Permanent water hardness

The addition of sodium carbonate also permanently softens hard water that contains calcium sulfate. As calcium ions form insoluble calcium carbonate to form soluble sodium sulfate, the calcium carbonate then sinks to the bottom. Sodium sulfate has no effect on the hardness of water. 

What is meant by water hardness Explain the difference between temporary and permanent hardness. 

The fourth basic reaction is the conversion of the permanent, noncarbonate hardness salts, such as calcium sulfate and calcium chloride, to produce more insoluble calcium carbonate. This reaction is achieved by the addition of soda ash. The total noncarbonate hardness is the sum of the calcium sulfate and calcium chloride present in the original raw water, plus that formed from magnesium sulfate or magnesium chloride in reaction 3. 

Hardness in water can be divided into two types - temporary and permanent. Temporary hardness is caused by the presence of dissolved calcium or magnesium hydrogencarbonates. Temporary hardness is so called because it is easily removed by boiling. 

A9.7.1.6 Speciation of the soluble form can be affected by pH, water hardness and other variables, and may yield particular forms of the metal ion which are more or less toxic. In addition, metal ions could be made non-available from the water column by a number of processes (e.g. mineralization and partitioning). Sometimes these processes can be sufficiently rapid to be analogous to degradation in assessing chronic classification. However, partitioning of the metal ion from the water column to other environmental media does not necessarily mean that it is no longer bioavailable, nor does it mean that the metal has been made permanently unavailable. 

A similar detergency maximum at almost the same oxyethylene content has been observed in the removal of oily soil from metal surfaces using similar surfactants in an alkaline, built formulation (Komor, 1969). The maximum here is at 68% oxyethylene (about 11 oxyethylene units per nonylphenol) at bath temperatures from 40 to 80°C. For a series of polyoxyethylenated nonrandom linear alkylphenols with Cg-Cig alkyl chains, optimum removal of sebum soil from cotton at 49°C and 50 and 300 ppm water hardness was obtained at 63-68% oxyethylene content (Smithson, 1966). A study of the removal of oily soil from cotton and permanent press cloths, and of clay from permanent press cloths by commercial POE alcohols, showed that POE Ci2-Ci4 alcohols with 60% or greater ethylene oxide content achieved the best soil removal (Cox, 1989). 

Throttling on the cooling water works fine, as far as pressure control is concerned. But if the water flow is restricted too much, the cooling-water outlet temperature may exceed 125 to ISS F. In this temperature range, water-hardness deposits plate out inside the tubes. Then the heat-transfer coefficient is permanently reduced by the fouling deposits. 

It is thus important to determine the relative amounts of calcium and magnesium, for addition of too much lime means that calcium ions are reintroduced into the water, i.e. it becomes hard again, the hardness being permanent. 

If the water is permanently hard due to MgS04, and lime is added, the precipitates calcium sulfate, CaS04, and magnesium hydroxide, Mg(OH)4, result, which are removed by sedimentation. 

The base exchange process removes both the temporary and permanent hardness salts from the water by allowing the water to flow through resin beads containing sodium zeolite, Na2Z. 

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