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The occurrence, mineralogy and geochemistry of the rare earth elements are briefly described. Their chemistry is discussed with respect to the different valency and oxidation states, reduction, natural radioactivity, magnetism and superconductivity, physical and chemical properties, inorganic compounds, salts, hydroxides, oxides, organic compounds, alkoxides, solid state, metals, ligands and intermetallic compounds, and complexes. Extraction techniques are broadly divided into precipitation, crystallisation, reactions accompanied by valency changes, thermal reactions, solvent extraction, ion exchange and chelation. Solvent extractants include alcohols, ketones, beta diketones, 8-hydroxyquinolines, cupferron, benzoyl phenyl hydroxylamines, TOPO, versatic acid, alkyl phosphoric acids, tributyl phosphate, alkyl phosphates, amines and quaternary ammonium salts and crown ethers; ion exchange resins include the cationic resins EDTA, DCTA and HEDTA, anionic resins and chelating exchange resins. Commercial extraction practice and coordination chemistry is discussed, the uses of rare earth elements surveyed and Brazilian research reviewed. Finally, analytical techniques for the rare earths are described in detail. There is a bibliography of 1 078 specific and 22 general references., The occurrence, mineralogy and geochemistry of the rare earth elements are briefly described. Their chemistry is discussed with respect to the different valency and oxidation states, reduction, natural radioactivity, magnetism and superconductivity, physical and chemical properties, inorganic compounds, salts, hydroxides, oxides, organic compounds, alkoxides, solid state, metals, ligands and intermetallic compounds, and complexes. Extraction techniques are broadly divided into precipitation, crystallisation, reactions accompanied by valency changes, thermal reactions, solvent extraction, ion exchange and chelation. Solvent extractants include alcohols, ketones, beta diketones, 8-hydroxyquinolines, cupferron, benzoyl phenyl hydroxylamines, TOPO, versatic acid, alkyl phosphoric acids, tributyl phosphate, alkyl phosphates, amines and quaternary ammonium salts and crown ethers; ion exchange resins include the cationic resins EDTA, DCTA and HEDTA, anionic resins and chelating exchange resins. Commercial extraction practice and coordination chemistry is discussed, the uses of rare earth elements surveyed and Brazilian research reviewed. Finally, analytical techniques for the rare earths are described in detail. There is a bibliography of 1 078 specific and 22 general references.

Molecular modelling with SYBYL software was used for examples taken from the literature, to determine whether it was a useful aid in accounting for solvent extraction results. The differences were investigated between the extractabilities of a number of dianions by diphosphonium extractants, in which the varying length of the bridging methylene chain connecting the two phosphonium centres offered an effective molecular recognition field. Modelling was also carried out of the metal complexes formed in the extraction of rare earth elements with dialkyl phosphoric acids and in the extraction of zinc with 8-hydroxyquinolines in the presence of various pyridinic adducts., Molecular modelling with SYBYL software was used for examples taken from the literature, to determine whether it was a useful aid in accounting for solvent extraction results. The differences were investigated between the extractabilities of a number of dianions by diphosphonium extractants, in which the varying length of the bridging methylene chain connecting the two phosphonium centres offered an effective molecular recognition field. Modelling was also carried out of the metal complexes formed in the extraction of rare earth elements with dialkyl phosphoric acids and in the extraction of zinc with 8-hydroxyquinolines in the presence of various pyridinic adducts.

Scheelite was floated from a low-grade (0.28% WO3) calcitic (96.30% CaCO3) scheelite ore using oleoyl sarcosine as collector. When alkylated 8-hydroxyquinoline was added concentrate grade increased from 8.07% to 33.54% and concentrate recovery from 55.1% to 73.4%. Infrared studies with pure calcite and scheelite minerals showed that while alkyl oxine is adsorbed on the scheelite surface, it is not adsorbed on the calcite., Scheelite was floated from a low-grade (0.28% WO3) calcitic (96.30% CaCO3) scheelite ore using oleoyl sarcosine as collector. When alkylated 8-hydroxyquinoline was added concentrate grade increased from 8.07% to 33.54% and concentrate recovery from 55.1% to 73.4%. Infrared studies with pure calcite and scheelite minerals showed that while alkyl oxine is adsorbed on the scheelite surface, it is not adsorbed on the calcite.

The new process, which has been tested at pilot scale, comprises: the simultaneous solvent extraction of palladium and platinum by a new Schering Berlin reagent, TN 1911; washing of the loaded extractant to remove co-extracted impurities; differential stripping of first platinum at pH 3 and then palladium with strong hydrochloric acid; and precipitation of palladium and platinum salts, followed by reduction to metal. The process is, unusually, a non-ammonia one requiring only small amounts of ammonia at the end where final purification may be necessary for particularly complex feed solutions. The testwork was carried out for the CCR division of Noranda Minerals to process second-stage gold barren solution without the use of ammonia because of the effluent treatment processes used within the complex., The new process, which has been tested at pilot scale, comprises: the simultaneous solvent extraction of palladium and platinum by a new Schering Berlin reagent, TN 1911; washing of the loaded extractant to remove co-extracted impurities; differential stripping of first platinum at pH 3 and then palladium with strong hydrochloric acid; and precipitation of palladium and platinum salts, followed by reduction to metal. The process is, unusually, a non-ammonia one requiring only small amounts of ammonia at the end where final purification may be necessary for particularly complex feed solutions. The testwork was carried out for the CCR division of Noranda Minerals to process second-stage gold barren solution without the use of ammonia because of the effluent treatment processes used within the complex.

As increasingly complex copper ores are mined for leaching, use of highly acidic leach solutions may be necessary to efffectively recover the contained metal values. Research by the US Bureau of Mines has identified a mixture of two commercially available extractants (LIX 860 and Kelex 100), based on aldoximes and substituted 8-hydroxyquinolines, which has a high transfer efficiency. A synthetic leach liquor, containing 5 g/L Cu at pH 0.9 was processed using the mixed extractant and a laboratory solvent extraction circuit. The loaded organic was stripped with a synthetic barren electrolyte compatible with electrowinning technology., As increasingly complex copper ores are mined for leaching, use of highly acidic leach solutions may be necessary to efffectively recover the contained metal values. Research by the US Bureau of Mines has identified a mixture of two commercially available extractants (LIX 860 and Kelex 100), based on aldoximes and substituted 8-hydroxyquinolines, which has a high transfer efficiency. A synthetic leach liquor, containing 5 g/L Cu at pH 0.9 was processed using the mixed extractant and a laboratory solvent extraction circuit. The loaded organic was stripped with a synthetic barren electrolyte compatible with electrowinning technology.

Scheelite was selectively floated from a calcitic low grade (0.28% WO3) ore using oleoyl sarcosine as collector and alkylated 8-hydroxyquinoline as modifier. Infrared studies with pure scheelite and calcite samples showed that hydroxyquinoline and alkylated hydroxyquinoline are adsorbed on the scheelite surface and not on the calcite surface., Scheelite was selectively floated from a calcitic low grade (0.28% WO3) ore using oleoyl sarcosine as collector and alkylated 8-hydroxyquinoline as modifier. Infrared studies with pure scheelite and calcite samples showed that hydroxyquinoline and alkylated hydroxyquinoline are adsorbed on the scheelite surface and not on the calcite surface.

8-Hydroxyquinoline derivatives such as Kelex 100 are well known commercial extractants for the recovery of gallium from Bayer process aluminate solutions. It is shown that an increase in the active component content of the extractant results in a substantial improvement of the resistance of Kelex 100 against oxidation, thus avoiding pronounced deleterious effects on the composition and performance of the Kelex 100 containing solvent when used in contact with concentrated aqueous caustic solutions on the presence of air., 8-Hydroxyquinoline derivatives such as Kelex 100 are well known commercial extractants for the recovery of gallium from Bayer process aluminate solutions. It is shown that an increase in the active component content of the extractant results in a substantial improvement of the resistance of Kelex 100 against oxidation, thus avoiding pronounced deleterious effects on the composition and performance of the Kelex 100 containing solvent when used in contact with concentrated aqueous caustic solutions on the presence of air.

The advantages of TN 1911 in comparison to other solvent extraction reagents for platinum and palladium refining are demonstrated., The advantages of TN 1911 in comparison to other solvent extraction reagents for platinum and palladium refining are demonstrated.

The effect was studied of S-hydroxyquinoline (SHQ) on the flotation of ultrafine diaspore and kaolinite. Flotation tests on the single minerals indicated that both the collection and selectivity of SHQ were poor. Tests on mixtures of the synthetic minerals showed that the recovery of Al2O3 improved significantly when the SHQ concentration was equal to or less than 1/10 that of sodium oleate. At two sodium oleate concentrations, the zeta potentials of kaolinite decreased as the SHQ concentration increased from 0 to 0.000 5 mol/l. Diaspore exhibited different behaviour, indicating that the adsorption mechanism of SHQ on the surface of the two minerals may be different. FTIR studies showed that the adsorption of SHQ was dominated by hydrogen bonding and complex formation, which made the surface of the minerals initially lyophobic and promoted collection., The effect was studied of S-hydroxyquinoline (SHQ) on the flotation of ultrafine diaspore and kaolinite. Flotation tests on the single minerals indicated that both the collection and selectivity of SHQ were poor. Tests on mixtures of the synthetic minerals showed that the recovery of Al2O3 improved significantly when the SHQ concentration was equal to or less than 1/10 that of sodium oleate. At two sodium oleate concentrations, the zeta potentials of kaolinite decreased as the SHQ concentration increased from 0 to 0.000 5 mol/l. Diaspore exhibited different behaviour, indicating that the adsorption mechanism of SHQ on the surface of the two minerals may be different. FTIR studies showed that the adsorption of SHQ was dominated by hydrogen bonding and complex formation, which made the surface of the minerals initially lyophobic and promoted collection.

The advantages of solvent extraction include selectivity, quantitative removal of metal from solution and recycling of the extractant. In precious metals, solvent extraction can be used for metal recovery from dilute solutions and from more concentrated solutions such as those found in refining operations. Several extractants can be used for gold recovery from cyanide solutions. These include modified amines, solvating extractants such as tributyl phosphate, and guanidines. Extractants used for the separation of platinum group metals fall into three basic categories: solvating extractants such as long-chain alcohols, ethers and tributyl phosphate; anion exchange extractants such as long-chain alkyl amines; and coordinating extractants such as oximes or dialkyl sulphides. Solvent extraction equipment for batch processing and continuous processing is briefly considered., The advantages of solvent extraction include selectivity, quantitative removal of metal from solution and recycling of the extractant. In precious metals, solvent extraction can be used for metal recovery from dilute solutions and from more concentrated solutions such as those found in refining operations. Several extractants can be used for gold recovery from cyanide solutions. These include modified amines, solvating extractants such as tributyl phosphate, and guanidines. Extractants used for the separation of platinum group metals fall into three basic categories: solvating extractants such as long-chain alcohols, ethers and tributyl phosphate; anion exchange extractants such as long-chain alkyl amines; and coordinating extractants such as oximes or dialkyl sulphides. Solvent extraction equipment for batch processing and continuous processing is briefly considered.

It is shown that for Kelex 100 the selectivity for copper (II) over iron (III) is lost when the water soluble precursor of the reagent, 8-hydroxyquinoline, is added to the reagent mixture, or when the inert organic diluent is removed from the organic phase. LIX 65N and its water soluble precursor salicyladoxime are selective for copper (II) over iron (III) but the selectivity is reduced in the absence of a supporting inert diluent. The reasons for the results are discussed with reference to thermodynamic data., It is shown that for Kelex 100 the selectivity for copper (II) over iron (III) is lost when the water soluble precursor of the reagent, 8-hydroxyquinoline, is added to the reagent mixture, or when the inert organic diluent is removed from the organic phase. LIX 65N and its water soluble precursor salicyladoxime are selective for copper (II) over iron (III) but the selectivity is reduced in the absence of a supporting inert diluent. The reasons for the results are discussed with reference to thermodynamic data.

The extraction rate for copper from sulphate solutions using the active component of LIX 34 was found to be one order of magnitude lower than that using the active component of LIX 65N . This is probably attributable to the large size of the molecule in the former case which makes the reorientation of its charged copper intermediary at the interface slow and to its low surface activity. Extraction concentration and pH affected extraction rate in a similar way for both extractants., The extraction rate for copper from sulphate solutions using the active component of LIX 34 was found to be one order of magnitude lower than that using the active component of LIX 65N . This is probably attributable to the large size of the molecule in the former case which makes the reorientation of its charged copper intermediary at the interface slow and to its low surface activity. Extraction concentration and pH affected extraction rate in a similar way for both extractants.

Kelex 100, 100S and 108 are industrial chelating extractants mainly composed of branched alkyl derivatives of 8-hydroxyquinoline. They have found widespread application as chelating extractants of Cu(II), Ga(III) and Ge(IV). The compositions of all three reagents were investigated by gas chromatography and mass spectroscopy. It was found that Kelex 100S and distilled Kelex 100 are of high and similar purity. They contain 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline as the main component and small amounts of two inert furoquinoline-type impurities. Kelex 100S is probably obtained by fractionation of Kelex 100. Except for the rate of phase separation, comparison of the two compositions does not reveal any clear reason why Kelex 100S possesses the improved properties that have been demonstrated experimentally, especially as far as resistance against oxidation or the kinetics of metal extraction are concerned. Kelex 108 contains 7-(2-ethylhexyl)-8-hydroxyquinoline as the active substance but important amounts of unreacted 8-hydroxyquinoline and di(2-ethyl-hexyl)-8-hydroxyquinoline are also present., Kelex 100, 100S and 108 are industrial chelating extractants mainly composed of branched alkyl derivatives of 8-hydroxyquinoline. They have found widespread application as chelating extractants of Cu(II), Ga(III) and Ge(IV). The compositions of all three reagents were investigated by gas chromatography and mass spectroscopy. It was found that Kelex 100S and distilled Kelex 100 are of high and similar purity. They contain 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline as the main component and small amounts of two inert furoquinoline-type impurities. Kelex 100S is probably obtained by fractionation of Kelex 100. Except for the rate of phase separation, comparison of the two compositions does not reveal any clear reason why Kelex 100S possesses the improved properties that have been demonstrated experimentally, especially as far as resistance against oxidation or the kinetics of metal extraction are concerned. Kelex 108 contains 7-(2-ethylhexyl)-8-hydroxyquinoline as the active substance but important amounts of unreacted 8-hydroxyquinoline and di(2-ethyl-hexyl)-8-hydroxyquinoline are also present.

Two aromatic-type chelating agents, 1,10 phenanthroline and 8-quinolinol, were tested as specific depressants for magnetite in the cationic silica flotation of magnetic taconite concentrates from operating plants in Minnesota. Micro and batch flotation tests, with zeta potential and adsorption measurements, were used. In the presence of a cationic collector, dodecylammonium chloride (DAC) the Fe-phenanthroline surface chelate electrostatically repelled DAC and magnetite was depressed. The negatively charged Fe(quinolinol)2(OH)2- on the magnetite surface attracted the cationic collector and made magnetite flotable and was therefore ineffective for depressing magnetite., Two aromatic-type chelating agents, 1,10 phenanthroline and 8-quinolinol, were tested as specific depressants for magnetite in the cationic silica flotation of magnetic taconite concentrates from operating plants in Minnesota. Micro and batch flotation tests, with zeta potential and adsorption measurements, were used. In the presence of a cationic collector, dodecylammonium chloride (DAC) the Fe-phenanthroline surface chelate electrostatically repelled DAC and magnetite was depressed. The negatively charged Fe(quinolinol)2(OH)2- on the magnetite surface attracted the cationic collector and made magnetite flotable and was therefore ineffective for depressing magnetite.

The studies showed that alkyl oxine increased the negative zeta potential of scheelite to a less negative value but did not change that of calcite; the zeta potentials of both minerals became more negative when treated with quebracho. Conditioning with alkyl oxine before adding quebracho increased the flotation efficiency of oleoyl sarcosine for scheelite but not for calcite. Infrared studies also showed that oxine and alkyl oxine were chemically adsorbed on to the surface of scheelite but not calcite. It was concluded that both can be usd as scheelite activators in the separation of scheelite from calcite, preventing the depressant action of quebracho on the scheelite by decreasing the negative charge on its surface., The studies showed that alkyl oxine increased the negative zeta potential of scheelite to a less negative value but did not change that of calcite; the zeta potentials of both minerals became more negative when treated with quebracho. Conditioning with alkyl oxine before adding quebracho increased the flotation efficiency of oleoyl sarcosine for scheelite but not for calcite. Infrared studies also showed that oxine and alkyl oxine were chemically adsorbed on to the surface of scheelite but not calcite. It was concluded that both can be usd as scheelite activators in the separation of scheelite from calcite, preventing the depressant action of quebracho on the scheelite by decreasing the negative charge on its surface.

The rate of extraction of aluminium (III) from sodium hydroxide solutions by Kelex 100 in kerosene has been investigated under non-equilibrium conditions. It is inferred that aluminium (III) is taken up through the formation of activated species such as Al(OH)3.OH- and Na+Al(OH)3.OH-., The rate of extraction of aluminium (III) from sodium hydroxide solutions by Kelex 100 in kerosene has been investigated under non-equilibrium conditions. It is inferred that aluminium (III) is taken up through the formation of activated species such as Al(OH)3.OH- and Na+Al(OH)3.OH-.

Both the oxines form 1:3 simple chelates with Nb. Synergistic extraction was observed in the extraction of Nb on the addition of 5-nitro-8-quinolinol, as an adducting ligand in the presence of 8-quinolinol forming a di-adduct, NbQ3.(5-NO2-8-HQ)2. Synergy coefficients of the Nb adducts of the mixed ligands were evaluated. Synergistic enhancement was also observed with pyridine and its methyl derivatives with Nb-NO2-8-quinolinate, forming mono-adducts., Both the oxines form 1:3 simple chelates with Nb. Synergistic extraction was observed in the extraction of Nb on the addition of 5-nitro-8-quinolinol, as an adducting ligand in the presence of 8-quinolinol forming a di-adduct, NbQ3.(5-NO2-8-HQ)2. Synergy coefficients of the Nb adducts of the mixed ligands were evaluated. Synergistic enhancement was also observed with pyridine and its methyl derivatives with Nb-NO2-8-quinolinate, forming mono-adducts.

Test results are presented concerning the application of 8-hydroxyquinoline as a flotation collector of strontium minerals. The best results were achieved at a concentration of 5 x 10(-4) M hydroxyquinoline at 0.5 mg/ml at pH 9., Test results are presented concerning the application of 8-hydroxyquinoline as a flotation collector of strontium minerals. The best results were achieved at a concentration of 5 x 10(-4) M hydroxyquinoline at 0.5 mg/ml at pH 9.

Various 5-substituted 8-hydroxyquinolines were synthesised and studied for the liquid-liquid extraction of gallium from strongly basic Bayer aluminate solutions, for which purpose Kelex 100 (a 7-substituted 8-hydroxyquinoline) has good selectivity but a low rate of phase transfer. Two of the molecules synthesised extracted gallium ions but only one did so selectively with respect to aluminium. Its rate of phase transfer was lower than that of Kelex 100., Various 5-substituted 8-hydroxyquinolines were synthesised and studied for the liquid-liquid extraction of gallium from strongly basic Bayer aluminate solutions, for which purpose Kelex 100 (a 7-substituted 8-hydroxyquinoline) has good selectivity but a low rate of phase transfer. Two of the molecules synthesised extracted gallium ions but only one did so selectively with respect to aluminium. Its rate of phase transfer was lower than that of Kelex 100.

Equilibrium data for iron(III) in beta-alkenyl-8-hydroxyquinoline (Kelex 100 manufactured by Sherex Chemical Co.) were obtained in connection with solvent extraction in the recovery of copper from hydrometallurgical leach solutions. An equation for the thermodynamic equilibrium model was derived by linear regression analysis of the data., Equilibrium data for iron(III) in beta-alkenyl-8-hydroxyquinoline (Kelex 100 manufactured by Sherex Chemical Co.) were obtained in connection with solvent extraction in the recovery of copper from hydrometallurgical leach solutions. An equation for the thermodynamic equilibrium model was derived by linear regression analysis of the data.

Solvent extraction based refining processes for precious metals undoubtedly offer several advantages over the traditional precipitation methods. Thus, their usage by industry is expected to become standard practice. This paper briefly reviews the pertinent chemistry and the current commercial processes which apply solvent extraction techniques to the refining of precious metals. Solvent extraction processes currently employed by three precious metals refiners are presented. A recently developed solvent extraction process which uses alkylated derivatives of 8-hydroxyquinoline as the basis for the separation of precious metals is briefly discussed., Solvent extraction based refining processes for precious metals undoubtedly offer several advantages over the traditional precipitation methods. Thus, their usage by industry is expected to become standard practice. This paper briefly reviews the pertinent chemistry and the current commercial processes which apply solvent extraction techniques to the refining of precious metals. Solvent extraction processes currently employed by three precious metals refiners are presented. A recently developed solvent extraction process which uses alkylated derivatives of 8-hydroxyquinoline as the basis for the separation of precious metals is briefly discussed.

Alpha-nitroso-beta-naphthol, 8-hydroxyquinoline, cupferron and sodium oleate were investigated to find an effective chelating collector for wolframite slime flotation. Minimising the chelating collector dosage by using neutral oil synergist was also studied. Dosage by using neutral oil synergist., Alpha-nitroso-beta-naphthol, 8-hydroxyquinoline, cupferron and sodium oleate were investigated to find an effective chelating collector for wolframite slime flotation. Minimising the chelating collector dosage by using neutral oil synergist was also studied. Dosage by using neutral oil synergist.