تمیز کردن چهار فلز سنگین از خاکستر بادی
Abstract
Graphical abstract
1. Introduction
2. Experimental
3. Results and discussion
4. Conclusions
Acknowledgements
Appendix A. Supplementary data
References
Abstract
Municipal solid waste incineration (MSWI) fly ash contains significant amounts of heavy metals (e.g., Cd, Cu, Pb and Zn) and is therefore considered to be a hazardous waste requiring proper treatment prior to its disposal. In this work, an integrated hydrometallurgical process for treatment of MSWI fly ash was evaluated. Valuable metals, e.g. Cu and Zn, were first recovered by combining leaching and extraction sequentially. In the next step, the t removal of Cd and Pb from the remaining leachate using four types of iron-based adsorbents was evaluated. The leaching was optimized with respect to pH, leaching time and liquid to solid ratio. A test done under optimal conditions gave metal releases of 100% and 80% for Cu and Zn as well as 100% and 85% for Cd and Pb, respectively. The resulting leachate was contacted with organic phases based on kerosene containing the extractants LIX860NeI for Cu extraction and Cyanex 572 for Zn extraction in two consecutive steps. Efficient extractions were achieved, thus demonstrating that the combination of leaching and extraction can be successfully used for the recovery of Cu and Zn. Adsorption of heavy metal ions on various iron based sorbents to detoxify the aqueous effluent from the extraction showed good removal efficiency (more than 95%) for both Cd and Pb. The results of this study show that the proposed integrated process is a promising tool that can be used in the strategy for metal recovery and detoxification of MSWI fly ash.
Introduction
Over the past few decades, incineration has become a widely prevalent alternative for municipal solid waste management all over the world (Song et al., 2017), due to the energy recovery and reduction in the volume and mass of waste (Narayana, 2009). However the MSWI process produces a considerable amount of fly ash which is commonly rich in leachable heavy metals, thus posing a serious threat to the environment and human health. Fly ashes have been classified as a hazardous waste (MEE, 2016), which must be treated properly to prevent environmental pollution (GarciaLodeiro et al., 2016). China is one of the largest municipal solid waste producing countries in the world. It is reported that the MSW generated was approximately 170 Mt in 2016, with an annual increase of 8e10% (Xin-gang et al., 2016). Meanwhile, for the aim of proper treatment, the proportion of incineration in the waste disposal (waste to energy) will be increased from 31% in 2015 to 54% in 2020 in China according to the “۱۳th Five-Year” National Municipal Solid Waste Disposal Facilities Construction Plan. The amount of municipal solid waste incineration fly ash generated will increase rapidly as a consequence. However, only a few landfill sites designed for the disposal of hazardous waste like MSWI fly ash in China are now in service (Cheng and Hu, 2010) while the construction of new sites lags behind the construction of incineration plants. Therefore, it is urgent to drive the processing options available due to the huge capacity gap.