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 solutions. From the economic point of view, water was used as a model extracting solvent. Furthermore, the recycling effi-
ciencies of REEs were in the range of 76.0 % (Gd) to 87.3% (Pr), except for Ce (8.29%).
PCDP-M-SHM was synthesized as follows: β-cyclodextrin hybrid (CDP@Fe3O4) was functionalized with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl (PC88A) doped in silica . The silica hybrid preparation doped with PC88A (SHM) was mixed with β-CD, tetrafluoroterephthalonitrile (TFP), Fe3O4 particles, K2CO3, and an anhydrous THF/DMF (9:1) and refluxed for 48 h under N2 atmosphere at 85 °C, then purified by various solvents using an external magnet.
 François Nkinahamira, Shanshan Guo, Meixian Cao, Yiqing Zhang, Bahareh Asefi, Senlin Sun, Meiling Feng, Qian Sun, Chang-Ping Yu: A closed-loop system to recycle rare earth elements from industrial sludge using green leaching agents and porous β-cyclodextrin polymer composite. Resources, Conservation and Recycling 180, May 2022, 106152. https://doi.org/10.1016/j.resconrec.2021.106152
 François Nkinahamira, Alaaeddin Alsbaie, Yuwen Wang, Xiaoyong Yang, Tian-Yuan Chen, Meixian Cao, Meiling Feng, Qian Sun, Chang-Ping Yu: Recovery and purification of rare earth elements from wastewater and sludge using a porous magnetic composite of β-cyclodextrin and silica doped with PC88A. Separation and Purification Technology 266, 1 July 2021, 118589.