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Removing Chromium(VI) from Wastewater by Anionic Liquid Ion Exchange (A-LIX)

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Cost and performance rept.

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Chromium Cr is widely used within the Department of Defense DoD and industry for critical metal plating, corrosion control and surface finishing requirements. However, the hexavalent Cr VI anion is toxic and must be removed from wastewaters prior to discharge. The current technology to remove Cr VI involves Cr VI reduction to Cr III followed by precipitation. While the precipitation process is effective, it generates large amounts of hazardous sludge. These sludges represent the single largest type of hazardous waste at many DoD maintenance facilities. As noted in Table 1, based on Air Force Air Logistic Center AF-ALC data, it has been estimated that about 1,960 tons per year of hazardous sludges are generated by the DoD primarily as a result of efforts to curtail CrVI discharges. The high cost of handling CrVI in wastewater and the associated sludge generation is the key reason behind the DoD need to eliminating CrVI use2. While DoD and others are evaluating alternatives to Cr VI, it is still the material of choice for corrosion resistance. Until all use of chromium is eliminated, there will be chromium discharges. Therefore, an improved Cr VI removal technology is needed. This project demonstrated the Anionic Liquid Ion Exchange A-LIX process for chromium separation and concentration for recycle. A-LIX technology continually extracts the chromate anion, from plating shop wastewater using a water immiscible tertiary amine extractant in a closed-loop process. The chromate anion is later stripped from the extractant phase of this process and the chromium is concentrated as sodium chromate. The A-LIX process produces a clean water stream that meets chromium discharge requirements, eliminates the need for the reducing agent, and drastically decreases plating shop wastes. A-LIX may also eventually lead to effective water recycle and reuse.

Subject Categories:

  • Physical Chemistry
  • Metallurgy and Metallography
  • Water Pollution and Control

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