Leaching behaviour and chemical - mineralogical of construction and demolition waste (concrete and gypsum)

Abstract

The widespread concern on recycling construction and demolition waste (CDW) aims to minimize waste generation and reduce dependency on natural resources. Therefore, release behaviour of chemical elements from CDW needs to be controlled to avoid the increment of accumulation in the environment. The objectives of the research are to evaluate pH dependent leaching behavior and determine the chemical - mineralogical characteristics for CDW (concrete and gypsum) by X-ray Florescence (XRF) and X-ray Diffractometric (XRD) analysis. The obtained results were compared with Environmental Quality Act (1974), EU Landfill directive (1999) and National Secondary Drinking Water Regulation (1986) in order to evaluate the acceptance criteria before the recycling process. The chemical - mineralogical analysis showed that the highest concentration and variety of chemical compounds was found in waste concrete (WC) rather than waste gypsum (WG). However, the highest concentration of chemical elements, such as Ca, Mg, Fe, Zn, Cu, SO42 and CI were mostly leached from WG. Again, WG demonstrated pH dependent leaching behavior, particularly for the elements of Ca, Mg, Fe, Zn, Cu and Mn. The composition of Se in both wastes had exceeded standard limits of Environmental Quality Act (1974). The element Cr found in WC was highest in the alkaline region. The concentration of SO42 in WG was found to be higher than that of WC, without influence by pH and the results had exceeded the standard limits of National Secondary Drinking Water Regulation (1986) and EU Landfill directive (1999). The concentration of SO42 within WG needs to be controlled since the value obtained was more than one order of magnitude than that of WC, due to the ability of WG to be utilized as part of raw material for the production of an environmentally friendly recycled building material.