Interactions of Cd2+, Co2+ and MoO42− Ions with Crushed Concrete Fines

Victoria K Elmes,Nichola J Coleman

doi:10.3390/jcs5020042

Abstract

Construction and demolition activities generate approximately two thirds of the world’s waste, with concrete-based demolition material accounting for the largest proportion. Primary aggregates are recovered and reused, although the cement-rich fine fraction is underutilised. In this study, single metal batch sorption experiments confirmed that crushed concrete fines (CCF) are an effective sorbent for the maximum exclusion of 45.2 mg g−1 Cd2+, 38.4 mg g−1 Co2+ and 56.0 mg g−1 MoO42− ions from aqueous media. The principal mechanisms of sorption were determined, by scanning electron microscopy of the metal-laden CCF, to be co-precipitation with Ca2+ ions released from the cement to form solubility limiting phases. The removal of Co2+ and MoO42− ions followed a zero-order reaction and that of Cd2+ was best described by a pseudo-second-order model. The Langmuir model provided the most appropriate description of the steady state immobilisation of Cd2+ and Co2+, whereas the removal of MoO42− conformed to the Freundlich isotherm. Long equilibration times (>120 h), loose floc formation and high pH are likely to limit the use of CCF in many conventional wastewater treatment applications; although, these properties could be usefully exploited in reactive barriers for the management of contaminated soils, sediments and groundwater.

Highlights

Long equilibration times (>120 h), loose floc formation and high pH are likely to limit the use of concrete fines (CCF) in many conventional wastewater treatment applications; these properties could be usefully exploited in reactive barriers for the management of contaminated soils, sediments and groundwater
Laboratory-prepared CCF were selected for this study, rather than those obtained by crushed demolition waste, to provide a well-characterised, reproducible, uncontaminated sample against which the performance of real Construction and demolition (C&D) waste can be evaluated in future research
50 wt% of light brown grains of flint aggregate were retained in the CCF among the grey grains of crushed cement (Figure 1a)

Summary

Introduction

Construction and demolition (C&D) waste represents approximately two thirds of the world’s refuse [1,2]. Concrete-based demolition material accounts for the largest proportion, estimated to be between 75 and 88%, with the USA, China and Europe generating 320 Mt, 240 Mt and 510 Mt, respectively, per annum [3,4]. Concrete is the second most consumed resource with a global production of around one tonne per person per annum (~3.8 billion cubic metres), which will inevitably enter the C&D waste stream in the future [5]

Methods

Results

Discussion

Conclusion