Leaching characterisation and geochemical modelling of minor and trace elements released from recycled concrete aggregates

Abstract

The pH dependent release of Cd, Cr, Cu, Mn, Mo, Ni, Pb, V and Zn from different recycled concrete aggregate samples was determined. Geochemical speciation modelling was applied on the concentrations of Cu, Cr, Mo and Ni in the leachates in order to predict the measured concentrations and the specific release mechanisms. The model was able to reproduce the characteristic pH dependent release patterns for these elements and reasonable to sometimes excellent matches between the predicted and measured concentrations were achieved. Binding of Mo and Cr as oxyanions (MoO 4 2− and CrO 4 2− ) to ettringite was modelled with fair agreement for Cr only. For Cu and Ni, the predicted and measured concentrations agreed well for the partly carbonated sample at high alkaline pH (11)(12)(13). The importance of complexation to humic substances was also shown in samples derived from construction debris.

Effects of extraction methods and factors on leaching of metals from recycled concrete aggregates

“…Recycled concrete aggregate use is widespread in many countries but it is shown that RCA materials have potential to leach metals (Engelsen et al 2009(Engelsen et al , 2010Chen et al 2013). The cement paste in RCA is believed to be the primary source of leached constituents (Engelsen et al 2010), and certain cement additives such as fly ash (mostly class C but also to a lesser extent class F) and steel slag (produced from both basic oxygen furnace (BOF) and electric arc furnace (EAF)) may intensify this issue as appreciable amounts of metals have been shown to leach from these industrial by products (Li et al 2006;Cetin et al 2012aCetin et al , b, 2014Daniels and Das 2014).…”

“…The cement paste in RCA is believed to be the primary source of leached constituents (Engelsen et al 2010), and certain cement additives such as fly ash (mostly class C but also to a lesser extent class F) and steel slag (produced from both basic oxygen furnace (BOF) and electric arc furnace (EAF)) may intensify this issue as appreciable amounts of metals have been shown to leach from these industrial by products (Li et al 2006;Cetin et al 2012aCetin et al , b, 2014Daniels and Das 2014). Engelsen et al (2009) showed the pH of RCA tended to be highly alkaline.…”

A review of sample preparation and its influence on pH determination in concrete samples

“…Webster and Loehr (47) (53) used an L:S ratio of 2.5. Nevertheless, the most widely used ratio was 10, once again varying the procedures that were followed prior to measurement (54)(55)(56)(57)(58).…”

ENCORT-CDW - Evaluation of the European recovery target for construction and demolition waste

“…Regarding the leaching of PCB-7, the results demonstrate the low solubility of these organic substances and are in compliance with earlier studies. (Engelsen et al, 2010) b Data from three sample batches and the test is conducted at L/S = 1.5 (Engelsen et al, 2012a) In a longer time perspective, quantification of the leaching studied in the laboratory and at field sites, identification of the processes governing leaching and the development of proper framework for assessing the environmental risk related to leaching will become increasingly important. This is due to the fact that the cement and concrete produced today and demolished in the future are increasingly produced with alternative raw materials and waste derived fuels (e.g.…”