Bicarbonate-carbonate distribution

In Fig. 8.3, the measured pH-values of the investigated lakes are grouped by frequency. Two ranges of pH values appear in the recent investigation, one at pH 6 to 8 and a second at pH 2.5 to 4. Also seen from the literature (Pietsch 1979 Harvey 1980), a third pH range is revealed and a combined picture of all measured pH-values shows a three-modal frequency distribution. The ranges of pH-values and the concentrations of dissolved Al and Fe reflect the buffering potential of mainly three systems the bicarbonate/carbonate system, the Al(OH)x system, and the Fe(OH)x system. 

The saturation indices discussed previously can be calculated based upon total analytical values for all possible reactants. Ions in water, however, do not tend to exist totally as free ions [21]. Calcium, for example, may be paired with sulfate, bicarbonate, carbonate, phosphate, and other species. Bound ions are not readily available for scale formation and such binding, or reduced availability of the reactants, decreases the effective ion-activity product Saturation indices such as the LSI are based upon total analytical values rather than free species primarily because of the intense calculation requirements for determining the distribution of species in water. Speciation breakdown of all species in a given water requires numerous computer iterations to achieve the following [22] ... 

Sepa.ra.tlon, Sodium carbonate (soda ash) is recovered from a brine by first contacting the brine with carbon dioxide to form sodium bicarbonate. Sodium bicarbonate has a lower solubiUty than sodium carbonate, and it can be readily crystallized. The primary function of crystallization in this process is separation a high percentage of sodium bicarbonate is soHdified in a form that makes subsequent separation of the crystals from the mother hquor economical. With the available pressure drop across filters that separate Hquid and soHd, the capacity of the process is determined by the rate at which hquor flows through the filter cake. That rate is set by the crystal size distribution produced in the crystallizer. 

The component reactions in eqn. (2) are very fast, and the system exists in equilibrium. Additional carbon dioxide entering the sea is thus quickly converted into anions, distributing carbon atoms between the dissolved gas phase, carbonate and bicarbonate ions. This storage capacity is clear when the apparent equilibrium constants for the two reactions in eqn. (2) are examined, namely... 

Where FW contains bicarbonate or carbonate alkalinity (as calcium, magnesium, or sodium salts), these salts undergo thermal decomposition in the boiler, and the steam-volatile contaminant gas carbon dioxide is introduced into the steam distribution system, as shown ... 

Inorganic ligands in aqueous solutions, and in particular in natural freshwaters, include, in addition to H2O and OH, the major ions carbonate and bicarbonate, chloride, sulfate and also phosphate [29], The distribution of metal ions between these ligands depends on pH and on the relative concentrations of the ligands. The pH is a master variable with regard to the occurrence of hydrolysed species and to the formation of carbonate and bicarbonate complexes. 

The distributions of different acid-base pairs with pH are shown in Figure 3.1. Bicarbonate (HCO3 ) is the dominant carbonate species at near neutral pH silicic acid (H4Si04) is essentially undissociated at all pHs of interest and the ammonium ion (NH4+) is the dominant form of ammoniacal-N at pHs below about 8. Orthophosphate and sulfide have acidity constants near neutral pH. 

Lithium salts, generally in the form of the carbonate or bicarbonate, are rapidly absorbed from the gastrointestinal tract and reach a peak plasma concentration after 2- hours. Extreme fluctuations in blood lithium levels, which are associated with side effects such as nausea, diarrhoea and abdominal cramp, are reduced by using sustained release preparations. Lithium is not protein bound and therefore is widely distributed throughout the body water, which accounts for the adverse effects it has on most organ systems should it reach toxic levels. To avoid toxicity, and ensure optimal... 

Another simple addition reaction is the hydration of C02 to form the bicarbonate ion. Without catalysis the reaction may require several seconds,4 5 the apparent first-order rate constant being -0.03 s 1 at 25°C. Cells must often hasten die process. The specific catalyst carbonic anhydrase is widespread in its distribution... 

Isoenzymes III and VII have a more specialized distribution. Carbonic anhydrase III is abundant in adipocytes which use bicarbonate in fatty acid synthesis.7 Isoenzyme V is present in the mitochondrial matrix and is also abundant in both adipocytes and liver.7 8 Isoenzyme IV is a larger membrane-associated form, while VI is secreted into the saliva.10 Carbonic anhydrase has also been identified in E. coli.,11 in a methanobacterium,12 and in green plants.13 133 A 60-kDa carbonic anhydrase called nacrein is found in the organic matrix of the nacreous layer of the pearl oyster, the layer that forms aragonite (orthorhombic calcium carbonate) in the shell and in pearls.14... 

Both associated and nonassociated electrolytes exist in sea water, the latter (typified by the alkali metal ions U+, Na-, K+, Rb+, and Cs-) predominantly as solvated free cations. The major anions. Cl and Br, exist as free anions, whereas as much as 20% of the F in sea water may be associated as the ion-pair MgF+. and 103 may be a more important species of I than I-. Based on dissociation constants and individual ion activity coefficients the distribution of the major cations in sea water as sulfate, bicarbonate, or carbonate ion-pairs has been evaluated at specified conditions by Garrels and Thompson (19621. 

Hardness is a natural feature of waters, reflecting calcium and magnesium, as carbonates, bicarbonates and sulfates. It is normally very stable and would only require analysis if there was concern about scale formation in distribution and in plumbing in buildings. Low hardness may be a consideration if assessing the level of plumbing-related metals in water at the tap. 

The effluent water from the hardness removal reactor is basic and tends to deposit scales in distribution pipes. For this reason, this water should be stabilized. Stabilization is normally done using carbon dioxide, a process called recarbonation. Stabilization using carbon dioxide affects the concentration of the bicarbonate ion in the treated water. The concentrations of the SO4, Cl and NO3 ions are not affected, however, because they do not react with carbon dioxide. Their concentrations remain the same as when they were in the influent to the treatment plant. The original cation Na from the influent raw water is also not affected for the same reason that it does not react with carbon dioxide. Na is, however, introduced with the soda ash. 

Carbon dioxide behaves unlike other gases in the ocean. Most gases are not very soluble in water and are predominantly in the atmosphere. For example, only —1% of the world s oxygen is in the oceans 99% exists in the atmosphere. Because of the chemistry of seawater, however, the distribution of carbon between air and sea is reversed 98.5% of the carbon in the ocean-atmosphere systems is in the sea. Although this inorganic carbon is dissolved, less than 1 % of it is in the form of dissolved CO2 pco) most of the inorganic carbon is in the form of bicarbonate and carbonate ions (Table 3). 

---