Waste materials are hazardous if they display toxic, corrosive or other characteristics which have the potential to cause danger to health or the environment. New regulations to meet the requirements of the Landfill Directive contain controls on hazardous waste including the requirement to pre-treat hazardous waste prior to disposal and to ensure these wastes meet stringent waste acceptance criteria (WAC) on leachability. Waste from the cleaning of combustion gases produced from municipal solid waste (MSW) incineration is classed as hazardous by virtue of their corrosive properties. The majority of these air pollution control (APC) residues which contain dioxins, heavy metals and high levels of chloride are currently sent to landfill. To meet the new controls, pretreatment will be required to improve the handling properties and reduce the release of chloride ions into the environment. Ordinary Portland cement (OPC) is used to treat hazardous wastes. The solid form produced with the addition of OPC is however susceptible to degradation from aggressive leaching fluids and may release contaminants over time. Additives with high silica content can be used to interact with free lime produced during OPC hydration to improve the physical and chemical properties of the solid waste form. The treatment of MSW APC residues with sodium silicate and cement produces a solid waste form with a reduced structural integrity and a tendency to breakdown under attack from aggressive fluids. Silica 'gels' are formed during initial setting reactions which 'depolymerise' with fluid ingress to form new calcium rich silica 'gels' within cracks and voids of the solid waste form. Expansion due to water absorption and continual 'gel' formation causes structural failure. The addition of sodium silicate to sludges produced from a current treatment by mixing MSW APC residues with other mixed hazardous waste improves strength development by 'encapsulating' the waste sludge inside a calcium/silica 'gel'. This stops components of the sludge from interfering with normal OPC hydration. The treatment of MSW APC residues with sodium silicate will not produce a solid form to meet the new waste acceptance criteria. However, sodium silicate has the potential to improve handling and structural integrity of the sludge produced from the current treatment process.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:412056 |
| Date | January 2005 |
| Creators | Wilkes, Timothy |
| Publisher | University of Surrey |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://epubs.surrey.ac.uk/773426/ |
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