N. A. Grigorieva

Nickel(II) Extraction from Sulphate Media with Bis (2,4,4‐Trimethylpentyl)Dithiophosphinic Acid Dissolved in Nonane

The paper presents data on nickel(II) extraction from sulphate solutions with nonane‐diluted bis(2,4,4‐trimethylpentyl)dithiophosphinic acid (HR). An IR spectroscopy method is used to examine the state of HR in nonane, and it was shown to exist as a monomer up to a concentration of 0.1 M. With a further increase in concentration, the acid forms associated species. The value of the concentration of the monomeric form is determined as a function of the total HR concentration in nonane in the range of 0.0–1.0 M. Based on the comparative analysis of the extraction equilibrium data together with information from the visible and IR absorption spectra of the nickel extract, the configuration of the nickel(II) complex in the organic phase was determined to be a low‐spin, square‐planar complex. The complex composition was found to correspond to the formula NiR2. The complex is hydrated, with the water very likely being bonded in the outer coordination sphere.

Investigation of the State of Bis(2,4,4-trimethylpentyl)dithiophosphinic Acid in Nonane in the Presence of Electron-Donor Additives

Abstract An IR-spectroscopy method is used to examine the state of nonane diluted bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HR) in the presence of various electron-donor additives (L). Trioctyl amine (TOA), n-octanol, trioctylphosphine oxide (TOPO), tributylphosphate (TBP), and triisobutylphosphine sulfide (TIBPS) were used as additives. The formation of hydrogen bonded complexes (H-complexes) via proton transfer and a [TOAH+][R−] ion pair was shown to occur in the system containing HR and TOA. For the other additives, except n-octanol, during the formation of the H-complexes, hydrogen bonding without proton transfer takes place. In the HR and n-octanol mixture H-complexes having a structure in which the acid exhibits both proton and electron-donor properties are formed. The concentrations of the monomers (CHR ) and the activity coefficients for the dithiophosphinic acid (γ HR(tot) ) in the presence of the additives were calculated. It was shown that CHR and γ HR(tot) depend essentially on the type of additive and that their values decrease when passing from n-octanol to TOA. The strength of the interaction between HR and L decreases in the series TOA > TOPO > TBP > TIBPS > n-octanol. This series coincides with the basicity series of the additives. An antagonistic effect takes place when zinc is extracted with the HR and L mixture, where L is the trialkyl amine (TAA), the trialkyl phosphine oxide (TAPO), TBP, and n-octanol. A decrease in extraction is observed in the series TAA > TAPO > TBP > n-octanol. This series coincides with the series for decreasing HR activity in the presence of additives. Thus a decrease in the extractant activity resulting from the interaction between HR and L is the determinant factor during zinc extraction with bis(2,4,4-trimethylpentyl)dithiophosphinic acid in the presence of the electron-donor additives.

Cobalt and Nickel Recovery from Sulfate Media Containing Calcium, Manganese, and Magnesium with a Mixture of CYANEX 301 and a Trialkylamine

Abstract Data are presented on the solvent extraction of nickel and cobalt from sulfate solutions imitating the composition of partially neutralized liquors from the leaching of oxidized nickel ores using mixtures of 0.4 M CYANEX 301 (HR) with 0.4–0.5 M C7–C9 fraction of a trialkyl amine (R′3N) as the extractant. Nickel and cobalt are efficiently extracted in the pH range 6.2–6.5 and separated from Mn, Mg, and Ca in the extraction step. The separation factors for Co and Ni are high (102–103). Due to the formation of the stable adduct [R′3NH]+[R]− between the extractant components, nickel and cobalt can be stoichiometrically stripped with H2SO4 (1.0–2.0 M), allowing the production of concentrated solutions (> 100 g/L of total Co and Ni). The nickel strip liquors contain only a small amount of free acid (pH 1.5–2.0) after purification from cobalt, so they can be further processed using traditional technologies. A proposed flowsheet for nickel and cobalt recovery from such leach liquors has the advantages of ease of production of concentrated nickel and cobalt strip liquors in sulfate media and the stability of the extractant and strip liquor to oxidation by air or oxygen compared to other variants of CYANEX 301 applications.

Investigation of the State of Bis(2,4,4‐Trimethylpentyl)dithiophosphinic Acid in Nonane and Toluene Solutions

An IR spectroscopy method is used to examine the state of nonane and toluene diluted bis(2,4,4‐trimethylpentyl)dithiophosphinic acid (HR) in the concentration range of 0.025–1.0 M. It was found that in contrast to the “inert” solvent nonane, in which marked self‐association of the dithiophosphinic acid due to the formation of intermolecular SH…S hydrogen bonds begins at an HR concentration of ∼0.1 M, in the aromatic diluent toluene this process begins at HRtotal ⩾0.4 M. This result is explained by the interaction of the proton of the S‐H group of the dithiophosphinic acid with the π‐electron system of the toluene aromatic ring and the formation of SH…π hydrogen bonds, preventing the self‐association of the organic acid. The presence of the monomeric, dimeric, and tetrameric forms of the extractant in solution was shown to best describe the bis(2,4,4‐trimethylpentyl)dithiophosphinic acid‐nonane system. The formation constants of the dimers (K2 = 0.78 ± 0.07) and tetramers (K4 = 3.42 ± 0.26) have been calculated.

EXTRACTION OF INDIUM FROM SULFURIC ACID SOLUTIONS BY MIXTURES OF DI-(2-ETHYLHEXYL)PHOSPHORIC AND OCTANOIC ACIDS

ABSTRACT The extraction of indium from sulfuric acidic solutions by mixtures of di(2-ethylhexyl)phosphoric (D2EHPA, HR) and octanoic (HA) acids was studied. The state of D2EHPA in octanoic acid was investigated by IR-spectroscopy. It was shown that the nonideal behavior in this system occurs due to the partial dimerization of D2EHPA in organic phase. A strong antagonistic effect observed during the extraction of indium is caused by a HR–HA interaction at the expense of formation of intermolecular hydrogen bonds. Low indium concentrations and high excess of extracting agent, as well as application of “inert” diluents, result in the formation of In(HR2)3 compound in organic phase.

Redox Processes in the Organic Phase during Cobalt Extraction with the bis(2,4,4-trimethylpentyl)dithiophosphinic Acid and Trioctyl Phosphine Oxide Mixtures

The redox processes taking place in the organic phase during cobalt extraction with the mixtures of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HR, CYANEX 301) and trioctyl phosphine oxide (TOPO, CYANEX 921) have been studied. It was shown that CoR2 stabilization by the phosphine oxide prevents cobalt oxidation with air oxygen as well as with the disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (R–R). The introduction of TOPO into the extract containing Co(III) dithiophosphinate results in an increase in the rate of cobalt reduction to Co(II). Analysis of the interphase cobalt distribution as well as of the IR and electronic absorption spectra of the extracts showed that cobalt forms a pentacoordinated tetragonal-pyramidal high-spin complex with the dithiophosphinate ions and TOPO with a tetragonal-pyramidal geometry. The base of the pyramid is made up of sulfur atoms while an oxygen atom is on the top. The composition of the complex was found to be CoR2·TOPO. Examples of the possible use of the CYANEX 301 and trialkyl phosphine oxide (TAPO, CYANEX 923) mixtures in cobalt extraction technology are given.

Manganese extraction with mixtures of bis(2,4,4-trimethylpentyl)dithiophosphinic acid and trioctyl phosphine oxide

ABSTRACT It was shown that a strong synergistic effect (S ≈ 4000) takes place when extracting manganese (II) from sulfate solutions with mixtures of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (CYANEX 301) and trioctyl phosphine oxide (TOPO. The synergistic effect is caused by the formation of the mixed complex Mn-HR-TOPO. Analysis of the manganese partition between organic and aqueous phase as well as of the IR and electron paramagnetic resonance spectra of the extracts showed that manganese forms a hexacoordinated complex with the dithiophosphinate ions and TOPO with an octahedral geometry. The composition of the complex can be presented as MnR2∙2TOPO. Examples of the possible use of the CYANEX 301 and trialkyl phosphine oxide (TAPO, CYANEX 923) mixtures when processing manganese-containing liquors are given.

Silver Extraction from Hydrochloric Acid Solutions with the Disulfide of Bis(2,4,4-trimethylpentyl)Dithiophosphinic Acid

ABSTRACT Silver extraction from hydrochloric acid solutions with the disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid (L) in toluene is described in this work. Based on the analysis of the extraction data, it was concluded that silver extraction is due to the formation of the compound AgCl∙2L in the organic phase. An increase in the concentration of hydrochloric acid in the aqueous phase leads to a decrease in AgCl extraction because of the formation of non-extractable anionic complexes of silver. Solvent extraction efficiency decreases in the series octanol > decane > chloroform > toluene, which is due to the preferential solvation of the extracted complex by the solvent. A significant increase in the extraction of silver chloride with disulfide in the presence of octanol is caused by the strong interaction of the extracted compound and the alcohol, due to the chloride ion solvation by octanol. The possibility of using the disulfide for silver extraction from hydrochloric acid solutions containing metal impurities (Ni, Cu, Co, Zn, Fe (III), and Na) has been demonstrated. The degree of silver recovery in one stage was 98.62%, while the extractant showed high selectivity toward silver: the separation factors of silver over metal (βAg/Me) ranged from 9000 to 30,000. Almost complete silver stripping from the organic phase was achieved when using a mixture of thiourea and sulfuric acid solutions. The extraction characteristics of the disulfide are much better as compared to that of the well-known commercially available extractant triisobutylphosphine sulfide. The disulfide of bis(2,4,4-trimethylpentyl)dithiophosphinic acid can be used for efficient extraction of silver from industrial hydrochloric acid solutions of different origin.

Extraction of Non-Ferrous Metals and Iron with Systems based on Bis(2,4,4-Trimethylpentyl)Dithiophosphinic Acid (CYANEX 301), A Review

ABSTRACT Extraction is widely used in the hydrometallurgy of nonferrous metals. In addition to such well-known extractants as oxygen-containing organophosphorus or monocarboxylic acids, thio-substituted organophosphorus acids in particular, the commercially available extractant CYANEX 301, the active component of which is bis(2,4,4-trimethylpentyl)dithiophosphinic acid (HR), is of interest. This extractant is a sulfur-containing analogue of CYANEX 272 (bis(2,4,4-trimethylpentyl) phosphinic acid). In this review, the state of CYANEX 301 in various solvents in the absence and presence of electron-donor additives, the chemistry of the extraction processes of non-ferrous metals in the HR systems, the compositions of the extracted compounds, stability of the extractant in aggressive media, technological developments, and prospects for using CYANEX 301 in hydrometallurgy of non-ferrous metals are discussed.