Scale Deposition and Cycles of Concentration, Sections 10.8.11 and 10.8.12). In practice, many cooling systems with high-ionic-strength makeup water supplies can tolerate 1200 to 1400 ppm Ca hardness as CaCC>3 with a suitable and comprehensive treatment program. 

If significant phosphate is present, it is possible that a stabilized phosphate program has been used and the O-P ratios have not been maintained correctly, or the total phosphate reserve has been too high (check the makeup for phosphate content), or the reserve phosphate specific dispersant has been maintained at too low a level in relation to the calcium hardness. 

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. 

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