Magnesium water hardness

Uses Threshold inhibitor for calcium and magnesium water hardness applies. Incl. process aid in detergent mfg. general purpose cleaners heavy duly llqs. dishwasher liqs. hard surf, cleaners Properties M.w. 2500 vise. 60 cps pH 6.3 45% NV Rhodoline DF 6120 [Rhodia Novecare)... 

This produces sufficient concentrations of magnesium and calcium ions to render the water hard. The above reaction is readily reversed by boiling the water when the magnesium and calcium ions responsible for the hardness are removed as the insoluble carbonate. 

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. 

EDTA sequesters calcium and magnesium from hard water, preventing them from forming insoluble soap films (scum) with soaps and detergents. Chelators are sometimes used to sequester metal ions that interfere with dyes and perfumes. 

When there is a limitation of the phosphorus content in detergents of 1%, then addition of phosphonates can act as an alternative solution in combination with other polyvalent ion-binding substances. Especially when magnesium is a cause of water hardness the zeoliths can form precipitations. But phosphonates, like hydroxyethanephosphonic acid (HEDP) and ethylenediaminetetra-methylenephosphonic acid (EDTMP), are able to sequester magnesium ions as well. 

The difference in solubility between carbonates and hydrogen carbonates is responsible for the behavior of hard water, which is water that contains dissolved calcium and magnesium salts. Hard water originates as rainwater which dissolves carbon dioxide from the air and forms a very dilute solution of carbonic acid. 

A very important ligand (or chelating agent) for titrimetric analysis is the ethylenediaminetetraacetate (EDTA) ligand. It is especially useful in reacting with calcium and magnesium ions in hard water such that water hardness can be determined. The next section is devoted to this subject. 

A problem exists with this procedure, however, in that at basic pH values, many metal ions precipitate as the hydroxide, e.g., Mg(OH)2, and thus would be lost to the analysis. This occurs with the magnesium in the water hardness procedure alluded to earlier. Luckily, a happy medium exists. At pH =10, the reaction of the metal ion with the predominant HY - and Y4- species (Figure 5.21) is shifted sufficiently to the right for the quantitative requirement to be fulfilled, while at the same time the solution is not basic enough for the magnesium ions to precipitate appreciably. Thus, all solutions in the reaction flask in the water hardness determination are buffered at pH = 10, meaning that a conjugate acid-base pair... 

EDTA titrations are routinely used to determine water hardness in a laboratory. Raw well water samples can have a significant quantity of dissolved minerals that contribute to a variety of problems associated with the use of such water. These minerals consist chiefly of calcium and magnesium carbonates, sulfates, etc. The problems that arise are mostly a result of heating or boiling the water over a period of time such that the water is evaporated, and the calcium and magnesium salts become concentrated and precipitate in the form of a scale on the walls of the container, hence the term hardness. This kind of problem is evident in boilers, domestic and commercial water heaters, humidifiers, tea kettles, and the like. 

The contents of tap water vary among communities. In some areas, the water is hard. Hard water is water that contains large amounts of calcium or magnesium ions. Hardness can be measured in milligrams per liter (mg/L) of calcium or magnesium ions. Hard water makes it difficult to get hair, clothes, and dishes clean. In this lab, you will learn how hard water is softened and how softening water affects its ability to clean. You will also collect, test, and classify local sources of water. 

Multimedia filters, which consist of a top layer of coarse and low density anthracite, layers of silica, and then dense finest medium vitreous silicate, remove about 98% of particulates >20 tm. These filters are regularly back-washed to avoid buildup of particulates. Finer filters (S-lO tm) are used to remove suspended matter and colloidal materials. To prevent scaling due to water hardness, sodium ions generated from brine are exchanged with calcium and magnesium ions in the water. Activated carbon or metabisulfite is used to remove chlorine. 

Werner JJ, Arnold WA, McNeill K (2006) Water hardness as a photochemical parameter tetracycline photolysis as a function of calcium concentration, magnesium concentration, and pH. Environ Sci Technol 40 7236-7241... 

The impact of water hardness due to calcium or magnesium ions on detergents was explained in Section 7.3.1 The source of most Ca2+ and Mg2+ in hard water is the dissolution of limestone (CaCOs) or dolomite [CaMg(COs)2]. Magnesium carbonate is fairly soluble (1.26 mmol L 1 at ambient temperature), but CaCOs is much less so (0.153 mmol L 1). However, if the water contains dissolved CO2 (as indeed it will if it is exposed to the air see Exercise 14.9), the relatively freely soluble Ca(HCOs)2 forms, and the limestone slowly dissolves away ... 

Alkylbenzenesulfonic acids are light-colored, viscous liquids whose alkali and ammonium salts are soluble in water. The salts are neutral, relatively unaffected by water hardness, and stable toward alkaline and acid hydrolysis. Calcium and magnesium alkylbenzenesulfonates are less water-soluble than sodium or ammonium salts. They are, however, soluble in hydrocarbons and are used extensively in these media. LAS salts are stable to oxidation and can be incorporated in formulations containing oxidizing agents. Pure alkylbenzenesulfonates have been synthesized for property studies (60,61). 

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