Method of preparing hydrochloric acid and high purity ferrous sulfate hydrate crystals from hydrochloric acid waste pickle liquor

摘要

A method of recovering a wide range of hydrochloric acid concentrations and high quality ferrous sulfate by-product in several hydrate forms from waste pickle liquor containing ferrous chloride. The waste pickle liquor is concentrated in a concentrator crystallizer by boiling off water and free hydrogen chloride until ferrous chloride precipitates as a crystalline hydrate. Water and hydrogen chloride vapors from the concentrator crystallizer are directed to an acid vapor fractionator which produces an overhead line of substantially pure water that is condensed and discharged into a storage tank for subsequent use. Relatively weak hydrochloric acid from the bottom liquor in the fractionator is bled off and stored or mixed with stronger acid product formed at another stage of the process. The hydrate crystals of ferrous chloride are fed to a reactor where sulfuric acid is added to react with the ferrous chloride crystals thereby forming hydrogen chloride and ferrous sulfate monohydrate. Water and hydrogen chloride vapors from the reactor are discharged and condensed for producing the strong acid product. When the strong acid from the reactor is mixed with the fractionator bottoms, the resulting mixture is controlled to yield any one of several desired concentrations. A high quality ferrous sulfate by- product is produced as a result of at least two crystallizations occurring in the concentrator crystallizer and reactor, respectively. Even higher hydrates of ferrous sulfate may be produced by recrystallizing the ferrous sulfate monohydrate from the reactor thereby further improving the quality of the ferrous sulfate product.