Extraction of platinum-group metals from chloride solutions by salts of quaternary ammonium bases and binary extractants

Literature data are given on the extraction of platinum-group metals from hydrochloric acid solutions by salts of quaternary ammonium bases, as well as the authors’ data on the binary extraction of platinum metals from chloride solutions. The possibility is shown of using binary extractants based on quaternary ammonium bases (QABs) for efficient extraction and separation of platinum-group metals, as well as for simple reextraction of these metals from organic phases by water, contrary to the initial anion-exchange systems with QAB chlorides.     

Solvent Extraction of Weak Acids in Binary Extractant Systems

The interphase distribution of weak acids in systems involving salts of quaternary ammonium bases with organic acids (binary extractants) has been analyzed. Significant differences in the extraction depending on the composition of the aqueous and organic phases for weak acids compared with that for strong acids in binary extractant systems have been shown. The difference in the extraction of weak acids with binary extractants compared with neutral extractants has been also revealed. The experimental data were interpreted by two variants of distribution processes, when two extracted species are formed (R₄NX and HA) and for the case of forming extracted species with strong H-bonds (R₄NX · HA). The least square regression method showed that the proposed mechanisms well describe the extraction of monocarboxylic acids with the binary extractant (the smallest sum of squares of relative deviations was 0.025) at their low initial concentrations (<0.05 mol · L^?1). It was shown that the most effective extraction of monocarboxylic acids takes place from acidic solutions (at pH < 2) that indicates the possibility of their effective stripping from organic solutions with water.     

Interphase distribution of weak acids in systems with binary extractants

General dependences of interphase distribution of weak acids in systems containing binary extractants were studied. Substantial differences in the extraction dependences of the composition of the organic and aqueous phases were shown for weak acids compared to systems that contain strong acids and binary extractants, as well as weak acids and neutral extractants. The influence of hydrogen bonding between two extracted compounds was observed when low-molecular monocarboxylic acids were extracted with agents based on quaternary ammonium bases and organic hydroxy acids.     

Extraction of platinum and palladium from hydrochloric solutions by trioctymethylammonium dinonylnaphthalenesulfonate

We investigated the phase distribution of chloride complex platinum and palladium acids in the presence of the binary extracting agent trioctylmethylammonium dinonylnaphthalenesulfonate. During the extraction of H₂PtCl₆ and H₂PdCl₄, the distribution coefficients were found to decrease as long as the pH value was growing, in full accordance with the known general trend of binary extraction. In contrast to the extraction variant using quaternary ammonium bases with inorganic counterions, a binary system, which was based on dinonylnaphthalenesulfonic acid, could be used for the further aqueous reextraction of platinum metals from the organic phase because of the higher thermodynamic stability of the binary reagent in the two-phase system.     

Extraction of monocarboxylic acids by trioctylmethylammonium di(2-ethylhexyl)phosphate

The laws of the interphase distribution of saturated monocarboxylic acids in the system with the binary extracanttrioctylmethylammonium di(2-ethylhexyl)phosphate were studied. The extraction isoherms of monocarboxylic acids by 0.2 M solution of trioctylmethylammonium di(2-ethylhexyl)phosphate in toluene were obtained, and it was shown that they are rectilinear. The extractibility of acids decreases in the following order: butyric > propionic > formic> acetic> lactic, which corresponds to the anion-exchange order for the initial salts of quaternary ammonium bases. The mechanisms of the distribution of monocarboxylic acids were proposed. The study of the extraction of acetic and propionic acids as a function of the acidity of the aqueous phase revealed that the acids are extracted most efficiently from acid solutions. A decrease in the distribution coefficients with an increasing pH of the aqueous phase is observed, which indicates the possibility of efficient reextraction of monocarboxylic acids from organic solutions.     

INFLUENCE OF THE AMINE NATURE ON THE COMPOSITION OF PALLADIUM COMPLEXES IN SOLVENT EXTRACTION SYSTEMS

ABSTRACT

The extraction of palladium chloro complexes by di-n-octylamine and diamines of various structure as function of the composition of the aqueous and organic phases has been studied. The compositions of the extracted species are indicated and the mechanisms of their distribution are described. It was shown that from 1 to 3 M HC1 solutions. complexes such as (R₂NH₂)₂PdCl₄ solvated by molecules of dioctvlamine chloride are extracted. With increasing the initial concentrations of palladium or decreasing acidity of the aqueous phase, a direct coordination takes place, first of one and then two molecules of amine to atom of palladium with the formation of extracted compounds such as HC1 solutions by salts of amines, diamines and QAB ionic associates such as (AmH)₂PdCl₄, (AmH)₂)PdCl₄ and (R₄N)₂PdCl₄, respectively, are recovered into the organic phase. In systems containing trioctylamine, tetraoctylalkylenediamines (n = 4, 6) and QAB. ionic associates containing the dimeric complex anion, Pd₂Cl₆ ^2-, are also formed. When primary (n-octylaniline - OA) and secondary amines are used as extractants the formation of dimeric species in the organic phase is not observed.

The extraction of palladium from weakly acidic and neutral solutions can proceed through a combination of anion-exchange and coordination mechanisms with the formation of (AmH)[Pd(Am)Cl₃] in systems with primary and secondary amines, and through a coordination mechanism with the formation of complexes such as Pd(Am)₂Cl₂ in systems with primary, secondary and tertiary amines. When palladium is extracted by diamines with a short hydrocarbon chain (n=2) the formation of coordination compounds also takes place.     

Liquid-liquid distribution of metals in systems with trioctylmethylammonium dinonyl naphthalenesulfonate

The extraction of copper, nickel, cobalt, zinc, and iron chlorides by the solutions of trioctylmethylammonium dinonyl naphthalenesulfonate in toluene depending on the acidity of aqueous phase was studied. In the range of relatively high acidity (from 3 to 1 M HCl), an increase in the D _M values is observed with a growth in the concentration of hydrogen ions in aqueous phase; that corresponds to the principles of the binary extraction of chloro complex metal-containing acids. With a decrease in the acidity of aqueous phase, an increase in the distribution coefficients of metals is observed due to the change in the extraction mechanism and increase in the fraction of the complexes extracted as metal dinonyl naphthalenesulfonates. In the acidic range, the extractability of metals is mainly determined by the stability of complex metal-containing anions and qualitatively corresponds to the following order: Fe(III) > Cu(II) > Co(II) > Ni(II).     

Extraction of monocarboxylic acids with binary extracting agents based on amines and quaternary ammonium bases

The distribution of monocarboxylic acids is reported for extraction systems with binary extracting agents, namely, amine and quaternary ammonium base (QAB) salts of organic acids with widely varied acid dissociation constants (pK _a 1.5–10). Monocarboxylic acid extractability orders have been obtained for systems with binary extracting agents based on trioctylmethylammonium and trioctylammonium (TOA). The best extractability is shown by acids with long hydrocarbon radicals (butyric and caproic acids). Lactic acid is the least extractable. Extractive power orders have been obtained for QAB- and TOA-based binary extracting agents. For monocarboxylic acid extraction with QAB salts, the extractive power order correlates with the acid dissociation constants of the parent organic acids: trioctylmethylammonium p-tert-butylphenolate ≫ caprylate > dialkylphosphinate > dialkylmonothiophosphinate > dialkylphosphate > dinonylnaphthalene sulfonate > dialkyldithiophosphinate. The extractive power of the QAB-based binary extracting agents is much higher than that of the TOA salts.     

Back extraction of platinum metals from liquid membranes in an electric field

A new method for back extraction of platinum metals from the salts of tertiary amines and quaternary onium bases in the organic phase is proposed. This method allows the back extraction of platinum metals into diluted solutions of mineral acids over one stage. The method involves the passing of direct current through a system in which the extract containing a platinum metal is a liquid membrane. This method allows a practically complete back extraction of the anions PtCl₆ ^2-, RuNOCl₅ ^2- and Ru₂OCl₁₀ ^4- (the latter passes into the aqueous phase without breaking the dimer anion). It was found that when PtCl₆ ^2-, PdCl₄ ^2- and Ru₂OCl₁₀ ^4- are in a liquid membrane based on Oct₃NHCl in 1.2-dichloroethane, under the action of an electric field all these anions are transferred into aqueous 1 M HCl (E > 85%). To provide maximum back extraction of platinum metal anions, it is necessary to use small concentrations of extractants in 1.2-dichloroethane (0.1 M for Oct₃NHCl and 0.03–0.04 M both for Oct₄NCl and Ph₄PCl) over the period of the back extraction. Cyclic voltametry has demonstrated the determining role of chloroions in current transport through the interface of phases I and II.     

New binary extractants and prospects of their application

The distribution of chlorides and nitrates of lanthanides from aqueous solutions has been investigated in the absence of a salting out agent using a new binary extractant, methyl trioctyl ammonium dialkyl phosphinate compared with methyl trioctyl ammonium dialkyl phosphate. Isotherms of the extraction of lanthanides have ben obtained. The extraction stoichiometry of these metals in systems with binary extractants is determined. It has been found that, in the case of the extraction of nitrates of lanthanides by methyl trioctyl ammonium dialkyl phosphate and dialkyl phosphinate, extractable compounds of varying composition are formed. The extraction and separation of lanthanide chlorides by the conventional counter-current scheme and by the scheme based on the technology of free supported liquid membranes (FSLMs) have been experimentally and computationally investigated. It has been found that, when using the FSLM scheme, an increase in the degree of extraction and separation of lanthanides is observed.     

Extraction of Lithium Using TBP and the Noncoordinating Cation Exchanger Tetraphenylborate: Principles of Selectivity from Sodium and Higher-Valent Cations

Extraction of lithium, calcium, and some other metal cations using tetraphenylborate/tributyl phosphate mixtures has been studied. The possibility of a qualitative change in the cation exchange extraction series towards the preferential recovery of lowly-charged (singly-charged) metal cations was shown for these systems. A change in the separation factors for singly- over multiply-charged cations in this system, compared to the known commercially available extractants such as alkylphosphoric, carboxylic, and other organic acids, is several orders of magnitude and increases when passing from doubly- to triply-charged metal cations, reaching, for example, values of 10³ and more for the lithium/yttrium couple. It was assumed that the change in the extraction series was caused by the instability of the salts of the multiply-charged metal cations compared to that for the singly-charged cations due to the ionic character of the bond with the extracted metals and structural problems caused by the large volume of the tetraphenylborate anion. The investigated system can serve as a model for the development of a new class of extractants having a higher selectivity for singly-charged metal cations, in particular, for lithium.     

EXTRACTION OF LIGHT LANTHANIDE NITRATES BY TRI-n-BUTYL PHOSPHATE

The distribution of La, Pr, Nd, Eu, Gd and Tb nitrates between water and tributyl phosphate was investigated over a broad range of concentrations. It has been found that the distribution constant varies only slightly with the lanthanide atomic number, whereas the activity coefficients of the salts in concentrated organic solutions change considerably with both the lanthanide atomic number and concentration. Distribution ratios and separation factors for a number of binary mixtures were determined as a function of the composition at constant total concentration in each phase.     

脱芳复合萃取剂的研究进展

复合萃取剂包括传统复合溶剂和新型复合溶剂。前者是有机溶剂与有机溶剂或无机盐的复配,后者则是不同种类的离子液体复配,它们不仅具有对芳烃的溶解性好、选择性高的优点,而且萃取后,萃余油的收率相对较高,已经成为继单一萃取剂用于油品（石脑油、重整汽油和模拟油等）脱芳烃研究之后又一新的研究热点。本文综述了国内外脱芳烃复合萃取剂的研究进展,重点介绍了两类复合萃取剂（萃取剂与醇类、胺类溶剂或无机盐复配和离子液体复配）在油品萃取脱芳烃中的应用;根据复合萃取剂中助萃取剂的种类不同,对用于萃取脱芳烃的复合萃取剂进行了分类总结;介绍了不同种类的萃取剂复配与不同种类的离子液体复配的研究进展;最后指出复合萃取剂在分离芳烃应用中具有选择性高、分配系数高、操作工艺简单有效且成本低廉等优点,是工业上萃取脱芳烃今后的发展趋势。     

Extraction of uranyl nitrate with a binary extractant based on di(2,4,4-trimethylpentyl)phosphinic acid

The extraction of uranyl nitrate with methyltrioctylammomium di(2,4,4-trimethylpentyl)phosphinate is compared to uranyl nitrate extraction with constituent cation-and anion-exchange extracting agents at various compositions of aqueous and organic phases. In UO₂(NO₃)₂ extraction with quaternary ammonium nitrate and dialkylphosphinic acid solutions in toluene, the compounds (R₄N)₂UO₂(NO₃)₄ and UO₂A₂, respectively, are formed in the organic phase. The binary extraction of uranyl nitrate is characterized by larger distribution ratios than extraction with the initial quaternary ammonium nitrate. Under saturation conditions, the capacity of the binary extractant is two times higher than the capacity of the anion-exchange extractant at the same concentration. Uranyl nitrate extraction with a binary extractant can yield, in the organic phase, complexes in which the uranyl ion either forms a salt with the anion of the organic acid or is incorporated into an extractable complex anion, depending on its thermodynamic stability in the heterogeneous system.     

METAL-SOLVATE STOICHIOMETRY EVALUATION IN EXTRACTIONS BY SOLVATING TYPE NEUTRAL EXTRACTANTS-A NOVEL APPROACH

ABSTRACT

This paper reports a novel approach for the evaluation of the stoichiometry of the metal-solvate formed during the macro level extraction of metal salts from neutral media by neutral solvating type extractants. This method involves the measurement of the distribution coefficient for the extraction of the metal ion from neutral medium as a function of the concentration of the metal ion in the organic phase, and finding the organic loading at which the distribution coefficient is a maximum. This new approach has been verified by a study of the uranyl nitrate extraction by tri-n-butyl phosphate and di-n-butyl octanamide, as well as cerium(lll) nitrate extraction by TBP. In all these cases the solvation number measured by the new method was in agreement with the value reported by other techniques. The method was extended to a study of the thorium nitrate extraction by trialkyl phosphates, which yielded a solvation number of 3 for all the trialkyl phosphates studied.     

Selective Extraction of Scandium by a Long Alkyl Chain Carboxylic Acid/Organophosphonic Ester Binary Extractant

ABSTRACT

The organophosphorus extractant 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A) is widely used for solvent extraction of rare earth elements in an acidic leaching solution, but stripping of the loaded metals is difficult because of the high affinity between the metals and the extractant. Adding 100 times the concentration of neodecanoic acid (Versatic 10) to the extractant solution reduces the extraction ability for scandium (Sc) and enables quantitative stripping of the loaded Sc with a mild acidic solution, such as a 1 M mineral acid. The loading capacity is dependent on the PC88A concentration, so PC88A is the main species responsible for Sc extraction in the binary mixture. Nuclear magnetic resonance spectroscopy (NMR) of the organic phases suggests a potential interaction between the mixed extractants through the change in the hydrogen bonding. This causes an antagonistic effect and facilitates efficient Sc stripping from the extractant solution, so this method could be used for scandium recovery in industry.     

Extraction Processes for Bioproduct Separation

Abstract

The three-phase extraction process, a modification of reactive extraction, has been investigated for its applicability in the separation of organic acids from fermentation broth. It has been compared with reactive extraction, liquid membrane permeation, and supercritical fluid extraction.

These processes are based on the use of amine extractants, which have to be dissolved in nonpolar solvents, for the extraction of carboxylic acids, hydroxycarboxylic acids, and aminocarboxylic acids.

This paper considers the comparison of the above-mentioned processes. Furthermore, the extractability of acids from synthetic aqueous solutions and fermented broths has been compared. Principal consideration has been paid to the extraction of lactic acid, gluconic acid, citric acid, and L-leucine.     

New Sorbents for Metal Salts based on Cation Exchange Extractants and Anion Exchange Resins: Their Preparation and Properties

Preparation and properties of binary sorbents containing a salt of cation exchange organic extractant in the matrix of a strongly basic anion exchanger were studied. Analysis of isotherms of exchange of chloride ions for dialkyldithiophosphate ions in the systems of various anion exchangers led to the conclusion that the stability of the binary sorbents depends on the amount of free water in the sorbent matrix. To improve the stability, it was proposed to use low cross-linked anion exchange resins or to use cation exchange extractants of moderate molecular volume. On the example of anion exchanger ММ-22x6.5 in the dibutyldithiophosphate form, it was shown that the binary sorbents efficiently recover chlorides of non-ferrous metals. The recovery increases in the series Ca²⁺<<Ni²⁺<Zn²⁺<<Cu²⁺. Because, in the systems studied, the anions are recovered together with cations, this leads to an increase in metal recovery in the presence of salting-out agents, and allows the desorbtion of the salts with water or with solutions of complexing agents. The binary sorbents offer good prospects for the recovery and separation of metal salts.     

SXLSQA,A Computer Program for Including Both Complex Formation and Activity Effects in the Interpretation of Solvent Extraction Data

Abstract

A previously reported computer program for the interpretation of solvent extraction data in systems that can include two extractants, one acidic and one neutral, has been extended to treat the effects of: (1) variation of activity coefficients of solute species and of water activity in the aqueous phase, calculated by the Pitzer treatment; (2) variation of activity coefficients of solute species in the organic phase, calculated by the Hildebrand-Scott treatment; and (3) product species formed in the aqueous phase. The interaction parameters of the Pitzer treatment and the solubility parameters of the Hildebrand-Scott treatment can be refined along with the formation constants of various assumed product species to fit the data. Like its predecessor, the program is capable of fitting simultaneously a variety of data, including the distribution of an extractable cation, anion, or water, as well as spectra, vapor pressure, or heats of mixing for the organic phase. Use of the program is illustrated by modeling the extraction of water and HNO₃ from aqueous nitric acid by di(2-ethylhexyl)sulfoxide in dodecane.     

Separation of Cadmium,Cobalt, and Nickel by Solvent Extraction using the Nickel Salts of the Extractants

A new solvent‐extraction process for the separation of cadmium, cobalt, and nickel in sulphate solutions coming from the hydrometallurgical processing of spent Ni‐Cd batteries is proposed. The main innovation is to use nickel salts of the extractants, thus avoiding external pH control in the extraction operation. The extractants are first loaded with nickel in conditioning steps, using a neutralizer for pH control, and afterwards contacted with the aqueous processing solutions for extraction of interested metals with no further need of neutralization. This process is an alternative to the usual approach, which uses the sodium or ammonium salts of the extractants, avoiding introducing these cations in the process stream. Using this approach, the extraction of cadmium with nickel salt of 1 M DEHPA was performed at resulting pH values of 3.8–4.3 producing an organic phase loaded with 35 g/L Cd. Cobalt extraction with the nickel salt of Cyanex 272 was further achieved at resulting pH of 5.1–5.7 obtaining a organic loaded with 6.5 g/L Co.