Compositions: coating or plastic – Coating or plastic compositions – Metal-depositing composition or substrate-sensitizing...
Patent
1985-07-30
1988-05-03
Straub, Gary P.
Compositions: coating or plastic
Coating or plastic compositions
Metal-depositing composition or substrate-sensitizing...
106 97, 106109, 106117, 106118, 106120, 404 76, 405129, 423DIG2, C21F 900, C04B 702, C04B 714, C04B 734
Patent
active
047417765
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method of processing waste materials, for example hazardous waste materials.
Processes are known wherein wastes are converted into a solid mass or aggregate by treatment with a silicate and a cementitious material in the presence of water. The product may then be used for land-filling in appropriate sites. Thus, for example, GB-PS No. 1,485,625 discloses a process for treating a hazardous waste capable of being contained in an aqueous slurry, which process comprises adding a calcium-containing cement powder and a powder consisting of aluminium silicate and/or an aluminosilicate to the waste dissolved or dispersed in water, thereby forming a flowable slurry containing the waste and allowing the slurry to set into a rigid, rock-like mass. The preferred aluminosilicate is fly ash, which is a finely divided residue carried off with exhaust gases produced by the combustion of pulverised coal.
GB-PS No. 1,518,024 discloses a process for the treatment of toxic waste, which process comprises obtaining a low-molecular-weight silicic acid from a silicate (e.g. blast furnace slag or fly ash) by means of an acid, mixing the silicic acid with the waste in the presence of water and in a sufficiently acid medium to ensure at least partial dissolution of the waste, precipitating a gel from the aqueous mixture and hardening it to give a solid aggregate. A material, e.g. lime, that reacts with the gel to form a silicate may be added, as may a cementitious agent, e.g. Portland cement.
However, owing to the continuing pressure to dispose of large quantities of industrial waste with the minimum possible pollution of the environment, there is a need for a process that converts wastes into a solid form which has a lower leachability, especially with regard to toxic heavy metals, than has been achieved hitherto. Furthermore, in view of the desirability of putting to use quickly the sites filled with the converted waste, there is a need for a process that gives a product of rapid strength development and of good final strength.
The present invention now provides a method of processing a waste material in which said waste material is bonded with cement powder to form a solid material, characterised in that the waste material is also treated with flue dust.
A preferred flue dust is that obtained from the flue gases in the manufacture of cement. Various devices, for example precipitators and/or cyclones can be used to collect this flue dust. Such flue dust is predominantly a calcium carbonate and its oxide analysis may give up to 60% for calcium oxide, CaO. Commonly, the content of alumina will be only about 3-3.5%. By virtue of its CaO analysis value, the flue dust can be regarded as a basic or alkaline material.
The oxide analysis of dust, from the precipitators or cyclones of a cement works typically gives figures for the major components within the following ranges:
The flue dust need not normally be fractionated before use. Moreover, the flue dust need not be taken directly from the collecting means: it is possible to use material taken from stored or dumped deposits of flue dust.
The method of the present invention can be employed for the treatment of diverse waste materials, including toxic and other hazardous wastes. The invention is particularly advantageous in the treatment of waste materials, e.g. inorganic wastes, that are acidic and/or that contain one or more heavy metals (such as chromium, lead, mercury, cadmium, arsenic, iron, tin, zinc, nickel, copper, cobalt, vanadium, manganese or barium).
Waste materials treated by the present process are conveniently liquid, e.g. aqueous suspensions or solutions. However, a waste normally obtained in solid form or as a sludge can be mixed with water prior to or during the present process.
Typical wastes that can be treated by the present process include, for example, spent inorganic catalysts from the petrochemical, dyestuff or other chemical industries; mine tailings and drosses; wastes from the iron and steel and the non-ferrous metals industr
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Bye Gerald C.
Matthews Kenneth B.
Blue Circle Industries Limited
Straub Gary P.
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