Grantee Research Project Results
Final Report: High-Performance Extraction of Heavy Metals with Tethered Metal-Binding Ligands
EPA Contract Number: 68D98151Title: High-Performance Extraction of Heavy Metals with Tethered Metal-Binding Ligands
Investigators: Hammen, Richard F.
Small Business: ChelaTech Inc.
EPA Contact: Richards, April
Phase: I
Project Period: September 1, 1998 through March 1, 1999
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (1998) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)
Summary/Accomplishments (Outputs/Outcomes):
Objective of the Phase 1 Project. The overall Objective of this Project is to develop and commercialize a new generation of High Performance Extraction (HPE) media that selectively and economically remove heavy metal cations and anions from contaminated water. The business Objective of this project is to provide products and processes that cheaply extract toxic metals to zero discharge levels. Conventional ion exchange and metal extraction resins developed to date make use of ionic or metal chelating groups bound to the surface of a porous polymer support. Since the metal-binding functional groups are bound at the surface of the polymer, it is necessary for the exchanging ions in solution to diffuse through a stagnant boundary layer at the liquid-solid interface. This diffusion through the stagnant boundary layer is rate limiting and ion exchange extractions of metals are slow and costly processes. To avoid boundary layer diffusion limitations, ChelaTech, Inc. has developed a technology for covalently attaching a variety of tether molecules to porous silica gel. The tether length can be controlled and is made to be 15-400 angstroms long. The tether is then covalently coupled to an appropriate ligand or metal-binding reagent. By ?dangling? the reagent away from the solid surface, the reagent reacts with solute molecules pumped through the porous bed with unprecedented reaction and adsorption kinetics. This technology is being used to develop high performance extraction media that are selective for extracting mercury, cadmium, hexavalent chrome, and arsenate ions from contaminated water. The use of this extraction media allows for very efficient high velocity selective extraction of metal ions at flow rates over 40 times faster than possible with conventional technologies.Work Carried Out. The Phase 1 Project involved the Performance of Tasks to prepare and test products for the extraction of Mercury, Cadmium, chromium, and arsenic. After preparation of the media, the binding constants and metal adsorption capacity of the media products were measured. To test the efficacy off the products for extracting metals, metal-contaminated solutions of known concentration were passed through columns of the media and the water tested by state of the art analytical procedures for metal concentrations. To demonstrate the high velocity flow characteristics of the HPE media products, adsorption kinetics experiments were conducted. To assess the economics and durability of the HPE media, an accelerated attrition study was conducted. This was accomplished by contacting the media with a solution of hexavalent chrome, and the acids and bases used for regeneration of the medium. Finally, A Commercialization Assessment Report was prepared by Foresight Science and Technology to assist ChelaTech in identifying market segments for deploying this technology.
Results of the Work. High Performance Extraction media products were prepared with tethered ligands and ion exchange groups designed with selective removal of arsenate, chrome (VI), cadmium, and mercury. The media were tested for the metal ion adsorption capacity by a laboratory-scale version of the process being developed for commercial use. A column of the HPE media was plumbed into a high performance liquid chromatography (HPLC) system. The media were equilibrated and then a solution of the test metal was pumped through the column at flow rates 40 times faster than possible with conventional ion exchange resins on the market. The effluent of the column was monitored by a detector for the metal concentration. The test metal was pumped into the column until the medium became saturated with the metal, and then the metal began to appear in the column effluent. By measuring the appearance of the metal in the effluent, it is possible to model column performance with Langmuir binding isotherms and to obtain metal adsorption capacities and relative metal-ligand affinity constants. After saturation of the column with the metal, the non-complexed metal was rinsed from the column and the metal was recovered from the column by pumping an eluting solution through the unit. Elution of the metals from the HPE columns can be accomplished with 0.5-0.75 Bed Volumes of solution. The small volume of the regenerant solution offers a significant practical commercial advantage over the large solution volumes required to strip and regenerate existing ion exchange columns. After elution, the columns were regenerated by passage of one Bed Volume of regenerant solution into the column. To test the kinetics of the metal adsorption process, the adsorption isotherm experiments were conducted at flow rates from 10 to 40 times faster than conventional on exchange resins.
Once the capacity and operational parameters for use of the HPE columns were determined, solutions containing known concentrations of chrome, arsenic, mercury, and cadmium were treated to test the ability of this technology to remove metals to non-detectable levels. Mercury was extracted to non-detectable concentrations (< 0.5 PPP) by passage through HPE media at high flow velocities. In addition, chrome (VI) was extracted to non-detectable levels (< 0.1 ppm). To determine the robustness of the HPE media to the conditions of the water treatment process, the HPE media was exposed to concentrated solutions of hexavalent chromium., acid, and base,. The accelerated attrition test was equivalent to over 2200 cycles of operation of an extraction column. This exposure resulted in only a 10 percent degradation of column capacity. The combined results of the kinetics, capacity, and attrition study allowed the determination of costs for treating wastewater contaminated with mercury or hexavalent chromium. These results showed that the HPE media are capable of treating water at costs significantly lower then existing treatment processes.
Potential Commercialization Opportunities. During this Phase I Project, the EPA offered the assistance of Foresight Technologies, Inc., to prepare a Commercialization Plan for the technology. This was of great assistance to ChelaTech, because the report identified chrome extraction from metal-plating wastewater as a significant market opportunity. Foresight found that there is a high demand and good market accessibility for a process or technology that is capable of recovering chrome from metal plating wastewater solutions at a cost of less than $2.50 per thousand gallons. Results of this Research found that the operating cost of extracting chrome (VI) from a 1 ppm solution is $0.102 per thousand gallons. The cost for treatment of a 100 ppm solution is $1.01 per thousand gallons. This Phase 1 Research showed that very small extraction columns operating at a high flow velocity are effective at removing heavy metals from water. This is a great commercial significance, because the commonly excepted paradigm of existing wastewater treatment units is that reduction of contaminants to non-detectable levels becomes exponentially more expensive. The use of small units of HPE media can allow the very low-cost treatment of wastewater to zero discharge levels of purity. This Phase 1 Project was able to demonstrate the extraction of 2 highly different metal species. The core technology of ChelaTech Inc., which is the tethering of selective metal-binding ligands to porous supports, is highly versatile and applies to a number of large industrial markets. The industrial applications of this technology involved hydrometalurgical extraction of metals in mining, treatment of mining wastewater, treatment of metal plating wastewater, and remediation of Superfund sites contaminated with toxic heavy metals.
Supplemental Keywords:
Economic, Social, & Behavioral Science Research Program, Scientific Discipline, Toxics, Waste, Water, National Recommended Water Quality, hexavalent chromium, Physics, Remediation, Wastewater, Chemistry, Engineering, 33/50, Hazardous, Engineering, Chemistry, & Physics, Market mechanisms, Mercury, wastewater treatment, cadmium & cadmium compounds, wastewater remediation, metal ion removal, metal binding, metal recovery, pollution control, carbon dioxide, mercury & mercury compounds, emission reductions, cost effective, cadmium, extraction of metals, heavy metal contamination, control technologies, heavy metals, waste water treatment, ion exchange, metal ligandThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.