Temperatures weak solubility-temperature relationship

The solubility characteristics of a given substance in a solvent chosen have considerable influence on the selection of a suitable crystallization technique. In case of a weak solubility-temperature relationship, (as e.g. for NaCl) cooling crystallization is of course not the method of choice. Otherwise, when the solubility curves of two compounds differ signiflcanfly, these specific characteristics can be used for separation. For example, in the well-known hot leaching process, potassium chloride as target compound is separated from its mixtures with sodium chloride using the differences in the solubility functions (Figure 3.22). 

Acid-soluble metals such as iron have a relationship as shown in Fig. 28-2 7, In the middle pH range ( 4 to 10), the corrosion rate is controlled by the rate of transport of oxidizer (usually dissolved O9) to the metal surface. Iron is weakly amphoteric. At very high temperatures such as those encountered in boilers, the corrosion rate increases with increasing basicity, as shown by the dashed line. 

From eq 10.59, we see that the relationship of the mole fraction x with the scaling densities tpi and (pi is independent of either or b. Hence, the theoretical expressions for the temperature dependence of the mole fraction along the two phase boundaries, developed in the previous section, remain equally valid for weakly compressible liquid mixtures. This is the physical reason why eq 10.65 yields an excellent representation of the behaviour of the mole fraction x for liquid-liquid equilibria. As an example we show in Figure 10.5 closed solubility loops in 2-butanol + waterAs we explained earlier, closed solubility loops can be represented by the expansion of eq 10.65 provided that Ar is replaced by IATulI in accordance with eq 10.66. The closed solubility loops collapse into a double critical point at P = 85.6 MPa and T = 340 K. The implications of the theory for the behaviour near such a double critical point have been elucidated by Wang et Both near the upper critical solution temperature Ju and near the lower critical solution temperature Tl, Axcxc varies as A7 il in accordance with eq 10.65a. Near the double critical point both 7 j and 7 approach the temperature I d of the double critical point. Hence, near the double critical point... 

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