The lactate ion is chiral, with two enantiomers, D and L. The L isomer is the one normally synthesized and metabolized by living organisms, but some bacteria can produce the D form or convert the L to D. Thus calcium lactate also has D and L isomers, where all anions are of the same type. Some synthesis processes yield a mixture of the two in equal parts, resulting in the DL salt. Both the L and the DL forms occur as crystals on the surface of aging Cheddar cheese. The solubility of calcium L-lactate in water increases significantly in presence of d-gluconate ions, from 6.7 g/dl) at 25 °C to 9.74 g/dl or more. Paradoxically, while the solubility of calcium L-lactate increases with temperature from 10 °C to 30 °C, the concentration of free ions decreases by almost one half. This is explained as the lactate and calcium ions becoming less hydrated and forming a complex. The DL form of the salt is much less soluble in water than the pure L or D isomers, so that a solution that contains as little as 25% of the D form will deposit racemic DL-lactate crystals instead of L-lactate. The pentahydrate loses water in a dry atmosphere between 35 and 135 °C, being reduced to the anhydrous form and losing its crystalline character. The process is reversed at 25 °C and 75% relative humidity.
Preparation
Calcium lactate can be prepared by the reaction of lactic acid with calcium carbonate or calcium hydroxide. Since the 19th century, the salt has been obtained industrially by fermentation of carbohydrates in the presence of calcium mineral sources such as calcium carbonate or calcium hydroxide. Fermentation may produce either D or L lactate, or a racemic mixture of both, depending on the type of organism used.
Calcium lactate may be added to animal rations as a source of calcium.
Chemistry
The compound was formerly an intermediate in the preparation of lactic acid for food and medical uses. The impure acid from various sources was converted to calcium lactate, purified by crystallization, and then converted back to acid by treatment with sulfuric acid, which precipitated the calcium as calcium sulfate. This method yielded a purer product than would be obtained by distillation of the original acid. Recently ammonium lactate has been used as an alternative to calcium in this process.
Water treatment
Calcium lactate has been considered as a coagulant for removing suspended solids from water, as a renewable, non-toxic, and biodegradable alternative to aluminum chloride.
Bioconcrete
Addition of calcium lactate substantially increases the compressive strength and reduces water permeability of bioconcrete, by enabling bacteria such as Enterococcus faecalis, Bacillus cohnii, Bacillus pseudofirmus and Sporosarcina pasteurii to produce more calcite.
