Differences during the last 15years in materials' composition in Municipal Solid Waste Incineration (MSWI) regarding bottom ash (BA) were assessed as a function of particle size (>16, 8-16, 4-8, 2-4, 1-2 and 0-1mm). After sieving, fractions >2mm were carefully washed in order to separate fine particles adhering to bigger particles. The characterization took into account five types of materials: glass (primary and secondary), ceramics (natural and synthetic), non-ferrous metals, ferrous metals and unburned organic matter. The evaluation was performed through a visual (>2mm) and chemical (0-2mm) classification. Results showed that total weight of glass in the particles over 16mm has decreased with respect to 1999. Moreover, the content of glass (primary and secondary) in BA was estimated to be 60.8wt%, with 26.4wt% corresponding to primary glass in >2mm size fractions. Unlike 1999, in which glass was the predominant material, ceramics are currently the major phase in bottom ash (BA) coarse fractions. As for the metals, respect to 1999, results showed a slight increase in all size fractions. The greatest content (>22wt%) of ferromagnetic was observed for the 2-4mm size fraction while the non-ferrous type was almost non-existent in particles over 16mm, remaining below 10wt% for the rest fractions. In the finest fractions (<2mm), about 60 to 95% of non-ferrous metals corresponded to metallic aluminium. The results from the chemical characterization also indicated that the finest fractions contributed significantly to the total heavy metals content, especially for Pb, Zn, Cu, Mn and Ti.

The main goal of this paper is to obtain a granular material formulated with Municipal Solid Waste Incineration (MSWI) bottom ash (BA) and air pollution control (APC) fly ash to be used as secondary building material. Previously, an optimum concrete mixture using both MSWI residues as aggregates was formulated. A compromise between the environmental behaviour and the economy of the process was considered. Unconfined compressive strength and abrasion resistance values were measured in order to evaluate the mechanical properties. From these results, the granular mixture was not suited for certain applications owing to the high BA/APC fly ash content and low cement percentages used to reduce the costs of the final product.Nevertheless, the leaching test performed showed that the concentrations of all heavy metals were below the limits established by the current Catalan legislation for their reutilization. Therefore, the material studied might be mainly used in embankments, where high mechanical properties are not needed and environmental safety is assured.

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The reutilization of the by-products from the calcination of natural magnesite for environmental solutions is conditioned by the availability of MgO, CaO and other compounds. In order to overcome their great heterogeneity, an exhaustive chemical and physical characterization is necessary in order to assess their potential applications. In this study, the acid neutralization capacity (ANC) test was used to categorize three types of byproducts (LG-MgO, LG-D and LG-F), which mainly differed according to source ore and processing conditions. The experimental data concerning the leaching of Mg 2+ , Ca 2+ , Fe 2+ and SO 4 2− was corroborated with geochemical predictions using the modelling software Visual MINTEQ. Likewise, the main solubility-controlling mineral phases were also identified. According to the results, there is a buffer capacity within the pH 8-10 range, mainly dominated by the neutralization of MgO/Mg(OH) 2 , equilibrium with a small contribution from the carbonate content at lower pH values. The release of sulphates showed a non-pH dependency attributed to the solubility of CaSO 4 and elemental sulphur present in petcoke. For dust materials, leaching of Fe was minimal above pH 6 owing to the insoluble nature of the Fe 2 O 3 /Fe 3 O 4 pair. Accordingly, the by-products labeled as LG-D and LG-F are better suited for stabilizing solid wastes or wastewater that are acid while LG-MgO is more appropriate for alkaline residues such as contaminated soils. In both cases, a suitable pH range in which pH-dependent heavy metals and metalloids show minimum solubility can be obtained. The use of these by-products guarantees an environmentally friendly alkali reservoir for the long-term stabilization of heavy metals and metalloids at a very competitive price as a substitute for the widely used lime.