A novel application of hematite precipitation for high effective separation of Fe from Nd-Fe-B scrap

Abstract

Rare earths, e.g. neodymium (Nd), praseodymium (Pr) and dysprosium (Dy), are abundant in the rare earth sintered magnet scrap (Nd-Fe-B scrap), but their recycling is tedious and costly due to the high content of impurity Fe. Herein, a novel approach was developed to effectively recycle rare earths from the scrap via an integrated acid dissolution and hematite precipitation method. The scrap contained 63.4% Fe, 21.6% Nd, 8.1% Pr and 3.9% Dy. It was dissolved in nitric, hydrochloric and sulfuric acids, separately. Nearly all impurity Fe in the scrap was converted to Fe3+ in nitric acid but was converted to Fe2+ in hydrochloric and sulfuric acids. After hydrothermal treatment, the rare earths in the three acids were almost unchanged. From nitric acid, 77.6% of total Fe was removed, but total Fe was not from the hydrochloric and sulfuric acids. By adding glucose, the removal of total Fe was further increased to 99.7% in nitric acid, and 97% of rare earths remained. The major mechanism underlying total Fe removal in nitric acid was the hydrolysis of Fe3+ into hematite, which was promoted by the consumption of nitrate during glucose oxidation. This method effectively recycled rare metals from the waste Nd-Fe-B scrap and showed great potential for industrial application.

Visible Light Active Silver Decorated Iron Titanate/Titanium Dioxide Nanohybrid for Sterilization of Explants Grown by In Vitro Technique

“…The dilute HNO 3 washing step was essential to leach out the maximum amount of Cl − ions and helps to oxidize free Fe 2+ to Fe 3+ ions. [ 48 ] With the addition of H + to the residue, all disordered Na‐titanate complex transfers to H 2 TiO 3 and H 2 Ti 3 O 7 , ultimately transforming into an amorphous anatase phase. [ 40 ]…”

“…The dilute HNO 3 washing step was essential to leach out the maximum amount of Cl − ions and helps to oxidize free Fe 2+ to Fe 3+ ions. [48] With the addition of H + to the residue, all disordered Na-titanate complex transfers to H 2 TiO 3 and H 2 Ti 3 O 7 , ultimately transforming into an amorphous anatase phase. [40] Silver ion (Ag + ) was immediately added to the residue with ultrasonication in order to minimize the agglomeration of the nanoparticles, resulting in a well-dispersed homogeneous product.…”

Perspective on pH adjustment in hydrometallurgical recycling of valuable metals from waste

“…This phenomenon was not observed at room temperature but occurred at high temperatures ( Figures 2B, C ) ( Lin et al, 2019 ; Qu et al, 2021 ). For example, about 10 g/L Fe was stable in the leachate of Nd-Fe-B waste and removed by 77.6% as hematite ( Figure 2D ) after heating at 160 C for 10 h, whilst the leachate pH dropped from 0.38 to 0.19 ( Lin et al, 2019 ). Similar hydrolysis of Al at 270°C was also reported to cause a decrease in leachate pH ( Figure 2E ) ( Qu et al, 2021 ; Li et al, 2023 ).…”

“… (A) Thermochemistry reactions of H + generation and consumption ( Xiaobei, 2014 ), (B) removal efficiency of Fe/Cu by hydrothermal treatment ( Zhu et al, 2020b ), (C) XRD patterns of Fe-bearing deposits ( Zhu et al, 2020b ), (D) SEM images of Fe-bearing deposits ( Lin et al, 2019 ), (E) fitted plot of Gibbs value versus temperature of Fe/Al hydrolysis ( Bian et al, 2022 ), pictures of (F) nitrate reacting with organics and (G) emission of NxO in the thermal reaction of nitrate to organics, and (H) removal efficiency of Fe/heavy metals after hydrothermal treatment with the addition of sucrose ( Yuxin et al, 2023 ). …”

High Performance of Commercial PAC on the Simultaneous Desulfurization and Denitrification of Wastewater From a Coal-Fired Heating Plant

“…This wet oxidation is especially accelerated in the presence of metal cations. For instance, by introducing glucose and ferric ions, the redox reaction between nitrates and glucose was initiated and rapidly equilibrated in 3-7 h (Lin et al, 2019), while the remaining nitrate was less than 1 g/L. Nitrate removal can be achieved effectively, but the synergic removal of sulfates has been rarely reported until now.…”