Tungsten recovery from alkaline leach solutions as synthetic scheelite

The recovery of tungsten from alkaline leach solutions has been studied examining the effect of temperature, pH, Ca/WO₃ molar ratio and nature of the precipitated calcium tungstate. The precipitation kinetics of calcium tungstate, upon the addition of aqueous sodium tungstate to calcium solutions, was followed by potentiometric measurements using a calcium ion-selective electrode. Two models, a crystal growth model and a second-order reaction opposed by zero-order reaction, have been used to test the experimental data. Both models show that the apparent activation energy of CaWO₄ precipitation falls in the range 58 to 67 kJ mol^− 1.The kinetic data shows that the maximum recovery of precipitated calcium tungstate occurs at pH ≥ 8.5 with a 10% excess of CaCl₂ at 50 °C over a period of 20 min using sodium tungstate solutions of 100 g L^− 1 and 150 g L^− 1 WO₃.     

Kinetics and mechanism of stripping of Mn(II)–D2EHPA complex by sulphuric acid solution

The kinetics of stripping of Mn(II)–D2EHPA chelate (MnA₂.HA.H₂A₂) existing in kerosene phase by aqueous sulphuric acid solutions at constant sulphate ion concentration of 0.50 M have been investigated by the constant interfacial area stirred (Lewis) and non-stirred (Hahn) cells. Both pseudo-rate constant (q) or (rate / area) and flux (F) methods of the rate data treatment have been applied. The empirical rate equations have been derived. Results have been compared among themselves and other published works on Mn(II)–D2EHPA chelate stripping kinetics. Rate constants obtained from (q) or (rate / area) and (F) methods differ in magnitude and units and an explanation of this has been given.An analysis of rate equations obtained from the Lewis cell experimentation (F_b = 10^− 4.1[MnA₂.HA.H₂A₂]_(o)(1 + 0.005[H⁺]_(i)^− 1)^− 1 (1 + 7.94[H₂A₂]_(o)^0.5)^− 1) suggests that the process is chemically controlled at lower aqueous acidity and higher free D2EHPA concentration regions; whereas, it is diffusion-controlled at higher aqueous acidity and lower free D2EHPA concentration regions. In the investigated D2EHPA concentration and aqueous acidity regions, majority of data fall in the intermediate controlled region. The suggested mechanisms are supported by the values of activation energy (E_a). In the kinetic regime, the reaction step: MnA⁺ → Mn²⁺ + A⁻ occurring in the bulk aqueous phase is the slowest step which proceeds through S_N2 mechanism as indicated by the comparable higher negative value of ΔS^± in the stated condition.In Hahn cell technique, the empirical rate equation is: F_b = 10^− 5.9[MnA₂.HA.H₂A₂]_(o)(1 + 0.0025[H⁺]_(i)^− 1)^− 1(1 + 2.8[H₂A₂]_(o)^0.5)^− 1. Analysis of this equation together with the E_a value of 12–42 kJ/mol indicate that the stripping process is completely diffusion controlled in the low pH and extractant concentration region and in other parametric condition, that is intermediate controlled. For both cells, the ratio of (k_f) to (k_b) equals almost to K_ex of 10^− 2.44 obtained from the distribution study.     

Identification of arsenato antimonates in copper anode slimes

It was found that, in copper electrolyte, the combination of As(V) and Sb(V) can form arsenato antimonic acid (AAAc) and, the reactions of AAAc with As(III), Sb(III), and Bi(III) can produce the precipitates of arsenato antimonates. During copper electrorefining, the As, Sb, and Bi deposited into the anode slime from the electrolyte are dominant in the forms of arsenato antimonates. It is extremely difficult to separate pure arsenato antimonates from copper anode slimes, while it is easy to synthesize arsenato antimonates using H₂O₂ to oxidize As(III) and Sb(III) in copper refining electrolyte. The composition and structure of the arsenato antimonates were determined with chemical analysis, IR and XRD techniques. The characteristic bands in the IR spectra of arsenato antimonates are δ of As–OH and Sb–OH at 1126.8 cm^− 1, ν_as of As–OH at 1029.7 cm^− 1, ν_as of As–OX(X = As, Sb) at 819.5 cm^− 1, ν_as of Sb–OH at 618.4 cm^− 1, ν_as of Sb–OY(Y = As, Sb) at 507.2 cm^− 1, and ν_as of Sb–OBi at 470 cm^− 1.The arsenato antimonates form irregular masses of amorphous structure because there are many OH groups in AAAc, the OH groups bond with As(III), Sb(III), and Bi(III) at random, which makes the arsenato antimonates formed in copper refining electrolyte have no fixed ratios for As/Sb/Bi. The formation of the arsenato antimonates can be expressed as follows:aH₃AsO₄ + bH[Sb(OH)₆] + cMeO ⁺ →Me_cAs_aSb_bO_{(3a+5b+c/2+1)}H_{(a+5b−2c+2)}·xH₂O + cH⁺ + (a + b + c / 2 − 1 − x)H₂O, where Me = As(III), Sb(III) and Bi(III); a ≥ 1, b ≥ 1, c ≤ (3a + b)     

Sorption behaviour and mechanism of ytterbium(III) on imino-diacetic acid resin

The sorption behaviour and mechanism of a novel chelate resin, imino-diacetic acid resin (IDAAR), for Yb(III) has been investigated in HAc–NaAc medium. The sorption of Yb(III) obeys the Freundlich isotherm. Optimum sorption for Yb(III) on IDAAR is at pH 5.13 and the statically saturated sorption capacity is 187 mg/g resin at 298 K. Yb(III) can be eluted using 1~2 mol L^− 1 HCl and the resin can be regenerated and reused without apparent decrease of sorption capacity. The apparent sorption rate constant is k₂₉₈ = 1.57 × 10^− 5 s^− 1; the apparent activation energy is 13.8 kJ mol^− 1 and the enthalpy change ΔH of IDAAR for Yb(III) is 29.8 kJ mol^− 1. The sorption mechanism of IDAAR for Yb(III) was examined by using chemical methods and IR spectrometry. The molar coordination ratio of the functional group of IDAAR to Yb(III) is 3:1 with the coordination compound formed between oxygen atoms in the functional group of IDAAR and Yb(III).     

The oxidation of thiosulfates with copper sulfate. Application to an industrial fixing bath

This paper presents the transformation of thiosulfate using Cu(II) salts, such as copper sulfate, at pH between 4 and 5. The nature and kinetics of this process were determined. In the experimental conditions employed, the reaction between thiosulfates and Cu(II) ions produces a precipitate of CuS and the remaining sulfur is oxidized to sulfate, according to the following stoichiometry: 1 mol thiosulfate reacts with 1 mol Cu²⁺ and 3 mol H₂O, generating 1 mol copper(II), 1 mol sulfate and 2 mol H₃O⁺. In the kinetic study, the apparent reaction order was ≈ 0 with respect to H₃O⁺ concentration, in the interval 1.0 · 10^? 4–1.0 · 10^? 5M H₃O⁺; of order 0.4 with respect to Cu²⁺ in the interval 0.21–0.85 g L^? 1 Cu²⁺; and of order 0 with respect to S₂O₃^2? in the interval 0.88–2 g L^?1 S₂O₃^2?. The apparent activation energy was 98 kJ mol^? 1 in the interval 15–40 °C. On the basis of this behavior an empirical mathematical model was established, that fits well with the experimental results. The thiosulfate transformation process using copper(II) sulfate was applied to an industrial fixing bath that proceeded from the photographic industry; after this, the resulting effluent contained less than 10 mg L^? 1 of thiosulfates.     

Carrier-mediated transport of uranium from phosphoric acid medium across TOPO/n-dodecane-supported liquid membrane

Present studies deals with the application of supported liquid membrane (SLM) technique for the separation of uranium (VI) from phosphoric acid medium. Tri-n-octyl phosphine oxide (TOPO)/n-dodecane is used as a carrier and ammonium carbonate as a receiving phase for the separation of uranium (VI) from the phosphoric acid medium. Throughout the study PTFE membranes are used as a support. The studies involve the investigation of process controlling parameters like feed acidity of phosphoric acid, carrier concentration and stripping agents. The effect of nitric acid and sodium nitrate in feed is also studied. It is found that there is negligible transport of uranium (VI) from pure phosphoric acid medium but it increases to very significant amount if 2 M nitric acid is added to feed phase. More than 90% uranium (VI) is recovered in 360 min using 0.5 M TOPO/n-dodecane as carrier and 1.89 M ammonium carbonate as stripping phase from the mixture of 0.001 M H₃PO₄ and 2 M of HNO₃ as a feed. The flux and permeability coefficient are found to be 9.21 × 10^− 6 mol/m² s and 18.26 × 10^− 5 m/s, respectively. Lower concentration of phosphoric acid with 2 M HNO₃ and higher concentration of carrier is found to be the most suitable condition for maximum transport of uranium (VI) from its low-level sources like commercial phosphoric acid.     

Cadmium extraction from chloride solutions with model N-alkyl- and N,N-dialkyl-pyridine-carboxamides

N-alkyl- and N,N-dialkyl-pyridine-carboxamides with the amide group at the 2nd, 3rd or 4th position were used to recover cadmium(II) from acid chloride solutions. It was found that N,N-dialkyl-pyridine-carboxamides in toluene diluent are effective extractants for the recovery of cadmium from chloride solutions at pH < 2. Cadmium extraction ability rises as the distance of the amide group from the pyridine nitrogen increases. In strongly acid chloride media, extractants (L) with N,N-dialkyl-amide group at position 3 or 4 in the pyridine ring form cadmium ion pairs: (LH⁺)₂(CdCl₄²⁻) but the dialkyl derivative of picolinamide probably forms the complex (LH⁺)₂(CdCl₄²⁻)(LHCl). Monoalkyl-pyridine-carboxamides are not suitable for cadmium extraction from chloride solutions because in weak-acid systems (pH > 3, [Cl⁻] = 0.02–4 M) the N-alkyl-pyridine-3-carboxamides form very slightly soluble cadmium complexes and the N-alkyl-pyridine-2-carboxamides do not extract cadmium(II) from chloride solutions under these conditions. In strongly acid systems ([HCl] = 0.01–4 M) N-alkyl-pyridine-2-carboxamide with a branched carbon chain is ineffective, but the hydrochlorides and cadmium complexes of the rest of the N-alkyl-amides are slightly soluble in hydrocarbon diluents. In ethanol solutions hydrophobic pyridine-3-carboxamides form (CdCl₂)_nL₂ complexes (n = 2 or 3) with cadmium chloride.     

Stripping of copper from CYANEX® 301 extract with thiourea–hydrazine–sodium hydroxide solution

The stripping of copper from the organic extract of bis(2,4,4-trimethylpentyl) phosphinodithioic acid, CYANEX® 301, using an aqueous mixture of thiourea, hydrazine and sodium hydroxide has been investigated. The optimal concentrations of the aqueous solution were found to be 1.0 M, 5 × 10^− 2 M and 5.0 M, respectively which led to 95% stripping of copper from CYANEX 301 with concomitant regeneration of the extractant. The characterization of the stripped copper product was done using a combination of microanalyses, cyclic voltammetry and X-ray diffractometry (XRD). The product was made up of two non-stoichiometric copper sulfides, Cu_xS with x = 1.60 and 1.77. Cu_1.60S was the major product. Hydrazine appears to play the role of reducing the disulfide species of CYANEX 301, R₂P(S)S–S(S)PR₂, formed during the extraction step, back into CYANEX 301, whereas thiourea provides a source of sulfur in the formation of the stripping products.     

Leaching kinetics of synthetic CaWO4 in HCl solutions containing H3PO4 as chelating agent

In this study, the dissolution kinetics of synthetically prepared CaWO₄ in HCl solutions containing H₃PO₄ was studied. The effects of process parameters such as stirring speed, temperature and acid concentrations on the dissolution rate of CaWO₄ were investigated. The reaction rate was found to be of 1 / 3 and 2 / 3 order with respect to HCl and H₃PO₄ concentrations, respectively, and the activation energy for the dissolution reaction to be 60 kJ mol^− 1. The rate equation for the dissolution reaction was derived using the Avrami equation and the rate determining step was the chemical reaction on the surface of solid particles.     

Chemistry of the Ca–Se(IV)–H2O and Ca–Se(VI)–H2O systems at 25 °C

The Ca–Se(IV)–H₂O and Ca–Se(VI)–H₂O systems were studied by contacting either selenious acid or selenic acid solution with calcium oxide to attain equilibrium at 25 °C for one month. Analysis of the final solid phases and the associated solution, together with X-ray diffraction analysis and a study into the graphed relationships, showed the existence of three calcium selenites in the Ca–Se(IV)–H₂O system — Ca₂SeO₃(OH)₂·2H₂O (Se(IV) = 4.8 × 10^− 5–2.8 × 10^− 4 M); CaSeO₃·H₂O (Se(IV) = 2.8 × 10^− 4–0.86 M) and Ca(HSeO₃)₂·H₂O (Se(IV) > 0.86 M). It also showed four calcium selenates in the Ca–Se(VI)–H₂O system — Ca₂SeO₄(OH)₂ (Se(VI) = 0.21–0.39 M); CaSeO₄·2H₂O (Se(VI) = 0.40–9.1 M); CaSeO₄ (Se(VI) = 10.2 M) and CaSe₂O₇ (Se(VI) > 10.8 M). The X-ray diffraction analyses reported and SEM analyses indicate a high degree of crystallinity of all seven compounds. The stability and solubility regions for these compounds were defined versus pH, and the conventional solubility constants and conditional free energies of formation for the less soluble CaSeO₃·H₂O, Ca₂SeO₃(OH)₂·2H₂O, CaSeO₄·2H₂O and Ca₂SeO₄(OH)₂ were calculated from solubility data obtained.     

Modelling of zinc transport through a supported liquid membrane

The transport of zinc (II) from an aqueous solution containing zinc (II), iron (II), calcium (II) and magnesium (II) through supported liquid membrane using di-2-ethylhexyl phosphoric acid dissolved in kerosene as a mobile carrier was studied. The effects of temperature, rate of feed and stripping phase and concentration of stripping phase on the mass transfer coefficients of aqueous boundary layers and membrane were studied. A transport rate model has been derived taking into account diffusion through the feed side aqueous boundary layer, diffusion of carrier–zinc complex through the supported liquid membrane and diffusion through the stripping side aqueous boundary layer as simultaneous controlling factors. The mass transfer coefficient data of the side of the feed phase were correlated in the form of Sh = 0.0047 Re^1.349 Sc^0.3333. This correlation was used to calculate the mass transfer coefficient of the aqueous film at the side of the stripping phase. For some parameters and their levels, the mass transfer coefficients, k_f, k_m and k_s (m s^− 1), were calculated.     

Product inhibition by sulphide species on biological sulphate reduction for the treatment of acid mine drainage

It is well recognised that the product of sulphate reduction, i.e. the sulphide species formed, may inhibit the biological process. In this paper, we further the kinetic study of biological sulphate reduction using the mixed population of complete oxidisers growing on acetate for which kinetic data has been reported previously as a function of sulphate concentration, temperature, dilution rate and volumetric sulphate loading using chemostat culture by Moosa et al. to provide kinetic insight into this inhibition.The effect of a feed sulphide concentration in the range 0.50 to 1.25 kg m^− 3 on the biological sulphate reduction process is established using chemostat culture at pH 7.0 ± 0.2. Further, the chemical speciation of sulphide as undissociated H₂S or dissociated HS⁻ on process inhibition is reported through the variation of operating pH across the range pH 6.0 to pH 7.5 at a sulphate feed concentration of 2.5 kg m^− 3. It is clearly shown that inhibition is chiefly mediated by the undissociated H₂S sulphide species, rather than the total sulphide concentration. This inhibition was shown to affect the maximum specific growth rate constant and the death rate constant in the Contois rate equation presented previously while having negligible effect on KS describing substrate affinity.     

Cathodic reactions of Cu2+ in cupric chloride solution

In this study we demonstrate the kinetics of Cu²⁺ reduction in concentrated cupric chloride solutions. Experiments were carried out near the boiling point of the solution ([NaCl] = 280 g/l and [Cu²⁺] = 1–40 g/l) at T = 90 °C, atmospheric pressure, pH = 2. Electrochemical methods such as cathodic polarization curves and cyclic voltammetry were used to investigate the cathodic reactions of copper complexes. To identify the nature and the rate-controlling steps of the reactions, rotating disk electrode (RDE) experiments were conducted. The chemical environment studied was similar to that of the Outokumpu HydroCopper^TM process, which uses a cupric chloride solution to leach copper from the mineral chalcopyrite.The results suggest that the cathodic reactions are the reduction of [CuCl]⁺ to the complex [CuCl₃]²⁻, the reduction of [CuCl₃]²⁻ to solid copper and hydrogen evolution. The diffusion coefficient and the unit rate constants for the solution species were calculated. The exchange current density and rate constant for electron transfer were also estimated. A simulation was made of the cathodic polarization curve and it was in good agreement with the experimental data.     

Extraction of gold(III) in hydrochloric acid solution using monoamide compounds

The extraction and separation properties of Au(III) using two monoamide compounds, N,N-di-n-octylacetamide (DOAA) and N,N-di-n-octyllauramide (DOLA), which have different side chain lengths attached to the carbonyl carbon (CH₃ for DOAA and n-C₁₁H₂₃ for DOLA), were investigated. The solvent extraction of some precious and base metals (Au(III), Pd(II), Pt(IV), Rh(III), Fe(III), Cu(II), Ni(II) and Zn(II)) in HCl solutions was carried out using DOAA and DOLA diluted with n-dodecane and 2-ethylhexanol. A good selectivity for Au(III) extraction with 0.5 M extractant is obtained at lower HCl concentrations (< 3.0 M) in both systems. The extractability of Au(III) with DOAA is greater than that with DOLA. In the 0.5 M DOAA–3.0 M HCl system, a third phase is formed when the Au(III) concentration in the initial aqueous phase is over 39 g/L. In contrast, third phase formation is not found in the 0.5 M DOLA–3.0 M HCl system, and its loading capacity of Au(III) is about 79 g/L. The Au(III) extracted in the organic phase is effectively back-extracted by 1.0 M thiourea in 1.0 M HCl solution in both systems, while some thiourea is precipitated using the organic phase containing 20 g/L of Au(III). The back extraction of Au(III) using water is poor in the DOAA system, but possible in the DOLA system.     

Characterization and alkaline decomposition/cyanidation of beudantite–jarosite materials from Rio Tinto gossan ores

Jarosite-type minerals are the major silver carriers in the gossan ores from Rio Tinto (Spain). Two types of minerals were found: one corresponding to beudantite variable enriched in sulfate; the other is potassium jarosite containing various amounts of arsenate and lead. They are isostructural with cell parameters intermediate between those reported for end members. Silver is present in both jarosites as dilute solid solution (230 ppm Ag in average). The cyanidation of potassium jarosite in saturated Ca(OH)₂ at 70–100°C consists of two step in series: a slow step of alkaline decomposition followed by a fast step of Ag complexation from the decomposition solids. The alkaline decomposition is characterized by the simultaneous removal of sulfate and K ions and the formation of an amorphous hydroxy-arsenate of Fe, Pb and Ca. The kinetics are chemically controlled, with an activation energy of 86.5 kJ mol⁻¹. The nature of the alkaline decomposition of beudantite was similar but extremely slow at ≤100°C.     

The precipitation of ammonium uranyl carbonate (AUC): Thermodynamic and kinetic investigations

The aim of this study is to determine the predominant chemical reaction during precipitation of ammonium uranyl carbonate (AUC) based on thermodynamic analysis and to investigate its kinetics. Four chemical reactions were considered. The Gibbs free energies, Δ_rG°(T) derived from the Ulich calculations as a function of temperature have been determined between 293.15 K and 353.15 K. The predominant chemical reaction of AUC precipitation was UO₂(NO₃)₂·6H₂O_(aq) + 6NH_3(g) + 3CO_2(g) → (NH₄)₄UO₂(CO₃)_3(s) + 2NH₄NO_3(aq) + 3H₂O_(l). According to the AUC precipitation kinetics results, the reaction best fits a second order rate equation. The rate constants k₂ were calculated at 313.15 K and 330.15 K and the activation energy E_a determined using the Arrehenius equation was found as 17.4 kJ/mol.     

BROGIM®: A new three-phase mixing system testwork and scale-up

BROGIM® is a mixing concept for bioleach tanks that provides high oxygen transfer performances, by means of an air dispersing flat blade turbine at the bottom, and mixing, with low power-consuming propellers at the upper part of the rotating shaft. Oxygen transfer performances of this system have been firstly determined in a small-scale testwork in an 850-l tank. A pilot-scale study in a 65-m³ tank enabled to define rules for the scaling-up procedure. The paper describes the philosophy for the scale-up of the mixing system installed in industrial tanks of up to 1250 m³ operating volume.At industrial scale, it has been shown that the BROGIM® system exhibits little power differences between gassed and ungassed conditions, for air flowrates up to 24,000 Nm³ h^− 1 comparatively to what was found at smaller scales. The agitator is able to run with or without air with no need for oversizing the power of the electrical driving motor.A procedure for oxygen transfer coefficient (k_la) determination in real conditions has been tested. It is essentially based on gas balance measurement for establishing the oxygen uptake rate and dissolved oxygen measurement at different levels in the tank.     

Hydrothermal purification and enrichment of Chilean copper concentrates: Part 1: The behavior of bornite,covellite and pyrite

The nature and basic kinetics of the hydrothermal reactions of bornite, covellite and pyrite with copper sulfate solutions were investigated, as a previous study on the behavior of the bulk Chilean copper concentrates. The reaction of bornite produced digenite at < 160 °C and djurleite above this temperature. The reaction products formed a continuous, non porous layer. The rates were of zero order with respect [Cu²⁺]_(aq), and the activation energy was ～ 100 kJ/mol. Covellite was transformed to digenite at < 200 °C and to chalcocite (Q and M) at > 200 °C. The reaction was characterized for an irregular nucleation and growth of the products, which were non-protective. The order with respect the [Cu²⁺]_(aq) was 0.6 and the activation energy ～ 110 kJ/mol. The pyrite reaction was significant at > 200 °C and extensive at 240 °C. It produced a mixture of digenite/chalcocite-Q, with small amounts of djurleite. The transformation has a high Philling–Betworth ratio (～ 1.6), causing the break of the product layers. The reaction order and the activation energy were also 0.6 and ～ 110 kJ/mol, respectively. The rate of the bornite reaction should be controlled by solid-state ionic diffusion, whereas for covellite and pyrite the rates should be limited by electrochemical processes. Towards the hydrothermal transformation, the reactivity of the main phases present in Chuquicamata-type concentrates was: bornite > chalcopyrite > covellite > sphalerite > pyrite.     

Separation and preconcentration of trace indium(III) from environmental samples with nanometer-size titanium dioxide

This work assesses the potential of an adsorptive material, nanometer TiO₂, for the separation and preconcentration of trace indium ions from various aqueous media. The adsorption behavior of nanometer TiO₂ for indium ions was investigated. It was found that the adsorption percentage of the indium ions was more than 96% in pH 3.5–4.0, and the desorption percentage of In(III) ions was more than 99% in pH ≤ 1.5. Good relative standard deviate (1.5%) and lower analytical detection limit (0.45 µg?mL^? 1) were obtained. The adsorption equilibrium was well described by the Langmuir isotherm model with monolayer adsorption capacity of 4566 µg g^? 1 (25 °C). The accuracy of the method is confirmed by analyzing the certified reference material (GBW-07405, GBW07406). The results demonstrated good agreement with the certified values.