Waste incinerator residue treatment: Variability implications.

Air pollution control residues are a hazardous waste, collected when controlling the flue gas emissions created within modern energy from waste 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

Chemical and spectroscopic characterization of insoluble and soluble humic acid fractions at different pH values

Background: Humic acids (HA) are organic molecules with complex structure and function and variable properties. They are insoluble in strongly acid pH conditions. At present, it is not clear how much is the amount of HA in solution at the pH of natural soils nor are known the characteristics of the different soluble fractions and their possible association with the inorganic phase of soil. The scope of this work was to characterize the soluble and insoluble fractions obtained by acidifying Na humate solution at pH values 3, 5, and 7 and to compare these fractions with the HA obtained at pH 1. At each pH, the precipitate and the soluble fractions were separated and characterized by elemental analysis, total acidity and carboxylic group content, infrared, and 13 C NMR and 1 H NMR spectroscopy. Results: The HA fraction insoluble at pH 1 had a high acid group content and aromaticity but a low content of Oand N-containing groups. At pH 3, a fraction with nearly the same characteristics was obtained. At pH 1 and pH 3, the inorganic phase bound to the insoluble humic material was largely constituted by clay minerals and some Al and Fe hydroxides. The soluble fractions at pH values 1 and 3 were very poor and they were composed of a silica gel-like phase associated with polar organic material rich in carboxylic and metal-carboxylate groups. At pH values 5 and 7, only a small fraction of the Na humates precipitated. The fractions remaining in the solution were mainly composed of organic material particularly rich in aromatic and aliphatic groups, while the inorganic phase contained phyllosilicates. The fractions insoluble at pH values 5 and 7 contained a large amount of inorganic material that consisted mainly of phyllosilicates. Conclusions: The soluble fractions obtained at pH values 5 and 7 represent the humic component that in environmental situations would be dissolved in the soil solution. Our findings could be very useful for a more detailed investigation into the way HA influence plant metabolism under environmental-like conditions, both as regards pH conditions and interaction with the mineral fraction