2004 Progress Report: A Novel Ion Exchange Process for Selective Removal of As(V) and Enhanced Stability of Process ResidualsEPA Grant Number: R831431
Title: A Novel Ion Exchange Process for Selective Removal of As(V) and Enhanced Stability of Process Residuals
Investigators: Zhao, Dongye , Barnett, Mark
Institution: Auburn University Main Campus
EPA Project Officer: Richards, April
Project Period: November 1, 2003 through October 31, 2005
Project Period Covered by this Report: November 1, 2003 through October 31, 2004
Project Amount: $99,452
RFA: New Technologies for the Environment (NTE) (2003) RFA Text | Recipients Lists
Research Category: Nanotechnology , Sustainability , Pollution Prevention/Sustainable Development
The objectives of this research project are to: (1) develop a new class of polymeric ligand exchangers (PLEs) for highly selective removal of arsenate from water; (2) characterize the new materials with respect to sorption capacity, kinetics, arsenate selectivity, breakthrough behaviors, and regeneration through a series of batch and column experiments; (3) test the reusability of spent regenerant brine; and (4) develop an engineered approach to treat the spent regenerant to minimize brine need and waste volume and to maximize the stability of the resultant process waste residuals.
The major findings are summarized as follows:
- Compared to conventional strong base anion exchange resins, the copper-loaded PLE, DOW 3N-Cu, was found to offer more than 10 times greater treatment capacity for arsenate in fixed-bed column runs, and the arsenic selectivity of DOW 3N-Cu is 60 to120 times greater based on the binary arsenate/sulfate separation factor. Consequently, DOW 3N-Cu potentially can cut down the regenerant needs and the amount of process waste residuals by 90 percent.
- Two new PLEs, XAD1180-2N, and XAD16-2N, were synthesized based on two commercially available matrices (XAD 1180 and XAD 16). The new PLEs showed equally great selectivity for arsenic as DOW 3N-Cu. The total arsenic capacity, however, was limited by their lower overall capacity. Nonetheless, the new PLEs were able to treat nearly 1,000 bed volumes of contaminated water per operation run and can be easily regenerated for multiple uses. We found that the lowered overall capacity of the new PLEs was caused by the unusually high cross linkage of the XAD resins’ matrices.
- The arsenate sorption kinetics of DOW 3N-Cu is comparable to that of typical conventional macroporous sorbents. The intraparticle diffusivity was determined to be 1.4 x 10-8 cm2/s.
- All PLEs can be regenerated very efficiently using 4-6 percent NaCl at pH approximately 9.1 and can be used in multiple cycles (> 10) of operation without any loss in capacity.
- The same spent brine can be used repeatedly for regenerating the PLEs more than five times without major treatment other than pH adjustment.
- Arsenic in the spent regenerant can be removed effectively (> 99%) using aluminum salts (sulfate or chloride) at a Al:As molar ratio of greater than 5.0 and a pH range of 5.0 to 8.0. The treated brine, upon pH adjustment, offered equally high regeneration efficiency, which further cuts down the regenerant needs.
- Toxicity Characteristic Leaching Procedure (TCLP) results indicate that the arsenic leachability in the process sludge can be reduced by 80 percent when the Al:As molar ratio is increased from 5 to 10.
- Waste extract test results indicate that the arsenic leachability in the process sludge can be reduced by 50 percent when the Al:As molar ratio is increased from 5 to 10.
- Continue to optimize the treatment recipe for minimizing the volume and reducing the leachability of the As-laden spent brine. Emphasis will be placed on the effects of aging, temperature, type of the coagulants (Fe vs. Al), pH, and metal dosage.
- Continue to synthesize a polymer matrix with better controlled cross-linkage and porosity for preparing PLEs of greater total capacity.
- Conduct a cost analysis of the PLE-based process. The cost and benefit of the process will be compared with those for other technologies used for As removal .
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 18 publications||5 publications in selected types||All 5 journal articles|
||An B, Fu Z, Xiong Z, Zhao D. Preparation and characterization of a new class of polymeric ligand exchangers for selective removal of arsenate from drinking water. Separation Science and Technology||
||Steinwinder T, An B, Zhao D. Engineered treatment of As-laden spent regenerant brine for enhanced stability of process waste residuals and for reuse of the spent regenerant. AWWA Journal (to be submitted, 2005).||