Concentrated pickling liquor

Spent pickle liquor in the acid pickling wastewaters is listed as hazardous waste K062, regulated under RCRA, as it contains considerable residual acidity and high concentrations of dissolved iron salts.2 Exhausted pickling baths are mainly composed of nitrate (150 to 180 g/L), fluoride (60 to 80 g/L), iron (III) (30 to 45 g/L), chromium (III) (5 to 10 g/L), and nickel (II) (3 to 5 g/L). 

Spent pickle liquor is considered a hazardous waste (K062) because it contains considerable residual acidity and high concentrations of dissolved iron salts. For example, spent pickle liquor and waste acid from the production of stainless steel is considered hazardous. The hazardous constituents in K062 are lead, nickel, and hexavalent chromium. Waste pickle liquor sludge generated by lime stabilization of spent pickle liquor is not considered hazardous unless it exhibits one or more of the characteristics of hazardous waste. An estimated 6 million tons of spent pickle liquor are generated annually in the U.S.1... 

Flydrochloric acid regeneration. This process is used to treat the spent pickle liquor containing free hydrochloric acid, ferrous chloride, and water that is obtained from steel finishing operations. The liquor is concentrated by heating to remove some of the water, followed by thermal decomposition in a roaster at temperatures (925 to 1050°C) sufficient for complete evaporation of water and decomposition of ferrous chloride into iron oxide (ferric oxide, Fe203) and hydrogen chloride (HC1) gas.19 The iron oxide is separated for offsite recovery or... 

Continuous ion exchange also facilitates the separation of metals in high-concentration aqueous solutions. A process was developed in South Africa to recover spem hydrochlotic add from pickle liquors. The Metsep process used three continuous countercurrent fluidized-bed columns to separate zinc and iron (Fe ) in hydrochloric acid prior to recovery in a pyrohydrolysis teacTOt. The flowsheet for the process is given in Figs. 13.2-2 and 13.2-3. Separation is possible with feed streams containing about 20 g/L zinc. 120 g/L iron, and 30 g/L hydrochloric acid. A special weak base anion-exchange resin was used with a specific gravity of about 1.2 g/cm. This was vital, since the feed solution density was about I.I g/cro. Selective separation of the chloride complexes of Zn and Fe is relatively easy since die latter does not... 

Woodall-Duckham Also called the Babcock W-D process. A process for recovering hydrochloric acid and metal oxides from spent metal chloride solutions, such as those obtained from metal pickling and ilmenite beneficiation. The liquor is first concentrated by evaporation, and then atomized in a heated spray-tower. Water evaporates from the droplets in the upper part of the tower, and chlorides are converted to oxides in the hotter, lower part. Developed by Woodall-Duckham in the 1960s by 1992, over 150 installations were in use worldwide. Now offered by Babcock Woodall-Duckham, United Kingdom. 

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