Application of natural organic residues in the remediation of metals from e-waste

Contaminants, such as potentially toxic metals from e-waste, have been affecting soil, water and ecosystems throughout the world. Thus, the search for low cost natural substances, able to complex such metals, is a matter of both environmental and economic interest. Humic substances (HS) are the main natural organic complexing agents in ecosystems, and their alkaline extraction leads to a poorly soluble residue, which is often discarded, in spite of its great potential for chelating potentially toxic metals. Since both the structure and complexing capacity of HS might be significantly affected by the way of extraction, this study comparatively evaluated the implications of exhaustive and non-exhaustive extractions on physical–chemical and structural properties of different natural organic residues (NOR) obtained. Furthermore, adsorption studies were carried out in order to compare the influence of different extractions on the resulting NOR capacities to retain copper ions. The milder extractions, involving non-exhaustive procedures, led to a NOR with better copper adsorption, which was then selected to test the retention of copper from an e-waste leachate. Results evidenced the potential use of NOR for copper removal (340 μg Cu2+ g−1 of NOR), as well as other potentially toxic metals, such as iron, manganese and chromium, thus showing a promising application of this material in the environmental remediation of soils and waters.