CITRIC ACID RECOVERY
The first step of citric acid recovery involves the
precipitation of oxalic acid, possibly in the form of calcium
oxalate at low pH, and subsequent separation from the medium
containing the mycelium through rotating filters or centrifuges.
Citric acid is then precipitated at pH 7.2 and 70-90 °C and
recovered by filtration and drying. If a purer product were
desired, it is dissolved with sulfuric acid, treated with charcoal
or ion exchange resins, and again crystallized as anhydrous
citric acid (above 40 °C) or as a monohydrate (below 36.5 °C)
(60). In surface processes, the mycelium is sometimes
squeezed to increase the recovery yield.