Efficient recovery of rare earth elements from discarded NdFeB magnets by mechanical activation coupled with acid leaching.

Due to the increasing demands and supply shortages for rare earth elements (REEs), the recovery of REEs from discarded NdFeB with high REE content has become extremely important. In this paper, a hydrometallurgical coupling process involving mechanical activation and selective acid leaching was proposed for the recovery of REEs from discarded NdFeB magnets. The effects of ball milling activation speed, hydrochloric acid concentration, and solid-liquid ratio on the leaching efficiencies of REEs in NdFeB magnets were studied. The results indicated that the ball milling activation method could enhance the reactivity of the samples through the action of mechanical force, which promoted the leaching efficiency and leaching speed of REEs. Under the optimum conditions (650-rpm activation speed, 0.4 M hydrochloric acid, 100 g/L solid-liquid ratio), the leaching efficiency of REEs increased up to 99% with low hydrochloric acid consumption and the leaching speed of REEs was triple than that of without activation. The final purity of recovered rare earth oxides reached up to 99.9%. All results demonstrated that ball milling activation coupled with selective leaching of hydrochloric acid could be an effective and environment-friendly strategy to achieve the recovery of REEs.

Bioleaching of indium from waste LCD panels by Aspergillus niger: Method optimization and mechanism analysis.

Using Aspergillus niger (A. niger) to produce low-concentration organic acids is challenging for dissolving In3O2 from waste LCD (liquid crystal display) panels with high toxicity. In this study, three bioleaching approaches from the general and the optimized fermentation systems were investigated respectively to compare indium recovery effects and firstly clarified its bioleaching mechanism. The indium bioleaching efficiency can be improved from 12.3% to 100% by fermentation method optimization. Carboxy groups from organic acids and proteins were the critical substances to release H+ for leaching indium mainly competed with iron via reactions analysis. The effective components increased after optimizing, including the dissociative H+ concentration, the effective carboxyl groups for leaching metal oxides, and the output of oxalic acid. A. niger biomass prevented the contact between H+ and In3O2 and adsorbed In3+ adverse to indium recovery. The bioleaching effects of fermentation broth for indium can be further promoted by controlling bioleaching process parameters.

A novel strategy for harmlessness and reduction of copper smelting slags by alkali disaggregation of fayalite (Fe2SiO4) coupling with acid leaching.

Copper smelting slags are difficult to achieve harmlessness and reduction because of the presence of abundant of fayalite (Fe2SiO4). This work proposed a novel strategy for harmlessness and reduction of copper smelting slags by alkali disaggregation of Fe2SiO4 coupling with acid leaching. The disaggregation changed the Fe2SiO4 phase by NaOH and released the embedded harmful and valuable metals. The evaluation of disaggregation effect mainly depends on further acid treatment. Especially the total leaching efficiency of As, Zn, Fe, Cu and Pb was achieved 99.7%, 62.5%, 41.5%, 99.9% and 99.1% under diluted HNO3-H2O2 system, respectively. Compared with the non-disaggregated control, the efficiency was accordingly increased by 73.3%, 71.1%, 18.6%, 72.2% and 22.4%. Meanwhile, the content of As, Cu and Pb in the slags decreased from 1165.5 mg/kg, 30085.9 mg/kg and 5008.8 mg/kg to as low as 5.2 mg/kg, 21.2 mg/kg and 15.6 mg/kg, respectively. Interestingly, the strategy brought out 48.1% of the weight reduction of the copper smelting slags. The favorable effect was mainly attributed to the broken of Fe-O-Si bond thereafter improving the acid leaching activation. Therefore, the proposed strategy could potentially be a new method to realize harmlessness and reduction of copper smelting slags.

4-Dimethyl-amino-N'-(2-hy-droxy-3,5-diiodo-benzyl-idene)benzohydrazide.

The title mol-ecule, C(16)H(15)I(2)N(3)O(2), adopts an E configuration about the C=N bond. The dihedral angle between the two benzene rings is 6.4 (2)°. An intra-molecular O-H⋯N hydrogen bond occurs. In the crystal, mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains propagating in the c-axis direction.

(E)-N'-(3-Hy-droxy-benzyl-idene)-3-nitro-benzohydrazide.

The title compound, C(14)H(11)N(3)O(4), was prepared by the reaction of 3-nitro-benzohydrazide with 3-hy-droxy-benzalde-hyde. The mol-ecule adopts an E configuration about the C=N bond. The dihedral angle between the two benzene rings is 32.3 (2)°. In the crystal, the mol-ecules are linked through inter-molecular N-H⋯O, O-H⋯N, and O-H⋯O hydrogen bonds, forming chains in the a-axis direction.

N'-(4-Hy-droxy-benzyl-idene)-4-nitro-benzohydrazide.

The title compound, C(14)H(11)N(3)O(4), was prepared by the reaction of 4-nitro-benzohydrazide with 4-hy-droxy-benz-alde-hyde. The whole mol-ecule of the compound is approximately planar, with a mean deviation from the least-squares plane through all the non-H atoms of 0.050 (2) Å; the dihedral angle between the two benzene rings is 2.0 (2)°. In the crystal, the benzohydrazide mol-ecules are linked through inter-molecular O-H⋯O and N-H⋯O hydrogen bonds, forming layers in the bc plane.

N'-(3-Hy-droxy-benzyl-idene)-4-nitro-benzohydrazide.

The title mol-ecule, C(14)H(11)N(3)O(4), is approximately planar, with an inter-planar angle between the two benzene rings of 5.8 (2)°. In the crystal, four mol-ecules are linked by an R(4) (4)(12) motif with pairs of strong O-H⋯O and N-H⋯O hydrogen bonds. The motif is situated about the crystallographic centres of symmetry and it is composed of two pairs of parallel mol-ecules. This quadruplet of mol-ecules is further extended by symmetry-equivalent hydrogen bonds to form layers parallel to the (10) plane. In addition to the hydrogen bonds, there is also a weak π-π inter-action between the benzene rings.

(E)-N'-(2,4-Dichloro-benzyl-idene)-3-nitro-benzohydrazide.

The title compound, C(14)H(9)Cl(2)N(3)O(3), was prepared by the reaction of 3-nitro-benzohydrazide with 2,4-dichloro-benzalde-hyde. The mol-ecule adopts an E configuration about the C=N bond. The dihedral angle between the two benzene rings is 4.6 (2)°. In the crystal, the hydrazone mol-ecules are linked through inter-molecular N-H⋯O hydrogen bonds, forming chains along the c axis.