Acidic Thiocyanate Solutions Research Articles

Heap sulphuric-thiocyanate leaching of gold and uranium

The article evaluates the main parameters of simultaneous heap leaching of gold and uranium from oxidised gold-uranium ore using sulphuric acid thiocyanate solutions. Pilot tests for the simultaneous heap leaching of gold and uranium were carried out using oxidised crushed gold-uranium ore with a size of -40+0 mm. The gold and uranium content in the ore was 0.80 and 266 g/t, respectively. Experiments were carried out using a percolation column with a diameter of 300 mm and a height of 2000 mm The ore mass in the column was 180 kg. The temperature during the tests was in the range of 17–25°C. Leaching was carried out under the following conditions: H2SO4 concentration – 5 g/dm3, SCN– concentration – 0.5 g/dm3, Eh – 490–510 mV, Fe3+ ion concentration – 1.0–1.5 g/dm3. Acid-soluble minerals contained in the ore comprised the source of iron ions. Hydrogen peroxide was used to oxidise Fe2+ ions. Pilot tests were carried out in a closed cycle with separate sorption of gold and uranium. Based on the research results, gold recovery reached 90%, while uranium recovery was 55%. Following gold and uranium leaching, the loaded activated carbons and ion exchange resins were obtained. It was established that the gold content on activated carbons was 0.5–0.6 mg/g, while the uranium content on ion exchange resins amounted to 30–35 mg/g. The reagent consumption was as follows: H2SO4 – 10.5 kg/t, KSCN – 0.94 kg/t, H2O2 – 0.65 kg/t. It is shown that the technology for simultaneous heap leaching of gold and uranium with sulphuric acid thiocyanate solutions offers efficient processing of the ore. The recovery rates of gold and uranium are comparable to those obtained during pilot tests for heap leaching of the ore using conventional technology, involving the individual twostage leaching of these metals using sulphuric acid and cyanide solutions.

Electrochemical dissolution behavior of gold and its main coexistent sulfide minerals in acid thiocyanate solutions

Electrochemical tests were developed to investigate the electrochemical dissolution behavior of gold and its main coexistent sulfide minerals in acid thiocyanate solutions. The optimal leaching conditions for gold in acidic thiocyanate system were pH 2, 0.15 mol·L−1 thiocyanate and 0.2 g·L−1 Fe3+. Fe3+ addition to the acidic thiocyanate system promoted gold dissolution significantly, arsenopyrite dissolution was inhibited, chalcopyrite dissolution was increased, and the dissolution behavior of other associated minerals remained mostly unchanged. Thiocyanate made gold and associated mineral leaching easier. The galvanic corrosion effect of gold and its main coexistent sulfide minerals in an acidic thiocyanate-free system was that the chalcocite, arsenopyrite and pyrite acted as a cathode to reduce anodic gold dissolution; galena as an anode undergoes oxidation to inhibit anodic gold dissolution. There was almost no galvanic corrosion behavior between stibnite, yellow sphalerite and black sphalerite and gold. Thiocyanate addition changed the galvanic corrosion behavior of stibnite and yellow sphalerite in the thiocyanate system, which inhibited anodic gold dissolution. In the acidic thiocyanate system in the presence of ferric iron, the arsenopyrite promoted anodic gold dissolution, the chalcocite and gold were mostly free of galvanic corrosion, and the remaining minerals inhibited anodic gold dissolution.

A Novel Viewpoint of Imidazolium Salts for Selective Extraction of Cobalt in the Presence of Nickel from Acidic Thiocyanate Solutions by Ionic-Liquid-Based Solvent-Extraction Technique

In this study, the selective extraction and stripping conditions of Co(II) from acidic thiocyanate solution containing Co(II) and Ni(II) by ionic-liquid-based solvent-extraction technique using symmetric and asymmetric imidazolium bromide salts substituting butyl and isobutyl groups were experimentally optimized. The molecular structure effect of imidazolium bromide salts (IMs) have been determined as main factor to extract Co(II). The executive parameters on stripping and extraction processes, such as IMs concentration, pH, thiocyanate concentration, stripping reagent type, and concentration, were experimentally investigated. Molecular variation of organometalic complex (adduct) consisting of IMs and Co-SCN, were illuminated by comparision of ATR-FTIR spectrums of pure and Co-SCN loaded IMs. Stoichiometric rates of the adduct was verified with slope analysis. In light of these examinations, Co(SCN)3− has been determined as prominent Co-SCN species in aqueous media. Symetric IMs were identified as more effective than asymmetric ones on selective separation of Co(II) from Ni(II). Under optimum conditions, 99.20% of Co(II) was extracted and 93.33% of Co(II) was recovered with higher separation factors especially in diluted solution, whereas, Ni(II) extractions were negligible. We have concluded that the separation power of this study is high in Co(II)/Ni(II) containing dilute solutions and it can be used in preconcentration purposes effectively.

The stability of selected sulfide minerals in sulfuric acid and acidic thiocyanate solutions

The stability of pyrite, chalcopyrite, chalcocite, covellite, bornite and enargite at pH 2 in the absence and presence of thiocyanate has been determined by linear sweep voltammetry and chronoamperometry under conditions pertaining to the thiocyanate leaching of gold (pH 2 and 602–702mV vs. SHE). Electrochemical measurements indicated that the decomposition rate of all sulfide minerals increased with an increase in oxidation potential with pyrite and chalcopyrite being the least reactive and chalcocite and bornite being the most reactive of the examined sulfides. The oxidation rate of covellite and enargite was higher than that of pyrite and chalcopyrite but much lower than that of chalcocite and bornite. It was found that the variation of pH from pH 1 to pH 3 has minimal effect on the oxidation rate of pyrite and chalcopyrite. In the presence of 0.05M thiocyanate at pH 2 and in the potential range of interest for gold leaching (602–702mV vs. SHE), the effect of thiocyanate was not significant on the oxidation of selected sulfides.

Improved adsorption and separation of palladium(II) and platinum(IV) in strong hydrochloric acid solutions using thiocyanate‐retaining tannin gel

AbstractA tannin gel (TG) synthesized from condensed tannin molecules has a remarkable ability to adsorb various metal ions in aqueous solutions. In the present study, we have investigated the adsorption behaviors of palladium and platinum ions, Pd(II) and Pt(IV), in strong HCl solutions using the thiocyanate‐retaining tannin gel (SCN‐TG) prepared by adsorption of thiocyanate ion (SCN−) onto the TG in acidic thiocyanate solutions as reported previously (Ind Eng Chem Res 2011, 50, 12366). Although the adsorption rate of Pt(IV) is slow compared to that of Pd(II), the SCN‐TG was able to adsorb both Pd(II) and Pt(IV) in a 1 M HCl solution, where the TG can never adsorb them. Besides, we have succeeded in the selective adsorption of Pd(II) from the mixture solution of Pd(II) and Pt(IV) at a temperature somewhat lower than room temperature using the SCN‐TG. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Thiocyanate hydrometallurgy for the recovery of gold.: Part II: The leaching kinetics

Acid thiocyanate leaching of gold was investigated in the presence of ferric sulfate as an oxidant. According to leaching kinetic studies the initial rate of gold leaching is slow, and not significantly dependent on thiocyanate (0.05–0.2M) and ferric (0.1–1.0g/L) concentrations. Ferrous and cupric ions had no effect on leaching kinetics under the conditions studied. In contrast, silver (I) and copper (I) ions significantly impeded the rate of gold leaching. The electrochemical experiments (linear sweep voltammetry and chronoamperometry) indicated that the anodic reaction for gold leaching in acid thiocyanate solutions is the limiting step for the leaching process. Gold dissolution and thiocyanate oxidation participate simultaneously in the anodic process. The addition of thiourea noticeably enhanced the rate of gold leaching. Fourier transform infrared spectroscopy (FTIR) studies demonstrated that thiocyanate and its complexes with the metal ions involved in the leaching systems (Fe (III), Cu (II), Cu (I) and Ag (I)) had very weak adsorption properties at the gold surface.

Preparation of Thiocyanate-Retaining Tannin Gel for Adsorption Recovery of Palladium from Strong Hydrochloric Acid Solutions

A tannin gel (TG) synthesized from condensed tannin molecules has a remarkable ability to adsorb various metal ions in aqueous solutions. In the present study, we have introduced thiocyanate ions (SCN–) into the TG by adsorption process in acidic thiocyanate solutions to improve its adsorbability for palladium ion, Pd(II). To determine the optimum conditions for preparing the SCN–-retaining tannin gel (SCN-TG), we have investigated the introduction mechanism of SCN– into the TG at 298 K and HCl concentrations less than or equal to 1 M, where the decomposition of SCN– can be negligible. The adsorption amount of SCN– onto the TG increased with increasing HCl concentration, indicating that SCN– is adsorbed onto the TG through the electrostatic attraction between anionic SCN– and the protonated hydroxy groups in the TG at higher HCl concentrations. Using the resultant SCN-TG and the TG, we have conducted the Pd(II) adsorption experiment at molar-level concentrations of HCl and found that the SCN-TG can adsorb...

Application of fluoride to enhance aluminum cementation of gold from acidic thiocyanate solution

The cementation of gold from acidic thiocyanate solution was studied using aluminum powder. The related parameters such as pH, thiocyanate concentration, gold concentration, temperature, stirring speed, aluminum/gold mass ratio, presence of iron (III) and gas atmosphere were systematically investigated. The results show that temperature and deoxygenation were determined to positively affect the gold recovery. Conversely, the presence of iron (III) inhibits significantly the cementation reaction. The addition of fluoride into leach solution could overcome the inhibitory effect of iron (III) and enhance the gold cementation rate. It was established that the rate of the reaction was first-order with respect to the gold concentration. The activation energy was found to be 41.9kJ/mol and the cementation process was considered to be chemically controlled without the presence of ferric ion and the addition of fluoride ion in solution. A possible cementation mechanism was proposed.

A thermodynamic study of the dissolution of gold in an acidic aqueous thiocyanate medium using iron (III) sulphate as an oxidant

Species distribution and pH-potential diagrams have been constructed for the gold/iron/thiocyanate/sulphate/water system in the pH and concentration ranges expected in the practical leaching process. Apart from elucidating the complex chemistry of such a system, these diagrams were used to predict: the feasibility of; the optimum experimental conditions for; and the significant factors affecting the leaching of gold with acidic thiocyanate solutions in the presence of iron (III) sulphate.

塩基性チオシアン酸アンモニウム溶液による銀の溶解

The effect of oxidizing agent, concentration of ammonium thiocyanate, pH and the temperature on the dissolution of silver in basic ammonium thiocyanate solution were studied.The following have been concluded: 1. Cu (II) and oxygen gas are necessary to dissolve silver effectively.2. Dissolution rate of silver is proportional to the concentration of thiocyanate at lower concentrations of thiocyanate, but it becomes constant independently of the concentration at higher concentrations.3. When the concentration of thiocyanate is high enough to make the dissolution rate of silver independent of the concentration, the dissolution rate increases almost proportionally to the increase in the concentration of Cu (II).4. When the rate is proportional to the concentration of thiocyanate, the activation energy obtained is rather high and the rate determining step is assumed to be the chemical reaction of thiocyanate ion with silver on its anodic sites on the surface of silver particles. 5. When the rate dissolution is almost proportional to the concentration of Cu (II), the rate determining step is the diffusion of Cu (II) ions to the surface of silver particles.6. Overall reactions are considered as follows: Ag+Cu (NH3) 42++6SCN-=Ag (SCN) 43-+Cu (SCN) 2-+4 NH3 Cu (SCN) 2-+4 NH3+H++1/4 O2=Cu (NH3) 42++2SCN-+1/2 H20 These phenomena are quite the same as those of the dissolution of silver in acidic thiocyanate solution using Fe (III) as oxidizing agent.

Reactivity of surface iron(III)-thiocyanate complexes characterized by the dissolution of hematite in acidic thiocyanate solutions

Reactivity of surface iron(III)-thiocyanate complexes characterized by the dissolution of hematite in acidic thiocyanate solutions

ChemInform Abstract: Spectroelectrochemical Characterization of Iron(III)

AbstractThiocyanate Complexes in Acidic Thiocyanate Solutions at an Optically Transparent Thin‐Layer‐Electrode Cell.

Spectroelectrochemical characterization of iron(III)-thiocyanate complexes in acidic thiocyanate solutions at an optically transparent thin-layer-electrode cell

Etude du processus d'oxydoreduction du couple Fe(III)/Fe(II) en solutions acides. On obtient l'espece (SCN) 3 − par l'intermediaire du radical anionique (SCN) 2 − ˚

The Liquid-Liquid Extraction of Zinc with Polyethylene Glycol and Poly(oxyethylene)-type Nonionic Surfactants

Abstract The Zn(II) extraction was made from its acidic thiocyanate solution, using polyethylene glycol and its mono(alkylphenyl) ether as extractants. The effects of the number of oxyethylene groups (–O–CH2–CH2–) per molecule and of the kind of the counter cation of thiocyanate on the extractability are described, together with some other factors affecting the Zn(II) extraction.

Diphenyl(2-pyridyl)methane as a solvent for thiocyanate complexes of zinc in aqueous mineral acids

Tracer (∼10−8 M) zinc can be quantitatively extracted with 0.1M diphenyl(2-pyridyl)methane (DPPM) in benzene from neutral and acidic aqueous thiocyanate solutions in a single extraction. In all cases, extraction times of 1–5 min are sufficient for equilibration. The effects of the concentration of the mineral acids, the reagent, complexing and salting-out agents and phase-volume ratios on the metal extraction are reported. The metal is predominantly extracted through solvation, and the extraction of the metal as Zn(SCN)2(DPPM)2 is indicated. Among the common salts only sodium chloride exerts a slight depressing effect on extraction when present in high concentration. The metal can be stripped from the organic phase with aqueous oxalate, citrate or acetate solutions in a single operation. Distribution coefficients and separation factors for a number of metal ions, relative to zinc, are reported for 0.2M potassium thiocyanate media that contain the optimal concentration of mineral acid. The method can be employed for the simultaneous preconcentration of toxic metals such as zinc, copper and mercury from neutral aqueous solution in water pollution studies.

Liquid—liquid extraction of zinc from aqueous thiocyanate solutions with 5-(-4-pyridyl)nonane in benzene

5-(4-Pyridyl)nonane dissolved in benzene has been applied to the extraction of zinc, down to very low concentration (< 10 −6 M), from aqueous thiocyanate solutions. The metal can be quantitatively extracted from neutral and acidic thiocyanate solutions (up to 5 M HCl, 0.25 M HNO 3 or 0.25 M H 2SO 4) in a single extraction. Equilibration times of 5 min are sufficient for almost complete extraction. The optimum thiocyanate concentration range is 0.05–0.5 M. Among the common anions chloride exerts a slight depressing effect on extraction from neutral solution when present in high concentration. The extraction mechanism and the composition of the extracted complexes of zinc are discussed. The metal is predominantly extracted by means of a solvate mechanism. The effect of chloride, nitrate, sulphate, acetate, citrate, oxalate and ascorbate ions on the extraction of zinc is described. Several elements, including those of interest in separation of zinc, have been tested for extraction from O.1 M KSCN at the optimal concentrations of the mineral acids, and the separation factors estimated.

Liquid-liquid extraction of some actinides with polyethyleneglycol and its derivatives

Polyethyleneglycol (PEG) and its derivatives of high molecular weight were found to be employed as useful extractants for the solvent extraction of uranium. The extraction behaviors of uranium and neptunium were investigated, particularly concerning the dependence of the extractibility of uranium(VI) on the molecular weight of PEG. A dominating species of the extracted uranium(VI) thiocyanate complexes was assumed to be NH4 UO2(SCN)3·(PEG). The extraction of protactinium was also preliminarily studied. The extraction of these actinides from an acidic thiocyanate solution increased in the order: uranium(VI)>protactinium(V)>neptunium(V).

ChemInform Abstract: ANALYTICAL APPLICATION OF CATALYTIC POLAROGRAPHIC CURRENT OF NICKEL(II) IN ACIDIFIED THIOCYANATE SOLUTIONS CONTAINING COBALT(II)

AbstractBei der polarographischen Reduktior in angesäuerter Thiocyanat‐Lösung zeigt Ni(II) eine katalytische Welle mit ausgeprägtem Maximum, die für Ni‐Bestimmung geeignet ist.

Analytical Application of Catalytic Polarographic Current of Nickel(II) in Acidified Thiocyanate Solutions Containing Cobalt(II)

Abstract Simple and sensitive methods have been developed for the determination of nickel(II), based on the catalytic polarographic current in acidic thiocyanate solution in the presence and absence of cobalt(II). The basis of the methods and the effect of variables have been investigated and elucidated. In the absence of cobalt(II), thiocyanate solution containing large amounts of hydrogen ions serves a supporting electrolyte, while an acidic thiocyanate solution containing tetra-n-butylammonium salts is suitable for the determination of nickel(II) in the presence of cobalt(II). These methods are applicable to the determination 2×10−6 M nickel(II) in the presence and absence of 1×103 M cobalt(II).

Catalytic current of cobalt(II) and cobalt(III) in acidic thiocyanate solutions at mercury electrodes

Cobalt(II) or cobalt(III) after its one electron reduction in thiocyanate solution containing perchloric acid or acetate buffer at dropping and stationary mercury electrodes exhibited a catalytic current in the potential region between −1.0 and −1.25 V vs . SCE. The characteristics of the catalytic current have been investigated by conventional polarography, cyclic voltammetry, chronoamperometry and controlled potential electrolysis. A mechanism which involves the cyclic regeneration of cobalt(II) by the oxidation of electrodeposited metallic cobalt with thiocyanate ion has been presented. Hydrogen ions act as a neutralizing agent on the reduction products of thiocyanate ion, cyanide and sulphide ions. The regeneration of cobalt(II) has been postulated from the fact that the reaction of Raney cobalt with thiocyanate ions affords divalent cobalt, cyanide and sulphide ions.