Leaching equilibrium relations

Equilibrium relations in leaching usually are simpler than in liquid-liquid equilibria, or perhaps only appear so because few measurements have been published. The solution phase normally contains no entrained solids so its composition appears on the hypotenuse of a triangular diagram like that of Example 14.8. Data for the raffinate phase may be measured as the holdup of solution by the solid, K lb solution/lb dry (oil-free) solid, as a function of the concentration of the solution, y lb oil/lb solution. The correspond-... 

Since the water movement will be very slow compared with the rate at which the wastes dissolve, we are concerned first and foremost with equilibrium solubility. Also, if only to relate behaviour on the geological time scale to that on the laboratory time scale, we will need to know about the mechanisms and kinetics of dissolution and leaching. The waste forms envisaged at present are glass blocks containing separated fission products and residual actinides fused into the glass and, alternatively, the uranium dioxide matrix of the used fuel containing unseparated fission products and plutonium. In the... 

Here k is the rate constant, and Kj is the equihbrium constant for an exchange reaction between protons and the metal M, at the surface. Oelkers argues that when the term Kfa +la Y is small, significant M, remains in the surface leached layer, and the rate equation simplifies in that the denominator becomes unity. For such a case, the logarithm of the far-from-equilibrium rate becomes linearly related to the logarithm of the activity of the aqueous species M, and is dependent only upon pH and activity of M,. Oelkers (2001b) has used this simplified rate equation to describe dissolution of basalt glass... 

In contrast, the presence of these cations has been observed to decrease the rate of dissolution of several feldspars (Sjoberg, 1989 Nesbitt et al, 1991 Stillings and Brantley, 1995) and to decrease the thickness of the leached layers formed on the feldspar surface. Schweda (1990), Nesbitt et al. (1991), and Brantley and Stillings (1996) proposed that feldspar dissolution in acidic solution far from equilibrium is related to competitive adsorption of and other cations on the surface of feldspar. Brantley and Stillings derived a rate equation based on a leached layer and Langmuir adsorption model ... 

Leaching and extraction tests are widely used for assessing trace element mobility and phytoavailability. As measurements in these protocols are made in equilibrium conditions, only thermodynamic information is obtained. However, kinetic extraction—desorption studies are a more correct approximation to the distribution of species in natural media. The desorption rate constants of the trace elements in sediments and soils can be related to their mobility and toxicity. Detailed studies are needed in this area. 

Separation by Solvent Extraction and Its Related Technique Nakamura et al. (2007) studied the solvent extraction separation of rare earths and alkali earths using PC-88A using the solution obtained by total leaching of phosphor wastes. Extraction equilibrium constant for each element was initially obtained assuming the stoichiometries for trivalent rare-earth ions (and Al " ") shown in Eq. (4) and for alkali-earth ions (M " ") as... 

With all t the catalysts from Ni Alg were most active. As to PM catalysts their activity is increased up to 75% A1 (ref.9). As shown above the composition Ni A1 5 is related by a solid solution on the NlAl-basls with a maximum possible deficit of Ni atoms. Alloys with a higher Hi content are close to equilibrium NiAl. whereas with the smaller one they have other phases (HiAl. Ni Al ). Apparently, the highest activity of these catalysts is due to the fact that as a result of MA Nj Al leaching the largest quantity of most dispersive Ni is formed, which is fixed on unleached NiAl particles. The thing is that richer nickel alloys are leached to a less extent and contain less Ni skeleton phase. Whereas Ni2.Al3 and NiAl leaching yields are not so fine particles of an active metal. 

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