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 Amount: $99,452
RFA: New Technologies for the Environment (NTE) (2003) RFA Text | Recipients Lists
Research Category: Nanotechnology , Sustainability , Pollution Prevention/Sustainable Development
This research addresses the urgent technology need for cost-effective arsenic (As) removal in small drinking water systems and for minimizing the environmental impacts of process waste residuals. The overall objective of this project is to develop an innovative, selective ion exchange (IX) process that: 1) removes As(V) more cost-effectively than current IX processes; and 2) minimizes the volume and As-leachability of process waste residuals. The specific research goals are: (1) to prepare and characterize a new class of IX materials, referred to as polymeric ligand exchangers (PLEs), for highly selective removal of As(V); and (2) to develop an engineered approach to reuse the spent regenerant and to minimize the volume and As-leachability of process waste residuals.
The proposed study will test the following key hypotheses:
1. the PLEs will remove As(V) highly selectively and more effectively than
conventional IX materials;
2. the PLEs can be regenerated efficiently with brine, and the process will produce a much smaller volume of spent brine compared to current IX processes; and
3. an engineered treatment of the spent brine can be achieved to reduce As leaching from the final process residuals and to reuse the spent regenerant.
1) Sorbents Preparation. Two chelating resins containing pyridine nitrogen donor atoms will be used for preparing PLEs. Cu2+ will be used as the metal ion. The effects of types and strength of donor atoms on PLEs' metal sorption behavior will be tested. Copper capacity and stability will be determined as a function of solution chemistry. The nature of copper bonding to the polymers will be explored by spectroscopic studies.
2) Characterization of the Sorbents. Batch equilibrium and kinetic tests will be carried out to test the As sorption capacity and rate of PLEs in the presence of various competing ions. Arsenate sorption isotherms will be constructed for PLEs and other resins in binary and multi-component systems. Arsenate/co-solute binary ion exchange separation factors will be determined and compared. Effects of solution pH, temperature, ionic strength, concentration of competing anions, metal ions such as Fe3+, and DOM on sorption capacity will be investigated. The rate-limiting step will be determined using interruption test method. The intraparticle diffusion coefficient will be determined and then compared to that of standard resins. Fixed-bed column runs will be carried out to test the dynamic behaviors of the proposed fixed-bed process. Breakthrough curves of arsenate, competing anions, DOM and pH will be measured using bench-scale column set-up. Arsenic breakthrough profiles as affected by influent compositions, pH, bed dimension, and hydrodynamic conditions such as superficial liquid velocity (SLV) and empty bed contact time (EBCT) will be determined and optimized. Copper bleeding from PLEs will be measured during saturation runs and regeneration runs by trapping any fugitive Cu2+ from the column using a separate bed of virgin DOW 3N.
3) Regeneration and Engineered Formation of Stable Waste Residuals. Regeneration efficiency will be tested using ~1 M NaCl at pH ~4.0-5.0. Optimal conditions such as brine concentration, pH, EBCT, and SLV will be identified. Fe or Al oxyhydroxides will be employed to remove As from the spent brine. Engineered formation of As-laden, Fe- or Al-sludge will be achieved through controlling the time (both kinetics of formation and aging), temperature, and pH. The As-leachability of the product solid wastes will be tested following the TCLP as well as in miscible-displacement column experiments. In addition, in-situ molecular-level speciation of As in the wet residual will be studied with synchrotron XAS. Following the engineered treatment, spent brine will be reused for regeneration.
4) Cost and Benefit Analyses. Cost and benefit of the proposed process will be benchmarked against conventional processes used for As removal.
This research directly addresses the needs identified in the EPA solicitation for innovative technologies "that address the treatment of arsenic" and can "provide low capital and operating cost, simplify operation, require minimal monitoring and maintenance, and reduce residual waste generation." If successful, this research will: 1) produce a new class of IX materials with high As-selectivity; 2) develop a cost-effective treatment process that can substantially reduce the water utilities’ compliance costs; and 3) develop an engineered approach for formation of low-volume and highly stable waste residuals.