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Kozin, L. F.; Berezhnoi, E. O.; Bogdanova, A. K.

doi:10.1023/a:1022283921842

Cited by 11 publications

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“…Adsorption layers formed on the gold electrode surface during electrolysis in TCA solutions were studied by Auger spectroscopy (Auger spectrometer JAMP-10S, manufactured by JEOL, Japan). The procedure of measuring Auger spectra and microimages of surfaces covered with adsorption layers is described in [2]. Figure 1 shows an anodic current vs. potential dependence of gold ( i a vs. E curves) at a polarization rate ν = 0.010 V/s and TCA concentration C TCA of 2.81 × 10 -3 (curves 1 , 2 ) and 5.62 × 10 -3 M (curves 3 -5 ) in 0.1 M H 2 SO 4 .…”

Section: Methodsmentioning

confidence: 99%

“…According to earlier studies [1,2], TCA is oxidized by Fe(III) ions to give formamidine disulfide ( FADS ) : (NH 2 )NHC=S-S=CNH(NH 2 ) molecules (see Eq. (1)).…”

Section: Introductionmentioning

confidence: 99%

“…(2)), which interact with TCA molecules in the diffusion layer volume to give trithiocarbamide ions [{NH 2 ) 2 C=S} 3 Au] + (see Eq. (3)) according to the following reactions: Hence, at corrosion dissolution of gold in acidic solutions, TCA plays the role of both oxidant (FADS) and ligand in a two-step formation of gold(I) trithiocarbamide complex [2]. TCA is unstable in aqueous solutions and undergoes hydrolysis to give hydrosulfide and sulfide ions, which are adsorbed at the gold surface and interact with Au(I) ions, the final products of its oxidation to form complex adsorption layers (ALs) [2].…”

Section: Introductionmentioning

confidence: 99%

“…For this reason, the rate of gold dissolution in TCA solutions depends on the preparation time of TCA solutions, the conditions of FADS formation, the duration of the contact between gold electrode and TCA solution, the temperature, etc. [2][3][4][5]. During the corrosion oxidation of gold in TCA solutions in the presence of iron(III) ions, FADS molecules adsorb by their sulfur atoms that carry induced negative charges ( δ -) on the positively charged gold surface [1,2].…”

Section: Introductionmentioning

confidence: 99%

“…[2][3][4][5]. During the corrosion oxidation of gold in TCA solutions in the presence of iron(III) ions, FADS molecules adsorb by their sulfur atoms that carry induced negative charges ( δ -) on the positively charged gold surface [1,2]. It seemed of interest to study the kinetics of gold dissolution in TCA solutions by using a "pure" oxidant, viz., anodic current.…”

Section: Introductionmentioning

confidence: 99%

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Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

2005

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Kinetics and mechanism of gold electrooxidation in sulfuric acid solutions of thiocarbamide ( TCA ) are studied by measuring voltammograms ( VA ) of gold and glassy carbon ( GC ) electrodes. In a potential ( E ) range from -0.2 to 1.2 V ( SCE ), VA of a gold electrode demonstrate three peaks. The first and the second peaks correspond to gold electrooxidation to [AuTCA ads ] + and [Au(TCA ads ) 3 ] 3+ ions at E of 0.152 and 0.554 V, while the third one corresponds to TCA electrooxidation. The electrooxidation of TCA on GC electrodes is characterized by two VA peaks at 0.983 and 1.437 V. The first peak corresponds to the formation of formamidine disulfide (FADS) ( k a1 = 6.40 × 10 -4 cm/s), while the second peak corresponds to TCA oxidation to sulfides and hydrosulfides ( k a2 = 7.78 × 10 -5 cm/s). The composition of adsorption layers formed at the Au electrode is analyzed by Auger spectroscopy. The introduction of sodium sulfide into TCA solutions eliminates the formation of adsorption layers and accelerates Au oxidation in such solutions. The rate constants of gold electrooxidation k a = 6.31 × 10 -3 cm/s and Au(I) electroreduction k c = 5.46 × 10 -4 cm/s in TCA solutions are estimated. Kinetic parameters (charge transfer coefficients, reactions orders in carbamide) are determined and the mechanisms of Au and TCA oxidation in sulfuric acid solutions are proposed.

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Section: Methodsmentioning

confidence: 99%

“…According to earlier studies [1,2], TCA is oxidized by Fe(III) ions to give formamidine disulfide ( FADS ) : (NH 2 )NHC=S-S=CNH(NH 2 ) molecules (see Eq. (1)).…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

2005

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The Effect of Sodium Thiocyanate on the Corrosion Dissolution Rate of Silver in Thiosemicarbazide Solutions

Kozin

Danil’tsev

2005

Prot Met

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The effect of thiocyanate on the corrosion dissolution rate of silver in thiosemicarbazide (TSC) ammonium-chloride-bromide solutions was studied by using gravimetry and rotating disc electrode technique. The corrosion dissolution of silver was shown to be preceded by the formation of dithiosemicarbazide molecules due to the oxidation with iron (III) ions. The "second ligand" phenomenon is discussed, which consists in an increase in the corrosion dissolution rate of silver upon adding sodium thiocyanate (STC) to a TSC solution because of the decrease in the adsorption layer thickness. A synergism was discovered in the case of the corrosion dissolution of silver in a solution containing both thiosemicarbazide and sodium thiocyanate. The composition of the adsorption layer formed on a silver electrode and involving silver, sulfur (AgHS and Ag 2 S), as well as carbon, nitrogen, and oxygen forming the base of adsorption layers, was investigated by means of Auger spectrometry. The kinetic parameters (rate constants and reaction orders) were determined and a mechanism of the corrosion dissolution of silver in TSC, STC, and TSC + STC solutions is proposed.

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Extraction of Gold from ores and concentrates by leaching with the use of cyanides and alternative reagents

Kozin

Melekhin

2004

Russ J Appl Chem

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The problems associated with gold mining are considered from the standpoint of application of heap leaching, a method for gold recovery. Data on the kinetics and mechanism of gold dissolution in cyanide and alternative solvents [thiocarbamide solutions containing Fe(III) ions and hypochlorite-chloride bromine-bromide, iodine-iodide, and copper-thiosulfate solutions], which make it possible not only to improve the working efficiency in gold mining, but also to lessen the contamination of the environment with highly toxic compounds.The method of heap leaching (HL) is a geotechnological method for processing of low-grade goldcontaining ores and rejects of concentration plants. Alkaline solutions of cyanides are used in enormous amounts as solvents for gold [1,2], which gives rise to quite a number of ecological problems. From the standpoint of environment protection [3], it is unsafe to use the HL technique in countries with fertile soils and high population density. Therefore, an exceedingly important problem of the HL technique is that alternative solvents for gold are to be developed [3].In the HL of gold, special attention is given to taking into account the natural factors, absence of rifts, density of the surface layer of soil, presence of clay strata, and absence of compounds of such elements as arsenic, selenium, cadmium, thallium, lead, etc. in the ores. An exceedingly important specific feature of the HL technique is the possibility of processing of both moderate amounts of gold-containing ores and concentrates (tens and hundreds of thousands of tons) and enormous quantities of gold-containing raw materials of technological origin (tens and hundreds of millions of tons) [1,2]. At present, the HL of gold is the most cost-effective method for leaching of lowgrade gold-containing ores. However, despite the high economical efficiency of the HL of gold, proper attention is not, paradoxically, paid to the environment protection in gold-mining regions [3].The rise in gold output in many countries all over the world is clearly seen from the data in Fig. 1. A steep rise in the output of gold has been noted in Fig. 1. Output of gold, Q Au in some countries. (N ) Years; the same for Fig. 2.

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Cited by 11 publications

References 0 publications

Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

Kinetic Parameters and Mechanism of Gold Electrooxidation in Thiocarbamide Solutions

The Effect of Sodium Thiocyanate on the Corrosion Dissolution Rate of Silver in Thiosemicarbazide Solutions

Extraction of Gold from ores and concentrates by leaching with the use of cyanides and alternative reagents

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