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<br />W <br />-.J <br />W <br />...... <br /> <br />29 <br /> <br />shale increases with increase in velocity of flow. The same trend <br /> <br />holds for unweathered crushed shale (Figure 2.3) and for unweathered <br /> <br />shale rocks (Figure 2.4). These curves also demonstrate that the <br /> <br />unweathered shale is richer in soluble minerals and that dissolution <br /> <br />rate decreases with increase in size of dissolving mineral particles, <br /> <br />The large impact of particle size on dissolution rate is demonstrated <br /> <br />in Figure 2.5. Note that the unweathered large particles of shale <br /> <br />dissolve slower than the finer weathered shale, although SMC is <br /> <br />higher in the former. <br /> <br />2.1.3Analysis of Results <br />Rate of dissolution is controlled by the solute concentration <br /> <br />gradient between the bulk solution (the main body of flowing water) <br /> <br />and the region near the surface of the dissolving mineral crystal. <br /> <br />It is also inversely proportional to the thickness 0 of this so- <br /> <br />called doubl e-Iayer, 0 decreases as flow velocity increases and, <br /> <br />therefore, dissolution rate increased with increase in velocity as <br /> <br />depicted in Figures 2,2 - 2,5. <br /> <br />The rate of dissolution is also proportional to the surface area <br /> <br />of the dissolving mineral that is in contact with,the bulk solution, <br /> <br />This surface area is per unit weight or per unit macro-surface area <br /> <br />of mineral particles, Dissolution rates were, thus, larger for U <br /> <br />runs than for R runs, <br /> <br />The shape of the BC-time curves for the lab experiment can also <br /> <br />be explained. For a given run, the exposed surface area and 0 are <br /> <br />relatively constant. The only factor which affects the dissolution <br /> <br />rate is the diffusion gradient between the 0 layer and the rest of <br />