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A closed-loop system to recycle rare earth elements from industrial sludge using green leaching agents and porous β-cyclodextrin polymer composite

https://doi.org/10.1016/j.resconrec.2021.106152Get rights and content

Abstract

Industrial sludge is classified as hazardous waste as well as a resource of valuable metals and needs to be adequately treated for the sake of the environment and economy. This study reports a green approach for extracting and purifying rare earth elements (REEs) from industrial sludge using environmentally friendly washing solutions ((NH4)2SO4, N, N-Bis(carboxymethyl) glutamic acid (GLDA), tetrabutylammonium bromide ionic liquid (TBAB), and water) and a porous β-cyclodextrin polymer composite (PCDP-M-SHM) respectively. The results showed that there is no significant difference between used extracting solutions. However, the speciation study indicated that most REEs in the sludge sample were bounded to a water-soluble fraction. Therefore, for economic reasons, water was used for further studies. Furthermore, the recycling efficiencies after the purification of leached REEs with PCDP-M-SHM were in the range of 76.0 % (Gd) to 87.3% (Pr), except for Ce (8.29%).

Moreover, cost evaluation and sensitivity analysis studies were performed to investigate the applicability of the reported method at the industrial level. The cost evaluation results estimated $3676 as the cost of processing 1 ton of sludge with revenue of $710/ton of sludge. Finally, the sensitivity analysis test affirmed the profitability to depend on the cost of PCDP-M-SHM. Based on the future market price of REEs, the proposed closed-loop recycling approach could be a promising green solution for environmental problems related to mining, processing, and conservation of REEs resources as well as industrial sludge disposal.

Section snippets

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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