(117au) Extractive Crystallization of Calcium Acetate Deicer from Water Plant Residuals

There are a large number of water treatment plants that need to use chemical softening of the water to bring hardness of the water to acceptable levels. The lime-soda softening process produces significant amounts solid residuals containing calcium carbonate, magnesium hydroxide and unreacted base that need to be disposed of. Discharge of the residuals to surface waters is prohibited. Hence much of this material is applied to agricultural lands or landfilled at considerable cost due to the high dewatering and transportation costs. In this study, the use of the residuals to produce calcium acetate by reacting the sludge with acetic acid for use as a chemical deicer during winter for snow and ice control. Currently, the industrial process for the production of calcium-magnesium-acetate (CMA) deicer is conducted by reacting acetic acid and dolomite lime in the aqueous phase. The reaction product solution containing CMA would then be subjected to evaporation process to produce dry powder as product. This concentration step via evaporation of water is costly as it consumes a great deal of energy. In this project, an extractive crystallization process using ethyl acetate as a solvent was studied to reduce energy costs associated with the synthesis of calcium acetate from water plant residuals.

Extractive crystallization was used to synthesize calcium acetate from water plant residuals or calcium carbonate and acetic acid using two immiscible phases. The aqueous phase containing calcium carbonate was used as the calcium source while the ethyl acetate organic phase containing acetic acid was used as the acetic acid source. The neutralization reaction takes place at the interphase of the two phases and then the produced calcium acetate migrates to the aqueous phase. By adjusting the phase ratios, an aqueous phase that is saturated with respect to calcium acetate can be produced. This paper will present data on the optimization of the water to organic phase ratios in the effective conversion of the reactants to the desired deicer product. Data will also be presented on the effects of mixing the two phases on the reaction and conversion rate.