A study of calcium salt precipitation in solutions of malic and tartaric acid

Abstract

Calcium salt precipitation was studied in solutions of L( + )tartaric acid and L( - )malic acid in both water and ethanol/water mixtures. Calcium tartrate and calcium malate precipitated separately in an interrelated process. Calcium malate crystallization was strongly dependent on seed crystals. Calcium malate and calcium tartrate act as seed particles for calcium malate precipitation. There was no evidence of a calcium malate-tartrate 'double salt' precipitation. The crystallization kinetics indicate that most of the calcium tartrate precipitated quickly in an initial third order followed by a later third order process. Calcium malate precipitated slowly in two stages like the tartrate but the second stage lasted for many days. The addition of seed crystals shifted the calcium malate precipitation to a first order mechanism. The rate constants were determined for these different stages. Calciumcarbonate provided faster crystallization than calcium hydroxide for both the tartrate and malate precipitations. Ethanol increased the rate of crystallization of calcium tartrate generally and that of the malate with calcium carbonate.