Patent Number: 
Section: description

Embodiments of the invention will now be described by the following examples. Arsenic Sodium Arsenite 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filer (ashxe2x80x94to soak up excesss water), and 160 gm of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 2.1 ppm which was much less than the allowed limit of 5.0 ppm. Powdered arsenic 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filler (ashxe2x80x94to soak up excess water), and 160 g of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 4.1 ppm which was less than the allowed limit of 5.0 ppm. Arsenic Trioxide 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filler (ashxe2x80x94to soak up excess water), and 160 g of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 4.1 ppm which was much less than the allowed limit of 5.0 ppm. Arsenic Pentoxide 100 g, aluminium sulphate 50 g, ferric chloride 20 g, calcium carbonate 50 g and water 300 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 400 g of calcium carbonate and caustic magnesium oxide, 400 g of a filler (ashxe2x80x94to soak up excess water), and 160 g of a mixture of 50 g aluminium sulphate, 100 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 4.1 ppm which was much less than the allowed limit of 5.0 ppm. Powdered Arsenic 100 g, aluminium sulphate 50 g, calcium carbonate 20 g and water 150 ml are slurried together and left to stand for 10 minutes during which separation of the metal occurred and flocculation was observed. This slurry was added to a slurry of a settable composition which contained 200 g of calcium carbonate and caustic magnesium oxide, 400 g of a filer (ashxe2x80x94to soak up excess water), and 10 g of a mixture of 30 g aluminium sulphate, 60 g citric acid and 10 g soda ash. The thickness of the total mixture could be adjusted by addition of water to form a mouldable composition which can have a slump value of between 80-120 (i.e. about that of a cement slurry). The total mixture was poured into moulds and set. A Leach rate analysis showed an arsenic leach of 1.0 ppm which was much less than the allowed limited of 5.0 ppm. Mercury Mercury from a mercury-containing brine sludge is encapsulated: in the following manner. The brine sludge contains between 100-200 mg of mercuric per kilogram of sludge. The sludge additionally contains 10-29% calcium carbonate, 1-9% magnesium hydroxide, 10-29% sodium chloride, 1-9% soil/dust and 30-60% water. The sludge is a waste produce from brine purification. The sludge is an odourless brown sludge insoluble in water. The sludge has a pH of 11.6 and a specific gravity of 1.29. 1 kg of the brine sludge, 900 g of settable composition, 270 g of water, 50 g of aluminium sulphate and 50 g of citric acid were mixed in a mixer. If desired, water is added to form a mouldable composition. The mixture is poured into moulds and set. A leach rate analysis showed a mercury leach of less than 0.01 parts p/million making the encapsulated composition safe for unlined tip storage. Nickel and Chromium 150 ml of an undiluted fully concentrated nickel and chromium containing residue (containing 360 mg p/litre chromium and 28,000 mg p/litre nickel), 400 ml water, 150 g calcium carbonate and 40 g of aluminium sulphate are mixed together to form a slurry. To the slurry is added 300 g of calcium carbonate and caustic magnesium oxide, 60 g of aluminium sulphate, 34 g of citric acid, 6 g of soda ash, 1 kg of filler (powerhouse ash) and an additional 50 ml of water. The thickness of the total mixture can be adjusted with water to form a mouldable composition. The mixture is poured into moulds and left to cure for T.C.L.P. tests (Toxic Characteristic Leachate Procedures). After 30 days of testing, a leach rate of below 0.2 parts p/million was established showing that the encapsulated product is suitable for storage in an unlined tip. 150 ml of an undiluted fully concentrated nickel and chromium containing residue (containing 3.1 mg p/litre chromium and 1,100 mg p/litre nickel), 400 ml water, 150 g calcium carbonate and 40 g of aluminium sulphate are mixed together to form a slurry. To the slurry is added 300 g of calcium carbonate and caustic magnesium oxide, 60 g of aluminium sulphate, 34 g of citric acid and 6 g of soda ash, 1 kg of filler (powerhouse ash) and an additional 50 ml of water. The thickness of the total mixture can be adjusted with water to form a mouldable composition. The mixture is poured into moulds and lets to cure for T.C.L.P. tests (Toxic Characteristic Leachate Procedures). After 30 days of testing, a leach rate of below 0.2 parts p/million was established showing that the encapsulated product is suitable for storage in an unlined tip. Radioactive Monazite Tests were conducted using a powdered sample of the mineral monazite. Monazite is a monoclinic phosphate of the rare earth elements containing the cerium groups (Ce, La, Y, Th) PO4, as well as some uranium and thorium. Monazite is relatively abundant in beach sands, and is one of the principal sources of rare earth minerals and thorium. Thorium is used as a radioactive source in scientific instruments. Rare earth compounds are used in various manufacturing processes, including the manufacturing of glass and certain metals. Analysis of the monazite material employed in the tests found that it contained 246 Becquerels per gram (Bq/gm) of thorium-232 and 28 Bq/gm of uranium-238. The half life of the thorium contained in the monazite is approximately 4.5 billion years (4.5xc3x97109). The monazite particle size can be from dust (approx. 0.1 xcexcm) up to particles of approximately 1.0 mm, ideally. The lead tailings, caustic magnesium oxide and calcium carbonate were all preground to approximately 110 xcexcm, ie. 90% passed through a 150 xcexcm sieve. 300 grams of monazite, of radioactivity 246 becquerels per gram thorium and 28.1 becquerels per gram uranium, 400 grams of caustic magnesium oxide and a mixture of 480 grams of lead tailings (ex Mt. Isa) and 320 grams calcium carbonate were thoroughly dry mixed with 100 grams of aluminium sulphate and 25 grams of citric acid. To this was added 300 mLs of water to form a thick rapidly setting paste. The thickness of the total mixture could be adjusted by the addition of water to form a mouldable composition. The total mixture was poured into moulds and allowed to set. The radioactivity of the encapsulated monazite mixture was measured to be 44.60xc2x10.20 becquerels per gram thorium and 5.06xc2x10.21 becquerels per gram uranium. A leach rate analysis (TCLP test) was carried out at 14 days and 28 days to determine the leachable uranium and thorium. At 14 days the leachable uranium was less than 0.05 micrograms per litre and the leachable thorium was 0.25 micrograms per litre. At 28 days the leachable uranium was 0.05 micrograms per litre and the leachable thorium was 0.45-0.50 micrograms per litre. Gamma spectroscopy was carried out on the TCLP solutions to determine the levels of radioactive uranium and thorium at 14 and 28 days. At 14 days the leachable uranium radioactivity was below detectable levels or equivalent to  less than 1 part per million and the leachable thorium radioactivity was 0.034xc2x10.007 becquerels per gram. At 28 days the leachable uranium radioactivity was below detectable levels or equivalent to  less than 1 per million and the leachable thorium radioactivity was below detectable levels or equivalent to  less than 2 parts per million. 500 grams of monazite, of radioactivity 246 becquerels per gram thorium and 28.1 becquerels per gram uranium, 450 grams of caustic magnesium oxide and a mixture of 360 grams of lead tailings (ex Mt. Isa) and 240 grams calcium carbonate were thoroughly dry mixed with 100 grams of aluminium sulphate and 25 grams of citric acid. To this was added 310 mLs of water to form a thick rapidly setting paste. The thickness of the total mixture could be adjusted by the addition of water to form a mouldable composition. The total mixture was poured into moulds and allowed to set. The radioactivity of the encapsulated monazite mixture was measured to be 70.20xc2x10.30 becquerels per gram thorium and 8.01xc2x10.31 becquerels per gram uranium. A leach rate analysis (TCLP test) was carried out at 14 days and 28 days to determine the leachable uranium and thorium. At 14 days the leachable uranium was less than 0.05 micrograms per litre and the leachable thorium was 0.15 micrograms per litre. At 28 days the leachable uranium was 0.05 micrograms per litre and the leachable thorium was 0.15-0.45 micrograms per litre. Gamma spectroscopy was carried out on the TCLP solutions to determine the levels of radioactive uranium and thorium at 14 and 28 days. At 14 days the leachable uranium radioactivity was below detectable levels or equivalent to  less than 1 part per million and the leachable thorium radioactivity was below detectable levels or equivalent to  less than 2 parts per million. At 28 days the leachable uranium radioactivity was below detectable levels or equivalent to  less than 1 part per million and the leachable thorium radioactivity was 0.038xc2x10.007 becquerels per gram. 800 grams of monazite, of radioactivity 246 becquerels per gram thorium and 28.1 becquerels per gram uranium, 400 grams of caustic magnesium oxide and a mixture of 300 grams of lead tailings (ex Mt. Isa) and 200 grams calcium carbonate were thoroughly dry mixed with 100 grams of aluminium sulphate and 25 grams of citric acid. To this was added 400 mLs of water to form a thick rapidly setting paste. The thickness of the total mixture could be adjusted by the addition of water to form a mouldable composition. The total mixture was poured into moulds and allowed to set. The radioactivity of the encapsulated monazite mixture was measured to be 104.0xc2x10.41 becquerels per gram thorium and 12.0xc2x10.42 becquerels per gram uranium. A leach rate analysis (TCLP test) was carried out at 14 days and 28 days to determine the leachable uranium and thorium. At 14 days the leachable uranium was 0.05 micrograms per litre and the leachable thorium was 0.25 micrograms per litre. At 28 days the leachable uranium was 0.10 micrograms per litre and the leachable thorium was 1.10-1.40 micrograms per litre. Gamma spectroscopy was carried out on the TCLP solutions to determine the levels of radioactive uranium and thorium at 14 and 28 days. At 14 days the leachable uranium radioactivity was below detectable levels or equivalent to  less than 1 part per million and the leachable thorium radioactivity was below detectable levels or equivalent to  less than 2 parts per million. At 28 days the leachable uranium radioactivity was below detectable levels or equivalent to  less than 1 part per million and the leachable thorium radioactivity was 0.038xc2x10.007 becquerels per gram. In each of the above examples 9 to 11 the leach rate solutions were all less than 10 parts per million (ppm) for thorium and uranium, indicating successful encapsulation of the radioactive material. It should be appreciated that various other changes and modifications can be made to the embodiments without departing from the spirit and scope of the invention, the nature of which is to be determined from the foregoing description and the appended claims. Furthermore, the preceding examples are provided for illustrative purposes only, and are not intended to limit the scope of the process of the invention.