Bicarbonate-calcium-type

Saline soils vary considerably in their salt content, type of salt, structure and ease to be reclaimed. Dominant anions are chlorides, sulfates and carbonates, sometimes nitrates and bicarbonates. Sodium salts occur most frequently, but calcium and magnesium compounds are common as well, while mixtures of various salts and complex minerals are not exceptional. The non-salt solution contains mainly calcium salts (50-80%) magnesium (15-35%), potassium (2-5%) and sodium (1-5%) make up the remaining cations. In saline soils, however, the percentage of Ca2+ is lower, and the values of K+, Mg2+ and Na+ is higher. 

Again, there are several choices of extractant, and the preferred one depends mainly on the type of soil under test. One of the most widely used procedures is the Olsen method (Olsen ef al., 1954), which was developed in the USA to correlate crop response to fertilizer on calcareous soils. The amount of P extracted will vary with temperature (increases by 0.43 mg P kg- per degree rise between 20°C and 30°C) and shaking speed, so conditions should be standardized. The extractant is 0.5 M sodium bicarbonate adjusted to pH 8.5. The bicarbonate competes with phosphate on the adsorption sites extracts, and removes most, but not all of it, together with some soluble calcium phosphate. Addition of phosphate-free activated carbon before shaking is necessary if coloured soil extracts are obtained, and then they will require filtration. 

Figure 2. Bulk calcium transport by the osteoclast. Net acid transport is driven by the vacuolar-type H+-ATPase with a specialized large membrane subunit. Transport is balanced by chloride transport, probably involving both a chloride channel (CLIC-5) and a chloride bicarbonate antiporter (CLCN7). Supporting transport processes include chloride-bicarbonate exchange. Insertion of transporters is specific for subcellular locations and involves interaction of transporters with specific cytoskeletal components, including actin (See Colour Plate 29)...

Boone et al. (1968) centrifuge cells through a discontinuous 10-20% Ficoll gradient made up in Eagle s minimum essential medium modified for suspension (i.e. lacking calcium and bicarbonate and containing 10 times the normal phosphate concentration). They use an A-1X zonal centrifuge rotor and spin for 1 h at 1000 r.p.m. at 20°C, and obtained clear separation of different cell types (HeLa and rabbit thymocytes). 

Thus, water containing HC03 indicates C02-indueed interactions with rocks, and the balancing cations indicate the types of rocks passed calcium comes from interaction with limestone, and calcium and magnesium together come from interaction with dolomite potassium and, even more often, sodium in bicarbonate water come from silicate rocks rich in potassium or sodium feld-spars. 

Calcium hardness may either be carbonate or noncarbonate. The solubility product constant of CaC03 is K p = [Ca ][C03 ] = 5(10 ) at 25°C. A low value of the K p means that the snbstance has a low solnbility a valne of 5(10 ) is very low. Because of this very low solubility, calcium hardness is removed throngh precipitation of CaCOs. Becanse there are two types of calcinm hardness, there corresponds two general methods of removing it. When calcinm is associated with the bicarbonate ion, the hardness metal ion can be easily removed by providing the hydroxide radical. The of the bicarbonate becomes neutralized by the OH provided forming water and the ion necessary to precipitate calcinm carbonate. The softening reaction is as follows ... 

The next part of the string subscript is CaHCOs. This refers to the type of species involved. This is not really the correct formula for calcium bicarbonate, but because it is used as a subscript, it can be easily taken to mean calcium bicarbonate. Thus, the symbols Mj-cauco, and Mcaeco, refer to the total mass of calcium bicarbonate and the partial mass of calcium bicarbonate, respectively. Calcium bicarbonate, CaCHCOgjg, is said to be the type of species involved. 

Now, consider the fractional variables. For example, consider/Mgca and/o,. As in the mass variables, the first subscript of the fractional variable refers to the type of fraction of the mass. Thus, in /MgCa. the type of fraction is the fraction of Mg and, considering the fact that when Mg and Ca are used as subscripts, they refer to the noncarbonate forms of hardness,/MgCa stands for the fraction of the noncarbonate form of magnesium hardness, with Ca reminding about the relationship./ gca could just simply be written as /wg and they would be the same, but Ca is there, again, just as a reminder that it is also involved in the chemistry of the reaction. By the convention we have just discussed, /ca stands for the fraction of the noncarbonate form of calcium hardness. As a further example, to what does /cauco, refer The is the fraction of the calcium carbonate (bicarbonate) hardness. 

As discussed in Chapter 10, if T is used as the first subscript, then it refers to the total of the type of species that follows it. In our example variables, this T is not present. For example, in Mca(HC03)2kgeqAb the T is not present but the hrst subscript is calcium bicarbonate, which is the type of species involved, and there can be no other calcium bicarbonate. Thus, in this instance, the T is not needed. The second subscript in our example is kgeq. From previous conventions, this would be the reason for the existence of the calcium bicarbonate however, kgeq cannot be a reason for the existence of calcium bicarbonate, since it is a unit of measurement. Therefore, if we see a unit of measurement used as a subscript, that simply indicates the unit of measurement of the type of mass. Thus, kgeq is the unit of the calcium bicarbonate. The last subscript, Al, is the one which is the reason for the existence of the calcium bicarbonate. 

Now, consider the fractional variables such as /AicaCHco,) and /Aicao- Take /Aica(Hco3)3 first. By convention, the first subscript Al is the type of fraction of the species involved. In this instance, it would refer to the mass of alum, which could be Mai or MAikeq, if the masses are expressed as absolute mass or equivalent mass, respectively. The second subscript, Ca(HC03)2, is the reason for the existence of Al, which means that calcium bicarbonate is the one reacting with the alum in this fraction. Thus, in other words, /AicacecOjjj is the fraction of the alum that is reacted by calcium bicarbonate. By the same token, /Aicao is the fraction of alum that is reacted by lime. Other symbols of fractional variables can be interpreted similarly. 

Example 15.1. Isothermal Evaporation of a Natural Water Leading to CaCOj Precipitation Compute pH and solution composition during isothermal evaporation (25 C) for three types of calcium bicarbonate-containing waters... 

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