Crystal growth and dissolution

If both crystallization and dissolution processes were purely diffusion controlled in nature, they should exhibit a true reciprocity the rate of crystallization should equal the rate of dissolution at a given temperature and under equal concentration driving forces, i.e. at equal displacements away from the equilibrium saturation conditions. In addition, all faces of a crystal would grow and dissolve at the same rate. These conditions rarely, if ever, occur in practice. 

Dissolution rate data obtained under forced convection conditions can be correlated by means of equation 6.64 or 6.65. As described in section 6.2.2, equation 6.64 is the preferred relationship on theoretical grounds, since Sh = 2 for mass transfer by convection in stagnant solution (Re = 0), whereas equation 6.65 incorrectly predicts a zero mass transfer rate (Sh = 0) for this condition. However, at reasonably high values of Sh ( 100) the use of the simpler equation 6.65 is quite justified. The exponent of the Schmidt number b is usually taken to be and for mass transfer from spheres the exponent of the Reynolds number a = 

Data plotted in accordance with equation 6.65 for the dissolution of potash alum crystals yield the relationship (Garside and Mullin, 1968) 

Rowe and Claxton (1965) have shown that heat and mass transfer from a single sphere in an assembly of spheres when water is the fluidizing medium can be described by 

Another correlation used for predicting rates of mass transfer in fixed and fluidized beds is that of Chu, Kalil and Wetteroth (1953). The y-factor for 

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The geochemical fate of most reactive substances (trace metals, pollutants) is controlled by the reaction of solutes with solid surfaces. Simple chemical models for the residence time of reactive elements in oceans, lakes, sediment, and soil systems are based on the partitioning of chemical species between the aqueous solution and the particle surface. The rates of processes involved in precipitation (heterogeneous nucleation, crystal growth) and dissolution of mineral phases, of importance in the weathering of rocks, in the formation of soils, and sediment diagenesis, are critically dependent on surface species and their structural identity. 

Geochemical kinetics is stiU in its infancy, and much research is necessary. One task is the accumulation of kinetic data, such as experimental determination of reaction rate laws and rate coefficients for homogeneous reactions, diffusion coefficients of various components in various phases under various conditions (temperature, pressure, fluid compositions, and phase compositions), interface reaction rates as a function of supersaturation, crystal growth and dissolution rates, and bubble growth and dissolution rates. These data are critical to geological applications of kinetics. Data collection requires increasingly more sophisticated experimental apparatus and analytical instruments, and often new progresses arise from new instrumentation or methods. 

Interface reaction is another necessary step for crystal growth and dissolution. After formation of crystal embryos, their growth requires attachment of molecules to the interface. The attachment and detachment of molecules and ions to and from the interface are referred to as interface reaction. (During nucleation, the attachment and detachment of molecules to and from clusters are similar to interface reaction.) For an existing crystal to dissolve in an existing melt. 

More examples and mathematical details of crystal growth and dissolution under various conditions can be found in Section 4.2. Furthermore, Lasaga... 

F. C. Frank, On the kinetic theory of crystal growth and dissolution process, in Growth and Perfection ofGrystals, eds. R. H. Doremus, B. W. Roberts, and V. Turnbull, New York, John Wiley Sons, 1958... 

A number of macroscopic observations have been carried out on crystal formation and dissolution in various solvents by the use of optical and electron microscopes. The kinetic and dynamic properties of crystal growth, and dissolution have been investigated in various chemical contexts. The structural analysis of crystals is an indispensable method in chemistry. However, it is still difficult or even impossible to answer the question how a crystal is born. 

Figure 10.4(b) Fluidized bed crystallizer (dimensions in mm). (1) Packing of glass beads (2) and (3) Stub pipes (4) Removable eylindrieal basket. (Reproduced by permission of the American Institute of Chemical Engineers 1984 AIChE from Influence of Hydrodynamics on Crystal Growth and Dissolution in a Fluidized Bed, Budz, J., Karpinski P.H., and Z. Name, AIChE Journal, vol. 30, no. 5, pp. 710-717 (1984).)... 

If crystal growth and dissolution, which occur in a parallel way are both purely diffusional, all crystal faces should at equal distance from equilibrium, grow and dissolve at the same rate. In reality growing planes are planar, while dissolving pianes become pitted and eroded (3,4), indicating that in the latter case an increased rate of mass transfer is taking place. Such pitted surfaces may again initiate secondary nucleation. 

Frank, F.C. (1958) Kinematic theory of crystal growth and dissolution processes. In Doremus, Roberts and Turnbull (1958), 411-420. 

Frank, F. C., On the kinematic theory of crystal growth and dissolution processes, II, Z. Phys. Chem. Neue Folge, 77, 84-92, 1972. 

Tawashi and Piccolo, gyg examined recent theories of crystal growth and dissolution, and have considered the role of substances which act as inhibitors of these two processes. F.D. C. Blue No.1, at concentrations of 100 mcg,/ml, reduces the dissolution rate of sulfaguanidine by 55%. This finding is consistent with the theory that dye molecules are preferentially adsorbed at the primary dissolution sites on the sulfaguanidine crystal. Polyvinylpyrrolidone inhibits the crystal growth of sulfathiazole. It has been proposed that the polymer forms a non-condensed, netlike film over the sulfathiazole crystal surface. 

Bosbach, D., Jordan, G. Rammensee, W. (1995). Crystal growth and dissolution kinetics of gypsum and fluorite An in situ Scatming Force Microscope study. Eur. J. Mineral, 7, 267-276. 

Crystal growth and dissolution are closely related. If the temperature does not remain constant on storage of suspensions continual dissolution and re-... 

Two-dimensional nucleation tequites ideally smooth crystal surfaces which exist in reality only under exceptional circumstances. In reality, imperfections of the crystal surface play the predominating role for nucleation in electrolytic crystal growth and dissolution. The presence of dislocations on the surface enhances the formation of nuclei for growth and dissolution drastically. The real process consists, therefore, of an alternating combination of layer growth and nucleation. The relation between these two processes depends very much on components of the solution and can be widely modified by the presence of adsorbates. The same situation is foimd in electrolytic dissolution of crystals. 

Crystal growth and dissolution processes on an edge are catalyzed by the activated sites and increase with their number and the strength of the bonds between the corresponding anion terminations and the aqueous species. 

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