Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Patent
1993-06-17
1995-10-10
Taylor, Dennis L.
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
405128, 488249, 210751, A62D 300, B09B 300
Patent
active
054572738
DESCRIPTION:
BRIEF SUMMARY
This invention relates to solidification of solid processing waste and in particular to solidification of photographic waste to render it more environmentally acceptable.
The overflow from a photographic processor will typically consist of environmentally undesirable substances such as heavy metal ions, sequestering agents, substances that have a high oxygen demand and colour developing agents and their derivatives, straight disposal of which contravenes sewer regulations in many parts of the world. It is therefor essential that the overflow is converted by chemical or physical means to a liquid which can be poured into the sewer and/or a residual solid which can be removed to a place of safe and legal disposal.
The use of an alkali metal silicate as one additive in treating certain industrial processing waste, such as radioactive and metal plating wastes, has been disclosed, for example, in Japanese Patent Publication No. 60237398 and U.K. Patent No. 1432091 respectively.
Co-pending PCT application No. PCT/EP 91/01680 and PCT/EP 91/01681 describe the addition of chemical reagents to precipitate, adsorb or otherwise remove harmful pollutants in particular in photographic waste processing. Japanese Patent Publication No. 51099854 describes the use of an oxide, hydroxide or water soluble salt of an alkaline earth metal to precipitate heavy metal ions in a photographic waste effluent.
Japanese Patent Publication No. 63291680 discloses the use of a solidifying agent in the final stage of treatment of photographic waste, wherein the solidifying agent is a hardener, such as cement, or a desiccant such as silica gel. The liquid absorbing agent is a powder or particle with a diameter of 0.01-3 mm which is not soluble in water.
The use of a water-soluble silicate, in particular an alkali metal silicate, in the field of photographic waste effluent treatment has nowhere been documented. However, it has now been found that such an addition to a photographic waste that has previously been treated by adding thereto an alkaline earth compound or another compound with an oxidation number (or valency) greater than one, such as manganese, with or without other additions, hardens it over a period of a few days and renders it glass-like. The resulting `glass` is less permeable to water than the original solid and therefore it is less likely that polluting compounds will wash out from the treated waste compound compared to that which is untreated. Consequently the precipitated photographic waste is more convenient and safer to transport and less harmful to the environment if used for landfill. Moreover, the process is inexpensive and any waste spillage is much easier to remove.
The effluent to be treated may, for example, have arisen from any of the photographic processes described in Item 308119, Research Disclosure December, 1989, Industrial Opportunities Ltd., Hants., U.K., and especially sections XIX, XX and XXIII thereof.
The method applies to any solid waste that has been generated by adding an alkaline earth compound, or another compound with an oxidation number greater than one, to processing solutions in order to precipitate metals and/or oxysulphur compounds. For example waste generated by addition of calcium hydroxide or a mixture of calcium salts and another metal hydroxide, may be particularly suitable. However it is important for the processing solution not to contain ammonium ions to prevent liberation of free ammonia, unless appropriate safety measures are taken.
According to the present invention therefore, there is provided a method of treating photographic effluent containing metal ions with an oxidation number greater than one, comprising the addition of a water-soluble silicate to the effluent in an amount to render it glass-like and less permeable to water.
The silicate may be added to the treated effluent suspension and the mixture separated, for example by filtration or centrifugation, or alternatively it may be added to the pre-separated solid.
Although any water-soluble silicate may be used, convenien
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Fyson John R.
Glover Edward C. T. S.
Glover Martyn S.
Eastman Kodak Company
Everett John R.
Taylor Dennis L.
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