No abstract

The paper characterises the phases formed in a solidification/stabilisation (s/s) matrix resulting from a blend of air pollution control residue and co-fired pulverised fuel ashes, activated with a waste, aluminium containing, NaOH solution. Characterisation was performed by X-ray diffraction, simultaneous thermal analysis (thermogravimetric analysis and differential thermal analysis) and SEM. The effects of varying air pollution control/pulverised fuel ashes ratio, curing temperature and time and liquid phase (NaOH or deionised water) on the hydration products in the s/s matrix were studied, as were the changes in phase composition during regulatory leach testing. The principle phases in the s/s matrix, dependent on the process conditions, included Ca(OH) 2 , CaCO 3 , NaCl, C-S-H (I), Friedel's salt, katoite, zeolitic phases Na-P1 and sodalite, CaClOH and vishnevite. Some retention of chlorides within Friedel's salt and sodalite during leach testing was observed; however, most was released due to its presence as NaCl. Sulphates were retained as vishnevite during leach tests.

Recent changes in UK coal supply have resulted in the production of high-lime ash from a major UK power station. This paper offers results collected during a project to compare the key performance characteristics of concretes using an ASTM class C (high lime) and an ASTM class F (low lime) ash as a partial replacement for Portland cement. Mixes were produced using 40% replacement of Portland cement by weight, with pulverised fuel ash, and a water/cement (w/c) ratio of 0?4. Characteristics examined included workability, compressive strength, water permeability, water absorption, chloride permeability using the rapid chloride permeability test, resistance to sulfate attack, and freeze-thaw resistance. The results showed that the concrete containing the ASTM class C ash was superior in all of these areas except for sulfate resistance. Workability and compressive strength tests were also performed on mixes containing 60, 70, 80 and 90% replacement levels with the class C ash, all with 0?4 w/c ratio. Results showed a steady increase in the workability and a decrease in the compressive strength. Samples made at 90% replacement level showed extreme unsoundness and could not be tested for strength.

Air pollution control residues are a hazardous waste, collected when controlling the flue gas emissions created within modern energy from waste (EfW) incinerators. They are inherently variable with regards to mineralogy and morphology. However, this variability is frequently neglected throughout the scientific literature concerned with their management. This work characterises residues collected from five different UK facilities and highlights the implications of their compositional variability for the performance of products resulting from a stabilisation/solidification treatment. It is demonstrated that the variability is of significance for the mineralogy and several key engineering properties of the products, and links between the properties of the residues and the behaviour of the products are shown. Residue variability should be considered when researching technical management options. Treatments are likely to require modification in order to satisfy performance envelopes for individual batches of residue.