Chapter 6.4 Stabilisation and solidification of hazardous wastes
Notes on this chapter
The material in this chapter gives an overview of the essential issues in the stabilisation
and solidification (S/S) of hazardous wastes. Some of the issues may also appear in other
chapters. It is desirable however to consolidate the topic into a single chapter so that
trainers will have a complete picture of the objectives and processes involved in the S/S
of hazardous wastes.
The slides briefly outline the main issues. For further details, trainers should consult the
references given below.
List of slides
Title slide
Slide 2 Immobilisation
Slide 3 Aims of S/S of hazardous waste
Slide 4 Waste pre-treatment
Slide 5 Stabilisation
Slide 6 Solidification
Slide 7 Additives
Slide 8 Key factors
Slide 9 Waste assessment
Slide 10 Performance tests
Slide 11 Properties of S/S treated wastes
Slide 12 Re-use applications for S/S waste
Slide 13 Wastes typically treated by S/S
Slide 14 Case study 1 UK
Slide 15 Schematic of S/S plant part 1 stabilisation
Slide 16 Schematic of S/S plant part 2 solidification
Slide 17 Waste types treated by UK plant
Slide 18 Treated waste specification
Slide 19 Key considerations
Slide 20 Summary
Background notes
1 Stabilisation and solidification aim to immobilise the toxic constituents of hazardous
wastes to prevent them leaching from the wastes once disposed.
2 Immobilisation is accomplished by reducing the solubility of the waste components,
and by physically isolating the waste and decreasing its surface area. S/S therefore
involves both physical and chemical processes.
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3 Different terms – such as immobilisation, fixation, solidification and stabilisation - are
used to describe the various techniques whereby certain hazardous wastes are converted
into a suitable form for long-term disposal. This text uses ‘immobilisation’ as an umbrella
term to include both stabilisation and solidification.
3 S/S technologies are often used to treat the residues from other treatment processes
such as fly ash from incineration or sludges from heavy metal precipitation. The
technologies are most suitable for treating inorganic wastes. Organic constituents in the
waste may make the application of S/S techniques unsafe and inappropriate.
4 S/S technologies are effective in treating a variety of difficult to manage inorganic
wastes. They can be used for wastes containing mixtures of contaminants and can
economically treat large waste volumes. However, certain waste components may
interfere with the reactions and setting of the solidification binders used.
5 The chemistry of S/S wastes treatment is complex. Selection of a suitable solidification
binder depends on correctly predicting complex interactions between waste components
and binders to ensure acceptable and reliable results. Although there is no definitive
guide to successfully selecting a binder, processing method and disposal regime, a wellstructured testing programme guided by an understanding of the mechanisms involved in
S/S systems will reduce uncertainty.
6 In the USA, S/S has been identified as the Best Demonstrated Available Technology
(BDAT) for treating a wide range of hazardous wastes. It is increasingly used for treating
contaminated soil at sites being redeveloped.
7 While the principal aim of S/S is to produce an end product less environmentally
threatening than the original waste, there may be an added benefit if the S/S waste can be
put to practical use. This could provide economic and environmental advantages eg
because of the avoided need for disposal. Nevertheless, concerns about the long-term
performance of S/S products and the possible exposure of human or ecological receptors
to contaminants restrict end-use options. In practice, relatively few S/S- treated wastes
have been re-used to date.
8 S/S may improve the handling and physical characteristics of hazardous wastes.
However S/S technologies for hazardous waste should primarily be regarded as prelandfill waste treatment processes. S/S is often the final waste treatment stage prior to
disposal.
9 Apart from the limited opportunities to re-use S/S treated wastes, they should be
disposed in a secure landfill site. They should not be co-disposed with other wastes such
as MSW as the acid leachate produced by these may cause severe degradation of S/S
wastes.
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Sources of further information
Batstone, R; Smith, JE & Wilson, DC editors (1989) The safe disposal of hazardous
wastes: The special needs and problems of developing countries World Bank,
Washington, Technical paper No 93 in 3 volumes ISBN 0-8213-1144-1 (available as pdf
files from www.worldbank.org/publications/)
Conner, JR (1989) Chemical fixation and solidification of hazardous wastes, Van
Nostrand Reinhold, New York ISBN 0-4422-0511-2
De Bruin, T (1990) Co-disposal and encapsulation Waste Management & Research Vol
8 No 2
Gilliam, TM & Wiles, Carlton C Editors (1992) Stabilization and Solidification of
Hazardous, Radioactive and Mixed Wastes: 3rd volume, American Society for Testing &
Materials STP 1123, Philadelphia ISBN 0-8031-1443-5
Guyer, Howard H (1998) Industrial processes and waste stream management Wiley
ISBN 0-4712-9984-7
LaGrega, MD; Buckingham, PL; Evans, JC & ERM Group (1994) Hazardous Waste
Management McGraw Hill, New York ISBN 0-07-019552-8
Lohwongwatana, B; Soponkanaporn, T & Sophonsridsuk, A Industrial hazardous waste
treatment facilities in Thailand Waste Management & Research Vol 8 No 2
Means, JL, Smith LA & Nehring, KW (1994) The application of solidification /
stabilisation to waste materials Lewis Publishers, USA ISBN 1-5667-0800-9
Mehu, J; Keck, G; & Navarro, A Editors (1999) Proceedings of Waste Stabilisation and
Environment, 13-16 April 1999, Lyon, France (available from E.et.T@wanadoo.fr)
Nash, JM; Cheung, B; Fung, CH; Lei PK, Mak, PW; Rootham, RC; Stokoe, MJ & Tong,
R (1991) Control and treatment of hazardous (chemical) waste in Hong Kong Waste
Management & Research Vol 9 No 3
Razzell, WE (1990) Chemical fixation, solidification of hazardous waste, Waste
Management & Research, Vol 8 No 2
Technical guidelines from the Secretariat of the Basel Convention www.basel.int
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