| Abstract: | The initial dissolution rate of sand into sodium hydroxide solution (12.5 mol/L) over a wide range of temperatures (150 to 220°C) and pressures (0.47 to 2.29 MPa) has been determined. A semi-empirical equation was found to fit the dissolution data obtained at different temperatures and at different particle sizes. The influence of temperature on the reaction extent led to the activation energy of the dissolution, Ea = 74.41 kJ/mol. Six samples of sieved silica having narrow particle size distribution 38–40, 100–125, 212–200, 400–500 and 850–1000 μm were reacted with 12.5 mol/L sodium hydroxide solution at 220°C. The effect of particle size, i.e., surface area of the grains, on the initial rate of dissolution (denoted v0) has been described by an empirical equation. Evidence is given here showing that the general assumption of the simple proportionality between the rate of reaction and the exposed surface of solid is not always confirmed. |
