Effects of heavy metal contamination on pozzolanic reaction in clay and challenges with sustainable remediation

Abstract

Sustainability is more relevant than ever before, hence having sustainable remediation methods is essential. Today, most of the remediation is done through “dig and dump”, an old and a non-sustainable method. Instead, using waste and natural materials, and utilising natural pozzolanic reactions, can minimise the remediation footprint and maximise its results. The purpose of this study is to evaluate the influence of heavy metals on pozzolanic reactions on reconstituted kaolin and natural sensitive clay from Gothenburg, by mixing the clays with copper nitrate (Cu(NO3)2) and adding calcium hydroxide (Ca(OH)2) and silicon oxide (SiO2), acting as a binder that creates a cementitious mass. The effect of contamination and binding was investigated by performing geotechnical tests to compare the strength and stiffness of clay with different mixtures of the binders. Different curing methods were also evaluated to examine governing factors during sample preparation. Furthermore, another aspect was to investigate the challenges with implementing sustainability when remediating. This was done through interviews with Skanska and governing authorities such as the Swedish EPA. A thorough literature study was also conducted to evaluate previous studies on the subject. contamination affected both the physical and chemical properties of the clays tested. The clay mineralogy is crucial, since the behaviour of the Gothenburg clay and kaolin clay was opposite to each other. This has been proven by having higher strength and stiffness for the uncontaminated Gothenburg clay compared to the contaminated clay, while the opposite was observed for kaolin. Finally, sustainability management is lacking in knowledge and usage of new technologies. There is a wide knowledge in the sector, but it needs to be spread and more widely available in form of better handbooks. It was also shown that more sustainable guideline values are needed, to prevent unnecessary remediation. The literature showed a great lack of usage of sustainable remediation methods, and it must be more beneficial to use sustainable methods prior to old “dig and dump” methods.