Goethite, a typical iron-containing monomineral in red mud, was synthesized under the simulated Bayer digestion condition during the alumina production. The effects of dissolved organic compounds including sodium formate, sodium acetate, sodium oxalate, sodium salicylate and disodium phthalate on the settling performance of goethite slurries were studied. The settling performance of the slurries was also investigated with the addition of self-made hydroxamated polyacrylamide flocculant (HCPAM). The adsorption mechanism of dissolved organic compounds on the goethite surfaces was studied by FT-IR and XPS, respectively. The results show that the addition of organic compounds lowers the settling performance of the slurries and a deterioration in settling performance is observed in the order of sodium oxalate > sodium salicylate (∼ disodium phthalate) > sodium formate > sodium acetate. Moreover, HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the goethite slurries, but it can only partially improve the settling performance of the goethite slurries containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that these organic compounds are chemically adsorbed on the goethite surface.

In this paper, a synergist complex of Ni(II) with naphthalene-2-sulfonic acid (HNS) and n-hexyl 4-pyridinecarboxylate ester (LI), which are corresponding short chain analogues of active synergistic extractants dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexyl 4-pyridinecarboxylate ester (4PC, LII), was prepared and characterized by Nuclear Magnetic Resonance (1H-NMR), elemental analyses, Fourier Transform Infrared Spectroscopy (FT-IR) and Electrospray Ionization Mass Spectrometry (ESI-MS) spectroscopic studies. Single crystals of the nickel synergist complex have been grown from a methanol/water (10/1) solution and analyzed by single crystal X-ray diffraction. The crystal structure of the nickel synergist complex shows that Ni(II) is coordinated by four water molecules and two monodentate LI ligands and there is no direct interaction of the Ni(II) with sulfonic oxygen atoms of naphthalene-2-sulfonic acid anions, while hydrogen-bonded interactions of the coordinated water molecules with sulfonic oxygen atoms of naphthalene-2-sulphate anions were observed. In addition, in order to provide parallels to solvent extraction, the extracted Ni(II) complex with HDNNS and 4PC is also prepared and studied using FT-IR and ESI-MS technology. Compared with their corresponding free ligand, similar shifts assigned to the stretching vibration of the pyridine ring and SO in both the nickel synergist complex and the extracted Ni(II) complex suggest that in the non-polar organic phase, Ni(II) is also coordinated by LII ligands, while the sulfonic oxygen atoms of dinonylnaphthalene sulfonate anions not directly bonded to Ni(II) form hydrogen bonds with water molecules (coordinated with Ni(II) or/and solubilized in the non-polar organic phase). For the ESI-MS spectrum of the extracted Ni(II) complex in non-polar organic phase, there exists a peak at m/z values of 1058.76, which indicates that the extracted Ni(II) complex in the non-polar organic phase may have a coordination structure, [Ni(H2O)4(LII)2](DNNS)2, similar to the coordination structure of the nickel synergist complex.

To develop selective ligands for the separation of copper(II), nickel(II) and cobalt(II), the solvent extraction and coordination chemistry of a bidentate chelating ligand, N,N-dioctyl-2-aminomethylpyridine (AMPO), and a tridentate chelating ligand, tert-butyl 2-(N-octyl-2-picolyamino)acetate (AMPA), were investigated. The ligands exhibit excellent extraction ability and high selectivity towards copper(II) over nickel(II) and cobalt(II) in the simulated electrolysis anolytes. Two novel copper(II) complexes, [Cu2(AMPO)2Cl4] (1) and [Cu(AMPA)Cl2] (2), were synthesized and fully characterized. The solid-state structures of the complexes 1 and 2 were established by single crystal X-ray diffraction. The results show that the complex 1 consists of isolated dinuclear molecules unit with two bridging chloro ligands and the geometry around Cu(II) displays a slightly distorted square pyramid, and the complex 2 is also best described as a slightly distorted square pyramid in reasonable approximation distance. The stoichiometric ratios and association constants of the copper(II) complexes with AMPO and AMPA were also determined in CH3OH/H2O mixtures by UV−Vis spectrometry, respectively. The interactions between the ligands and the metal ions (Cu2+, Ni2+ and Co2+) were correspondingly evaluated by X-ray photoelectron spectroscopy (XPS) and electrospray ionization-mass spectrometry (ESI-MS), and the results reveal that AMPO can be correspondingly coordinated through tertiary amine N atom and pyridine N atom with the three metal ions of copper(II), nickel(II) and cobalt(II), and AMPA can be coordinated through tertiary amine N atom, pyridine N atom and the carbonyl O atom only with copper(II) not with nickel(II) or cobalt(II). All the results indicate that AMPA could be a better candidate for the deep removal of copper(II) from the nickel or cobalt electrolysis anolyte.Two novel copper(II) complexes, [Cu2(AMPO)2Cl4] (1) and [Cu(AMPA)Cl2] (2), were synthesized and fully characterized. The solid-state structures of the complexes 1 and 2 were established by single crystal X-ray diffraction. The results show that the complex 1 consists of isolated dinuclear molecules unit with two bridging chloro ligands and the geometry around Cu(II) displays a slightly distorted square pyramid, and the complex 2 is also best described as a slightly distorted square pyramid in reasonable approximation distance. The stoichiometric ratios and association constants of the copper(II) complexes with AMPO and AMPA were also determined in CH3OH/H2O mixtures by UV−Vis spectrometry, respectively.Download high-res image (155KB)Download full-size image

•A new copper(II) synergist complex was synthesized at room temperature.•Bridged the gap between the solid state structure and the solution structure.•The atomic arrangement shows three-dimensional networks.•The copper(II) complexes were further investigated by (FT-IR) and ESI-MS.•The copper(II) complexes in solution and solid state possess similar structure.In continuation of our interest in the coordination structure of the nickel(II) complex with dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexyl 4-pyridinecarboxylate ester (4PC), it was observed that the coordination sphere was completed by the coordination of two N atoms of pyridine rings in ligands 4PC and four water molecules while no direct interaction between Ni(II) and deprotonated HDNNS was observed. To investigate whether the coordination structure of nickel(II) with the synergistic mixture containing HDNNS and 4PC predominates or not in the copper(II) complex with the synergistic mixtures containing HDNNS and pyridinecarboxylate esters, a copper(II) synergist complex with n-hexyl 3-pyridinecarboxylate ester (L) and naphthalene-2-sulfonic acid (HNS, the short chain analogue of HDNNS), was prepared and studied by X-ray single crystal diffraction, elemental analyses and thermo gravimetric analysis (TGA), respectively. It was shown that the composition of the copper(II) synergist complex was [Cu(H2O)2(L)2(NS)2] and formed a trans-form distorted octahedral coordination structure. Two oxygen atoms of the two coordinated water molecules and two N atoms of the pyridine rings in the ligands L defined the basal plane while two O atoms from two sulfonate anions of the deprotonated HNS ligands occupied the apical positions by direct coordination with Cu(II), which was distinguished from the coordination structure of the nickel(II) synergist complex as reported in our previous work. In the crystal lattice, neighboring molecules [Cu(H2O)2L2(NS)2] were linked through the intermolecular hydrogen bonds between the hydrogen atoms of the coordinated water molecules and the oxygen atoms of the sulfonate anions in the copper(II) synergist complex to form a 2D plane. In order to bridge the gap between the solid state structure of the copper(II) synergist complex and the solution structure of the extracted copper(II) complex with the actual synergistic mixture containing L and HDNNS in the non-polar organic phase, the structures of the two copper(II) complexes were further investigated by Fourier transform infrared spectroscopy (FT-IR) and electrospray ionization mass spectrometry (ESI-MS), and the results indicated that the extracted copper(II) complex in the non-polar organic phase might possess a similar coordination structure as the copper(II) synergist complex.Download high-res image (252KB)Download full-size image

Hydration grossular and hematite monominerals were synthesized. The effects of dissolved organic compounds (including sodium formate, sodium acetate, sodium oxalate, sodium salicylate or disodium phthalate) on the settling performance of hydration grossular or hematite slurries were studied. The settling of the slurries was also investigated with the addition of sodium polyacrylate (PAAS) or hydroxamated polyacrylamide flocculant (HCPAM). The adsorption mechanism of organic compounds on monominerals surfaces was studied by FT-IR and XPS, respectively. A deterioration in settling is observed in order of disodium phthalate>sodium salicylate>sodium oxalate>sodium formate (or sodium acetate). Moreover, PAAS can efficiently eliminate the negative effects of organic compounds on the settling performance of the hydration grossular slurry. HCPAM can efficiently eliminate the negative effects of sodium formate, sodium acetate and sodium oxalate on the settling performance of the hematite slurry, but it only partially improves the settling performance of hematite slurry containing sodium salicylate or disodium phthalate. FT-IR and XPS results show that organic compounds are physically adsorbed on hydration grossular surface, and chemisorptions of organic compounds occur on hematite surface with a bidentate chelating complex.

Hydroxamated polyacrylamide (HPAM) was synthesized from polyacrylamide (PAM) with high relative molecular mass under the optimum reaction conditions (pH 12 and a molar ratio of hydroxylamine to amide groups of 1.5 at 50 °C for 12 h). The hydroxamate groups of HPAM were verified by Fourier transform infrared spectrum (FT-IR). 46% (molar fration) hydroxamate groups and 23% (molar fraction) carbonyl groups on HPAM were determined by conductometric titration combined with Kjeldahl’s microanalysis method. The settling performance achieved at different flocculant dosages was investigated with high goethite-containing red mud slurry of simulated Bayer process synthesized in laboratory. It turns out that the settling performance of high goethite-containing red mud was better with HPAM. The average settling rate of red mud in the first 5 min and the turbidity of supernatant after settling for 30 min are 2.36 m/h and 507 NTU, respectively, at a flocculant dosage of 120 g/t, which is similar to that achieved with Hx-600.

A novel silica-supported 2-aminomethyl pyridine adsorbent was synthesized using a post-grafting route. This synthetic route involved the reaction of 2-aminomethyl pyridine (AMP) with γ-chloropropyltrimethoxysilane (CPTS) prior to immobilization on the silica support. Based on the extensive evidences that amines and acids can play an important role in silanization as an activator, meglumine and a mixture of hydrochloric acid and ethanol were utilized as a gentle but effective catalyst. Accordingly, three different synthetic pathways were investigated and the catalysis mechanisms of the amine and/or acid were discussed in detail. The synthesized silica-supported 2-aminomethyl pyridine adsorbent under both amine and acid catalyzed conditions was abbreviated as Si-AMP-M-H and characterized, its adsorption properties of Cu2+, Ni2+ and Co2+ were also studied. The adsorption capacity of Si-AMP-M-H for Cu2+ is comparable to commercial silica-supported AMP adsorbent. And the possible adsorption mechanism of Cu2+ onto Si-AMP-M-H is discussed. Moreover, Si-AMP-M-H shows a favorable selectivity for Cu2+ in simulated cobalt electrolyte solution in the presence of nickel. Adsorbed Si-AMP-M-H can be readily regenerated by acid-ammonia treatment. The results suggest that the Si-AMP-M-H prepared here could be promising for cobalt hydrometallurgical purification processes.

Structural changes of mechanically activated titanaugite were investigated systematically using X-ray diffraction, particle size analysis, and scanning electron microscopy. The hydrochloric acid leaching behavior of mechanically activated titanaugite and ilmenite single minerals and their mixtures also was studied. The results show that with increasing milling time, the crystallite size, lattice strain, and particle size changed continuously. Mechanical activation evidently improved the leaching reactivity of titanaugite and ilmenite with 20 wt pct HCl at 378 K (105 °C). The leaching behavior of ilmenite was promoted at the initial stage and then was inhibited when mixed with a mass ratio of titanaugite to ilmenite of 1:1. When the mass ratio of titanaugite to ilmenite decreased to 1:9, the leaching of titanaugite was promoted, whereas the leaching of ilmenite was inhibited throughout the whole process. The leaching inhibition of ilmenite is related to the formation of hydrous silicon dioxide from the dissolution of titanaugite.

A novel silica-supported 2-aminomethyl pyridine adsorbent was synthesized using a post-grafting route. This synthetic route involved the reaction of 2-aminomethyl pyridine (AMP) with γ-chloropropyltrimethoxysilane (CPTS) prior to immobilization on the silica support. Based on the extensive evidences that amines and acids can play an important role in silanization as an activator, meglumine and a mixture of hydrochloric acid and ethanol were utilized as a gentle but effective catalyst. Accordingly, three different synthetic pathways were investigated and the catalysis mechanisms of the amine and/or acid were discussed in detail. The synthesized silica-supported 2-aminomethyl pyridine adsorbent under both amine and acid catalyzed conditions was abbreviated as Si-AMP-M-H and characterized, its adsorption properties of Cu2+, Ni2+ and Co2+ were also studied. The adsorption capacity of Si-AMP-M-H for Cu2+ is comparable to commercial silica-supported AMP adsorbent. And the possible adsorption mechanism of Cu2+ onto Si-AMP-M-H is discussed. Moreover, Si-AMP-M-H shows a favorable selectivity for Cu2+ in simulated cobalt electrolyte solution in the presence of nickel. Adsorbed Si-AMP-M-H can be readily regenerated by acid-ammonia treatment. The results suggest that the Si-AMP-M-H prepared here could be promising for cobalt hydrometallurgical purification processes.

In this paper, a synergist complex of Ni(II) with naphthalene-2-sulfonic acid (HNS) and n-hexyl 4-pyridinecarboxylate ester (LI), which are corresponding short chain analogues of active synergistic extractants dinonylnaphthalene sulfonic acid (HDNNS) and 2-ethylhexyl 4-pyridinecarboxylate ester (4PC, LII), was prepared and characterized by Nuclear Magnetic Resonance (1H-NMR), elemental analyses, Fourier Transform Infrared Spectroscopy (FT-IR) and Electrospray Ionization Mass Spectrometry (ESI-MS) spectroscopic studies. Single crystals of the nickel synergist complex have been grown from a methanol/water (10/1) solution and analyzed by single crystal X-ray diffraction. The crystal structure of the nickel synergist complex shows that Ni(II) is coordinated by four water molecules and two monodentate LI ligands and there is no direct interaction of the Ni(II) with sulfonic oxygen atoms of naphthalene-2-sulfonic acid anions, while hydrogen-bonded interactions of the coordinated water molecules with sulfonic oxygen atoms of naphthalene-2-sulphate anions were observed. In addition, in order to provide parallels to solvent extraction, the extracted Ni(II) complex with HDNNS and 4PC is also prepared and studied using FT-IR and ESI-MS technology. Compared with their corresponding free ligand, similar shifts assigned to the stretching vibration of the pyridine ring and SO in both the nickel synergist complex and the extracted Ni(II) complex suggest that in the non-polar organic phase, Ni(II) is also coordinated by LII ligands, while the sulfonic oxygen atoms of dinonylnaphthalene sulfonate anions not directly bonded to Ni(II) form hydrogen bonds with water molecules (coordinated with Ni(II) or/and solubilized in the non-polar organic phase). For the ESI-MS spectrum of the extracted Ni(II) complex in non-polar organic phase, there exists a peak at m/z values of 1058.76, which indicates that the extracted Ni(II) complex in the non-polar organic phase may have a coordination structure, [Ni(H2O)4(LII)2](DNNS)2, similar to the coordination structure of the nickel synergist complex.