Investigation of the structure of neodymium-di-(2-ethylhexyl) phosphoric acid combinations using electrospray ionization and matrix-assisted laser desorption ionization mass spectrometry and nuclear magnetic resonance spectroscopy

Neodymium-di-(2-ethylhexyl) phosphoric acid (DEHPA) species forming in the organic phase during solvent extraction of neodymium with solutions of DEHPA have been studied. Two samples were prepared: one with a low molar ratio of neodymium to DEHPA, which is liquid and clear, and the other with a high molar ratio of neodymium to DEHPA (complete loading), which has the consistency of a gel. Electrospray ionization (ESI) and matrix-assisted laser desorption ionization (MALDI) mass spectrometric investigations show numerous compounds, in addition to the generally assumed species dimeric DEHPA and Nd(DEHP-DEHPA)₃, in the liquid sample. The nuclear magnetic resonance (NMR) spectroscopic investigation of pure DEHPA and of completely loaded sample confirm the formula of pure DEHPA and of the organic part of Nd(DEHP)₃. Furthermore, chemical analysis of a dried, completely loaded sample also proves the existence of the species Nd(DEHP)₃. Results of X-ray powder diffraction measurements of this sample agree well with literature data.     

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.     

Technology of Chloride-Ion Utilization from Filtrates of Carbonate Circuit of Nickel Production

The problem of sulphate solution purification, in particular solutions of carbonate branch after nickel precipitation, from chloride ion can be solved effectively by extraction process. Trialkylamine available commercially (TAA) (alkyl—C₈-C₁₀ and C₇-C₉) has been used in this study. The dependences of chloride ion extraction on temperature, pH and composition of aqueous phase, and composition of organic phase have been investigated. Triethylbenzene, kerosene, diesel oil, syntin with different additions (2-ethylhexanol, hexanol, tributylphosphate) were used as the solvents. The optimum composition of organic phase (0.5-0.6 M TAA in kerosene with addition of 2-ethylhexanol) and the conditions of chloride ion extraction from sulphate solutions have been determined. Chloride ion stripping from organic phase was conducted by alkali solutions to obtain a concentrated solution of sodium chloride.

The technology of chloride ion recovery from filtrates of carbonate branch of nickel plant (Norilsk Mining and Metallurgical plant) has been developed and tested on an industrial scale. The initial filtrate contained in g/l: chloride ion I6-I8, sulphate ion 60-65, impurities of metals. After purification, the chloride ion concentration in solution was less than 0.3 g/l (chloride ion recovery was more than 95%). After stripping of chloride ion with alkali solution, the stripping solutions containing 200-220 g/l NaCl and < 2 g/l sulphate ion. The stripping solutions underwent an electrolysis to obtain chlorine and sodium hydroxide solutions.

The developed technology allows recovery of chloride ion from sulphate solution.     

New Environment-Friendly Approach for Bastnasite Metallurgic Treatment (I): Extraction of Tetravalent Cerium from Sulphuric Acid Medium with Di(2-ethylhexyl) Phosphoric Acid

Bastnasiteisamainsourceofrareearthproducts inwhichCeO2/REOisabout50%.Atpresent,a cidity leachingcombinedwithalkali conversion method[1]iscommonlyusedinthebastnasitetreat ment.Thismethodisunfriendlytotheenvironment becausetheradioactiveelementofthoriuman…     

The extraction of iron(III) from aqueous acid solutions by di(2-ethylhexyl)phosphoric acid

The extraction of iron(III) from aqueous solutions containing sulphuric, hydrochloric and nitric acids by di(2-ethylhexyl)phosphoric acid (DEHPA) in kerosene has been investigated under different conditions. As a result, it is found that although extraction is dominated by an ion-exchange reaction, the rate of iron(III) extraction from sulphuric acid solutions to reach equilibrium is relatively slow in comparison with that from hydrochloric or nitric acid solutions. In the extraction from aqueous solutions containing hydrochloric or nitric acid, however, the DEHPA combines with iron(III) according to the solvating reaction at higher aqueous acidity. From studies on the rate of the extraction from sulphuric acid solutions, examined under non-equilibrium, it is confirmed that dependencies of extraction rate on hydrogen ion and DEHPA concentrations are in the first and inverse first orders, respectively. The hydrolyzed species is considered to interpret the extraction mechanism in this system.     

Extraction of nickel,cobalt and other metals [Cu,Zn, Fe(III)] with a commercial β-diketone extractant

The extraction of nickel, cobalt, copper and zinc from ammoniacal solutions of ammonium carbonate or ammonium sulphate by solutions of Hostarex DK-16 in kerosene has been investigated as a function of phase contact time, aqueous-phase pH and organicphase reagent concentration. Besides copper, Hostarex DK-16 also partially extracts iron (III) from moderately acidic solutions whereas nickel, cobalt(II), copper and zinc are extracted from neutral or ammoniacal ammonium sulphate and ammonium carbonate solutions. Extraction decreases in the following order of metals: Cu > Co > Ni > Zn. Cobalt(III) is not extracted, but the complex of cobalt(II) with Hostarex DK-16 is slowly oxidized to a cobalt(III) complex which cannot be stripped even when 10 N sulphuric acid is used. Absorption spectra for cobalt complexes with Hostarex DK-16 (purified by preparative thin-layer chromatography) in benzene also suggest oxidation of cobalt(II) to cobalt(III) in the organic phase. Nickel, cobalt(II), zinc and copper can be stripped easily from organic solution with dilute solutions of sulphuric acid. Hostarex DK-16 extracts iron very slowly, nickel moderately rapidly and copper, cobalt(II) and zinc rapidly. Slope analysis and extraction isotherms suggest that the complexes CuR₂, NiR₂ ·HR and CoR₂·HR are present in the organic phase. Nickel can easily be separated from cobalt by extraction with Hosterex DK-16 after oxidation of cobalt in aqueous ammoniacal solution by hydrogen peroxide; however, LIX 64N seems to be a more promising extractant owing to the higher extraction of nickel under analogous conditions and the poorer extraction of zinc in comparison with Hostarex DK-16.     

Determination of organic phase complexes formed on extraction of iron(III) from aluminium nitrate solutions with versatic 10

The extraction of Fe(III) from concentrated aluminium nitrate solutions by Versatic 10 in Escaid 110 was studied, using an AKUFVE system for the determination of extraction isotherms at constant pH values. The extraction data were analysed initially by classical slope analysis but this was found to be inadequate due to the complexity of the organic phase speciation. A statistical technique was then used to evaluate the compositions of the organic phase complexes by finding the best fits to the extraction data. Equilibrium constants governing the extraction of these complexes were calculated. Independent measurements of the amount of Versatic acid bound in the organic iron complexes were made by quantitative infrared analysis of organic extracts. Agreement between the statistical and infrared results was good. Complexes of the general form (Fe(OH)_3? V_n·sHV)_x were found, where n varied from 1 to 2 and s from about 0.5 to 2.5, with both decreasing as the iron loading in the organic phase was increased. Values of 2 or 3 were generally found for x, indicating the predominance of dimers and trimers.     

Chemically based model to predict distribution coefficients in the Cu-LIX 65N and Cu-KELEX 100 systems

A chemically based thermodynamic model to predict the distribution coefficients have been developed for the Cu-LIX 65N and Cu-KELEX 100 systems. The predictive model makes use of the aqueous phase cupric sulfate complex stoichiometric stability constant expressed as its degree of formation, their extraction mechanism, and the equilibrium constant for the extraction reaction. The distribution coefficient of copper can be predicted by the equation K_d = k₁α_o ², where is the ratio of the equilibrated organic concentration to the equilibrated hydrogen ion concentration in the aqueous phase, k₁ is the effective equilibrium constant containing the quotient of the activity coefficients of the reacting species and α_o is the degree of formation of the free cupric ion in the equilibrated aqueous phase. Excellent agreement between the experimental data and the predicted values was obtained. Formerly Graduate Fellow, Iowa State University     

Cuprous hydrometallurgy Part IV. Rates and equilibria in the reaction of copper sulphides with copper(II) sulphate in aqueous acetonitrile

Copper(II) sulphate in solutions of aqueous acetonitrile leaches copper from copper sulphides to form stable copper(I) sulphate solutions. Covellite and chalcopyrite are oxidised and leached more rapidly in the early stages of leaching with acidic CuSO₄/CH₃CN/H₂O than with acidic iron(III) sulphate in water. A redox equilibrium between copper(I) sulphate, copper(II) sulphate and partially leached solid copper sulphide, Cu_xS, is established. The equilibrium concentration of Cu₂SO₄ and the value of x in Cu_xS, in solutions saturated with CuSO₄, are interdependent if the acetonitrile concentration is constant. This behaviour is considered in terms of the structural and electrochemical changes which occur, in the solids Cu₂S and CuS, as leaching proceeds. According to the activities of acetonitrile, of copper(I) sulphate and of copper(II) sulphate, i.e. according to the redox potential of the solution, CuS either can be oxidised by copper(II) sulphate to a less copper-rich copper sulphide and even to sulphur, or reduced by copper(I) sulphate to a more copper-rich sulphide, up to Cu₂S, in acidic solutions containing CuSO₄, Cu₂SO₄, CH₃CN and water. This observation leads to an easy method of generating Cu₂S from CuS or from sulphur.     

Chemically based model to predict distribution coefficients in the Cu-LIX 65N and Cu-KELEX 100 systems

A chemically based thermodynamic model to predict the distribution coefficients have been developed for the Cu-LIX 65N and Cu-KELEX 100 systems. The predictive model makes use of the aqueous phase cupric sulfate complex stoichiometric stability constant expressed as its degree of formation, their extraction mechanism, and the equilibrium constant for the extraction reaction. The distribution coefficient of copper can be predicted by the equationK _d =κ₁α₀ϕ², where ϕ is the ratio of the equilibrated organic concentration to the equilibrated hydrogen ion concentration in the aqueous phase,k ₁ is the effective equilibrium constant containing the quotient of the activity coefficients of the reacting species and α₀ is the degree of formation of the free cupric ion in the equilibrated aqueous phase. Excellent agreement between the experimental data and the predicted values was obtained.     

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.     

Study on separation of rare earth elements in complex system

The effect of the feed acidity, acetic acid concentration and rare earth concentration on the distribution ratio, separation coefficient and extraction capacity of light rare earth elements were studied in the P204(DEHPA)-HCl system and P507(HEH/EHP)-HCl system both containing acetic acid, respectively. The results showed that the distribution ratio and separation coefficient decreased with increasing of acidity, and increased with increasing of acetic acid concentration and rare earths concentration, and the extraction capacity increased with increasing of acetic acid concentration. When pH value of feed was 2.0, [RE]/[acetic acid] was 1:1 and rare earth concentration 0.35 mol/L, in P204(DEHPA)- HCl system with acetic acid, the maximum separation coefficient(β) reached to β_{Ce /La}=4.09, β_Pr/Ce=1.96 and β_Nd/Pr=1.53, and the separation ability of this extraction system was better than P507(DEHPA)-HCl system.     

Solvent extraction of gallium(III) from sodium hydroxide solution by alkylated hydroxyquinoline

The distribution equilibria and kinetics of the extraction of gallium(III) from sodium hydroxide solutions by 7-(5,5,7,7-tetramethyl-locten-3-yl)-8-hydroxyquinoline (Kelex 100, designated HQ in the following) in kerosene have been examined under various conditions. From the dependence of the distribution coefficient on the concentrations of aqueous hydroxide and Kelex 100 it is deduced that the extraction can be expressed as Ga(OH)⁻₄(a) + 3 HQ(o) ⇄ GaQ₃(a) + OH⁻(a) + 3 H₂ O(a). Furthermore, the kinetic results suggest that gallium(III) is taken up through the formation of either of two different activated species, Na⁺[Ga(OH)₃ ], OH⁻ and Na⁺ · Na⁺[Ga(OH)₃], depending on the concentration of sodium hydroxide in the aqueous phase.     

Purification of Cobalt Solutions from Manganese by Extraction with Mixture of Organic Acids

extraction on pH and composition of the aqueous phase, and concentration of extractants have been investigated. D2EHPA was shown to extract the metals, but monocarboxylic acids took part in extracting the complex formed by means of additional solvation.

Electronic adsorption spectra of extracts of cobalt and manganese di (2-ethylhexyl) phosphates in SMA show that there are mainly octahedral complexes in extracts. It confirms the formation of a mixed extracted complex in organic phase. In contrast to the systems with “inert” solvents, manganese oxidation by air does not occur due to stabilization of manganese (II) in octahedral complex. The conditions of purification of cobalt chloride and cobalt sulphate solutions from manganese were determined and tested on a pilot scale. According to the technological scheme the cobalt solution after purification from iron was purified from manganese by extraction with 0.6-0.8 M D2EHPA in a monocarboxylic acids (C₁-C₉ solution. Scrubbing of extracts from cobalt and stripping of manganese were conducted by hydrochloric or sulhpuric acids depending on the type of initial solution. Purified cobalt solution practically does not contain manganese and cobalt recovery was 99.5%. The suggested scheme of purification has been applied at the Norilsk Mining and Metallurgical plant for processing of manganese by-product.     

The extraction of Zinc(II) from sulphate and chloride solutions with kelex 100 and versatic 911 in kerosene

Zinc(II) is extracted from sulphate or chloride solutions by Kelex 100 (HX) in kerosene, comparable extraction taking place under more acid conditions from chloride media. The addition of Versatic 911 (HA) leads to synergistic enhancement of extraction; equilibrium studies with the mixed extractants indicate that a mixed complex of the form ZnX₂ · (HA)₂ is extracted, and infra-red spectra suggest that Versatic is present as a solvating agent. The effect of chloride ion concentration on extraction was examined, and tracer studies showed that chloride takes no part in the constitution of the extracted zinc complex.     

The extraction of Fe(III) from ammonium chloride solutions with capric acid

Extraction equilibria in the FeCl₃NH₄Clcapric acidCCl₄ system were investigated. Using slope analysis the results were interpreted in terms of the formation of the binuclear species [Fe(OH)R₂]₂ and [Fe(OH)₂R·HR]₂ in the organic phase. From calculations of the complex formation function and the experimental data it was shown that the effect of Fe(III) hydrolysis in the aqueous phase on metal extraction may be neglected.     

Ce~(4 ) Extraction Mechanism from RE Sulfate Solution Containing Fluorine with DEHPA

RE sulfate solutioncontaining fluorine is obtainedfrom bastnasite which is roasted inair and then leached with sulfuricacid. Solvent extraction of Ce4 with DEHPA in sulphonatingkerosene from the solution is investigated. It is found that fluorineion is extracted into organic phasewith Ce4 . The extraction mechanism is proposed by slope analysisand studying the influence ofaqueous acidity, fluorine concentration and DEHPA concentrationon CF- /cC4 in equilibrium organic phase.Ce~(4 ) Ext…     

Recovery of High Purity Y2O3 by Solvent Extraction Route Using Organo-Phosphorus Extractants

A rare earth concentrate assaying about 60% Y₂O₃, is generally obtained directly from Y rich minerals like xenotime or from monazite after preliminary fractionation of rare earths chloride as is practised currently at Indian Rare Earths Ltd.. Alwaye. Using this intermediate concentrate. SX process has been developed in our laboratory to purify Y (>99.9%) in presence of NH₄SCN. The process parameters for DEHPA and PC 88A systems have been optimised using a computer program in BASIC. The DEHPA flowsheet has been tested at bench-scale to produce several kilograms of 93% Y₂O₃. During these trials certain problems were faced due to high acidities. With PC 88A there were no problems and the flowsheet based on the solvent was confirmed at pilot-plant level. The solution containing 93% pure Y₂O₃, is purified further by another cycle of SX with 50% TBP in kerosene in presence of 1.0 M NH₄ SCN. The impurities are extracted leaving >99.9% pure Y₂O₃ in the aqueous phase. The process parameters optimised for obtaining >90% recovery of Y₂O₃ are described.     

The influence of the diluent on the extraction of iron(III) from aluminium sulphate solutions by the amine primene 81R sulphate

The extraction of iron(III) from aluminium sulphate solutions by the amine Primene 81R sulphate has been studied using 15 diluents of different types. The results are discussed in terms of the composition of the diluent and aggregation of the amine sulphate in solution, the dielectric constant and polar nature of the diluent, and interfacial tensions between aqueous media and amine sulphate solutions in the diluents. The best extraction results were obtained with diluents such as toluene and benzene.