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

Abstract : Chromium (Cr) is widely used within Department of Defense (DoD) and industry for critical metal plating, corrosion control, and surface finishing requirements. However, the hexavalent Cr (Cr (VI) anion is toxic and must be removed from wastewaters prior to discharge. The current technology to remove Cr (Cr (VI) involves Cr (Cr (VI) reduction to Cr (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 1-1, based on 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 Cr (Cr (VI) discharges. The high cost of handling Cr (Cr (VI) in wastewater and the associated sludge generation is the key reason behind the DoD need to eliminating Cr (Cr (VI) use. 2 While DoD and others are evaluating alternatives to Cr (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 (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.