Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste – By fixation in stable solid media
Reexamination Certificate
2000-02-15
2002-06-04
Griffin, Steven P. (Department: 1754)
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
By fixation in stable solid media
C588S003000, C588S004000, C588S015000, C588S018000, C588S253000, C588S252000, C588S256000
Reexamination Certificate
active
06399848
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to settable compositions which can encapsulate hazardous waste materials and relates particularly, though not exclusively, to a method of encapsulating hazardous waste materials including heavy metals such as arsenic, nickel, chromium residues and mercury as well as radioactive materials.
BACKGROUND TO THE INVENTION
Arsenic and arsenic containing compositions have been widely used in Australia as sheep and cattle dips, and have also been used in pesticides. Mercury and mercury containing compositions have also been widely used in Australia and other countries. With the phasing out of arsenic and mercury compounds (due to their toxicity), a large stockpile of waste arsenic and mercury components exists.
Organo nickel and chromium, and nickel and chromium containing compositions are widely used in Australia and other countries. Metal plating and anodising processes use these compounds, and the processes generate waste nickel and chromium residues which are quite concentrated and are stored in drums. The residue is hazardous and toxic and a large stockpile of waste nickel and chromium components exists.
The above mentioned hazardous waste materials and toxic components are housed in drums which have a limited life. The components in the drum are typically in the form of a contaminated liquid or sludge which is almost impossible to safely encapsulate. The sludge contains a variety of contaminants such as rust from the drum, waste particles, solids, and a variety of liquids.
Radioactive materials and components are also hazardous substances. Apart from their use as fuel for nuclear reactors, radioactive materials also have medical applications and other industrial applications. For example, radioisotopes are used in the medical field for the diagnosis and treatment of various types of illness. In some industries, for example in the mining industry, a radioactive source is used in certain types of instruments for measuring, for example, the thickness of materials. However, one of the problems associated with using radioactive materials is finding a socially and environmentally acceptable method of disposing of the radioactive waste materials. Various proposals have been put forward for encasement or encapsulation of radioactive materials which can than be safely disposed of by burial in uninhabited regions of the Earth.
Attempts to encapsulate hazardous waste materials in concrete have met with limited success as concrete and cement do not bind well in the presence of contamination. However, concrete or concrete like products are ideal for encapsulation as the concrete is hard, has a very long life, and can be moulded prior to setting.
SUMMARY OF THE INVENTION
The present invention is directed to a method by which hazardous waste materials or components thereof can be encapsulated, even if the materials are contaminated with other impurities.
According to one aspect of the present invention there is provided a method of encapsulating a hazardous waste material or component thereof, the method comprising: adding the hazardous waste material to a settable composition, the composition comprising a calcium carbonate and a caustic magnesium oxide, forming a slurry, and allowing the slurry to set to encapsulate the waste material or components thereof.
According to another aspect of the invention there is provided a method of encapsulating an arsenic component selected from the group consisting of arsenic, sodium arsenite, arsenic trioxide or arsenic pentoxide, the method comprising:
adding to the arsenic component a sulphate, an iron chloride and/or an alkaline agent, and water to form a slurry, mixing the slurry with a settable composition, the composition comprising a calcium carbonate and a caustic magnesium oxide, and allowing the composition to set to encapsulate the arsenic component.
It is found that when encapsulated in this matter, very little arsenic is leached out of the set composition which has a concrete like appearance.
Indeed, leach rates are less that the allowed leach rate of 5.00 ppm arsenic. The sulphate which is added to the slurry is preferably an aluminium sulphate. The alkaline agent is preferably a carbonate such as calcium carbonate. The iron chloride can comprise ferric chloride.
Suitable ranges include:
Arsenic component—100 weight units (e.g. grams),
Sulphate—10-80 weight units, more preferably about 50 weight units,
Alkaline agent (e.g. calcium carbonate)—10-80 weight units.
Ferric chloride (if present)—5-50 weight units.
To form a slurry 100-500 weight units of water per 100 weight units of arsenic component can be added.
According to a further aspect of the invention there is provided a method of encapsulating mercury or components thereof, the method comprising: adding the mercury or components thereof to a settable composition, the settable composition comprising a calcium carbonate and a caustic magnesium oxide, forming a slurry, and allowing the slurry to set to encapsulate the mercury or components thereof.
It is found that when encapsulated in this matter, very little mercury is leached out of the set composition which has a concrete like appearance. Indeed, leach rates are less than the allowed leach rate of 5.00 ppm mercury.
The mercury waste is typically stored as a sludge. One source of mercury waste is from Clarriflocculator sludge, or Brine sludge. This sludge contains between 100-200 mg of mercury per kilogram of sludge, as well as water, dust/soil, and other impurities, which makes encapsulation in concrete unsatisfactory.
Suitable ranges for the method include:
Mercury containing sludge—1000 grams,
Settable composition—1000 grams,
Water—270 ml.
Additives—100 grams.
According to a still further aspect of the invention there is provided a method of encapsulating nickel. and chromium or components thereof, the method comprising:
adding the nickel and chromium or components thereof to a settable composition, the settable composition comprising a calcium carbonate and a caustic magnesium oxide, forming a slurry, and allowing the slurry to set to encapsulate the nickel and chromium and components thereof.
It is found that when encapsulated in this matter, very little nickel and chromium is leached out of the set composition which has a concrete like appearance. Indeed, leach rates are less than the allowed leach rate of 0.2 ppm nickel and chromium.
The nickel and chromium waste is typically stored as a thick liquid or sludge. One source of nickel and chromium waste is from the metal plating and anodising industry. This liquid can contain between 10 mg-28,000(?)mg of nickel and about 10 mg-200,000 mg chromium per kilogram of liquid, as well as water, dust/soil, and other impurities, which makes encapsulation in concrete unsatisfactory.
If desired, a filler can be used. The filler can include an ash, but other fillers are envisaged. The filler can comprise between 10-90% of the set composition, and more preferably between 40-60%
Suitable non-limiting ranges for the method include:
Nickel and chromium containing liquid—150 ml,
Settable composition—300 grams,
Water—400 ml.
Additives—100 grams.
According to yet another aspect of the invention there is provided a method of encapsulating radioactive materials, the method comprising: adding the radioactive materials to a settable composition, the settable composition comprising a calcium carbonate and a caustic magnesium oxide, forming a slurry, and allowing the slurry to set to encapsulate the radioactive material therein.
It is found that when encapsulated in this matter, virtually no radioactive material is leached out of the set composition which has a concrete-like appearance. Furthermore, radioactivity levels of the leached material are well below the background radiation level.
The method of encapsulation according to the invention is particularly suited to low to mid level radioactive material, for example, monazite. Preferably, the radioactive material is added to the settable composition in the form of a powder. Preferably the radioactive mate
Collard & Roe P.C.
Dolomatrix International Limited
Nave Eileen E.
LandOfFree
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