Magnesium bicarbonate

The lime or lime—soda process results in the precipitation of calcium as calcium carbonate and magnesium as magnesium hydroxide. The solubiUties of these compounds are shown in Figure 4 as functions of pH. When lime is used alone, only the carbonate hardness is reduced. The carbonate hardness is present as calcium or magnesium bicarbonate. The additional use of soda ash can reduce the noncarbonate hardness by providing additional carbonate ion. The reactions involved in the various steps of the process are Hsted below ... 

If calcium or magnesium bicarbonates are present in water, the rise in temperature decomposes them, and subsequent evolution of carbon dioxide will result In a higher corrosion rate, while at the same time calcium and magnesium carbonates may deposit on the metal surface. This scale may be protective, thus slowing the corrosion rate however, it can create concentration cells if it is deposited loosely, exposing parts of the surface. 

Carbon dioxide and calcium carbonate The effect of carbon dioxide is closely linked with the bicarbonate content. Normal carbonates are rarely found in natural waters but sodium bicarbonate is found in some underground supplies. Calcium bicarbonate is the most important, but magnesium bicarbonate may be present in smaller quantities in general, it may be regarded as having properties similar to those of the calcium compound except that on decomposition by heat it deposits magnesium hydroxide whereas calcium bicarbonate precipitates the carbonate. 

Although the presence of hardness is reported as calcium carbonate, in reality, for most water supplies the most common major contributors to total dissolved solids are calcium and magnesium bicarbonates. These dissolved solids most readily produce crystalline scales and thus predominantly contribute to boiler system deposits unless removed by some form of pre-boiler, external treatment process. 

Under alkaline BW conditions, if magnesium bicarbonate is not removed by softening or other pretreatment processes, it forms brucite, an insoluble flocculant sludge of magnesium hydroxide [Mg(OH)2],... 

As a consequence of the rapid scaling potential of calcium and magnesium bicarbonates and related salts, it is not only cost-effective with regard to BD and internal chemical treatment savings but also opera-... 

Apart from calcium and magnesium bicarbonates, most natural sources of MU water commonly contain some small amounts of silica and other dissolved minerals, salts, and contaminants. Under a wide variety of operational circumstances, every one of these common materials may contribute to complex boiler scales and deposits, especially the silicates. Thus, it is necessary to ensure that water chemistries are properly balanced and controlled. 

In addition to the formation of calcium carbonate sludge, some of the carbonate decomposes giving sodium hydroxide, which precipitates magnesium bicarbonate, and chloride, etc. as the hydroxide and is then incorporated into the carbonate sludge. Silicates are also often removed in the process as serpentine. Additional caustic may also need to be added, depending on the natural alkalinity present in the MU water. 

Carbonation of its slurry with carbon dioxide at 4 to 5 atm pressure yields magnesium bicarbonate ... 

Each of the dissolved minerals in any given source of makeup water has a potential for causing difficulties to a greater or lesser extent. For most water supplies, the commonest and highest levels of dissolved solids are the temporary hardness salts, calcium and magnesium bicarbonates. These are also the dissolved solids that most readily produce crystalline scales and thus contribute to cooling system deposits. Bicarbonates and carbonates provide the total alkalinity (M alkalinity) in most cooling waters, and normally there is no free hydroxide alkalinity. 

Calcium bicarbonate Ca(HC03)2 magnesium bicarbonate Mg(HC03)2... 

Many ways of deaddifying paper have been considered (1-5) and these include the use of calcium hydroxide/caldum bicarbonate solutions (Barrow s method) the use of magnesium bicarbonate in alcohols and other methods which to date have not been developed to any extent commercially. The main drawback with these methods are either the requirement to deblnd the book, or their labour intensive character they are thus expensive. The only bulk deaddlfication... 

The washing of the sheets In aqueous magnesium bicarbonate. The pH s of the untreated and treated paper were similar after this treatment. 

Deacidifying Agents. Magnesium bicarbonate solution (pH 6.4) was made from laboratory grade magnesium hydroxide using dry ice as the source of carbon dioxide (10). 

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