Investigations into the long-term behaviour of chemically immobilised wastes and residues in underground cavities

Where residues from waste incineration plants are deposited underground, there will be a potential hazard associated with the soluble heavy metal content of these residues, which may be released by the ingress of geogenous water. Geogenous conditions and long-term variations in the chemical environment must therefore be taken into account in laboratory investigations.

The underground deposition of residues from waste incineration plants may have negative environmental effects.  The main hazard potential stems from the soluble heavy metal content of these residues, which may be mobilised by contact with geogenous water.

The object of this project was the conduct of laboratory investigations in order to determine the behaviour of wastes used as backfill for excavation workings in hard coal mines.

Conventional proprietary bonding agents have been used for the bonding of residues and the immobilisation of pollutants.  Investigations have focused on the effects of the addition of cements and water glass as bonding agents upon the properties of fresh mixtures, load-settlement behaviour, compression strength, permeability and the retention of pollutants.


Results:

• The mobility of heavy metals present in residues is critically dependent upon the chemical environment.
• The influence of Portland cement or water glass upon compaction behaviour is limited.  A comparison of cements has revealed that, with its faster setting properties, alumina cement has a favourable influence upon load-settlement behaviour.
• Given limited permeability, increases in temperature and pressure are generally associated with higher specific discharges of heavy metals, which may be reduced by the addition of bonding agents.

Conclusion
For the evaluation of the environmental impact of the deposition of residues from waste incineration plants, geogenous conditions and long-term variations in the chemical environment must be taken into account in laboratory investigations.

Source Of Supply: The final report (call number F 95 B 2506, in German) can be borrowed from Technische Informationsbibliothek (TIB) Hannover, Welfengarten 1B, 30167 Hannover.



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