Separation and recovery of iron and scandium from acid leaching solution of red mud using D201 resin

Red mud is a byproduct of alumina refining of bauxite ores, and is a significant source for extracting scandium. However, a large amount of iron in red mud makes it difficult to recover scandium because Fe(III) and Sc(III) have similar physicochemical properties. In this study, a new method was developed for selective separation of iron and scandium in acid leachate of red mud using D201 resin. Theoretical calculations indicate that the ferric species mainly exists as FeCl₃ or FeCl₄⁻ at chloride concentration above 6.65 mol/L, while scandium still exists as ScCl₂⁺, making it possible to selectively separate iron from scandium through anion resin adsorption. The factors affecting the adsorption of iron and scandium such as chloride concentration, resin dosage, adsorption time, and temperature were evaluated in batch experiments. The Langmuir model was successfully applied to both iron and scandium adsorption, and the maximum adsorption capacities of iron and scandium are 147.06 and 0.95 mg/g, respectively, indicating a significant difference between iron and scandium. Raman analysis further demonstrates that the iron is adsorbed onto D201 resin as FeCl₄⁻ anion.     

Application of P507 and isooctanol extraction system in recovery of scandium from simulated red mud leach solution

The current recovery technique of Sc was complicated and the chemical consumption was high. This was due to the low content of Sc in resources and the difficulty of stripping. In this research, the isooctanol was added into the 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507) extraction system to reduce the extraction and improve the stripping of Sc. The maximum stripping ratio of Sc from loaded organic phase by sulfuric acid can increase from 10% (without isooctanol) to 99% (with 15 vol% isooctanol). In the extraction test of the simulated red mud leaching liquor, the separation factors between Sc and Zr, Sc and Ti are 36 and 350, separately. At the same time, other metals are almost not extracted. The high selectivity and stripping of Sc suggest that the P507 with isooctanol extraction system can be applied in the practical Sc recovery process.     

A review on solvent extraction of scandium

This review article on the development course of scandium solvent extraction covers: (i) neutral phosphorus extractants; (ii) acid phosphorus extractants; (iii) carboxylic acid extractants; (iv) amine extractants; (v) chelating extractants; (vi) synergistic extractants. Those extractants are of valuable reference for developing new separation process of scandium from red mud, titanium dioride and other rare earth resources.     

Selective separation of iron and scandium from Bayer Sc-bearing red mud

In this study, we investigated the separation of iron and scandium from Sc-bearing red mud. The red mud object of our study contained 31.11 wt% total iron (TFe), 0.0045 wt% Sc, hematite (Fe₂O₃) and ferrosilite (FeO·SiO₂) as the main Fe-bearing minerals. The Sc-bearing red mud was treated by a novel deep reduction roasting and magnetic separation process that includes the addition of coke and CaO to extract Fe and enriching Sc from the Sc-bearing red mud. The addition of coke and CaO enhances the transformation of hematite (Fe₂O₃) to metallic iron (Fe⁰) and magnetite (Fe₃O₄) as well as the transformation of ferrosilite into metallic iron (Fe⁰). The test results show that utilizing the new process a Fe concentrate with a TFe content of 81.22 wt% and Fe recovery of 92.96% was obtained. Furthermore, magnetic separation tailings with Sc content of 0.0062 wt% and Sc recovery of 98.65% were also obtained. The test results were achieved under the following process conditions: roasting temperature of 1373 K, roasting time of 45 min, calcium oxide dosage of 20 wt%, coke dosage of 25 wt%, grinding fineness of 90% < 0.04 mm, and magnetic field intensity of 0.24 T. The major minerals in the Fe concentrate are metallic iron (Fe⁰) and magnetite (Fe₃O₄). The main minerals in the magnetic separation tailings with a low TFe content of 2.62% are CaO·SiO₂, Na₂O·SiO₂, FeO·SiO₂, Ca₃Fe₂Si₃O₁₂, CaAl₂SiO₆ and CaFe(SiO₃)₂.     

Preparation of ultra-high pure scandium oxide with crude product from titanium white waste acid

Recovery of scandium from titanium white waste acid is an essential source of scandium. Simple and economical production of high purity scandium remains a challenge. A new extractant, N,N,N',N'-tetracyclohexyl-diglycolamide (TCHDGA), was synthesized, and the separation performance of scandium from impurity metal ions (Ti, Mn, Ba, Fe, Al and Mg) was investigated. The effects of mixing time, acid concentration and temperature on the scandium extraction were considered. The extraction mechanism was studied by infrared spectroscopy and the Equimole Series Method. Under optimized conditions, the extractant shows a strong affinity to scandium in the nitric acid medium and high extraction separation factors between scandium and these impurity metal ions. A process for the purification of scandium was established. The crude product obtained from titanium white waste acid, 95% purity scandium oxide, can be purified to 99.99% after only one step of extraction, scrubbing, and stripping. This technology is economical and straightforward and can realize the high-value recovery of scandium in the titanium white waste acid.     

Separation and recovery of scandium and titanium from red mud leaching liquor through a neutralization precipitation-acid leaching approach

Selective recovery of scandium and titanium from red mud leaching solution was achieved through neutralization precipitation followed by acid leaching approach.In the neutralization precipitation section,the effects of pH,temperature and reaction time on metal precipitation efficiency were investigated.Under the optimal co ndition,the precipitation efficiencies of scandium and titanium were 93.74% and 99.47%,respectively.In the acid leaching section,the effects of acidity,temperature,reaction time,and raffinate to acid solution ratio on leaching efficiency were investigated.Under the optimal condition,the leaching efficiencies of scandium and titanium were 99.97% and 5.44%,respectively.The loss of scandium and titanium were 6.3% and 5.9%,respectively.Compared with the traditional extraction procedure of scandium in red mud,this method could separate titanium from scandium effectively,which is beneficial for the purification of the products and improvement of value of the metal.     

Thermodynamic properties of liquid Cd-Pb-Sn solutions and analytical calculation of the phase diagram

Abstract

The relative partial thermodynamic properties of Cd in liquid Cd-Pb-Sn alloys have been investigated in the temperature range 680–840K by an emf technique. Data have been represented by general , power series expansions in the composition variables, and the liquidus surfaces when Cd or Sn are the primary crystallization products have been calculated analytically.

Résumé

Les propriétés thermodynamiques partielles du cadmium dans les alliages Cd-Pb-Sn liquide ont été étudiées dans une fourchette de température comprise entre 680 et 840K par la mesure de force électromotrice. Les données sont représentées par un développement en série des variables de composition. Les surfaces du liquidus ont été calculces analytiquement dans le cas où le cadmium ou l' étain est le produit prima ire de cristallisation.     

Extraction kinetics of neodymium from chloride medium using HEH/EHP saponified with magnesium bicarbonate solution

Magnesium bicarbonate solution is considered as an environmentally friendly extractant saponification agent for the solvent extraction of rare earth elements due to its advantage of minimum water pollution.In order to reveal the extraction regularity, optimize production-process and guide the use of this new extraction system, the extraction of Nd(Ⅲ) in chloride medium with HEH/EHP saponified by magnesium bicarbonate solution was investigated with the self-designed constant interfacial area cell. Besides, the effects of stirring rate, temperature, specific interfacial area and concentration of Mg-HEH/EHP on the extraction rate of Nd(Ⅲ) were systematically investigated. Results show that, the rate of extraction is governed by both diffusion and chemical reaction, and the extraction reaction takes place at the interface. The apparent activation energy of the extraction reaction is 16.88 kJ/mol. The corresponding rate equation is deduced. The mechanisms and rate-determining step are speculated based on interfacial reaction models, which is consistent with the experimental results.     

Rational design of novel carboxylic acid functionalized phosphonium based ionic liquids as high-performance extractants for rare earths

Developing the novel ionic liquids as the potential substitutes for conventional organic solvents in extraction of the rare-earth metals is highly desirable but challenges still remain. In this study, the well-designed carboxylic acid functionalized phosphonium based ionic liquids, (4-carboxyl)butyl-trioctyl-phosphonium chloride/nitrate, were synthesized and characterized. The as-prepared samples were tested as the undiluted hydrophobic acidic extractant for rare-earth metal ions, affording the maximal loading of 3 mol/mol towards Nd(III) in aqueous solution and the remarkable stripping performance. The results also reveal their excellent extractability and selectivity for Sc(III) in the mixtures of six rare-earth ions, as well as the outstanding separation properties between rare-earth and first row transition-metal ions (i.e., La/Ni, Sm/Co). Moreover, the extraction mechanism indicates that the extracted rare-earth complex via a proton exchange in the ionic liquid phase is structurally similar to the complexes obtained with neutral extractants. This work presents a prototype for the fabrication of the hydrophobic cation-functionalized ionic liquids for highly efficient rare-earth extraction and provides the future application in recycling of rare-earth metals from the spent magnets.     

Completely removing vanadium from ammonium molybdate solution using chelating ion exchange resins

Some chelating resins were used to remove a small amount of V (0.35 g/L V₂O₅) from ammonium molybdate solution with Mo concentration around 90 g/L. The results showed that vanadium can be easily extracted over molybdenum from ammonium molybdate solution by DDAS, CUW or CW-2 resins. More than 99.5% V and less than 0.27% Mo was extracted with a contact time of 60 min at pH = 7.4 and ambient temperature. The effluent was pure ammonium molybdate solution with a Mo/V gram ratio of more than 50,000 from an initial 255. Stripping of loaded resin was excellent using 5% ammonia solution, with a maximum V concentration of 20 g/L in comparison to 0.8 g/L Mo in the eluate. The mechanism for adsorption of V from ammonium molybdate solution by chelating resins was also proposed.     

Anion structural effects on interaction of rare earth element ions with Dowex 50W X8 cation exchange resin

The effect of the anion in the original rare earth element(REE) solution on the reversible ion exchange of Ce nitrate and Ce sulfate with the Dowex 50 W X8 was investigated using attenuated total reflection infrared(ATR-IR) spectroscopy, continuous flow reactor studies coupled with inductively coupled plasma mass spectroscopy(ICP-MS), and density functional theory(DFT). The simulated IR spectrum at the DFT B3 LYP/6-31 G(d) level was compared to the experimental results to characterize the IR spectrum, molecular interactions, and bonding of the ion exchanged species. The continuous liquid flow reactor studies show a capacity of 0.72 mmol/g sorbent for the Ce nitrateand 0.96 mmol/g sorbent for the Ce sulfate with the Dowex 50 W X8. The flow reactor studies reveal the type of solute anion(SO_4~((2-)) or NO_3~((-))) associated with the REE during cation exchange significantly affects the sorption capacity of the Dowex 50 W X8 ion exchange resin. The calculated REE binding energy(BE) and the DFT optimized structures suggest that the differences in sorption capacity is the result of the formation of different types of partially ionexchanged Ce_2~((3+))2 SO_4~((2-)) and Ce~((3+)) 3 NO_3~((-)). These results suggest that the solute anion affects the equilibrium constants of the Dowex resin by the formation of a charged layer capable of retaining the counterion. Modifying the sulfonic acid site(H+) in the Dowex 50 W X8 with the NH_4~+ counterion does not affect the sorption capacity and retention times of the Ce nitrate and Ce sulfate species. These results suggest that the counterions and co-ions having a finite size, may limit access to the Dowex sulfonate active site where the type of REE cation as a nitrate or sulfate in solution may significantly modify the sorption capacity of the ion exchange resin. Similar results are obtained during sorption with nitrates and sulfates of Sm and Yb.     

Extraction of scandium from red mud by acid leaching with CaF_2 and solvent extraction with P507

The extraction of Sc by acid leaching with CaF_2 and solvent extraction with P507 from red mud was proposed.The influence of acid leaching and solvent extraction on recovery of Sc was investigated.The CaF_2 can obviously improve the leaching efficiency of Sc and reduce the acid consumption.The leaching efficiency of Sc increases from 74% to 92% and the dosage of acid reduces under suitable conditions by adding 5% CaF_2.The minerals in red mud can easily be decomposed and leached into the acid solution with CaF_2 through analysis of XRD pattern.The particles of red mud become smaller and multihole.The Sc can be selectively extracted with 10% P507 at the pH value of 0.1 from the acid leaching solution.More than 98% of Sc and less than 10% of Al and Fe are extracted.The SC_2O_3 with purity of 99% is obtained after the process of reverse extraction with NaOH,H_2SO_4 dissolution,precipitation by oxalic acid and roasting at 750℃.     

Reaction between tetravalent cerium ion and chloride ion and effect of thiourea using cyclic voltammetry

To monitor the reaction between Ce⁴⁺ ion and Cl^– ion at the electron level, an electrochemical experiment was designed in this work. Herein, the intermediate and final products that may be produced during the redox reaction are directly tracked by using cyclic voltammetry, and the influences of Ce⁴⁺ ion concentration, temperature and F^– ion on the reduction peak potential of Ce⁴⁺ ion were investigated. The results show that Ce⁴⁺ ion reacts with Cl^– ion through an irreversible reaction without any intermediate products, and the rate-determining step of the reaction is diffusion during the electrode reaction. The effects of temperature (20–40 °C) and Ce⁴⁺ ion concentration (0.04–0.12 mol/L) on the reduction peak potential of Ce⁴⁺ ion can be ignored, but the higher the molar ratio of F^– to Ce⁴⁺ (0–3 mol/mol), the more easily the reduction of Ce⁴⁺ ion to Ce³⁺ ion occurs. Additionally, the Ce⁴⁺ ions are preferentially reduced by thiourea when thiourea is added in the HCl solution, and thiourea inhibits the oxidation of Cl^– ions to Cl₂ by forming a complex with Cl^– ions. This work provides a theoretical basis for the role of thiourea in inhibiting Cl₂ production and offers a new way to find new reductants.     

Optimization of both coercivity and knee-point magnetic field of Sm2Co17-type magnets via solid solution process

It is confirmed that phase homogenization is very important for improving the magnetic properties of 2:17-type Sm–Co sintered magnets. In this work, the influence of solid solution process on microstructure and magnetic properties of the Sm(Co_balFe_0.233Cu_0.073Zr_0.024)_7.6 sintered magnets was systematically studied. With the solid-solution treating duration (t_s) increasing from 0 to 4 h, intrinsic coercivity (H_cj) increases from 12.83 to 36.54 kOe, magnetic field at knee-point (H_knee) increases from 2.76 to 19.14 kOe, and the maximum energy product increases from 19.79 to 29.48 MGOe. The electron probe microanalyzer results reveal that there mainly exist gray and dark regions besides “white” rare earth-rich phase, and the content of Sm, Fe and Cu elements for the two kinds of regions changes a lot for the specimens. Furthermore, with t_s increasing up to 4 h, the elements content deviation between the gray and dark regions becomes small gradually from 3.94 at% to 0.27 at%, 7.66 at% to 0.21 at% and 7.27 at% to 0.16 at% for Sm, Fe and Cu elements, respectively. Moreover, transmission electron microscopy results show that the distribution of cell size is much more concentrated for aged specimens when t_s is 4 h. It is also found that the Cu concentration at cell boundaries for the 4 h solid-solution treatment case shows relatively higher values and greater concentration gradient (1.94 at%/nm). It is verified that sufficient solution treatment duration is prerequisite to form these homogeneous microstructural features, which are the key points for obtaining both high H_cj and H_knee.     

Kinetics and thermodynamics modeling of Nd(III) removal from aqueous solution using modified Amberlite XAD7

New adsorbent material was obtained by modification of commercial Amberlite XAD7 with thiourea that represents a non-toxic, cheap and environmentally friendly extractant. Prepared adsorbent was used for removal of neodymium ions from aqueous solutions. Thiourea modified Amberlite involved in this study shows good adsorption capacities (74.3 mg/g) and excellent efficiency during Nd removal process. In order to elucidate the mechanism of the Nd adsorption process kinetic, thermodynamic and equilibrium studies were performed, establishing this way which kinetic model better describes the Nd adsorption process. Moreover the thermodynamic studies prove that the Nd adsorption on thiourea modified Amberlite XAD7 is an endothermic and spontaneous process.     

Synergetic catalytic removal of chlorobenzene and NOx from waste incineration exhaust over MnNb0.4Ce0.2Ox catalysts: Performance and mechanism study

Nb doped MnCe_0.2O_x complex oxides catalysts prepared via a homogeneous precipitation method were investigated for synergistic catalytic removal of NO_x and chlorobenzene (CB) at low temperatures. The MnNb_0.4Ce_0.2O_x catalyst with a molar ratio of Nb/Mn = 0.4 exhibits excellent activity and the NO_x and CB removal efficiency reaches 94.5% and 96% at 220 °C, respectively. Furthermore, the NO_x and CB removal efficiency of MnNb_0.4Ce_0.2O_x still remains above 80% after injecting 300 ppm SO₂ and 7 vol% H₂O for 36 h. In addition, the presence of CB and NO_x + NH₃ can improve the NO_x and CB removal efficiency of MnNb_0.4Ce_0.2O_x, respectively. The analysis results from N₂-BET, Py-IR, H₂-TPR and NH₃-TPD reveal that the introduction of Nb increases the average pore size, pore volume and surface area, promoted the growth of Lewis acid amount obviously, and enhances redox ability of MnCe_0.2O_x at 100–250 °C. Moreover, the molecular migration process of NO_x, NH₃, CB and SO₂ in NH₃-SCR and CB oxidation reaction over MnNb_0.4Ce_0.2O_x catalysts were systematically studied. In situ DRIFTS, FT-IR and XPS also confirm that the adsorption of sulfate species and SO₂ on the surface of MnNb_0.4Ce_0.2O_x is inhibited effectively by the introduction of Nb in the presence of SO₂ and H₂O. Moreover, Nb additives also enhance the structural stability of MnNb_0.4Ce_0.2O_x, due to the interactions among Mn, Nb and Ce. The NH₃-TPD, H₂-TPR and in situ DRIFTS results also confirm that the MnNb_0.4Ce_0.2O_x still retains abundant acid sites and high redox ability in the presence of SO₂ and H₂O. In summary, MnNb_0.4Ce_0.2O_x catalysts represent a promising and effective candidate for controlling NO_x and CB at low temperatures.     

High-efficiency simultaneous extraction of rare earth elements and iron from NdFeB waste by oxalic acid leaching

Iron can not be recovered at high value because only rare earth elements are effectively recovered from NdFeB waste via oxidation roasting-hydrochloric acid leaching process.In this study,a new method for leaching NdFeB waste with oxalic acid was developed.The high-efficiency,simultaneous and high-value recovery of rare earth elements and iron was realized to simplify the process and improve the economic benefit.Results of the oxalic acid leaching experiments show that under the optimum leaching conditions at 90℃ for 6 h in the aqueous solution of oxalic acid(2 mol/L) with a liquid-solid ratio of60 mL/g,the iron leaching efficiency and precipitation rate of rare earth oxalate reach 93.89% and 93.17%,respectively.Rare earth oxalate and Fe(C₂O₄)3^3- were left in the residue and the leaching solution,respectively.The leaching mechanism was further analyzed by characterising the leach residues obtained through X-ray powder diffraction(XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy(SEM-EDS).Results of the leaching kinetics study indicate that the process of oxalic acid leaching follows the shrinking nucleus model,and the leaching kinetics model is controlled by the mixed factors of diffusion and chemical reaction.The leaching residue was calcined at 850℃ for 3 h and then decomposed into rare earth oxide,which can be directly used to prepare rare earth alloy via molten salt electrolysis.For the leaching solution,ferric oxalate solution was reduced using Fe powder to prepare the ferrous oxalate(FeC₂O₄-2H₂O).     

树脂从腐殖酸浸金液中吸附金的研究

本研究了大孔阴离子交换树脂从腐殖酸浸金液中吸附金的性质。结果表明，吸附过程以液膜扩散控制为主。实验测得吸附扩散系Ｋ＝１．９６×１０＾－４ｓ＾－１。实验还表明，溶液的ＰＨ值及温度越高时，树脂吸附金的速率越快。吸附过程可用Ｂｏｙｄ方程表达。     

Separation and recovery of associated rare earths from the Zhijin phosphorite using hydrochloric acid

The separation and extraction of associated rare earths from the Zhijin phosphorite mine is of great interest. Based on previous studies, the hydrolysis of phosphate ore using hydrochloric acid was systematically studied through extensive testing. Experiments were conducted to separate and recover the rare earths from the hydrolysis solution. Kinetic studies on the acidolysis of phosphorite using hydrochloric acid show that the use of hydrochloric acid in the acidolysis of phosphorite is mainly controlled by a chemical reaction and is also a diffusion-controlled reaction. When 210 L of HCL per 100 kg of phosphorite was used at 30 ℃ for 360 min, 96.1% of the P_2 O_5 and 95.0% of the rare earths are leached from the phosphorite. After defluorination and purification, the pH of the phosphate-acid solution is adjusted to 2.1 using sodium hydroxide, and a rare earth concentrate with rare earth content of 1.76 wt%is obtained; i.e., 90.1% of the rare earths are recovered. The rare earth content is increased to more than5 wt% through multiple enrichment processes, with a total yield of 59.5%.     

Enhanced photocatalytic degradation of organic dyes from aqueous environment using neodymium-doped mesoporous layered double hydroxide

Neodymium-doped Zn–Al layered double hydroxide (Nd/Zn-Al LDH) with excellent photocatalytic activity was prepared by a one-step hydrothermal method. The morphology and physicochemical properties of as-synthesized photocatalysts were well analyzed by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL), UV-diffuse reflectance spectroscopy (UV-DRS), and Brunauer-Emmett-Teller (BET) surface analysis. Doping Nd³⁺ into Zn–Al LDH enhances the overall catalytic activity of the nanocomposite, like better electron–hole pair separation, increase in interplanar distance, fast electron transfer, and large surface area. The as-prepared nanocomposite shows excellent degradation of three different dyes under visible light irradiation. The degradation efficiency of these dyes follows the order of Congo red > rose Bengal > fast green. Furthermore, liquid chromatography-mass spectrometry (LC-MS) was employed to propose a possible photocatalytic degradation pathway for Congo Red and Rose Bengal dyes by Nd/Zn–Al LDH. With the help of radical trapping experiments, it is revealed that during the photoexcitation process, the primary reactive intermediates are hydroxyl radicals.