At pickling in solutions containing sulfuric acid metal sulfates develops by the reaction of acid on the iron.
As the iron oxides dissolve the pickling bath is strengthened with iron sulfates while the acid proportion decreases. Such a bath is called dead bath or a dead pickling solution. Hence a modern and non-polluting plant should aim on recycling of this pickling bath. In the steel industry especially large-scale crystallization processes find application for the regeneration or treatment of pickling bath.
We offer the regeneration process for the reclamation of iron sulfate heptahydrate by means of cooling-crystallization. The pickling bath is cooled down to a very low temperature and thus iron sulfate heptahydrate (FeSO4 x 7H2O) crystallizes and the pickling solution, poor in iron sulfate, is led back into the pickling circuit.