Treatment and recovery of pickling liquors

Abstract
The aim of this paper is to present the scientific and technological techniques available for the treatment and/or recycling of waste liquors from steel pickling processes in the steelmaking industry. Due to their high iron and acid contents, pickling liquors are a source of environmental pollution. The production of this type of waste is estimated at 100 1/t steel. Because of their pollutant content and corrosiveness these liquids appear in the list of hazardous wastes in all legislations. In US legislation (US Resource Conservation and Recovery Act. Public Law 94–580) they appear with number K062. When seeking to resolve the environmental problems associated with this type of waste two main options are available: that of applying treatments which aim to neutralize the waste or that of recycling the different components which make up the liquors. In this second case the aim should be to recover the acid which can be recycled in the pickling baths and to recover the iron, obtaining products with different commercial outlets. The ion exchange processes, in this moment, are the best methods for acid recovery, like Recoflo process for sulphuric liquors and Lurgi process for hydrochloric liquors. For the iron dissolved in the liquors, oxiprecipitation process is common for both pickler agents. Oxiprecipitations can only be used for liquors when the pickler agent has been recovery before. This process obtains a similar iron elimination rate than other processes and yields an iron by‐product for its use, without further transformation, in other industries like electronic and painting ones.

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