Formation Of Chelate Complexes Research Articles

Nickel extractions from limonite type laterite ores by pressure leaching with aqueous solutions of polyamines

A new extraction method by pressure leaching has been applied to recover nickel from limonite type laterites. Pressure leaching was carried out with aqueous solutions of polyamines at temperatures above 180°C. During leaching goethite minerals containing most of the nickel in high-iron laterites are converted to hematite in alkaline solutions and nickel which is liberated from the goethite lattice is extracted by chelate-complex formation with polyamines. Pretreatment of the ores prior to leaching is not necessary. Recovery of nickel from the resulting pregnant solutions can be realized by solvent extraction methods. The only reagent consumed by this process is lime. Detailed studies were conducted to investigate the leaching mechanism which was found to be dependent both on the ore characteristics and on the chemistry of the polyamine containing leach solutions.

Kinetic Studies of Fast Equilibrium by High-performance Liquid Chromatography I. Ternary Complex Formation of N,N-Disubstituted Dithiocarbamate Chelates of Ni(II) and Cu(II)

Abstract The equilibrium of labile ternary complex formation of metal dialkyldithiocarbamate chelates (MA2+MB2\oversetk\undersetk−\ightleftharpoons 2MAB, K=[MAB]2/[MA2][MB2]) has been investigated by high-performance liquid chromatography, the separation process of which is so fast that kinetically unstable ternary complexes can be eluted with no disproportionation during the course of chromatography. High-performance liquid chromatography makes it possible to halt the progress of considerably fast reactions at the moment when the solution of reaction system is injected into the column. Thus, chromatograms obtained indicate the concentration of each species before chromatography, facilitating the determination of equilibrium constant K of Ni(II) and Cu(II) chelates. The equilibrium constants obtained are always 4.0, suggesting that ternary complex formation is controlled by a statistical factor. Disproportionation takes place by collision of two ternary metal chelates, the rate constants being of the order 101–102 M−1 s−1 (Ni(II) chelates) and 103 M−1 s−1 (Cu(II) chelates). The activation parameters of ternary complex formation have been obtained.

Study on the complex formation of cobalt chelates with polymer ligands

AbstractVariously composed copolymers from styrene and 4‐vinylpyridine (4‐VP) were prepared and their complex formation reactions with benzylbis(dimethylglyoximato)Co(III) [BzCo(III)(DMG)2] and N,N′‐ethylenebis(salicylideneiminato)Co(II) (Co(II)salen) were studied kinetically by the stopped‐flow rapid scanning spectroscopy. For the complex formation reaction with BzCo(III)(DMG)2, the relationship between the complex formation constant K and the content of 4‐pyridylethylene units in the copolymers showed an unusual bell‐type curve, and the K values were higher than the K value of complexation with pyridine. From the correlation between K, k (complex formation rate constant), and k′ (complex dissociation rate constant), it resulted that (1) the higher K values of the polymer systems are due to the lower k′ values compared with the pyridine system, and (2) the bell‐type change of the K values is also caused by the k′ values. In the case of Co(II)salen‐copolymer systems, two species of the complex, i.e., mono‐ and diaxial coordinated complexes were clearly identified by spectrometric kinetics, whereas the pyridine system gave only a mono‐axial coordinated complex. The diaxial coordination seems to lead to a much more favorable structure than the monoaxial one, due to the entropic gain or to the polymer chelate effect.

Solvent extraction of copper by benzoylacetone in a stirred transfer cell.

Novel separation technique using liquid surfactant membranes containing mobile carrier has recently attracted practical interest through individual ion recovery from brines and metallurgical wastes. In this paper, as a basic study of the selective separation and concentration of metal ion using liquid surfactant membranes, the extraction of copper with benzoylacetone was carried out using a stirred transfer cell. The effect of chelating complex formation on extraction rate was examined experimentally and theoretically. As a result, it became clear that the experimental results were explained by a diffusion model accompanied by the formation of chelating complex. In addition, the rate constant of complex formation and the mass transfer coefficient of benzoylacetone into aqueous phase were obtained.

Gel chromatography of rhenium(VII)

The gel chromatographic behaviour of the perrhenate anion on Sephadex G-10 and Bio-Gel P-2 was investigated. Chelate complex formation was observed on Sephadex at pH values below 3.0. K d values of about 4.5 were measured in neutral and alkaline solutions. No chelate complex Formation occurred on Bio-Gel P-2 within the stability range of this gel. K d values of 2.6 were found independently of pH variations. The results are compared with those for the behaviour of vanadium(V), molybdenum(VI) and tungsten(VI).

Das verhalten von molybdän(VI) und molybdän(V) auf dextran-und polyacrylamidgelen

The chromatographic behaviour of molybdate(VI) and molybdate(V) solutions on Sephadex G-10 and of molybdate(VI) solutions on Bio-Gel P-2 was investigated. Strongly increasing chelate complex formation with the gel matrix was observed with decreasing pH values for molybdates(VI) on Sephadex G-10 and on Bio-Gel P-2, the chelation still being more pronounced on the latter. Molecular sieve effects were observed between ph 10 and 4.0 on Sephadex G-10. Two species of pentavalent molybdates separated on Sephadex G-10. The character of 0.1 M aqueous solutions of Mo(VI), W(VI), V(V) and Re(VII) is compared by aid of elution profiles at pH 10, 6 and 3 on Sephadex G-10.

Das verhalten von Vanadin(V) auf dextran- und polyacrylamidgelen

The behaviour of vanadium(V) on dextran- and polyacrylamide gels investigated by column chromatographic experiments. In order to provoke possible molecular sieve effects, the two most tightly cross-linked gel types are used, i.e. Sephadex G-10 and Bio-Gel P-2. For 0.1 M solutions, molecular sieving of isopolyvanadates occurs already at pH 6.0 and the effect increases with decreasing pH values. However, a tendency for chelate complex formation with the gel matrix is also observed to increase with decreasing pH values. As for molybdate and tungstate solutions, complexation is more pronounced on polyacrylamide gels than on dextran gels.

Studies of the Liquid-Liquid Partition Systems. IV. The Solvent Extraction Study of Europium(III) Adduct Chelate Complexes with Six Acetylacetone Derivatives and Tributylphosphate

Abstract The extraction of europium(III) in 0.1 m sodium perchlorate with acetylacetone, benzoylacetone, trifluoroacetylacetone, benzoyltrifluoroacetone, froyltrifluoroacetone and thenoyltrifluoroacetone in chloroform and the adduct formation of these metal chelates with tributylphosphate have been studied at 25°C. It has been concluded that: (i) The β-diketones which have one trifluoromethyl group extract europium(III) better than those which have no trifluoromethyl group. The difference in the metal extraction with acetylacetone or trifluoroacetylacetone and the metal extraction with the homologues of these β-diketones seems to be mainly due to the aqueous chelate complex formation, (ii) A metal chelate with a β-diketone which has a trifluoromethyl group is a much better acceptor of tributylphosphate to form adduct complexes than a metal chelate with a β-diketone which has no trifluoromethyl group. (iii) The ability of the acetylacetone chelate or the trifluoroacetylacetone chelate to form an adduct is not very much changed by the replacement of the methyl group with a benzoyl, froyl, or thenoyl group.

Chelate complex formation as a basis for titration processes

Metal cations can be looked upon as LEWIS acids and their reaction with ligands during complex formation can be compared to the addition of the proton to a base. The complex formation reactions, however, lack sharp and definite endpoints and metal cations therefore cannot be titrated with ammonia, cyanide and other ligands in the same way as the hydrogen ion can be titrated alkalimetrically. The theoretical reason for this fact is discussed and it is shown that complex formations gain the characteristic properties of neutralisation reactions if the simple ligands are replaced by a polydentate group which is able to satisfy not only one, but several of the coordination points of the metal cation. A great number of titration processes can be based on such reactions.

Ethylenedinitrilotetraacetic Acid as a Solvent for Urinary Calculi

Ethylenedinitrilotetraacetic acid is now available commercially from Bersworth Chemical Co., Framingham, Mass. It forms stable chelate complexes with a number of metal ions, including calcium(1). We find that neutral aqueous solutions of this reagent dissolve urinary calculi rapidly. Urinary calculi are composed principally of calcium oxalate, urate, phosphate, and carbonate, with other salts and organic matter(2). The solvent action of ethylenedinitrilotetraacetic acid is undoubtedly due to the formation of soluble chelated calcium complexes. One stone which was composed of cystine, with no calcium present, was unaffected by the acid. Because of its effect on urinary calculi, we propose the short name “calsol” for ethylenedinitrilotetraacetic acid in this application. A 3% calsol solution was made up by dissolving 30 g of calsol and 10 g of sodium hydroxide in one liter of water and adjusting to pH 7.5 with additional sodium hydroxide. Approximately 2 g was required. For the purpose of comparing calsol with the currently used citrate solution of Suby, 3% sodium citrate was prepared according to his formula “G”(3). The solvent actions of these solutions were compared against 44 pairs of stones from 44 patients in the Squier Urological Clinic, Presbyterian Hospital, New York. The stones from any one patient were nearly identical in size and composition. They were classified into 3 types according to the principal anion present: oxalate, urate, and soft (phosphate-carbonate). Calcium was present in all stones, including the urates. The stones were individually immersed in the solutions for 24 hours and the percentage losses in weight determined. Care was taken to avoid breaking off small pieces of stones which had been softened by the solution. In each pair of stones the calsol-treated stone lost substantially more weight than the citrate-treated stone.

Formation of Chelate Complexes between Thiouracils and Heavy-Metal Salts

THE precipitation of heavy-metal salts by 6-benzylthiouracil in aqueous solution was observed some years ago1.