E-waste not only contains valuable metals but also hazardous materials such as heavy metals and organic pollutants (e.g., brominated flame retardants, polychlorinated biphenyls, and polycyclic aromatic hydrocarbons). Improper handling of these hazardous materials can result in their release into the air, water, and soil, potentially causing harm to surrounding ecosystems and human health due to their toxicity. Therefore, a fundamental criterion for sustainable urban mining is the safe handling of hazardous materials and the avoidance of generating significant amounts of these materials during the urban mining process. Other categories of environmental impact such as water usage, climate change (greenhouse gas emissions), and resource depletion are also important considerations when assessing the sustainability of an urban mining process.
Toxicity-related impacts can be examined from two aspects: ecotoxicity and human toxicity (Rigamonti et al., 2017):
- Ecotoxicity: the harmful effects on both the environment and organisms, such as fish, microorganisms, and plants.
- Human toxicity: adverse health effects on humans, which may include both cancer and non-cancer effects.
Rigamonti et al. (2017) describes the primary toxicity impacts of urban mining as carcinogenicity resulting from the recovery of steel and ferrous metals, and non-carcinogenic toxicity resulting from the recovery of printed wiring boards
Resource depletion impacts are primarily related to the depletion of fossil fuels, minerals, and metals, and are typically examined in environmental impact assessments. However, urban mining involves recovering metals from recycled electrical and electronic products, which can help avoid the depletion of these resources that would otherwise result from increased demand driven by economic development. Therefore, the “avoided impacts” of urban mining should be quantified and incorporated into environmental impact assessments for this practice.
Islam et al. (2020) conducted an exhaustive literature review on the latest technological approaches for urban mining, with a focus on analyzing the most important features and drawbacks of these methodologies.
Toxicity is a significant impact category that exhibits wide disparities among different technological approaches. While some methods, such as chlorination leaching, thiourea leaching, and Iodation leaching, are identified as having low toxicity, others, such as the cyanide leaching approach and the HCl+ oxidant leaching approach, exhibit greater degrees of toxicity.
Energy consumption (which contributes to fossil fuel depletion) is another significant impact category that exhibits wide disparities among different approaches. For instance, the plasma melting technology stands out for its high energy consumption (>2000 °C), while hydrometallurgical methods such as cyanide leaching and thiosulphate leaching, as well as electrochemical methods, are characterized by low energy consumption.
The “avoided impacts” of different urban mining approaches are not directly addressed in Islam et al. (2020) or prior studies. However, we can infer some idea of the avoided impacts of a technological approach from indicators such as the recovery rate and the types of metals that can be extracted using that approach. Approaches that have a higher recovery rate can result in greater avoided impacts, assuming the same amount of e-waste is being processed. Examples of methods that exhibit high recovery rates include Plasma melting technology and cyanide leaching.
Urban mining is a rapidly evolving field with ongoing advancements in technologies and methods aimed at improving its sustainability. By promoting a multidisciplinary approach and persevering in our efforts, we can overcome some of the sustainability challenges associated with urban mining. However, as consumers, we also have a role to play in promoting sustainability. By adopting more sustainable consumption habits, reducing excessive consumption, and properly recycling or upcycling electronic and electrical products, we can help minimize their environmental impacts and contribute to sustainability. It is important to recognize that while technological advancements can assist in mitigating these impacts, they cannot completely eliminate them.
References:
Islam, A., Ahmed, T., Awual, M. R., Rahman, A., Sultana, M., Aziz, A. A., Monir, M. U., Teo, S. H., & Hasan, M. (2020). Advances in sustainable approaches to recover metals from e-waste-A review. Journal of Cleaner Production, 244, N.PAG. https://doi.org/10.1016/j.jclepro.2019.118815
Rigamonti, L., Falbo, A., Zampori, L. et al. (2017). Supporting a transition towards sustainable circular economy: sensitivity analysis for the interpretation of LCA for the recovery of electric and electronic waste. Int J Life Cycle Assess 22, 1278–1287. https://doi.org/10.1007/s11367-016-1231-5
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