A method is presented to predict the short-term (months to years) and long-term (> 30 years) chemical behaviour of bottom ash from municipal solid waste incinerators in monofills. It is based on bottom ash composition and laboratory kinetic studies of bottom ash with water. Bottom ash after the quench tank is a reactive mixture in which slow and fast acid/base reactions occur. These intrinsic acid/base reactions continue for at least several months, and the end point is not yet known. The heavy metal concentrations observed in the aqueous extracts reflect primarily the advance of these reactions. Consequently leaching tests based solely on short-term (hours to months) extraction procedures cannot predict the chemical behaviour of bottom ash in monofills. However, laboratory experiments with samples of bottom ash, in which the intrinsic acid/base reactions have proceeded differently, provide useful information on the nature of chemical reactions significant in the short- and long-term.
The use and stock of construction materials has increased by two orders of magnitude over the past century. The composition of construction materials changes constantly, with the content of synthetic organic compounds and aluminium increasing since the 1940s. Today, construction wastes, which may experience a similar increase, are among the most abundant waste materials. A mass balance of a full scale construction waste sorting plant yielded the following results: the separation produced an organic fraction (25%), which is best treated in a municipal solid waste (MSW) incinerator, a metal fraction (3%) well suited for iron recycling, and two inorganic fractions (45 and 27% respectively) of a composition similar to the average earth crust. According to the composition and the reaction with water, leachates from landfills of construction wastes as well as of inorganic sorting fractions have to be treated for several decades. The chemical behaviour of the inorganic fractions is different from virgin construction materials. Thus, in order to reuse these fractions, specific additional experiments are needed. The potential of the mechanical sorting process to separate according to chemical properties appears to be limited. Nevertheless, the sorting fractions are better suited for landfilling and reuse than the initial construction waste.
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