Calcium hardness limits

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 ... 

NOTE Although the addition ofHF to HCl can be beneficial in helping to control the corrosion of steel (because fluoride ions form very stable self-limiting complexes with ferric ions), HF should not be used where significant hardness scales are present because calcium and magnesium fluorides (CaF2, MgF2) may be precipitated. 

Based on the anode material employed, eight (8) subdivisions (A-H) have been developed by the U.S. EPA.5 As may be noted (Table 32.1), the zinc anode is divided into two groups (subcategories D and G) based on the electrolyte types. This difference is also reflected in the substantial differences in the manufacture, as well as the waste generated by the two groups. Although a subcategory of nuclear batteries is indicated, hardly any data exist that describes its construction, leave alone the waste characteristics. Similar paucity in information exists on thermal batteries (such as calcium batteries), whose production and use are limited to few operations, especially in... 

Sulfuric acid has found limited use in boiler cleaning operations. It is not feasible for removal of hardness scales due to the formation of highly insoluble calcium sulfate. It has found some use in cases where a high-strength, low-chloride solvent is necessary. Use of sulfuric acid requires high water usage in order to rinse the boiler sufficiently. 

Unlike hard biological materials that are composed primarily of one compound (calcium phosphate) and perform a limited number of functions (primarily structural). 

Some surface water supplies have only 10 to 50 ppm or more of total calcium and magnesium hardness they are naturally soft waters and may also be described as lean waters, due to dissolved solids from all sources being limited to perhaps only 30 to 60 ppm TDS. Cooling systems using this quality of water as makeup may employ cycles of concentration (COC) of 7 to 1 Ox or more. Control of hardness scales tends not to be an onerous task for modem polymeric scale inhibitors, but lean water formulations must allow for more aggressive conditions and a real risk of some metal wastage. 

Despite efforts to comply with the limitations on feed water quality, CEDI systems can still foul and scale with microbes, organics, iron and manganese, and calcium- and silica-based scales. This usually occurs due to upsets in the pretreatment system or a deficiency in the system design that result in excursion in feed water quality to the CEDI system. Organics, metals, hardness, and silica problems are usually found on the membranes and sometimes on the resin (as is the case with organics). Biofouling is typically found on the... 

If the hardness is represented as parts of calcium per 100,000 parts of water, the limit without excess of softening agent is represented approximately by the values... 

The usefulness of soaps is limited by their tendency to precipitate out of solution in hard water. Hard water is water that is acidic or that contains ions of calcium, magnesium, or iron. In acidic water (such as the acid rain of environmental concern), soap molecules are protonated to the free fatty acids. Without the ionized carboxylate group, the fatty acid floats to the top as a greasy acid scum precipitate. 

The water that flows through your faucet has been treated to remove, or limit, a large number of pollutants. It is far from pure, however. For example, it still contains dissolved ions, such as Ca2+(aq), Mg2+(aq), Fe2+(aq), Fe3+(aq), and S042-(aq). These ions, especially calcium and magnesium, make it difficult to form lather with soap. Water with high concentrations of these ions is called hard water, partly because it is hard to lather. Water with relatively low concentrations of these ions lathers well. It is called soft water. 

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