Cations precipitation

Group III sulfides and hydroxides. /Left) Five Group III cations precipitatB as sulfides. These are NiS. CoS. and FeS (all of which are black], MnS (salmon), and ZnS (white). (Right) Jvio cations precipitate as hydroxides. AIIOHfo (white) and Cr(0H)3 (gray-green). 

Selig reported a potentiometric titration method for the analysis of procaine and some other organic cations precipitated by tetraphenylborate [67]. The development of ion selective coated-wire electrodes, and their application in the titration of procaine and other pharmaceutically important substances, was reported [68]. 

Heavy metal cations precipitate readily as hydroxides or carbonates in alkaline media. Dissolved carbonate content will be limited by calcite precipitation or by conversion of hydroxyl AFm to carbonate AFm. Hydroxide ions, on the other hand, are abundant. Here only the solids that may be present under oxic conditions will be discussed. Figure 5a shows the total dissolved heavy metal cation concentrations that would prevail if hydroxide precipitation were to be the dominant solubility-controlling process. Figure 5b shows the solubility of Ca metallate species, as these are likely to act as solubility-controlling phases for oxyanionic species. 

In order to achieve a satisfactory color yield, suitable cationic precipitants which exhaust straight onto the fiber must be used for deep dyeings. These products precipitate acid dyes and simultaneously have a fixing action as the binding link between the fibers and dye molecules. 

Figure 6 presents a scheme of an electrolysis cell for the isolation of reduction and oxidation products of nonaqueous solutions [15]. The electrolyte of the W.E. solution must be an alkyl ammonium salt because the reduction products of most of the commonly used solvents in the presence of metal cations precipitate as insoluble metal salts. The counter- and reference electrode compartments are separated from the working electrode compartment by two frits each. The separating units have pipes which enable the sampling of their solutions in order... 

Actinide Precipitant cation Precipitate Solubility in water at 20 3°C(mgAct./100gH20)... 

Regarding iron addition as described above, one important consideration is the removal of the iron ions (Fe or Fe ) in treated streams. These cation ions can easily be removed from treated water increasing the pH. This pH adjustment causes iron cation precipitation via the formation of iron hydroxide floccules. These floccules may entrap Ti02-suspended particles facilitating both iron cations and Ti02 removal from the treated water. 

The solution is made basic at this stage and more H2S is added. As we saw earlier, a basic solution produces a higher [S2-], which leads to precipitation of the more soluble sulfides. The cations precipitated as sulfides at this stage are Co2+, Zn2+, Mn2+, Ni2+, and Fe2+. If any Cr3+ and Al3+ ions are present, they will also precipitate, but as insoluble hydroxides (remember that the solution is now basic). The precipitate is separated from the solution containing the rest of the ions. 

Synthetic analogues of nonheme iron proteins include Fe tetramers, which form in good yield from FeCls and Na2S in methanol followed by treatment with NaHS and NaOCHs. Addition of a large cation precipitates (R4N)2(Fe4S4(SR)4) with R = Me, Et, and Bz" ... 

Many trace contaminants co-precipitate with Fe(III), behavior that can be problematic in many hydrometallurgical processes. However, such behavior is useful in removing arsenate from solutions, and has been tested for a broader range of contaminants. 2 There are unresolved questions on the long-term stability of such residues under ambient condilions.- - The theoretical basis behind cationic precipitation with Fe(III) or Al(ni) is essentially the same as the previous case—the formation of insoluble compounds, which have specific solubility products (A sp). ... 

In the case of one ISE technique, the dissolution was suspected to be insufficient. A citrate buffer was preferred to an acetate one. Moreover, it was stressed that the solution should be centrifuged prior to acidification. An alkaline filtration step allowed, however, to remove interfering cations (precipitation of Al, Fe, Ca, Mg etc.). Previous experience has shown that interfering cations could be removed if strong reagents were used which was the case. Consequently, the destruction method was accepted. 

FIGURE 8.29 A schematic presentation of the dependency of the electrophoretic mobility ( potential) on pH when the divalent cations precipitate as metal hydroxides on the particle surface at high pH. (a) Normal behavior for increasing electrolyte concentration, (b) Metal hydroxide (5) form at high pH. (c-d) Depending on the electrolyte concentration the second crossover point moves to lower pH due to enhanced surface precipitation. (From James, R.O. and Healy, T.W., J. Colloid Interface ScL, 40, 61, 1972. With permission of Harcourt Inc.)... 

To evaluate the importance of multivalent cation precipitation of surfactants by multivalent cations present in the formation brine or resulting from cation exchange and dissolution of minerals such as limestone, dolomite, etc., a very limited study of the calcium tolerance of selected alkylbenzene sulfonates was undertaken. 

Salting-out of alkylbenzene sulfonates from relatively dilute solutions by NaCl has been found to be substantial if the alkyl chain contains more than about 12 carbons. Similarly, the multivalent cation tolerance of alkylbenzene sulfonates in dilute solutions has been found to be small and strongly dependent on equivalent weight. In general, if the equivalent weight exceeds 350 (alkyl chain more than 12 carbons), the calcium tolerance appears to be extremely small. The addition of short-chain alcohols appears to be of limited benefit in preventing either salt-ing-out by NaCl or multivalent cation precipitation. 

GROUP CATION PRECIPITATING REAGENTS INSOLUBLE COMPOUND Ksp ... 

Since the chosen acids are relatively weak ones, to shift equilibrium (1.2.21) to the right, the cations precipitating chromate ions were added to the melt. Under these conditions the derivative of dichromate ion concentration... 

In tile test bromide is precipitated as silver bromide, and the precipitate s reaction toward nitric acid and ammonia is used to rule out other silver precipitates. Since a very high number of elements and also organic substances give a precipitate with silver nitrate, the description of selectivity below is not meant to be conclusive. It mainly deals with the other halogens and a few other inorganic cations. Precipitation with silver nitrate is also used for test (a) of 3.16. Chloride and test (a) of 3.19. Iodide, so the difference between the tests of these is dealt with in more detail. 

Table 6.3 Cations Precipitated by Hydroxyquinoline at Different pH. pH interval Cation...

Sodium cholate 431 1,700 0.367(8) 0.771-1- Forms unsoiubie complexes with divalent cations. Precipitates when pH < 6.5. 

The solution is made basic at this stage and more H2S is added. As we saw earlier, a basic solution prodnces a higher [S ], which leads to precipitation of the more soluble sulfides. The cations precipitated as sulfides at this... 

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