A spectroelectrochemical investigation of the influence of sodium diisobutyldithiophosphinate on silver dissolution in aqueous cyanide

Polarization studies have been carried out to determine the influence of diisobutyldithiophosphinate (DIBDTPI) on the dissolution of silver in cyanide solutions at pH 11. DIBDTPI was found to inhibit dissolution at concentrations similar to those used when this compound is applied as a flotation collector. The inhibition efficiency in 10^–2 mol dm^–3 CN^– was found to increase with increase in DIBDTPI concentration in the range 10^–6–10^–4 mol dm^–3, and with increase in time of exposure of the silver to the DIBDTPI solution. The inhibition efficiency found for 10^–4 mol dm^–3 DIBDTPI in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 64.6% and 95.0% for exposure times of 10 min and 2 h, respectively. These values are significantly less than those found previously for 2-mercaptobenzothiazole under the same conditions. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of DIBDTPI displacing cyanide from the silver surface. Voltammetry at 0.5 mV s^–1 indicated that adsorption of DIBDTPI involves charge transfer.     

A SERS spectroelectrochemical investigation of the interaction of 2-mercaptobenzothiazole with copper, silver and gold surfaces

The interaction of the sulfide mineral flotation collector, 2-mercaptobenzothiazole, with silver, copper and gold surfaces has been investigated by surface enhanced Raman scattering (SERS) spectroscopy. 2-mercaptobenzothiazole, the copper, silver and gold compounds of this species, and the dithiolate, 2,2-dithiobis(benzothiazole) were characterised by ¹³C NMR and Raman spectroscopy to provide a basis for identifying surface species. SERS investigations showed that, at pH 4.6 where the solution species is in the protonated form, and at 9.2, where it is present as the ion, adsorption on each metal occurs over a wide potential range. Attachment of the organic compound occurs through bonding between the exocyclic sulfur atom and metal atoms in the surface. X-ray photoelectron spectroscopy confirmed that the adsorbed layer was of monolayer thickness. Adsorption of the protonated 2-mercaptobenzothiazole occurs on copper at pH 4.6 at potentials below that at which charge transfer adsorption commences.     

2-巯基苯并噻唑季铵盐型复配水处理剂的合成及性能研究

为减少工业水处理剂的污染问题,采用2-巯基苯并噻唑为原料,通过巯基烷基化与水溶性的季铵基团结合,合成了3种带有季铵基团的苯并噻唑衍生物,并证实了它们的结构。缓蚀性能实验和杀菌实验表明氯化二甲基苄基[2-(2-苯并噻唑基硫代)乙基]铵的性能为最佳。     

鼓氧氰化法生产高纯度氰化银钾的研究

以电解银粉为原料，采用鼓氧氰化法合成了氰化银钾，保持金属银过量投料，控制氰化银钾溶液浓缩水量是得到高纯度和高收率产品的关键，此方法具有原料简单，产吕纯度高，生产操作容易，生产成本低和环保要求低的优点，适合中小企业生产。     

Inhibition of cobalt active dissolution by benzotriazole in slightly alkaline bicarbonate aqueous media

The efficiency of benzotriazole as inhibiting agent for the corrosion of cobalt was probed at pH ranging from 8.3 to 10.2 in a sodium bicarbonate solution, chosen to simulate mild natural environments. From electrochemical, Raman spectroscopy, atomic force microscopy and ellipsometry experiments, we have demonstrated that benzotriazole markedly affects the electrodissolution reactions, which become modeled by the formation of a [Co(II)(BTA)₂·H₂O]_n film according to two different mechanisms. Surface-enhanced Raman spectroscopy has shown that the polarization of a cobalt electrode at cathodic potentials with respect to its potential of zero charge allows a mechanism of specific adsorption of the neutral form of benzotriazole to take place through a suspected metal-to-molecule electron transfer and which follows Frumkin's adsorption isotherms. At the onset of the anodic dissolution, some experimental evidence suggests that these adsorbed neutral benzotriazole molecules deprotonate to yield a very thin [Co(II)(BTA)₂·H₂O]_n polymer-like and water-insoluble protective film, responsible for the inhibition of active dissolution processes occurring at slightly more anodic potentials. In the anodic dissolution region, deprotonated benzotriazole species present in the bulk solution favors the formation of a multilayered [Co(II)(BTA)₂·H₂O]_n film, which also contributes to the inhibition of any further cobalt dissolution usually observed at higher electrode potentials.     

UV-H2O2工艺对焦化废水中氰化物深度处理研究

在新颁布的《炼焦化学工业污染物排放标准》(GB 16171—2012)中,总氰化物的排放限值降至0.2 mg/L,这使得传统除氰工艺已无法满足处理要求。以某焦化厂经生化、混凝处理后的出水为研究对象,探究了UV-H2O2工艺用于深度除氰的可行性。实验结果表明:在p H=10、n(H2O2)∶n(CN)=250∶1的条件下,UV-H2O2工艺处理30 min后总氰去除率可达80%,出水总氰(<0.18 mg/L)满足新标准要求。     

Enhanced corrosion inhibition behavior of carbon steel in aqueous solution by Phosphoserine-Zn2+ system

The corrosion inhibition effect of carbon steel in aqueous solution was using a synergistic mixture of an environmentally friendly inhibitor system phosphoserine (PS) and Zn²⁺ using gravimetric studies, potentiodynamic polarization, and electrochemical impedance studies. Potentiodynamic polarization studies showed that the inhibitor system is a mixed type inhibitor. Electrochemical impedance studies of the metal/solution interface indicated that the surface film is highly protective against the corrosion of carbon steel in the aqueous solution. X-ray photoelectron spectroscopic analysis of the protective film exhibited the presence of the elements viz., iron, phosphorus, nitrogen, oxygen, carbon, and zinc. The chemical shifts in the binding energies of these elements inferred that the surface film is composed of oxides/hydroxides of iron, Zn(OH)₂, and [Fe(II)/(III)-Zn(II)-PS] complex. Further, the surface examination techniques viz., FTIR, SEM, and AFM studies confirm the formation of an adsorbed protective film on the carbon steel surface. Based on the results obtained, a suitable mechanism of corrosion inhibition is presented.     

Influence of agarose on the electrochemical behaviour of the silver and platinum aqueous acid electrolyte interface

The influence of agarose on the electrochemical behaviour of the interfaces silver/aqueous agarose + 0.014 M silver sulfate + 0.5 M sodium sulfate + 0.01 M sulfuric acid and platinum/aqueous agarose + 0.5 M sulfuric acid, at 298 K, was studied. Freshly prepared and aged agarose-containing solutions in the range of agarose concentration 0.01 c _aga 0.5% w/v were used. Viscosity, open circuit potential, solid sample infrared spectra and conventional voltammetric measurements were performed. The electrooxidation of adsorbates produced from both the homogeneous and heterogeneous decomposition of agarose-containing solutions on platinum was investigated. Results are discussed in terms of the structure and interactions of agarose molecules in sols and gels. The electrooxidation of adsorbed residues can be explained within the complex reaction pathway for the electrooxidation of saccharides previously discussed in the literature.     

An electrochemical study of gold cementation with zinc powder at low cyanide concentration in alkaline solutions

The half-reactions involved in gold cementation on zinc powder from low concentration alkaline cyanide solutions were studied in a steady state regime, employing electrodes of glassy carbon and graphite paste with zinc powder. The effects of pH, cyanide and initial gold concentrations were investigated using various electrochemical techniques. The results were used to determine the controlling step of the cementation at low cyanide concentration and to interpret the influence of the variables on this process. Mixed potentials and associated currents were determined from the Evans' diagrams constructed using sampled current–potentials curves from chronoamperometric results for half redox reactions. These values do not adequately describe the global cementation reaction because gold reduction in low cyanide concentration solutions is greatly influenced by a strong contribution from adsorptive processes. This behaviour is different from that found by other authors for concentrated gold and cyanide solutions, where the process is controlled by the complex ion diffusion (Au(CN)₂ ^–). The strong component of adsorption found in the present work does not permit the determination, using the Evans' diagrams, of the cementation velocity. Direct monitoring of the mixed potential was proposed, employing an electrode made of zinc powder in carbon paste submerged in a gold cyanide solution. The results of these experiments at low cyanide concentrations show that zinc oxidation is controlled by the formation of different passivating layers, the nature of which depended on the pH of the solution, and that the gold reduction reaction is strongly influenced by adsorption phenomena.     

The mechanism of electrode process in the system silver/silver cyanide complexes

The electrode's surface inhomogeneity was taken into account studying the mechanism of process. The effect of CN⁻ adsorption and partial surface coverage was investigated by electrochemical fast Fourier transform (FFT) impedance spectroscopy (0.03-3900 Hz). The isopotential solutions (E₀=−0.350 V) as well as solutions containing constant silver cyanide complex concentration (0.05 M) and different free cyanide ion concentrations (from 0.01 to 1.0 M) were studied. The exchange current density, re-calculated for only active area, gives electrochemical reaction order (R_CN=1.8 for α=0.5, and R_CN=2 for α=0.6) which is independent from CN⁻ concentration and from the composition of complexes prevailing in the bulk of electrolyte. The value of R_CN close to 2, obtained in a series of isopotential solutions confirms that in all cases the complex ions Ag(CN)₂⁻ take direct part in the charge transfer step.     

In situ Raman spectroscopy and electrochemical techniques for studying corrosion and corrosion inhibition of iron in sodium chloride solutions

The corrosion of single crystal pure iron in 3.5% NaCl solutions and its inhibition by 3-amino-5-mercapto-1,2,4-triazole (AMTA) have been studied using in situ and ex situ Raman spectroscopy, cyclic voltammetry (CV), open-circuit potential (OCP), potentiodynamic polarization (PDP), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS) measurements. CV experiments indicated that the iron electrode in the chloride solution alone showed an anodic peak at ∼−650 mV after the 5th cycle shifted to ∼−610 mV after the 20th cycle; another cathodic peak appeared at ∼−990 mV. In the presence of 1.0 mM AMTA, these two peaks shifted to ∼550 and −1050 mV, respectively. OCP, PDP, CA and EIS revealed that the presence of AMTA and the increase of its concentration move the corrosion potential to more positive values and decrease both the corrosion current and corrosion rate. This effect also increases with increasing the immersion time of iron electrode to 24 h in the test electrolyte. In situ and ex situ Raman investigations confirmed that the addition of AMTA molecules to the chloride solution strongly inhibits the iron corrosion through their adsorption onto the surface blocking its active sites and preventing its corrosion.     

Computational and electrochemical investigation for corrosion inhibition of nickel in molar nitric acid by piperidines

The adsorption and corrosion inhibition behaviour of four selected piperidine derivatives, namely piperidine (pip), 2-methylpiperidine (2mp), 3-methylpiperidine (3mp), and 4-methylpiperidine (4mp) at nickel in 1.0 M HNO₃ solution were studied computationally by the molecular dynamics simulation and quantum chemical calculations and electrochemically by Tafel and impedance methods. The results indicate a strong dependence of the inhibition performance on the nature of the metal surface, in addition to the structural effects of piperidines. Inhibition is accomplished by adsorption of piperidines on the metal surface without detectable changes in the chemistry of corrosion. Adsorption is predominantly chemisorptive in the active region and by hydrogen bond formation in the passive region. The potential of zero charge (PZC) of the nickel electrode was determined in 1.0 M HNO₃ solutions in the absence and presence of 10⁻² M 2mp, and the electrostatic (physical) adsorption was discussed. The inhibition efficiency of these compounds increases in the order: 4mp > 3mp > 2mp > pip. Molecular simulation studies were applied to optimize the adsorption structures of piperidine derivatives. The nickel/inhibitor/solvent interfaces were simulated and the charges on the inhibitor molecules as well as their structural parameters were calculated in the presence of solvent effects. Quantum chemical calculations based on the ab initio method were performed to determine the relationship between the molecular structure of piperidines and their inhibition efficiency. Results obtained from Tafel and impedance methods are in good agreement and confirm theoretical studies.     

Corrosion inhibition of copper in near neutral aqueous solutions by gamma-pyrodiphenone

The inhibition effect of gamma-pyrodiphenone (PD) on copper corrosion in near neutral sulphate solutions was investigated. Weight loss and polarization measurements show a high inhibition efficiency (>96%) of PD on copper corrosion at extremely low concentrations. PD suppresses active copper dissolution and oxygen reduction. The potentiodynamic cathodic reduction measurements showed an inhibition of oxide formation and stabilization of the Cu2O oxide in the presence of PD. XPS measurements suggested that the high inhibition effect of PD on copper corrosion is due to the adsorption of PD molecules, as a first stage, and the formation of a film with a polymer-like structure by coordination of PD with Cu2O on prolonged exposure.     

二氧化碳在银电极上发生电还原反应时的电极失活原因

在KHCO3水溶液中,利用线性扫描、塔菲尔曲线、恒电位电解、电化学阻抗谱方法,研究了CO2在银电极上发生电还原反应的动力学特征,发现当电解反应进行一段时间后,阴极表面生成了一层棕黑色物质附着在电极表面,导致生成CO的平衡电位负移,交换电流密度变小,电荷转移电阻增大,电流效率和电流密度迅速降低。用X射线光电子能谱(XPS)分析了有害物质的主要成分,证明阴极表面附着物主要为石墨碳和微量Zn,这些物质附着在阴极表面,导致电极失活,阻碍CO2电还原反应继续进行。     

黄铁矿烧渣中金银资源利用进展

我国每年生产排放的含金银黄铁矿烧渣数量较大,传统的堆填处理方法既污染环境又浪费了其中的可回收金属资源。对于烧渣中有价金属的回收主要集中于金银的提取。综述了黄铁矿烧渣的利用现状以及氰化法回收烧渣中金银的影响因素。着重讨论了金银存在状态、干扰元素、焙烧温度、氰化钠用量、氰化温度、氰化浸出时间对金银氰化回收的影响。并讨论了氰化法回收金银仍存在的一些问题和研究展望。     

On the nature of the active state of silver during catalytic oxidation of methanol

Under the applied high reaction temperatures (900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (O) apart from O atoms dissolved in the bulk (O). Methanol oxidation to formaldehyde proceeds through this O species as demonstrated by application of a variety of spectroscopic techniques.     

Surface enhanced Raman spectroelectrochemical studies of the corrosion films on iron and chromium in aqueous solution environments

“In situ” laser Raman spectra of the corrosion films on iron have been observed in aerated 5 M KOH and 0.15 M NaCl solutions via surface enhancement by the electrodeposition of a silver overlayer. Essentially the same spectra are observed in the two solutions as a function of applied potential in spite of a breakdown of passivity on iron in the chloride solution. Fe(OH)₂ and Fe₃O₄ are found in the prepassive potential region while FeOOH is present in the passive region. A film which is very difficult to reduce appears to be always present on the electrode surface even at hydrogen evolution potentials; this film is believed to be -FeOOH. Surface enhanced Raman spectra of the corrosion films on chromium have also been obtained in NaCl solution for the first time. The passive film has a composition that corresponds most closely to an amorphous form of Cr₂O₃, with some Cr(OH)₃ also present. The film is converted in the transpassive region to a higher oxide form, presumably CrO²⁻₄. Reversible reduction of this species to Cr₂O₃ is indicated.     

十八烷基丙撑二胺/硝酸银水溶液体系中纳米银粒子的制备及其在材料保护中的应用

本文采用了十八烷基丙撑二胺/硝酸银水溶液体系,成功地制备了较稳定的纳米银粒子,并对这两种制备方法进行了简单的比较;并对其材料保护中的应用进行了进一步的探讨。     

Effect of PgTPhPBr on the electrochemical and corrosion behaviour of 304 stainless steel in H2SO4 solution

Weight-loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements were used to study the inhibition of 304 stainless steel corrosion in 1 M H₂SO₄ at 50 °C by propargyltriphenylphosphonium bromide (PgTPhPBr). The inhibiting effects of propyltriphenylphosphonium bromide (PrTPhPBr) and propargyl alcohol (PA) were also studied for the sake of comparison. For the investigated compounds, Tafel extrapolation in the cathodic region gave a corrosion inhibition efficiency of 98% at 1 × 10^–3 M. Adsorption of both PgTPhPBr and PA was found to follow Frumkin's isotherm while adsorption of PrTPhPBr obeys that of Temkin. In the anodic domain, PgTPhPBr acted as a good passivator. The impedance spectra recorded at the corrosion potential (E _cor) revealed that the charge transfer process in the inhibited and uninhibited states controls corrosion of 304 stainless steel.     

An aqueous synthesis of photocatalyst by selective dissolution of titanium oxide/hydroxyapatite composite

A novel synthesis method of a highly active photocatalyst was proposed. Titanium dioxide (TiO₂) nano-particles were prepared by three-step procedure, precipitation of hydroxyapatite (HAp) on TiO₂ particles, heat treatment of the TiO₂/HAp composites, and acid treatment in hydrochloric acid. The unique point of this procedure is the selective dissolution of HAp to obtain exposed TiO₂ surfaces. The HAp precipitation was achieved by stirring TiO₂ powders in the mixtures of Ca(NO₃)₂ and NH₄H₂PO₄ aqueous solutions at pH 8.5. Then, the heat-treated TiO₂/HAp composites were treated with hydrochloric acid. The precipitated HAp avoided the direct contact of TiO₂ particles and suppressed the phase transformation from anatase-to-rutile >200 °C. The HAp also suppressed a decrease of specific surface area of TiO₂ during the heat treatment. The photocatalytic activities were evaluated from an absorbance decrease of methylene blue (MB) under ultraviolet (UV) irradiation. The MB photodecomposition was approximated to the first-order reaction and the reaction rate constants of the obtained TiO₂ powders heated at various temperatures were higher than those of conventional TiO₂ powders heated at same temperatures. The enhanced photocatalytic activity is attributed to the suppression effects for the phase transformation to rutile phase and the decreasing of specific surface area in the heat treatment.