THE DISSOLUTION RATE OF Ca(OH)2 IN AQUEOUS SOLUTIONS

Abstract

The dissolution rate of reagent grade Ca(OH)2 in aqueous solutions has been determined by means of a spinning disc method. The dissolution rate was found to be independent of disc velocity at a disc Reynold's Number above 9×l03. The dissolution rate is important for environmental applications such as flue gas desulfurization using Ca(OH)2 in wet scrubbers and spray dryer reactors, and for pH control. The lime discs were prepared under high pressure in a cylinder and determined to have similar thermogravimetric response to temperature as that of the parent lime powder. The discs were tested in a pH slat device where the dissolution rate was correlated to acid consumption required to maintain a preset value of pH. Limestone powder was used to verify the experimental system as the results could be compared with published data. Lime dissolution rate was measured as a function of disc velocity, ω (rpm), solution pH and temperature (K). The variation of dissolution rate with temperature was found to follow an Arrhenius type expression, and the activation energy of dissolution was found to be 15,188J/mol, Also, dissolution rate increased exponentially with decreased values of pH over the pH range of 6.5 — 3.0. A correlation which has been used to describe limestone dissolution rate was also found to express lime dissolution for disc Reynolds’ numbers < 104. This correlation has the form $\ (Ns) = -17.68 - 280(1/7”) - 0.105(pH) + 0.458 ln(w).