Full length articleA closed-loop system to recycle rare earth elements from industrial sludge using green leaching agents and porous β-cyclodextrin polymer composite
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INTRODUCTION
The globalization and urbanization of our society correlate with the increase of sludge generation, which increases the pressure on its management strategies (Gupta et al., 2021; Li et al., 2021). Industrial sludge is mainly disposed of via incineration and landfilling, which are energy-intensive processes (Pietrelli et al., 2019). In addition, landfills and thermal treatment were reported to contribute to environmental pollution through landfill leachate and aerosols pollution (Gulani et al.,
Chemical reagents
Extracting agents used included (NH4)2SO4, GLDA (solid content (40%) and density of 1.35 g cm−3), TBAB, which were purchased from TCI Development Co. Ltd. (Shanghai, China). The deionized water was prepared using a Milli-Q water purification system (Millipore, USA). The National Center of Analysis and Testing for Nonferrous Metals and Electronic Materials (NCATN) provided the stock solutions for element standards.
Sludge and its physicochemical properties
The industrial sludge was collected from a local REE industrial wastewater
Physicochemical characterization of the sludge
The pH value of sludge was 3.2, which is advantageous for leaching out metal elements without any further pH adjustment due to the increases of proton movement intensity in the acid medium (Wu et al., 2015). The EC can serve as a measure of soluble cations and anions, and the EC value for studied sludge was 3.76 mS cm−1. The high EC suggested releasing exchangeable elements from sludge due to competitive adsorption (Wang et al., 2018). Particle size analysis revealed that the sludge comprised
Conclusions
This study reported the green approaches for recycling REEs from industrial sludge using environmentally friendly extracting solutions (NH4)2SO4, GLDA, TBAB, and water) and PCDP-M-SHM as a composite that selectively adsorbs REEs from leachate. The results showed that there is no significant difference between extracting solutions used in this study. In addition, chemical speciation indicated that most REEs in industrial sludge were bounded to a water-soluble fraction favoring green leaching
Credit authorship contribution statement
François Nkinahamira: Conceptualization, methodology, data curation meaning, writing - original draft, review, and editing, software
Shanshan Guo: Methodology, validation, software
Meixian Cao: Investigation, software
Yiqing Zhang: Investigation, software
Bahareh Asefi: Investigation
Senlin Sun: Investigation, software
Meiling Feng: Validation
Qian Sun: supervision, funding acquisition, project administration, conceptualization, writing - review & editing
Chang-Ping Yu: Supervision, project
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
For financial support, the authors are grateful to the FJIRSM&IUE Joint Research Fund (No. RHZX-2018-005), Water Environment Safety and Water Quality Assurance Center of Xiamen (WES&WQGE201903), and the Chinese Academy of Sciences-The World Academy of Sciences (CAS-TWAS) president's fellowship program for developing countries.
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