Carbon speciation

Equilibrium with precipitation. The previous example calculated carbonate speciation admitting unrestricted solubility of all species. Actually, it is easily verified that the calculated calcium and carbonate concentrations exceed calcium carbonate solubility as measured by the solubility product... 

The measured 8 C- and 8 0-values of carbonates can be used to estimate the carbon and oxygen isotope composition of the fluid in the same way as has been discussed before for oxygen and hydrogen. The isotopic composition of carbon and oxygen in any carbonate precipitated in isotopic equilibrium with a fluid depends on the isotopic composition of carbon and oxygen in the fluid, the temperature of formation, and the relative proportions of dissolved carbon species (CO2, H2CO2, HCO2, and/or ). To determine carbonate speciation, pH and temperature must... 

Fung, K., Particulate Carbon Speciation by Mn02 Oxidation, Aerosol Sci. Technol., 12, 122-127 (1990). 

Braun, A. (2005). Carbon speciation in airborne particulate matter with C (Is) NEXAFS spectroscopy. 7 Environ. Monit. 7,1059-1065. 

Braun, A., Mun, B. S., Huggins, F. E., and Huffman, G. P. (2007). Carbon speciation of diesel exhaust and urban particulate matter NIST standard reference materials with C(ls) NEXAFS spectroscopy. Environ. Sci. Technol. 41,173-178. 

Solomon, D., Lehmann, J., Kinyangi, J., Liang, B., and Schafer, T. (2005a). Carbon K-edge NEXAFS and FTIR-ATR spectroscopic investigation of organic carbon speciation in soils. Soil Sci. Soc. Am. I. 69,107-119. 

Organic/elemental carbon speciation is performed on yg-sized samples using a thermal evolution technique (11) in which carbon is evolved in 2 discrete steps at 400°C in He and at 650<>C in 10% 02/He, then measured as OO2 by nondispersive infrared (NDIR) spectroscopy (Beckman Model 865). 13c/12c measurements are made by... 

King D. W. (1998) Role of carbonate speciation on the oxidation rate of Fe(II) in aquatic systems. Environ. Sci. Technol. 32, 2997-3003. 

The protonation of organic acid anions during alkalinity titration can cause serious errors in alkalinity determination and the use of the data for carbonate speciation and equilibrium chemical modeling. Errors in alkalinity depend on the same factors as for anion-cation balance and may vary from negligible values to as much as 1270% error as documented by Beck et (1974). Accurate values for alkalinity and carbonate speciation can be determined by direct measurement of CO2 evolved from acidified water samples. 

TABLE 6.6 Computed carbonate speciation, COj pressure, total carbonate Cj, and calcite saturation index, S4, of samples 1-8 from Slab Cabin Run... 

Figure 6.1 Notional carbon speciation in sediments. Profiles of carbon reservoirs observed in sediments, combined to give a qualitative picture of carbon cycling processes.

The carbonate speciation of the KCl, MgCl2 and NaCl solutions are given in Table I. The dependence of a upon one or several major forms of bicarbonate/carbonate was investigated for each of these solutions. 

Figure 1. Carbonate speciation in seawater at pH 6.0 and 8.1. The percent of H2CO3 pictured for pH 6.1 includes dissolved OO2.

In a first step, a generic approach for the precipitation/dissolution reactions without acid-based chemistry and inorganic carbon speciation is used. By a further step, these geochemical factors are included in order to obtain a more complete representation of the hydrogeochemistry in the aquifer. 

First a simple precipitation/dissolution reaction without carbon speciation and acid-based chemistry is considered (cf. Boudreau, 1997) using an approach similar to nonlinear adsorption/desorption (Langmuir isotherm). As shown above, the component A(jq) released by DOC biodegradation consuming a given electron acceptor can be buffered or precipitated by a precipitation/dissolution reaction... 

Using the simple approach of the precipitation/dissolution mechanism for rhodochrosite without inorganic carbon speciation the sampled variation of Fe and Mn along the Bahnbriicke transect could be verified. For the steady Fe and Mn profile is shown in Fig. 11.5. Note that the distances in Fig. 11.2 (geological transect) represent pathway distances along a flow path starting at the river bottom reflecting three-dimensional flow close to the river, and not linear distances to the Oder. 

The ratios of carbonate containing species in aqueous solution are a function of pH value as depicted by the weU-known carbonate speciation curve (Figure 6.13). Aqueous carbon takes on three different forms depending on the acidic or basic nature of the water. At pH 4.3, the concentration of bicarbonate (HCOs ) is 1% of the dissolved CO2, and neutralisation of carbonate (COs ) is virtually complete. Alkalinity is, thus, related to... 

Figure 6.13 Carbonate speciation curve. Aqueous carbon takes on three forms depending on the acidic or basic nature (pH) of water.

SIA manifold for carbon speciation in bathing waters. BTB bromothymol blue indicator Detector spectrophotometer (Xmax = 611 nm) Detector (MRC) multireflection cell coupled to light-emitting diode (Xmax = 660 nm) HC holding coil RC reaction coil SV selection valve. 

I.C. Santos, R.B.R. Mesquita, A. Machado, A.A. Bordalo, A.O.S.S. Rangel, Sequential injection methodology for carbon speciation in bathing waters. Anal. Chim. Acta 778 (2013) 38-47. 

The aim of this chapter is to describe both the high precision methods for the determination of total alkalinity At (potentiometric titration) and total dissolved inorganic carbon Ct (coulometry) that are the methods of choice today, and also a simpler method for total alkalinity (back titration) which does not require sophisticated computerised equipment. Thermodynamic calculations of carbonate speciation are also covered. 

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