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Comment PDF Separation Processes

Acid Recovery and Recycle Technologies

By Bryan Cullivan and Jared Cullivan |

This overview of a number of different methods for handling spent acids will help operators select the technology most suited for a given application The most common pickling, leaching and passivation acids are the mineral acids: sulfuric, hydrochloric and nitric. Mixtures of hydrofluoric acid and nitric acid are also used in cleaning, etching, passivating and chemical milling. Although the organic acids like acetic, phosphoric, citric, oxalic and tartaric have been used in small quantities and in limited applications, the mineral acids continue to dominate. In production uses of highly corrosive mineral acid, the rate of reaction slows as metal oxides dissolve into soluble salt. When the acids wane and reach the end of their effective life, they are either: 1) discarded as a hazardous waste; 2) neutralized into a solid waste sludge; or 3) processed through a recovery system to reclaim the valuable remaining acid. Focusing on the latter, this article describes the operation of the most prevalent acid-recovery and recycle technologies in use today. These include the following: Sulfuric acid recovery — low temperature crystallization (Figure 1) Hydrochloric acid recycle — pyrohydrolysis (spray roaster/fluidized bed) Hydrochloric…
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