Thermodynamics and mechanism of vanadium(IV) extraction from sulphate medium with D2EHPA,EHEHPA and CYANEX 272 in kerosene

Extraction of vanadium（IV） from sulphate acid solution was studied using organophosphorous-based extractants D2EHPA, EHEHPA and CYANEX 272 in kerosene. The different parameters affecting the extraction of vanadium（IV） under equilibrium conditions were separately investigated to elucidate the stoichiometry of the extracted species. The distribution ratio of vanadium increased with increasing equilibrium pH of the aqueous phase, concentration of the extractants and temperature. D2EHPA was found to be a stronger extractant, having greater pH functionality than EHEHPA and CYANEX 272. Extraction of vanadium（IV） by these organophosphorous-based extractants involved cation exchange mechanism, and the extracted species appear to be VOR2（HR）2 in the low equilibrium pH and VOR2 in the higher equilibrium pH, where HR refers to the three acidic extractants.

Solvent extraction of copper and zinc from bioleaching solutions with LIX984 and D2EHPA

The solvent extraction of copper and zinc from the bioleaching solutions of low-grade sulfide ores with LIX984 and D2EHPA was investigated. The influences of extractant content, aqueous pH value, phase ratio and (equilibration) time on metals extraction were studied. The results show that LIX984 has a higher selectivity for copper than for iron, zinc and other metals, and has the copper extraction rate above 97%, while the zinc and iron extraction rate is less than 1.6% respectively. Zinc extraction is carried out following the copper extraction from the raffinate. The zinc extraction with di(2-ethylhexyl) phosphoric acid(D2EHPA) is low due to its poor cation exchange. A sodium salt of D2EHPA is used and the zinc extraction rate is enhanced to above 98%. Though iron (Ⅲ) is strongly extracted before the extraction of zinc by D2EHPA, it is difficult to strip iron from the organic phase by sulfuric acid. The zinc stripping rate is above 99% with 100g/L sulfuric acid, while that of iron is 0.16%. Hence, the separation of zinc from iron can be achieved by the selective stripping.

Enhanced extraction of scandium and inhibiting of iron from acid leaching solution of red mud by D2EHPA and sodium chloride

D2EHPA(P204),tri-butyl-phosphate(TBP)and sodium chloride(NaCl)were attractive for selective extraction of scandium from acid leaching solution of red mud.The extraction parameters of P204 concentration(X_(P204)),NaCl concentration(C_(NaCl)),pH value,reaction time,stirring speed and O/A were investigated to extract scandium and separate iron from the acid leaching solution.The extraction mechanism was analyzed by Fourier transform infrared spectroscopy(FT-IR)and thermodynamic theory.The single-stage extraction efficiency of scandium,iron andβ(Sc/Fe)were 99.1%,9.4%and 1061.2,respectively,with C_(NaCl) of 75 g/L and XP204 of 0.75 at solution pH value of 1.2 and stirring speed of 200 r/min for 6 min,in which a good separation effect of scandium and iron was obtained.The vibration absorption peak Sc─O was contributed to the extraction of scandium with P204.The complex[FeCln]^(3−n) existed in the solution with adding NaCl into the acid leaching solution.The value of n was higher and the valence state of the complex[FeCln]^(3−n) was lower with an increase of chloride concentration,which restricts the extraction efficiency of iron with P204.The extraction of three stages in the counter-current simulation experiments was carried out according to the McCabe-Thiele diagram.Gibbs free energy change(ΔG)of−5.93 kJ/mol,enthalpy change(ΔH)of 23.45 kJ/mol and entropy change(ΔH)of 98.54 J/(mol·K)were obtained in the solvent extraction proces,which indicate that the extraction reaction is easily spontaneous and endothermic and a proper increase of temperature is conducive to the extraction of scandium.

Experimental Design in Solvent Extraction: A Study for Divalent Metals Separation in D2EHPA/Isoparaffin System

The solvent extraction process combined with tools of experimental design assists in developing procedures for separation and purification of elements or mineral compounds with high purity. In this work the technique was used to replace the traditional methods for the collection of basic information required for the development of a circuit of solvent extraction. According to the literature, several factors may influence the extraction of divalent metals by D2EHPA in sulfate media, among which the concentration of metals in solution. The objective was to study the variables affecting the separation process Mn/Ni/Co/Cu, such as the aqueous/organic (A/O), contact time, concentrations of the divalent metals in sulfuric medium, pH and solvent concentration. An investigation into the variables that control the process was done using a “cube + star” experimental design, with central point. The results demonstrate it is possible to obtain of a satisfactory mathematical model that describes the process.

Solvent extraction of scandium from leaching solution of red mud roasted with ammonium sulfate using D2EHPA/TBP

Red mud is an important secondary resource for scandium production.The red mud leaching solution containing scandium in this study was derived from environmentally friendly ammonium sulfate roasting and water leaching process.A synergistic extraction with a mixture of di(2-ethylhexyl)phosphate acid(D2EHPA)and tributyl phosphate(TBP)for recovery of scandium from red mud leaching solution is proposed.The effects of D2EHPA concentration,H_(2)SO_(4)concentration,rare earth elements,dosage of TBP,phase ratio(A/O),contact time and H_(2)O_(2)concentration on scandium extraction were investigated.The results show that more than 99%scandium is extracted under the optimal conditions while Fe,Al,Ti,Ca and rare earth elements(Ce,Y,La,Nd,Er,etc.)are hardly extracted.The stripping efficiency of Sc reaches above 92.37%under the optimal stripping conditions of 5 mol/L NaOH with an A/O of 1 at 90℃for 30 min.The proposed technology could provide an effective method for extraction of scandium from red mud leaching solution.

Mechanism of extractant loss in solvent extraction process (Ⅰ)——Transfer of saponified D2EHPA from organic phase to aqueous phase and its aggregation behaviour

The phenomenon of the loss of saponified D2EHPA(di(2-ethylhexyl)phosphoric acid,HA)from organic phase to aqueous phase and its aggregation behaviour were studied with FT-IR and DLS(dynamic light scattering)techniques based on the fact that saponified extractant can form reversed micelles orw/o microemulsions in n-heptane,a non-polar diluent.The results indicate that "normal rnioelles" or o/wmicroemulsions are formed from acidic extractant and its sodium salt in aqueous phase,and the micelle ormicroemulsion drop has a non-polar core which can solubilize nheptane,so the equilibrated aqueous phasecontaining extractant is a complex fluid rather than a "real solution".Therefore,the aqueous aggregate for-mation leads to the extractant loss in solvent extraction process.Strong electrolytes can prevent or lessen theextractant loss.The results of this paper provide a theoretical possibility for solving the problem ofextractant and solvent loss in liquid-liquid extraction industry.

Extraction and stripping of Cu and Ni from synthetic and industrial solutions of Sarcheshmeh Copper Mine containing Cu, Ni, Fe and Zn ions

The extraction and stripping of Cu and Ni ions from synthetic and industrial solutions of Sarcheshmeh Copper Mine containing Cu(770 mg/L),Ni(3200 mg/L),Fe(800 mg/L)and Zn(200 mg/L)were comprehensively investigated using D2 EHPA,LIX 984,Cyanex 302,Chemorex CP 150 and Acorga 5774 diluted in kerosene.The influential parameters such as mixing speed and time,concentration of extractant,p H and temperature were considered in extraction stage.Furthermore,stripping of Cu and Ni was examined using different inorganic and organic acids(sulfuric,hydrochloric,nitric and citric acids)with different concentrations.The results indicated that the highest extractions of Cu and Ni occurred within 3 min,with the mixing speed of 500 r/min,28℃and A/O ratio of 1:1.Moreover,Cu was extracted by LIX 984 at the concentration of 10%(v/v),whereas Ni was extracted by Cyanex 302 at the concentration of 30%(v/v),efficiently.The optimal p H for Cu and Ni extraction is in ranges of 2-3 and 4-5,respectively.Cu and Ni were selectively extracted with the recoveries of 85%,93%and 77%,82%from synthetic and industrial solutions containing Ni,Cu,Zn and Fe ions,respectively.The results of optimal condition showed that 96%of Ni and 93%of Cu were stripped from the synthetic and industrial solutions.Finally,four elements Zn,Fe,Cu and Ni were extracted in three stages with D2 EHPA,LIX 984 and Cyanex 302 extractants respectively with the least impurities.

Separation of hafnium from zirconium in hydrochloric acid solution with di(2-ethylhexyl)phosphoric acid by solvent extraction

The preparation of nuclear-grade zirconium and hafnium is very important for nuclear power. The separation of hafnium from zirconium in a hydrochloric acid solution by solvent extraction was investigated with di(2-ethylhexyl)phosphoric acid(D2 EHPA). The effects of hydrochloric acid concentration, extractant concentration,diluents, and temperature on the distribution coefficient of hafnium and zirconium were studied. The species extracted were ZrOA_2·2 HA and HfOA_2-2 HA. In this process, the separation factors varied with different diluents and followed the order octane > hexane > toluene > chloroform.A high separation factor value of 4.16 was obtained under the conditions of a solution containing 0.05 mol/L HCl and0.01 mol/L D2 EHPA for the separation of hafnium from zirconium. The extraction reaction was endothermic.

Solvent extraction of zinc from zinc sulfate solution

The extraction of zinc from zinc sulfate solution was investigated, using 20% saponified D2EHPA as an extractam and 260^# sulfonate kerosene as a diluent. The solution was stirred for 8 min at phase ratio （Vσ/Va） of 1.0：1.0, initial pH of 2.0 and stirring speed of 200 r/min. The results show that 75% zinc can be extracted from the zinc sulfate solution when the concentration of zinc is 18.7 g/L after being settled for 10 min. 88.60% zinc can be stripped by 196 g/L sulfuric acid, and zinc ion can be separated from ferric ion.

Distribution Behavior of Aminobenzoic Acid by Extraction with Di(2-ethylhexyl)phosphoric Acid

A series of extraction equilibrium experiments for aminobenzoic acid with di(2-ethylhexyl)phosphoric acid (D2EHPA) dissolved in n-octane or 1-octanol was carried out. The effects of aminobenzoic acid concentration,D2EHPA concentration and pH on the distribution ratio were discussed in detail. The infrared spectra of the organic phase loaded with solute illustrated that pH had little effect on the structure of the complex formed. There proceed ion association and cation-exchange.reaction in the extraction. An expression of the equilibrium distribution was proposed.

Thermodynamical and catalytic aspects of zinc separation from aqueous solution

The present research work examines extraction mechanism of zinc by D2 EHPA(Di-2-ethyl hexyl phosphoric acid) and comprehensively studies the main effective parameters on the process. Results of thermodynamic experiments showed that zinc extraction by D2 EHPA was endothermic and spontaneous, and thermodynamic parameters including entropy and enthalpy were + 27.37 J·mol^(-1)·K^(-1) and 25.21 kJ·mol^(-1), respectively.Gibbs free energy was varied between-7.21 kJ·mol^(-1) and-8.41 kJ·mol^(-1) with the variation of temperature from 20 °C to 70 °C. Solution ionic strength was increased by addition of potassium and lithium sulfate solution while addition of calcium sulfate decreased ionic strength whereby zinc extraction efficiency was also decreased.TBP showed positive synergism at concentration of 5%(v/v) and negative synergism effect at concentrations of2% and 10%. Simultaneous addition of both TBP and salt caused extraction efficiency to drop significantly and lower both TBP and ionic strength efficiency. Results showed that a continuous addition of TBP tends to effectively improve the zinc extraction efficiency. Experiments in the presence of catalyst Ni-Raney demonstrated that zinc extraction kinetic increases remarkably and due to easy recycling of the catalyst, we can propose a novel idea in solvent extraction field.

Solvent extraction of molybdenum from acidic leach solution of Ni–Mo ore

A P204 （D2EHPA） diluted with sulfonated kerosene was used for the selective extraction of molybdenum from an acidic Ni-Mo ore leach solution that was reduced using sodium thiosulfate. The results indicate that P204 （D2EHPA） is an effective extractant for the extraction of molybdenum. The extraction of Mo is more than 90 % at pH of 0.5, contact time of 10 min, and organic-to- aqueous phase （O/A） ratio of 1：1 with 10 vol% P204 （D2EHPA）. Molybdenum in the loaded organic phase can be effectively stripped with ammonium acid carbonate solution, and the stripping of molybdenum with 60 g.L-1 ammonium acid carbonate solution is 94.67 % at O/A ratio of 2：1 and contact time of 10 min.