And bicarbonate species

We now consider as an example an analysis (Table 15.1) of water from Mono Lake, California. The reported alkalinity of 34 818 mg kg-1 as CaC03 is equivalent to 700 meq of acid or 350 mmol of H2SO4. Since at this pH carbonate and bicarbonate species are present in roughly equal concentrations, we can quickly estimate the total carbonate concentration to be about 30 000 mg kg-1. We take this value as a first guess and model the titration with react... 

The authors ascribed the high activity of Au/thoria to a Schottky junction effect between the metal and oxide leading to an enhancement of active OH groups associated with oxygen deficiencies. The authors did observe formation of formate, carbonate, and bicarbonate species, but are still elucidating which, if any, of the species are important for the mechanism. 

Cooling the zirconia from 450 to 25°C in H2/CO2 resulted in the formation of carbonate and bicarbonate species. (Additional TPD studies, not shown, established that formate and methoxide species did not form during the adsorption of CO2 > under the conditions reported here.) The use of H2 0 to exchange groups on the... 

Figure 4 also shows the formation of carbonates from CO2 and a lattice oxygen. The nature of the surface sites involved in carbonate formation were not revealed in these studies. The results for [ 0] incorporation into the carbonate and bicarbonate species, following C 02 adsorption, suggest that these species are formed at different sites and that there is no direct conversion of the carbonate into the bicarbonate. 

By pulsing CO and O2 over the catalysts on the TAP reactor, it is revealed that both molecttles are adsorbed reversibly on the surface. The lower conversions obtained when CO, O2 and H2 are simultaneously pulsed over the catalysts compared with those obtained in the fix bed reactor, are due to thermal effects and heat transfer differences in both types of experiments. In spite of that, a shift to longer times is observed for the maximttm of the CO2 peak signal compared to the transient responses of reactants. This shift suggests that H2O derived species, which are formed by oxidation of H2, and bicarbonate species, which are related to the -OH of the support, are involved on the reaction mechanism. 

In experiments where Mono Lake water was acidified to remove carbonate and bicarbonate ions and again adjusted to pH 10, more than 90 percent of the soluble plutonium moved to the sediment phase. When carbonate ion concentration was restored, the plutonium returned to solution—strong evidence of the importance of inorganic carbon to solubility in that system(13). Early studies with Lake Michigan water, which has low DOC, had also implicated bicarbonate and carbonate as stabilizing ligands for plutonium at pH 8(14). This latter research characterized the soluble species as mainly anionic in character. 

The complexation of Pu(IV) with carbonate ions is investigated by solubility measurements of 238Pu02 in neutral to alkaline solutions containing sodium carbonate and bicarbonate. The total concentration of carbonate ions and pH are varied at the constant ionic strength (I = 1.0), in which the initial pH values are adjusted by altering the ratio of carbonate to bicarbonate ions. The oxidation state of dissolved species in equilibrium solutions are determined by absorption spectrophotometry and differential pulse polarography. The most stable oxidation state of Pu in carbonate solutions is found to be Pu(IV), which is present as hydroxocarbonate or carbonate species. The formation constants of these complexes are calculated on the basis of solubility data which are determined to be a function of two variable parameters the carbonate concentration and pH. The hydrolysis reactions of Pu(IV) in the present experimental system assessed by using the literature data are taken into account for calculation of the carbonate complexation. 

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. 

Alternatively, a true C02 adduct may not be formed, and instead an isomer of the M(I) bicarbonate species M(C0)(HC03)(PPh3)2 may be generated (see below). 

There are several uranium ore-bodies in the world that cannot be leached economically with sulfuric acid because of the high limestone content of the ore. Such ore-bodies are generally leached with an alkaline solution of sodium carbonate and bicarbonate. Carbonate also forms anionic complexes with the uranyl ion the predominant species being UC fCC 4- — and may therefore also be treated with anion-exchange resins. 

The Cu(l) bicarbonate complex previously mentioned (77) was synthesized by the reactions summarized in Scheme 7, which includes C02 insertion into copper hydroxide and alkoxide species. The insertion reaction of C02 with metal hydroxides to form bicarbonates is believed to occur... 

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