Linearity dissolution

Fig. 5.2a shows examples of the results obtained on the dissolution of 8-AI203. In batch experiments where pH is kept constant with an automatic titrator, the concentration of AI(III)(aq) (resulting from the dissolution) is plotted as a function of time. The linear dissolution kinetics observed for every pH is compatible with a process whose rate is controlled by a surface reaction. The rate of dissolution is obtained from the slope of the plots. 

For non-linear dissolutions, values were fitted with equation (1) using non-linear regression with RS/1 software (BBN Software Product Corporation, Cambridge, MA) ... 

Figure 7.5. Linear dissolution kinetics observed for the dissoiution ofy-A Oj (from Fvrrer and Stumm, 1986, with permission).

If we assume for a moment that the linear dissolution rates (LDR) are constant as long as the particle survives and that the flux (F) from the surface may be described in terms of moles silica/cm sec, then this surface flux times the molar volume (MV) of the mineral divided by the moles of Si per molecule ( Si) gives the rate at which the radius of a spherical particle or half the length of a cube will disappear by the dissolution process (9). 

Figure 13.6. (a) Linear dissolution kinetics observed for the dissolution of 6-AI2O3, representative of processes whose rates are controlled by a surface reaction and not by a transport step. (Data from Furrer and Stumm, (1986).) (b) Linear dissolution kinetics of frame silicates. Minerals used were pyroxenes and olivines their essential structural feature is the linkage of Si04 tetrahedra, laterally linked by bivalent cat-Fe -, Ca ). Plotted ate... 

In mineral dissolution reactions, net effects of dissolution can be translated into linear rates of recession of crystal surfaces in a direction perpendicular them. For dissolution of silicate minerals in water near 25°C under laboratory conditions, the linear dissolution rates are generally carbonate minerals calcite and dolomite, the linear dissolution rates are higher, I0o 1 mmyr 1, and for long period of time this translates into very high dissolution rates of more than 1 meter in 1000 years. 

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