Grantee Research Project Results
Final Report: Affordable, Large-Scale Manufacturing of High Surface Area Iron Powder
EPA Contract Number: 68D03033Title: Affordable, Large-Scale Manufacturing of High Surface Area Iron Powder
Investigators: Freim, John
Small Business: OnMaterials LLC
EPA Contact: Richards, April
Phase: I
Project Period: April 1, 2003 through September 1, 2003
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2003) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , SBIR - Waste , Small Business Innovation Research (SBIR)
Description:
Groundwater contaminated with halogenated hydrocarbons presents a widespread environmental challenge. Existing remediation protocols are often slow, expensive, and limited in their ability to accomplish an in situ remediation of the contaminated sites. Zero valent iron can effectively accomplish the reductive dechlorination of contaminated groundwater through the general reaction of Equation 1, where RX is a halogenated hydrocarbon (trichloroethylene, carbon tetrachloride, etc.), and RH is the reduced product.
Equation 1: RX + 2e- + 2H2O → RH + H2 + OH- + X-
Reaction rates often obey pseudo first-order kinetics, as depicted in Equation 2.
Equation 2: d[RX]/dt = -kobs[RX]
Previous work has suggested that the overall rate constant (kobs) can be subdivided into the sub-terms of Equation 3, where ksa (L hr-1 m-2) is an underlying material specific rate constant, saFe (m2/g) is the powder's specific surface area, and Fe (g/L) is the powder concentration in the liquid being treated.
Equation 3: kobs = ksa * saFe * Fe
Equation 3 shows that the overall rate constant scales directly with powder surface area, saFe. Today, low surface area iron powder typically is used to accomplish the detoxification reactions. Developing a cost-effective procedure to make higher surface area zero valent powder can significantly enhance powder reactivity. Equation 3 also shows that the overall rate constant scales with ksa. ksa is not a constant, but is a function of several variables that include the density of reactive surface sites, the thickness of any oxide surface layer, and the presence of secondary metals that serve to increase reaction kinetics. Promising secondary metals include palladium at low concentrations and lower-cost base metals (Cu) at greater concentrations. The ability to use secondary metals to increase ksa, combined with the increased powder surface area, will provide the remediation community a highly reactive iron powder offering several advantages that include:
· A substantial decrease in the amount of powder required to remediate a given site. Enhanced reactivity reduces the amount of powder required to detoxify a given quantity of contaminated groundwater. This is important because engineering costs for applying the powder typically exceed material cost and the ability to use less powder will allow for smaller, less-costly engineering solutions.
· The ability to treat normally stable compounds. Halogenated compounds exhibit widely different reaction kinetics. Some halogenated compounds (carbon tetrachloride, tetrachloroethylene) exhibit rapid kinetics while others (dichloroethane, dichloromethane, polychlorinated biphenyls [PCBs]) are resistant to most iron powders. These partially reduced compounds (daughter products) are problematic because they also are toxic and must be removed before groundwater is fully treated.
· The ability to augment bioremediation processes. Bioremediation techniques use special bacteria to accomplish the reductive dechlorination of some halogenated compounds. The bacteria use hydrogen in their metabolic process and iron produces hydrogen by reducing free protons in water. Beyond the ability to provide an in situ hydrogen source, iron can lessen the concentration of some halogenated compounds that are toxic to these bacteria. For example, some bacteria are effective for treating dichloromethane, but are killed when exposed to high concentrations of carbon tetrachloride and chloroform. First using iron to lessen the concentration of carbon tetrachloride/chloroform to acceptable levels and then following up with bioremediation can alleviate this problem.
Summary/Accomplishments (Outputs/Outcomes):
The Phase I feasibility study demonstrated the ability to make zero valent iron powder with the following features:
· Oxide-free powder with a surface area of 4-6 m2/g. This surface area is significantly greater than the powders used in today's remediation marketplace (typically less than 1 m2/g). OnMaterials' high surface area powder consists of thin flakes with a diameter of about 5 micrometers and a thickness of about 100-250 nanometers. The powders do not contain detectible quantities of iron oxide that is deleterious to product performance.
· Embedded hydrogenation catalysts. Published work has demonstrated that bimetallic systems (Fe/Cu, Fe/Pd) enhance hydrogen gas production and reaction kinetics. Prior art has employed an electrochemical reaction to deposit the secondary metals onto the particle surface. OnMaterials' synthesis process instead can incorporate the secondary metals within the iron powder. This is advantageous because better electrical contact between the two metals can be achieved, and unlike electroplated powder, the surface coating is less likely to separate from the particle as the reaction proceeds and the iron is depleted.
· Greatly accelerated reaction kinetics with no daughter products. Artificially spiked anaerobic water with a concentration of 250 µM trichloroethylene and 300 µM chloroform was used to evaluate powder reactivity. Pseudo first-order rate constants for trichloroethylene reduction were two-to-three orders of magnitude greater than coarser, commercial iron powders. Specifically, OnMaterials' powder exhibited the ability to fully decontaminate the liquid in less than 1 day. When hydrogen reduced and carbonyl iron powders were added to this water, trichloroethylene concentrations essentially were unchanged after 1 week. Another important feature of the OnMaterials powder was the ability to convert the trichloroethylene and chloroform directly into chlorine-free hydrocarbons without producing substantial quantities of toxic chlorinated reaction intermediaries.
Conclusions:
OnMaterials embarked on the Phase I project with the goal of producing a low-cost and kinetically active iron powder. The work produced powder with a surface area of about 4-6 m2/g; this is about 10-30 times greater than commercially available commodity powders. The Phase I work also demonstrated the ability to incorporate palladium and copper hydrogenation catalysts within the high surface area powder. The combination of the high surface area material and embedded copper and palladium produced a very kinetically active material. When added to an aqueous solution of trichloroethylene and chloroform, the OnMaterials powders enabled very rapid dechlorination kinetics when compared with commercially available iron powders. The OnMaterials process is capable of producing ton-plus quantities of state-of-the-art powder at $5-10/lb. Although more expensive than the slow-reacting commodity iron powders, this compares favorably to prices of $15-$100/lb for other high surface area iron powders. The highly reactive powder will allow for less costly engineering solutions, providing a substantial cost saving to the customer. The enhanced reactivity also will allow for the treatment of reduction-resistant groundwater contaminants such as PCBs. When successfully developed, scaled, and commercialized, the product can generate $10 million in annual sales and positively impact the $5 billion per year remediation marketplace for chlorinated solvents as well as other toxic chemicals including chromate, perchlorate, arsenic, and phosphate.
Supplemental Keywords:
high surface area powder, zero valent iron, remediation, reductive dechlorination, contaminated groundwater, trichloroethylene, carbon tetrachloride, chloroform, trichloroethane, arsenic, chromium, perchlorate, hydrogenation catalysts, small business, SBIR., RFA, Scientific Discipline, INTERNATIONAL COOPERATION, Waste, TREATMENT/CONTROL, Sustainable Industry/Business, cleaner production/pollution prevention, Remediation, Sustainable Environment, Treatment Technologies, Technology for Sustainable Environment, Civil/Environmental Engineering, Hazardous Waste, Hazardous, Environmental Engineering, hazardous waste treatment, dechlorination, contaminated sediments, iron powder, community involvement, bioavailability, remediation technologies, TCE degradation, hazardous chemicals, contaminated groundwater, information transfer, risk reduction strategies, hydrocarbons, outreach and education, pollution prevention, technology transfer, iron mediated reductive transformation, groundwater, heavy metalsSBIR Phase II:
Affordable, Large-Scale Manufacturing of High Surface Area Iron PowderThe 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.