A Redox-Recyclable Ion-Exchange System for Arsenic Removal

Period of Performance: 06/12/2003 - 03/12/2004

$100K

Phase 1 SBIR

Recipient Firm

Eltron Research, Inc.
4600 Nautilus Court South
Boulder, CO 80301
Principal Investigator

Abstract

This program will develop a novel electrochemically activated and deactivated ion-exchange system for removal of arsenic from industrial wastewater and groundwater. It is a liquid-liquid extraction system employing non-volatile, non-flammable alternative solvents instead of volatile organic compound (VOC) solvents, eliminating the primary objections to liquid-liquid processes while retaining their benefits. Ion-exchange resins circumvent use of VOC's, but elution with a "strip solution" is necessary to recover the target ion and regenerate the extractant, generating a large waste stream containing a low concentration of the target ion. Redox-active extractants make recovery in a small volume possible, but require chemical oxidants and reductants. We will electrochemically activate and deactivate the extractant in the conductive solvent. After ion-exchange, in which the target ion migrates into the solvent to ion-pair with the extractant, the phases are separated. The extractant is reduced and the target ion is released and recovered in a small volume for recycle or disposal without generation of large volumes of secondary waste, use of chemical oxidants or reductants, or loss of solvent, which can be reused. The technology will be applicable to many other target ions as well, and could eventually replace much of the anion-exchange technology now in place. This unique technology will combine the best features of liquid-liquid anion-exchange extraction and anion-exchange using resins, while avoiding many of the problems inherent in these systems, and will have added benefits as well. It will retain the fast kinetics of conventional liquid-liquid extraction systems, but will eliminate use of VOC solvents, which is the primary objection to liquid-liquid extraction. This will greatly reduce emissions to the environment and chemicals costs. Since RTIL's are intrinsic electrolytes, their use will also allow inexpensive and non-polluting electrochemical activation and deactivation of a redox-active extractant in situ. This will permit recovery of the target ion in a very small volume and will result in far fewer emissions and disposal and chemicals costs, as large quantities of a basic or acidic strip solution are typically required to regenerate conventional ion-exchange extractants. The proposed anion-exchange system will be applicable for removal of arsenate from industrial effluents and contaminated groundwater. It will find application in the wood preservation industry, which emits significant quantities of arsenate to the environment. Widespread contamination of groundwater with arsenic is a problem that must be addressed with new technologies, especially since the permissible level of arsenic in water has been reduced from 50 to 10 ppb. The costs for compliance are expected to be prohibitive, and needs may outpace current technology. This system will provide a cost-effective means of achieving compliance. It will be effective for the extraction of many other anionic contaminants as well, such as molybdate, antimonate, and large organic anions. This system offers important advantages over the ion-exchange technologies that are currently in place, including greatly reduced disposal and chemicals costs, reduced negative impact on the environment, and improved worker safety.