Di-(2-ethylhexyl) Dithiophosphoric Acid Research Articles

Design of Multistage Extraction System for Simultaneous Separation of Silver and Gold from Thiourea Solutions

This study is focused on the extraction and recovery of gold and silver from thiourea acid leaching ore liquors. In a first step, extraction is performed using di(2-ethylhexyl)dithiophosphoric acid (D2EHDTPA). The extraction of gold and silver takes place simultaneously, allowing the removal of both metals in a single equipment under the same operational conditions. Each metal is then recovered by selective stripping, using NH4SCN/H2SO4 solutions to separate the silver from the D2EHDTPA. Such treatment is followed by a second stripping system, where a (NH4)2S2O3 solution is used to recover gold. A mathematical model is developed to represent all the operations in the process flowsheet. Through this model, it is predicted that, for properly selected operating conditions, recoveries higher than 99.9% for silver, gold and thiourea (to be recycled) can be obtained. The data predicted by the model has a good fit with previously reported experimental data. The proposed process is a more sustainable approach, in comparison with the traditional process involving cyanide, and has potential to be economically feasible.

Extraction of Cadmium from Phosphoric Acid Media by Di(2‐ethylhexyl) Dithiophosphoric Acid

Di(2‐ethylhexyl) dithiophosphoric acid (D2EHDTPA) was examined for cadmium removal from phosphoric acid solutions. High extraction performance was achieved. By means of slope and saturation methods, the stoichiometry of the complex was postulated. Both methods indicated the presence of anhydrous CdR2 as being the metallic extracted complex, HR denoting the D2EHDTPA molecule. The stripping of cadmium from the organic phase was ensured by aqueous solutions of HCl; quantitative stripping was achieved with either HCl (4 M) or an HCl‐NaCl mixture.

Thiosubstituted Organophosphorus Acids as Selective Extractants for Ag(I) from Acidic Thiourea Solutions

This paper deals with the solvent extraction of silver from thiourea leaching Ag ore liquors as an alternative to the traditional process involving cyanide. The investigation of the extraction mechanism of silver from acidic thiourea solution had not been clearly established to date. The extraction behavior of silver using di(2‐ethylhexyl)dithiophosphoric acid (D2EHDTPA) and di(2,4,4‐trimethylpentyl) thiophosphinic acid (CYANEX 302) was studied. The effect of various parameters such as concentrations of metal, mineral acid, thiourea, and extractant has been investigated. The extracted complexes have been identified through a slope method analysis as AgX(HX)5 for CYANEX 302 and AgX for D2EHDTPA, where HX denotes the extractant. Moreover, complete stripping was ensured with a mixture of NH4SCN and H2SO4. In addition we showed that a first step of extraction with D2EHPA or CYANEX 272 results in the preferential separation of Fe(III) from the Ag(I) leach solution.

Zn(II), Cd(II) and Cu(II) separation through organic–inorganic Hybrid Membranes containing di-(2-ethylhexyl) phosphoric acid or di-(2-ethylhexyl) dithiophosphoric acid as a carrier

A membrane process for metal recovery from aqueous solutions was studied. Metal ions diffused from the feed solution to the stripping phase through an Hybrid Membrane containing di-(2-ethylhexyl) phosphoric acid (D2EHPA) and/or di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier. Such membranes were prepared by a sol–gel route including cellulose triacetate and polysiloxanes. Transport behaviour was evaluated for both carriers under similar experimental conditions. The transport experiments reported here concerned transport at different cycles and selectivity towards different metal ions. Using D2EHPA the membrane provided a selective transport of zinc to the stripping compartment of the membrane cell, while copper and cadmium remained in the feed compartment. Whereas, using D2EHDTPA as carrier the transport rate increased and the selectivity profiles were inverted in relation with those of D2EHPA. With a mixture of both extracting agents it was observed an intermediate behaviour in selective transport, being possible to modulate it.

Mass transfer determining parameter in facilitated transport through di-(2-ethylhexyl) dithiophosphoric acid activated composite membranes

Activated composite membranes (ACMs) containing di-(2-ethylhexyl) dithiophosphoric acid (D2EHDTPA) as a carrier have been found to facilitate the transport and separation of several cations. This paper describes an approach to the chemical characterisation of the transport phenomena of Zn 2+, Cd 2+, Cu 2+, Ni 2+, Sn 2+ and In 3+ by an ACM. The selectivity of D2EHDTPA based ACM towards different metal ions is presented and discussed focusing in Zn 2+ and Cd 2+ transport and recovery. Selectivity demonstrates that zinc ions are removable from mixtures due to the different extraction strength of D2EHDTPA. Such selectivity is based on the differences of the dynamic behaviour of the metal ions transport. In addition, a correlation of the chemical behaviour of those ACM systems with the corresponding solvent extraction systems has been found.

Mutual Action of Di(2ethlhexyl)dithiophosphoric Acid and Trioctylamine and the Mechanism of Zinc Ion Extraction by them

The extraction of zinc by di-(2-ethylhexyl) -dithiophosphoric acid(D2EHDTPA) -trioctylamine (TOA) was investigated. Conductance titration and interfacial pressure measurement showed that when D2EHDTPA and TOA were mixed they reacted and formed an electrolyte of ionic pairs. The extraction of zinc by the electrolyte was of antisynergistic nature, and the reaction was Zn2+ + 2BHA((o)) --> ZnA(2(o)) + 2B((o)) + 2H(+) (subscript (o) stand for oil phase). The zinc extraction was an endothermic reaction, the heat of reaction was 130.1 kJ . mol(-1). Some phenomena of interface concerned were also discussed.

Determination of structural and electrical parameters for activated composite membranes containing di-(2-ethylhexyl)dithiophosphoric acid as carrier

The paper reports the results obtained on the physicochemical characterisation of activated composite membranes (ACMs). Membrane samples containing different concentrations of di-2-ethyl-hexyldithiophosphoric acid (DTPA) as a carrier were prepared and characterised by different analytical techniques. The amount of the carrier incorporated in ACM appears to be directly proportional to the concentration of carrier in the casting solution. Respective distribution dependencies can serve as calibration graphs applicable for pre-calculation of extractant concentration in the casting solution to manufacture an ACM with a given carrier content. The carrier distribution in the membrane was evaluated by X-ray microanalysis (EDS), which allowed us to determine that only a limited concentration of the carrier can be incorporated into the top polyamide membrane layer, resulting in redistribution of the excess of extractant along the polymeric structure of the membrane. These results also correlate with those obtained by impedance spectroscopy measurements. The equivalent circuits associated with the different membrane samples agree with a two-layer model for the ACM containing a high concentration of carrier ( C DTPA > 0.5 M), which allows for the location of a larger amount of carrier into the polyamide layer. The results obtained by the indicated techniques are in good agreement with each other, and provide for the structural characterisation of the membrane.

SOLVENT - IMPREGNATED RESINS VIA ACID-BASE INTERACTION OF POLY(4-VINYLPYRIDINE) RESIN AND DI(2-ETHYLHEXYL) DITHIOPHOSPHORIC ACID.

ABSTRACT The immobilization of a strong metal chelator di(2-ethylhexyl) dithiophosphoric acid (DEHTPA) on poly(4-vinylpyridine) macroporous resin (Reillex(tm) HP and Reillex(tm)425) has been investigated. DEHTPA (ligand) adsorption mechanism was proposed on the basis of the SIR morphology and IR spectrophotometry study. Analysis of the ligand distribution between the poly(4-vinylpyridine) support and the aqueous phase was performed using curve-fitting computerized method. Equilibrium constants characterizing the DEHTPA - pyridine group interaction have been evaluated. Pore volume increase, due to this interaction, are noted. Preliminary metal extraction studies were performed.

Solvent impregnated resin (SIR) containing dialkyl dithiophosphoric acid on Amberlite XAD-2: extraction of copper and comparison to the liquid-liquid extraction

The extraction of Cu(II) from chloride solutions at 0.19 M Cl − ionic strength by solvent impregnated resins (SIR) containing di-(2-ethylhexyl) dithiophosphoric acid (DEHTPA) on the Amberlite XAD-2 polymeric support has been studied. The distribution of DEHTPA between the aqueous phase and the resin phase was determined as a function of both pH and loading of DEHTPA ligand (HL) on the resin. The Cu(II) extraction are presented as plots of log distribution coefficient versus pH and DEHTPA concentration in the resin phase. Graphical and computer, analysis showed that the extraction of Cu(II) can be explained by the formation of metal complexes in the resin phase of CuCl 2(HL) 8 and CuCIL(HL) 8 composition with values of equilibrium extraction constants K′ = 9.19 max 9.41 and K″ = 7.69 max 7.99, respectively.

Solvent impregnated resins: relation between impregnation process and polymer support morphology I. Di-(2-ethylhexyl)dithiophosphoric acid

The relationship between polymer support morphology and adsorption of di-(2-ethylhexyl)dithiophosphoric acid (DEHTPA) from alcoholic solution has been studied. As polymer supports investigated are the conventional commercial polymer adsorbents Amberlite XAD-2 and XAD-4 and two microporous polymer adsorbents prepared by post-polymerization crosslinking of swollen chloromethylated gel-type and macroreticular copolymers of styrene and divinylbenzene. Their morphology has been studied by nitrogen adsorption/desorption method. It was found that in the adsorption process DEHTPA fills the pore space gradually from the smallest pores up to pores with a diameter of approximately 10 nm.

Extraction of gallium(III) and aluminium(III) with O,O-dialkyldithiophosphoric acids

The extraction of Ga 3+ and Al 3+ with the liquid cation-exchangers di-n-butyldithiophosphoric acid (DBTPA) and di-(2-ethylhexyl)dithiophosphoric acid (DETPA) in kerosene, in the presence and absence of alcohols and tri-n-butyl phosphate (TBP) has been studied. Both Ga 3+ and Al 3+ can be extracted in the form of a neutral complex, MA 3, but the distribution coefficient of Ga 3+ is the higher by about two orders of magnitude, which can be the basis of the solvent extraction separation of gallium and aluminium. The differences can be explained by the interaction between the sulphur donor atoms of the extractants and the d 10 electronic shell of Ga 3+ as well as by the lower steric hindrance of ligands co-ordinated to Ga 3+.

Microemulsion formation and metal extraction in the system water/aerosol OT/extractant/isooctane

The effects of metal extractants anti-2-hydroxy-5-nonylbenzophenone oxime (HNBPO), Versatic 10, and di(2-ethylhexyl)dithiophosphoric acid (DEHDTPA) on the maximum water solubilization in Aerosol OT/isooctane-based systems have been investigated. DEHDTPA was found to substantially increase the water uptake, while HNBPO and Versatic 10 gave less improvement or a reduction in water uptake. The result is highly dependent on the presence of Cu 2+. In addition dithiophosphoric acid lowered the HLB temperature of the Aerosol OT-based system, even more so when combined with copper. The equilibrium distribution of copper in the liquid-liquid extraction by the Aerosol OT/Versatic 10/isooctane mixture clearly demonstrates the significance of a proper balancing of the hydrophilic/lipophilic properties of the surfactant mixture. Below the HLB temperature extraction takes place already at pH 1.8, while above the HLB temperature the extraction is efficiently obstructed at this pH.