Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – By fixation in stable solid media
Reexamination Certificate
1999-06-17
2002-03-12
Griffin, Steven P. (Department: 1754)
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
By fixation in stable solid media
C588S252000
Reexamination Certificate
active
06355857
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to a waste treatment process utilizing molten metals. More particularly, the invention relates to a treatment process utilizing molten metals to react chemically with certain waste materials in a waste stream and to alloy radioactive isotopes in the waste stream.
BACKGROUND OF THE INVENTION
Many waste treatment processes utilize thermal energy to break up waste materials into their constituent elements or more desirable compounds. The use of thermal energy to break down materials is referred to generally as pyrolization. Molten metals have also been used to react with certain waste materials in order to produce more desirable compounds or reduce the waste to constituent elements. In particular, molten aluminum has been used to react with halogenated hydrocarbons and produce aluminum salts. U.S. Pat. No. 4,469,661 to Shultz described the destruction of PCBs and other halogenated hydrocarbons by contacting the hydrocarbon vapor with molten aluminum. The aluminum was contained in low-boiling eutectic mixtures of aluminum and zinc or aluminum, zinc, and magnesium. Shultz also suggested eutectic reactant mixtures containing iron, calcium, and other metals. U.S. Pat. No. 5,640,702 to Shultz disclosed a molten metal treatment for wastes containing radioactive constituents. This patent to Shultz disclosed using lead in the molten reactant metal as a chemically active material for reacting with non-radioactive constituents in the waste to be treated.
U.S. Pat. No. 5,000,101 to Wagner disclosed a process for treating hazardous waste material with molten alkaline metal alloys. The molten metal alloy comprised approximately 50% aluminum, 5% to 15% calcium, 5% to 15% copper, 5% to 15% iron, and 5% to 15 zinc. U.S. Pat. No. 5,167,919 to Wagner disclosed a reactant alkaline metal alloy composition comprising between 40% to 95% aluminum, 1% to 25% iron, 1% to 25% calcium, 1% to 25% copper, and 1% to 25 % zinc. The '919 Wagner patent also disclosed that magnesium could be substituted for calcium. In both of these Wagner patents, the waste material was reacted in the molten alloy held at about 800 degrees Celsius.
In the process disclosed in the above-described Wagner patents, chlorine atoms in the waste material were stripped from the waste compound primarily by the highly reactive aluminum in the molten reactant alloy. The aluminum and chlorine combined to form aluminum chloride. Carbon from the original waste compound was liberated either in elemental form or as char (CH, CH
2
, or CH
3
). Both the aluminum chloride and liberated carbon sublimed to a gaseous state at the 800 degree Celsius reaction temperature and were drawn off and separated.
Many hazardous waste sites have different types of wastes mixed together. The mixed waste may include numerous different types of halogenated hydrocarbons, other non-radioactive wastes, and radioactive isotopes. These mixed wastes which include radioactive and non-radioactive materials have proven particularly difficult to treat. Although, many non-radioactive wastes may be treated chemically and broken down into benign or less hazardous chemicals, radioactive constituents of the mixed waste stream cannot be manipulated to reduce or eliminate their radioactive emissions. It is desirable to separate the radioactive constituents from the other materials in the mixed waste and place the radioactive constituents in an arrangement for safe, long term storage.
Storing radioactive waste poses several problems in itself. For a radioactive isotope which has a long half life, a quantity of the material remains radioactive for many years. Thus, a storage arrangement for this long-lived radioactive waste must be capable of securely holding the waste for a very long period of time. However, radioactive emissions, particularly alpha radiation, can interact with the material of a container intended to store radioactive waste. This interaction can cause the container to degrade relatively quickly, long before the radioactive waste itself has degraded.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a waste treatment process for treating radioactive waste materials, particularly mixed waste streams which include both non-radioactive wastes and radioactive constituents.
The waste treatment process according to the invention utilizes a molten reactant metal alloy including at least one chemically active metal for reacting with the non-radioactive material in the mixed waste stream being treated. The reactant alloy also includes at least one radiation absorbing metal. Radioactive isotopes in the waste stream alloy with the chemically active and radiation absorbing metals such that the radiation absorbing metals are able to absorb a significant portion of the radioactive emissions associated with the isotopes. Non-radioactive constituents in the waste material are broken down into harmless and useful constituents, leaving the alloyed radioactive isotopes in the molten reactant alloy. The reactant alloy may then be cooled to form one or more ingots in which the radioactive isotopes are effectively isolated and surrounded by the radiation absorbing metals. The ingots may be encapsulated in one or more layers of radiation absorbing material and then stored.
The chemically active metal in the reactant alloy may comprise any metal capable of reacting chemically with one or more non-radioactive constituents in the waste stream. Preferred chemically active metals include magnesium, aluminum, lithium, zinc, calcium, and copper. In the preferred form of the invention, a combination of these metals is included in the reactant alloy. The particular chemically active metal or combination of chemically active metals used in a particular application will depend upon the makeup of the wastes in the waste stream and the reaction products which are desired from the treatment process.
Each radiation absorbing metal included in the reactant alloy is matched with a particular radioactive isotope to be alloyed with the metals in the molten metal bath. That is, for each type of expected radioactive emission associated with a radioactive isotope to be alloyed, a radiation absorbing metal is included in the alloy for absorbing that particular type of emission. A particular radiation absorbing metal for absorbing a particular radioactive emission will be referred to herein as a corresponding radiation absorbing metal for that emission. Similarly, a particular radioactive emission which may be absorbed by a particular radiation absorbing metal will be referred to herein as a corresponding radioactive emission for that radiation absorbing metal. Preferred radiation absorbing metals include particular isotopes of lead, beryllium, cadmium, vanadium, yttrium, ytterbium, zirconium, and tungsten. One or more of these radiation absorbing metals may be used within the scope of the invention depending upon the radioactive isotopes to be alloyed in the molten metal. For purposes of this disclosure and the accompanying claims, a “radiation absorbing metal” comprises a metal which is capable of capturing a particular expected radioactive emission, that is, a particular emission at a natural decay energy level.
As used in this disclosure and the following claims, the “type of expected radioactive emission” associated with an isotope in the waste material to be treated refers to the particular type of both primary and secondary emission (alpha, beta, gamma, or neutron) characteristic of the isotope and any daughter isotope, and the characteristic energy level of each emission. The “expected radioactive emission” refers to each respective emission within each type of emission. For the purposes of this disclosure and the claims, a “primary radioactive emission” comprises the emission or emissions directly from the radioactive decay of an isotope. For most radioactive isotopes, the primary radioactive emissions will include either an alpha or beta emission at a characteristic energy level and a gamma emission at a characteristic ener
Clean Technologies International Corporation
Culbertson Russell D.
Griffin Steven P.
Nave Eileen E.
Shaffer & Culbertson L.L.P.
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