Preparation of Nd(III) carbonate by precipitation stripping of Nd(III)-loaded VA10

The preparation of fine particles of Nd(III) carbonate from kerosene solution, from which Nd(III) was extracted with versatic acid 10 (VA10) by a precipitation stripping technique using an aqueous NH₃-(NH₄)₂CO₃ solution as stripping medium, was studied. In preliminary experiments, we were unable to recover simple Nd(III) carbonate from Nd(III)-loaded VA10 by CO₂ gas bubbling, when water, (NH₄)₂CO₃, NH₄HCO₃, NaHCO₃, or NA₂CO₃ solution saturated with CO₂ was used as the stripping solution. To obtain simple Nd(III) carbonate, it is necessary to use more than the stoichiometric amount of NH₃ compared to VA10 and about 10 times as much (NH₄)₂CO₃ as Nd(III). The solution mixture of NH₃-(NH₄)₂)CO₃ acts as a pH buffer, an adductor for VA10, and a CO ₃ ²⁻ ion source. Although it was concluded that the precipitates are Nd₂(CO₃)₃·xH₂O (x⊧4), their X-ray pattern does not coincide with that quoted by JCPDS. By heating these precipitates, cubic Nd₂O₃ was obtained at 823 K, while, at 973 K, hexagonal Nd₂O₃ was formed. Since the stripping solution consisting of NH₃-(NH₄)₂CO₃ was highly alkaline, VA10 was also stripped in the aqueous phase. To use a closed-circuit system for the precipitation stripping of Nd(III) carbonate from Nd(III)-loaded VA10, it is important to regenerate VA10 in the organic phase. For this purpose, evaporation of NH₃ by air bubbling was studied. By bubbling air into a stripping solution warmed at 333 K, almost all the VA10 can be transferred to the organic phase.     

Aqueous oxidation of chalcopyrite in hydrochloric acid

The aqueous oxidation of chalcopyrite flotation concentrate is faster in HC1 than in H₂SO₄. Under certain conditions, FeCl₂ formed during reaction undergoes oxidation and hydrolysis (or vice versa) yielding α-Fe₂O₃ or β-FeOOH depending on the initial acidity, O₂ pressure, and temperature. A small fraction of sulfur oxidizes to soluble SO ₄ ^2- and a part precipitates as Fe(OH)SO₄. The precipitation of FeOOH is more enhanced in HC1 than in H₂SO₄ solution. Optimum leaching conditions are 110°C, 2010 kPaO₂, 2 N HC1, molar ratio CuFeS₂/HCl 0.8 to 0.9, and time of reaction 45 min. Under these conditions practically all the iron precipitates and the reaction can be described by the equations: CuFeS₂ + 2 HCl + 5/4 O₂ → CuCl₂ + FeOOH + 1/2H₂O + 2S and CuFeS₂ + HC1 + O₂ → CuCl + FeOOH + 2S. Copper ferrite, CuFe2O₄, precipitates if the final pH of the leach solution is ≥2.2, while CuCl precipitates if the initial acidity is increased to 3 N HC1.     

Determination of the association constant of sulfuric acid

The activities of HC1 and H₂SO₄ in aqueous solutions of HC1-H₂SO₄ and H₂SO₄-HC1O₄, respectively, were measured at 298 K by an electromotive force (emf) method. Using the activity data, the association constant,K*_{H 2SO 4} was calculated as a function of the effective ionic strength of the solution by a method similar to that proposed by Johnson and Pytkowicz. The association constant of H₂SO₄, which corresponds to the reciprocal value of the first ionization constant of H₂SO₄, decreased with an increase in the effective ionic strength and was correlated to the effective ionic strength,I _e (mol dm⁻³), as follows: logK*_{H 2SO 4} = 0.42 - 0.91I_e, 0 I_e1 The mean free activity coefficients of H₂SO₄ were calculated from the association constant of H₂SO₄ and were found to decrease with an increase in the effective ionic strength. Formerly Graduate Student, Department of Metallurgy, Kyoto University.     

Extraction mechanism of cerium（Ⅳ） in H2SO4/H3PO4 system using bifunctional ionic liquid extractants

The extraction of Ce（Ⅳ） in H2SO4/H3PO4 system was investigated systematically using bifunctional ionic liquid extractants（Bif-ILES） [A336][P507],[A336][P204] and [A336][C272] in n-heptane.The effects of H2SO4 concentration,extractant concentration and salting-out agent concentration were observed in detail.The extraction mechanism of Ce（Ⅳ） in H2SO4/H3PO4 system was obtained.The comparison with other extractants such as Cyanex923,TBP was also studied.Thermodynamic functions of the extraction reaction were calculated,showing that the extraction was an exothermic process.The separation of Ce（Ⅳ） from RE（Ⅲ） and Th（Ⅳ） was also investigated.The result indicated that Ce（Ⅳ） could be selectively extracted in this system.CePO4 nanoparticles were obtained in the process of stripping using H2O2 in H2SO4/H3PO4 system.X-ray diffraction（XRD）,scanning electron microscopy（SEM） and spectroscopy were adopted for the characterization of the sample.     

Speciation of the Fe(II)–Fe(III)–H2SO4–H2O system at 25 and 50 °C

This work presents theoretical and experimental results on the speciation of the Fe(II)–Fe(III)–H₂SO₄–H₂O system in concentrated solutions (up to 2.2 m H₂SO₄ and 1.3 m Fe). The aim was to study the chemical equilibria of iron at 25 and 50 °C in synthetic aqueous sulphuric acid solutions that contain dissolved ferric and ferrous ion species. Raman spectroscopy, volumetric titration and conductivity measurements have been carried out in order to study the presence of specific ions and to characterize the ionic equilibrium. A thermochemical equilibrium model incorporating an extended Debye–Hückel relationship was used to calculate the activities of ionic species in solution. Model calculations were compared with experimental results. Model simulations indicate that anions, cations and neutral complexes coexisted in the studied system, where the dominant species were HSO₄⁻, H⁺, Fe²⁺ and FeH(SO₄)₂⁰. This indicated that these solutions showed a high buffer capacity due to the existence of bisulphate ions (HSO₄⁻), which presented the highest concentration. A decrease in the concentration of H⁺ and Fe³⁺ took place with increasing temperature due to the formation of complex species. Standard equilibrium constants for the formation of FeH(SO₄)₂⁰ were obtained in this work: log K_f⁰ = 8.1 ± 0.3 at 25 °C and 10.0 ± 0.3 at 50 °C.     

Treatment of Chloride Waste Pickle Liquor by Solvent Extraction for the Recovery of Iron

A systematic study of the extraction of Fe(III) from chloride waste pickle liquor has been investigated using Cyanex 923 diluted with kerosene to recover iron values from the pickle liquor. Various parameters were studied to optimize the conditions for maximum recovery of iron. Extraction increases with increasing concentration of both hydrochloric acid and extractant. The species extracted into the organic phase appears to be HFeCl₂ with 1 M of the solvent. Effect of various salts as additives on Fe extraction was also studied and it was found that addition of NaCl enhanced the extraction about 2.5 times as compared to that without its addition.

Saturated loading capacity was found to be 60.9 g/L Fe in four contacts at O/A of 1. The stripping of Fe(III) with different concentration of hydrochloric acid and nitric acid from the loaded Cyanex 923 was found to increase up to 1 M of both the acids and then decrease with further increase in acid concentration up to 10 M. However, 100% stripping efficiency of Fe(III) was achieved with 0.8 M oxalic acid in two countercurrent stages at an aqueous:organic phase ratio of 3:1. Extraction parameters for maximum extraction of Fe(III) were optimized.     

Thermodynamic fundamentals of ferrous cake sulfitization

The Pourbaix diagrams of the systems SO₄^2??SO₃^2??H₂O and iron hydroxide (oxide)–H₂O are refined. The E(pH) dependence of the sulfitization of iron(III) hydroxide is refined with allowance for the regions of predominant phase constituents of the systems. The potential E–pH electrochemical equilibrium diagrams of the systems Fe(OH)₃–H₂SO₄–SO₃^2?–H₂O, FeOOH–H₂SO₄–SO₃^2?–H₂O, and Fe₂O₃–H₂SO₄–SO₃^2?–H₂O are plotted. These diagrams can be considered as a thermodynamic basis for the sulfite conversion of the ferrous cake of copper–nickel production.     

Removal and recovery of gallium from aqueous solutions by complexation with sodium di-(n-octyl) phosphinate

A new precipitation process is reported for the removal and recovery of gallium (III) from aqueous solutions using sodium di-(n-octyl) phosphinate. The complexes formed have low solubility in water and the ligand is easily regenerated, as previously reported for the precipitation of lead and zinc. The effects of different ligand-to-gallium mole ratios, pH and temperature are studied. Essentially complete removal of gallium was obtained at 22 °C using a ligand-to-gallium mole ratio of 3 and pH between 2 and 7.5. The effects of competing ions, such as SO₄²⁻, Cl⁻, Na⁺ and Ca²⁺, are documented. While there is a clear selectivity of gallium over Ca²⁺, the presence of Na⁺ cation and anions such as SO₄²⁻ and Cl⁻, instead of NO₃⁻, decreases the efficiency of the process. Gallium is recovered from the insoluble complexes using diethyl ether or chloroform in contact with an aqueous solution at different values of pH. While gallium is solubilized in the aqueous phase, the ligand is extracted into the organic phase. The ligand is recovered by evaporating the organic solvent.     

Kinetic and spectral studies of EHPG systems using chemi- and electrochemiluminescence methods

The systems containing EHPG, EHPG-OCH3 and EHPG-NH-Ac and Tb(Ⅲ) ions were used to study chemiluminescence (CL) and electrochemiluminescence (ECL) processes. In the CL studies the Fenton system (Fe(Ⅱ)/(Ⅲ)-H2O2) was used as a source of reactive oxygen species (ROS). Kinetic CL curves and CL spectral distributions were recorded. On the basis of the results obtained, it was demonstrated that Tb(Ⅲ) acted as a sensitizer. Similarly obtained CL decays in the systems of Fe(Ⅱ)/(Ⅲ)-EHPG (or its derivatives)-H2O2 and Fe(Ⅱ)/(Ⅲ)-EHPG (or its derivatives)-Tb(Ⅲ)-H2O2, independently on the Tb(Ⅲ) concentration, showed that the lanthanide ions did not influence the kinetics of the oxidation of EHPG (or its derivatives) in the Fenton systems. The CL intensity increased with the increasing concentration of Tb(Ⅲ) ions, which were the main emitters in the reaction systems. Spectrophotometric and luminescent studies of the systems before and after the additions of hydrogen peroxide proved that the excitation of the lanthanide ion was a result of energy transfer from the excited products of the oxidation of EHPG or its derivatives to the uncomplexed Tb(Ⅲ) ions. ECL was generated on the surface of a nonstructural modified aluminum electrode with the use of K2S2O8, H2O2 or KN3 as coreactants in aqueous solution. In these studies we employed Al electrodes covered with a 2-4 nm layer of Al2O3 doted with Tb(Ⅲ) or Dy(Ⅲ) ions. The electrodes were polarized using cathodic and anodic pulses of various amplitude and frequency. The relative ECL efficiencies were determined as a function of electric pulse parameters, electrolyte compositions and the thickness of barrier or porous layer of the Al2O3 electrode.     

Effects of iron and temperature on solubility of light rare earth sulfates in multicomponent system of Fe2(SO4)3-H3PO4-H2SO4 synthetic solution

Numerous light rare earth elements (LREE) minerals containing Fe and P were processed by sulfuric acid roasting method, and the leaching solution mainly comprises LREE sulfate, Fe₂(SO₄)₃, H₃PO₄, and H₂SO₄, however, the solubility data of LREE sulfates in this system is few. This work studies the solubility of LREE sulfates in independent LREE sulfate system RE₂(SO₄)₃-Fe₂(SO₄)₃-H₃PO₄-H₂SO₄ (RE = La, Ce, Pr or Nd) and mixed LREE sulfates system (La,Ce,Pr,Nd)₂(SO₄)₃-Fe₂(SO₄)₃-H₃PO₄-H₂SO₄ at different temperature (25–65 °C) and concentrations of Fe₂(SO₄)₃ (Fe₂O₃, 0–50.13 g/L), H₂SO₄ (0.5 mol/L), and H₃PO₄ (P₂O₅, 20.34 g/L) based on the industrial operating condition at low liquid and solid ratio 2:1. The solubility of each LREE sulfate in the independent system (La₂O₃, 12.25–20.88 g/L; CeO₂, 41.93–62.35 g/L; Pr₆O₁₁, 37.34–56.69 g/L; Nd₂O₃, 26.60–37.63 g/L) is much higher than that of the mixed system (La₂O₃, 6.95–11.03 g/L; CeO₂, 10.63–21.51 g/L; Pr₆O₁₁, 11.56–20.36 g/L; Nd₂O₃, 12.36–19.79 g/L) under the same other conditions. The results also indicate that, in the two systems, both Fe and the temperature have negative effects on the solubility of LREE sulfates. That may occur due to the complication reactions between the complexes of RESO₄⁺ and Fe(SO₄)₂^–. However, the influence degree of temperature and iron concentration on the LREE sulfates solubility varies in the two systems and among different LREE species. This research is of theoretical significance for optimizing the conditions of the sulfuric acid process for recovering the LREE from the mixed LREE bearing minerals as well as the single LREE containing secondary rare earth scraps.     

Purification of scandium from concentrate generated from titanium pigments production waste

Nowadays 80%of scandium in China is obtained from titanium pigments production waste through a complex purification process.The study mainly focused on the purification of Sc from its concentrate generated from titanium pigments production waste by solvent extraction.Several extractants have been tried and 10%D₂EHPA-5%TBP-85%sulfonated kerosene exhibited the best extraction performance towards Sc in 7 mol/L H₂SO₄solution,so it was selected as the oil phase.0.5%of H₂O₂was added into the concentrated solution which can effectively inhibit the extraction of Ti.Both the extraction and back extraction parameters are optimized.The preferred extraction conditions were obtained,i.e.,acidity:7 mol/L H₂SO₄,the phase ratio A/O:10,room temperature,mixed contact time:30 min,Sc concentrate:10 g/L,that the extraction rate of Sc in the above conditions was nearly 100%.NaOH was used for back extraction with the stripping rate 99%on the following conditions:5 mol/L NaOH stripping for 30 min at a phase ratio A/O:1 at 90℃.Finally,H₂C₂O₄was used to further purify the back extraction product and Sc₂(C₂O₄)₃precipitant fo rmed.The final product Sc₂O₃with a purity over 99.5%was obtained by calcining Sc₂(C₂O₄)₃at 1000℃for 2 h.A conceptual process for Sc purification was put forward and proved.The total recovery yield of Sc in the whole process is 95%.     

The extraction of iron(III) from aqueous sulphate solutions by primene sulphate

A study of the extraction of iron(III) from aqueous sulphate media by the primary amine Primene 81R at 50°C has been made. The compound extracted from the organic phase with Primene 81R sulphate in kerosene has been isolated and recrystallized from a methanol-acetone mixture and has been shown to have the stoichiometric formula 3(RNH₃)₂SO₄·(Fe(OH)SO₄)₂ represents the alkyl groups associated with the amine. It has been shown that the extraction of iron(III) occurs by an adduct formation reaction between primary amine sulphate molecules and the species IFe(OH)SO₄I₂ from the aqueous phase. On the basis of the experimental data and spectral studies a dimeric structure is suggested for the extracted complex.     

Removal of SO2 with oxygen in the presence of Fe(III)

A laboratory study of the aqueous oxidation of SO₂ in the presence of Fe(III) and Fe(II) has been conducted. The SO₂ concentration was 3930 ppm (3.93 × 10⁻³ atm or 398 Pa) in a gas stream with nitrogen and oxygen. The oxygen pressure was varied from 0 to 0.203 atmosphere. The initial concentration of Fe(III) ranged from 10⁻³ to 5-10⁻³ molar while that of Fe(II) was 5 × 10⁻³ molar. The temperatures were 298, 309.2, and 317.5 K. The solution pH was 1.83. The oxidation of SO₂ is intensive and yields from 90 to 97 pct recovery of incoming SO₂ when 5 × 10⁻³ molar Fe(III) and an oxygen pressure above 0.057 atmosphere are applied at 298 K. The reaction mechanism has been explained by determining the rate constants of the oxidation reactions from a kinetic model. The rate constants show that SO₂ is mostly oxidized by oxygen through formation of ferric-sulfite complex and that regeneration of ferric ion is possible under a normal oxygen pressure. The activation energy of the oxidation has been determined and has been found to be 13.5 Kcal/mole.     

Thermodynamic and application study of complicated extraction system Ce(IV)–HF–H3BO3–H2SO4 using Cyanex 923

This article aims to reduce the environmental pollution while maximizing the recovery of REEs as well as associate resource-fluorine (F) from bastnaesite. This paper investigates the extraction equilibrium process and mechanism of Ce(IV)–HF–H₃BO₃–H₂SO₄ system using Cyanex 923. Extraction equilibrium process of different systems, including HF–H₂SO₄, H₃BO₃–HF–H₂SO₄, and Ce(IV)–HF–H₂SO₄, were studied in detail and the corresponding extraction mechanisms were also determined. It is noteworthy that a synergistic effect between B–F and an antagonistic effect between Ce(IV)–F were discovered first in the extraction process by Cyanex 923. Besides, H₃BO₃ is found to be able to promote the extraction of F in quantitation by Cyanex 923. FTIR and ¹¹B and ¹⁹F NMR were adopted to characterize the different loaded organic phase. Based on these results, the extraction mechanism of complicated system Ce(IV)-HF-H₃BO₃–H₂SO₄ was further determined. Besides, the effect of H₃BO₃ on the extraction and stripping of Ce(IV) in complicated system was studied. Moreover, it shows that the addition of H₃BO₃ has nothing to do with the purity of obtained CeF₃ particle from bastneasite liquor in the practical system. Adding H₃BO₃ into bastnaesite leach liquor, on the one hand, will be beneficial for the recovery yield of Ce and F. On the other hand, it can avoid from environmental pollution caused by emission of F-containing waste water as well as reducing the waste residue.     

Extraction of molybdenum from acidic leach solution of Ni–Mo ore by solvent extraction using tertiary amine N235

Tertiary amine N235 diluted with sulphonated kerosene containing sec-octyl alcohol as a phase modifier was used to directly extract molybdenum from the acidic leach solution of Ni–Mo ore. The results indicated that the extraction of molybdenum can reach more than 88% using a solvent extraction system consisting of 10?vol.-% N235 and 10?vol.-% sec-octyl alcohol in sulphonated kerosene with an O/A ratio of 1:2 at room temperature for 20?min. The extracted molybdenum species of Mo₇O₂₁(OH)₃^3–, MoO₂(SO₄)₂^2– and MoO₂(HSO₄)₄^2– in loaded organic phase were identified, and the predominant species was Mo₇O₂₁(OH)₃^3–. Molybdenum in the loaded organic phase can be stripped with ammonia solution, and the stripping of molybdenum can reach 95.8% at an O/A ratio of 7:1, phase contact time of 10?min, and the ammonia concentration of 6?mol?L^?1.     

A solid-state emf study of ternary Ni-S-O,Fe-S-O,and quaternary Fe-Ni-S-O

Four two-phase equilibria in Ni-S-O, three two-phase equilibria in Fe-S-O, and one two-phase equilibrium and four three-phase equilibria in Fe-Ni-S-0 atP _{SO 2} ? 1 atm were studied using the following emf cell: $$Pt, O_2 (air) \left| {\begin{array}{*{20}c} {ZrO_2 \cdot CaO or} \\ {ZrO_2 \cdot Y_2 O_3 } \\ \end{array} } \right|\begin{array}{*{20}c} {mixture of phases, Au} \\ {SO_2 , S_2 , O_2 , SO_3 with P_T \simeq 1 atm} \\ \end{array} $$ The seven two-phase equilibria in Ni-S-O and Fe-S-O are NiS/Ni₃S₂, Ni₃S₂/Ni0, NiS/NiO, NiO/NiSO₄, Fe₂O₃/Fe₂(SO₄)₃, Fe₂O₃/FeSO₄, and FeSO₄/Fe₂(SO₄)₃, and the four three-phase equilibria and the one two-phase equilibrium in Fe-Ni-S-0 are sp + (Fe, Ni)S + (Fe, Ni)₄S₃, sp + (Fe,Ni)₄S₃ + (Fe, Ni)O, sp + (Fe, Ni)O + (Fe, Ni)SO₄, and Fe₂O₃ + sp + (Fe, Ni)SO₄ and sp + (Fe,Ni)S. The sp + (Fe, Ni)S two-phase equilibrium was measured by using mixtures containing a major portion of one phase and a minor portion of the other. The results are presented in terms of oxygen potential as a function of metal ratio,y _Ni =x _Ni/(x _Fe +x _Ni) at constant temperatures andP _{SO 2} = 1 atm. The calculated stability diagrams atP _{SO 2} = 1 atm from thermodynamic models are in agreement with experimental results. Several of the stability diagrams atP _{SO 2} = 0.1 and 0.01 are also calculated and presented.     

Solvent extraction and separation of Y(III) from sulfate,nitrate and chloride solutions using PC88A diluted in kerosene

Solvent extraction of yttrium (Y) from different aqueous solutions using the organic extractant 2- ethylhexyl phosphonic acid mono-2-ethylhexyl ester (PC88A) diluted in kerosene was investigated. Solution chemistry considerations were proposed to identify the predominant species in different aqueous media (H₂SO₄, HCl and HNO₃). In general, nitric and hydrochloric acids were found to be more efficient than sulfuric acid for yttrium extraction. Separation studies showed that nitric acid provide higher separation of Y(III) from light REES while sulfuric acid works better when separation of Y(III) from heavy REEs is desired.     

A novel extractant bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide for cerium(IV) extraction and separation from sulfate medium

By introducing the amine group into phosphorus extractant, a novel aminophosphine compound bis(2-ethylhexyl) ((2-ethylhexylamino)methyl) phosphine oxide (DEHAPO, abbreviated as A) was synthesized for the extraction of cerium (IV) (Ce(IV)) from sulfate medium (H₂SO₄). The influence factors including extractant concentration, H₂SO₄ concentration and temperature on the Ce(IV) extraction were investigated and discussed. It is found that the extraction ability of Ce(IV), thorium (IV) (Th(IV)) and rare earths (REs(III)) (La, Gd, Yb) decreases in sulphate medium in the following order: Ce(IV) > Th(IV) > REs(III). The extraction process is an exothermic reaction and the thermodynamic parameters were calculated. The extracted complex of Ce(HSO₄)₂SO₄·A in loaded organic solution was identified by the slope methods and further proved by FT-IR spectral analysis. Stripping studies indicate that Ce(IV) can be effectively stripped from the organic phase. The results of separation factors (β) and saturation loading capacity demonstrate that DEHAPO could be used to selectively extract Ce(IV) from sulphate medium with high separation efficiency and good extraction ability.     

Degradation of organics using LaFeO3 as a persulfate activator under low-intensity ultra-violet-light irradiation: Catalytic performance and mechanism

ABO₃-type perovskite oxides with abounding defect structures and diverse physical chemistry attributes have been extensively studied in heterogeneous catalysis. Semiconductor LaFeO₃ perovskites fabricated via the sol–gel method were used as peroxydisulfate (PDS) activators for methylene blue (MB) degradation under low-intensity ultra-violet (UV)-light to evaluate the degradation efficiency of organic pollutants and mechanism. The results indicate that under low-intensity UV irradiation, the developed UV/LaFeO₃/PDS system shows excellent degradation ability of organic pollutants in a wide pH range. Electron spin resonance and radical quenching experiments verify that SO₄^·?, ?OH, h⁺ and ¹O₂ are generated during the activation process, and ¹O₂ plays a dominant role in MB degradation. Reduction of low oxidation state Fe(II) and O₂^2?/O^? on the LaFeO₃ surface shows that oxygen vacancy, as the electron transfer mediator, enhances the redox cycle efficiency of Fe(II)/Fe(III). Photogenerated electrons of LaFeO₃ involved in the cyclic transformation of Fe(II)/Fe(III) and PDS activation further increase the number of active radicals and thus promote the synergistic effect of photocatalytic coupled with sulfate radical-based advanced oxidation processes.