Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Patent
1999-04-16
2000-10-17
Bagnell, David
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
588252, 106DIG1, C04B 1810, C04B 2804, A62D 300
Patent
active
061323551
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for rendering ash inert, in particular fly ash from urban incinerator smoke.
Urban incinerators (which are used to destroy household waste and/or hospital waste) produce occasionally considerable volumes of fly ash. The mineralogical composition of this ash hardly varies at all, irrespective of its origin, and alkali metal chlorides (NaCl and KCl), anhydrite, quartz, vitrified aluminosilicates, other relatively chemically inert oxidized residues (including SnO.sub.2), heavy metals (in particular zinc, lead, cadmium, mercury and chromium), organochlorine derivatives and noncombusted material are generally found therein, albeit in proportions which may range from unity to twofold, or even more. Aluminium metal is often found among the noncombusted material.
The presence of water-soluble substances, heavy metals and toxic organic material (dioxins, furans) may pose difficulties for the disposal of this fly ash and involves rendering them inert in a prior process intended to make them harmless to the environment.
Various processes have been suggested in order to render urban incinerator ash inert, these processes being directed towards stabilizing the heavy metals, mainly lead and cadmium. According to one of these processes (American U.S. Pat. No. 4,737,356), fly ash is treated with a water-soluble phosphate and lime so as to insolubilize the heavy metal ions in the form of metal phosphates. According to a similar process (European patent application EP-A-568,903), ash is treated with water and phosphate ions so as to adjust the pH to 6.9 and to insolubilize the heavy metals in the form of metal phosphates, the excess phosphate ions are bound by trivalent aluminium or iron ions and the reaction medium is basified with quicklime, CaO. According to European patent application EP-A-534,231, fly ash collected from a purification treatment of acidic fumes with lime are simply calcined at high temperature (between 375 and 800.degree. C.).
With the known processes which have just been described, the inert products formed are powders, which may pose difficulties for their handling and storage. One means of circumventing this difficulty consists in eliminating the fly ash in hydraulic mortars, with which solid, inert blocks are formed. To this end, in a known process for rendering a sludge contaminated with heavy metals inert, the sludge is mixed with Portland cement and fly ash so as to form a solid, compact and inert block (Roy A. Heaton H. C., Cartledge F. K. and Tittlebaum M. E. "Solidification/Stabilization of a Heavy Metal Sludge by a Portland Cement/Fly Ash Binding Mixture"--Hazardous Waste & Hazardous Material, Vol. 8, No. 1, 1991, pages 33-41). When applied to fly ash from smoke generated by incineration of urban waste in order to render it inert, this known process is not always satisfactory as the blocks obtained in this case are expanded by the presence of a large number of gaseous inclusions, thereby considerably increasing their volume and bulk and making them crumbly and relatively nonresistant to compression.
The invention is directed towards overcoming the abovementioned drawbacks of the known processes, by providing a process which efficiently renders inert ash comprising heavy metals and noncombusted aluminium metal, in solid, compact blocks which have good mechanical properties. The invention is also directed in particular towards providing a process which makes it possible to remove fly ash from urban incinerator smoke, in compact, non-expanded blocks which have good compression strength and satisfy the standardized toxicity tests, in particular the TCLP ("Toxicity Characteristic Leaching Procedure", USA) toxicity test.
Consequently, the invention relates to a process for rendering ash containing heavy metals and aluminium metal inert, which process is characterized in that a reactant selected from phosphoric acid and alkali metal phosphates is added to the ash, the phosphate-containing mixture thus obtained is subjected to puddling with water and a hydra
REFERENCES:
patent: 4226630 (1980-10-01), Styron
patent: 4737356 (1988-04-01), O'Hara et al.
patent: 4911757 (1990-03-01), Lynn et al.
patent: 5037479 (1991-08-01), Stanforth
patent: 5041398 (1991-08-01), Kauser et al.
patent: 5130051 (1992-07-01), Falk
patent: 5284636 (1994-02-01), Goff et al.
patent: 5429751 (1995-07-01), Hooykaas
patent: 5973220 (1999-10-01), Sasaki et al.
"Heavy Metals in Wastewater and Sludge Treatment Processes" by J. Lester. vol. 1, p. 2.
"Solidification/Stabilization of Heavy Metal Sludgy by a Portland Cement/Fly Ash Binding Mixture" by A. Roy et al.
Bagnell David
Lagman Frederick L.
Solvay ( Societe Anonyme)
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