Method of making and using nanoscale metal

Abstract

The invention provides methods of producing colloids of nanoscale metallic particles particularly useful in the in situ environmental remediation of chlorinated solvents. The methods include ball milling an elemental metal to form a colloid of nanoscale metallic particles having ideal size and metallurgical properties to enhance the reductive dehalogenation of halogenated hydrocarbons.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation-in-part of pending U.S. patent application Ser. No. 10 / 890,066, filed Jul. 12, 2004, which is a continuation of U.S. patent application Ser. No. 10 / 026,329 filed Dec. 19, 2001, now U.S. Pat. No. 6,777,449, which claims the benefit of U.S. Provisional Patent Application Ser. No. 60 / 257,917 filed Dec. 21, 2000.BACKGROUND OF THE INVENTION [0002] Since the mid-1990's, there have been a series of dramatic developments for the in-situ treatment of chlorinated solvents. The approach of the present invention is based on the sequential reduction of chlorinated hydrocarbons to innocuous end products such as methane, ethane or ethene. The process has been recognized in scientific circles but it is now being investigated for environmental applications. The process exploits the use of zero valence state elemental metals to reductively dehalogenate halogenated hydrocarbons. In addition, elemental metals may be used ...

AI Technical Summary

Benefits of technology

[0013] Through the manipulation of the colloid size, structure, and crystal structure using the above process it is possible to design colloids for variations in specific contaminant types, concentrations, groundwater or reactor flow velocities, subsurface permeability, and provide some control over the transport properties of the colloids during injection.

[0014] A colloid of the nanoscale size has several advantages in application for in-situ groundwater treatment or for use in above-ground treatment reactors. These advantages include higher surface area resulting in greater reaction kinetics. The increase in kinetics in turn, allows for a lower mass loading of iron in the treatment zone or reactor because the residence time required for complete dehalogenation is decreased. The small size and greater reactivity of the colloid allows for the application of the remediation technology through direct in-situ injection into the subsurface where the smaller size allows for advective colloidal transport. Additionally, the greater reactivity of the nano-sized iron allows for much lower overall iron mass requirements in the remediation processes.

[0015] To further enhance the physical and chemical character of the colloid, a metallic catalyst may be added to the metallic iron to create a bi-metallic colloid. The catalyst further increases the rates of reaction which lowers the amount of iron colloid that must be used to create an effective reductive dehalogenation treatment zone in the subsurface or in a surface reactor. Metals that may be used as a catalyst with the iron include palladium, platinum, nickel, zinc, tin and combinations thereof.

[0016] The enhancement of colloid reactivity by control of the production process results in the creation of a highly reactive colloid with unique properties which make it ideal for in situ injection. These properties include a size and mass that is large enough to minimize the effect of interfacial forces associated with colloids smaller than 50 to 100 nanometers, yet is small enough to avoid the effect of gravitational settling observed on colloids and particles larger than about 600 nanometers. The number of colloidal particles per unit mass is inversely proportional to the cube of the colloid diameter. A 500-nanometer colloid is one order of magnitude larger (10 times) than a 50-nanometer colloid. A gram of 50-nanometer colloid has 1000 times more colloid particles than a gram of 500-nanometer colloid. Since colloid aggregation rates are proportional to the square of the particle number, the 500-nanometer colloid is a million times less susceptible to unwanted aggregation compared to the 50-nanometer colloid. However, one gram of 500-nanometer colloids that has undergone reactivity enhancement by the modification of the metal crystal lattice, manipulation of non-crystalline atom to atom bonds, the addition of secondary metals to act as catalyst, and compounds that aid in the damping of unwanted side reactions will have the same reactivity as one gram of 50-nanometer colloids that rely purely on high surface area effects. These physical parameters all contribute to the production of a highly reactive colloid that also has high mobility in permeable subsurface materials.

Problems solved by technology

A key limitation on the development of the technology is the lack of availability of nanoscale metallic colloids.

The reducing reagents are expensive resulting in production costs that are irreducible at a level greater than $100 a pound.

Thus, this method is not practical for large scale application in groundwater remediation and for full-scale production in ton quantities.

These methods cannot be scaled up to produce the necessary amount of elemental nanoscale metal particles for use in environmental remediation procedures in a reasonable time or at a cost-effective price.

While by 1999 work in this field was being performed on ceramics or other non-metallic inorganic materials, there was no existing capacity for the production of iron colloids using mechanical attrition.

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