Sulfate species

DeCarvalho and Choppin (10, 11) previously have reported the stability constants, complexation enthalpies, and entropies for a series of trivalent lanthanide and actinide sulfates. As their work was conducted a pH 3, the dominant sulfate species was S0 and the measured reaction was as in equation 12. 

To elucidate the higher BE peaks [S(2p) 168.9, 169.6 eV], we examined the Naflon film Itself because It has -SOj" cation exchange sites. Only C(ls) and F(ls) peaks were observed. No S(2p]f peak was observed even after Ar" bombardment. This result suggests that the surface concentration of cation exchange sites Involving -SO3 Is low. Sulfur located well below the surface would, of course, hot be detected by XPS, We assign the higher BE S(2p) peak to a surface sulfate species (11),... 

Contamination from other L-iduronic acid-containing glycosaminoglycans (dermatan sulfate and heparan sulfate species) cannot usually be lowered below the 1-2% level, unless repeated precipitations or treatments with resin are made. As will be discussed in Section VIII, extensive... 

More-specific methods are available for identifying and quantitating the typical, amino sugar component of heparin (and some heparan sulfate species), namely, 2-deoxy-2-sulfoamino-D-glucose. Most of these methods are based on conversion of these residues into 2,5-anhydro-D-mannose by deamination with nitrous acid (see Section VIII,2). The 2,5-anhydro-D-mannose residues may be determined either colorimetrically,52-54 or fluorimetrically.55... 

Although usually less prominent than D-glucuronic acid, nonsulfated L-iduronic acid (probably incorporated as in 3) is also a constituent of irregular regions of heparin,8,12,85 and accounts for up to 20% of some heparan sulfate species.8,85,146... 

Although use of radio and stable isotope labels involving the trio of covalently-bonded nitrogenous functions in 3 and in 78, provided evidence that isocyano is the precursor of the isothiocyano and formamido groups [30, 81], it remains to be shown that a biosynthetic equivalent of the in vitro chemically-proven fusion process between isocyano and free sulfur (e.g., cf. Introduction) exists in the cells of sponges. In marine biota, various ionic forms of sulfur in a number of oxidation states, as well as organo-polysulfides are known. However, any association with the isonitrile group and a sulfated species has yet to be established. 

To model the brine s chemistry, we need to estimate its oxidation state. We could use the ratio of sulfate to sulfide species to fix ao2 > but chemical analysis has not detected reduced sulfur in the brine, which is dominated by sulfate species. A less direct approach is to assume equilibrium with a mineral containing reduced iron or sulfur, or with a pair of minerals that form a redox couple. Equilibrium with hematite and magnetite, for example,... 

We can check our results for the Red Sea brine against two independent pieces of information. In our results, sulfate species such as NaSO dominate reduced sulfur species such as H2S(aq) and HS-, in seeming accord with the failure of analysis to detect reduced sulfur in the brine. The predominance of sulfate over sulfide species in our calculation reflects the oxidation state resulting from our assumption of equilibrium with sphalerite. 

Fig. 8.7. Molal concentrations m, and activities a, of calcium and sulfate species in equilibrium with gypsum at 25 °C as functions of NaCl concentration, calculated using the B-dot equation (left) and the hmw activity model (right).

Figure 8.7 shows how concentrations and activities of the calcium and sulfate species vary with NaCl concentration. In the B-dot model, there are three ion pairs (CaCl+, NaSO, and CaS04) in addition to the free ions Ca++ and SO4 . 

In this case, the program converges to a relatively oxidized solution in which sulfur speciation is dominated by sulfate species. 

Sulfur oxyanions are similar to nitrate and nitrite in that they are mobile in soil and can be converted to many different forms (see Chapter 4, Figure 4.8). However, they are different from the other oxyanions in that they are the source of the essential nutrient, sulfur, and are deposited on soil from the atmosphere. Sulfate species can be determined by X-ray fluoresence (XRF), making their determination easier than the other oxyanions [21,22], Sulfur is discussed in more detail in Section 6.2.23. 

Figure 15. Cyclic voltammogratn on Pt(ll I) at 10 mV for various pH solutions of 0.8 - 4.6, when the respective anion concentration was kept at 0. M. (A) Sulfate solutions at [sulfate species] = O.IM. (B) Perchlorate solutions at [CIO4] = 0.1 A/. (C) Phosphate solutions at 0. M ionic strength of phosphate species. (From Ref. 62.)...

EQCM frequency of 20 Hz, which corresponds to a one-third monolayer of sulfate species adsorption/desorption. However, the electricity from the above cyclic voltammogram current is calculated to be about 1 x 10 C ctn i.e., 6 x 10 molecules cin" which is about one-tenth of a monolayer. This may indicate that sulfate adsorption on Au(lll) is associated with a partial charge transfer process. In Fig. 25b, an increase in EQCM frequency was observed as for (a), and a decrease in the frequency was observed at the Cu underpotential deposition region. The frequency change due to Cu underpotential deposition is determined to be 35 Hz,... 

Table 5.8 Effect of Temperature and Pressure on Sulfate Species Speciation in Seawater. ...

This SO2 chemical adsorption consumes the anion vacancies leading to the inhibition of a-02 adsorption. Additionally, the formation of sulfite and sulfate species over the surface is possible via a subsequent reaction of chemisorbed SO2 with Fe O and Fe O2. Although those sulfite and sulfate species formed after 3 h poisoning under 80 ppm SO2 were not detected by XRD (line (b) in Figure 19) possibly due to their limited amounts, their formation was confirmed by FTIR (line (c) in Figme 20) ... 

Several investigators have utilized thermal techniques for the separation of sulfate species collected on filter media with subsequent analysis by electron impact mass spectrometry, wet chemical analysis or sulfur flame photometry. In most instances the separation between sulfuric acid and its ammonium salts was incomplete or problems were encountered in recovering the species of interest from filters heavily laden with particulate (29-34). 

In contrast, with platinum, SO2 removal, while always greater than the unpromoted case, tends to decrease with increasing temperature. The presence of platinum increases the rate of oxidative adsorption of SO2 to the point that the capacity of alumina becomes the limiting factor rather than the rate. The capacity, limited by thermodynamics, decreases with increasing temperature because of the stability of surface sulfate species... 

The results from this "temperature programmed reduction" indicate that there are two regimes as indicated in Figure 16. In Regime 1, at temperatures above 1050°F there is virtually complete removal of SO2 under the conditions of our test. In Regime 2, characterized by the step jump downward at 1050°F in the amount of SO2 adsorbed in successive cycles, there is only partial removal of SO2. This observation suggests two kinds of surface sulfate species present on this material, one easily and another more difficultly removed as indicated by Andersson (47). 

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