Dissolution Rate Of Silver Research Articles

The novelty of silver extraction by leaching in acetic acid with hydrogen peroxide as an organic alternative lixiviant for cyanide

In this article, the dissolution kinetics of pure metallic silver in acetic acid with a hydrogen peroxide solution were carried out. The effects of stirring speed, acetic acid concentration, hydrogen peroxide concentration, and temperature were examined. The results show that increasing the stirring speed decomposes the hydrogen peroxide and negatively affects the dissolution rate of silver. In addition, an acetic acid concentration in the range of 0.25–1 M has a positive effect and a negative effect in the range of 1–3 M. A hydrogen peroxide concentration in the range of 0.5–2 M has a significantly positive effect on the dissolution rate, while it has a negative effect in the range of 2–3 M. The temperature in the range of 61.5–70 °C has a negative effect due to the decomposition of hydrogen peroxide. The shrinking core model was applied to all parameters to obtain the dissolution kinetics. The dissolution process of silver was controlled by the surface reaction-controlled shrinking core model, i.e. 1-(1-X)1/3 = kst, with an activation energy of 28.80 kJ/mol.

Assessment of the principal factors influencing the silver cyanidation process by using Plackett-Burman experimental design

For decades, the cyanidation process is frequently used for gold and silver extraction, as well as metal extraction as a sub-product of lead, zinc, and copper metallurgy. The present study focuses on the factors that influence silver extraction efficiency, which represents the rate of silver dissolution in a sodium cyanide solution. The screening design of Plackett and Burman has been performed to investigate the variables that have the most impact on the extraction of metal namely temperature, pH, free cyanide concentration, dissolved oxygen level, pulp density, lead nitrate ratio (Pb(NO3)2ratio), and setting time.To evaluate the meaning of the seven variables, twelve experiments were carried out and the result revealed that for a 95% confidence level, the chosen parameters for the model are meaningful in their whole. The following three factors were significant (P<0.05) when it comes to the silver cyanidation process including, setting time, pulp density, and free cyanide concentration. The variance analysis (ANOVA) using a Fisher test has shown that the setting time was considered to have the most significant effect for a significance level of 1% (Fstatistics=22.8328 > Fc=21.2). Likewise, for a 95% confidence level, both pulp density and free cyanide concentration have a major influence on the response. The Pareto diagram results clearly show that pulp density and setting time represent 20% of factors that have 80% effect on the silver extraction. Model validation verified that no statistically relevant distinction was made between the predicted and experimental results with the determination coefficient R2=0.93, this mean that the metal extraction is better fitted to the model and the predictability of the model is adequate to explain 93% of the variation in the dependent variable as a function of factor variation.

The impact of silver sulfide nanoparticles and silver ions in soil microbiome

The use of biosolids as fertilizers in agriculture can lead to the exposure of soil biota to sulfidised silver nanoparticles (Ag2S NPs), generated during the wastewater treatment procedures. Considering the crucial role of microorganisms on soil functions, we aimed to study the effects of 10 mg kg−1 soil of Ag2S NPs or AgNO3 on the soil microbiome, using an indoor mesocosm. After 28 days of exposure, Ag2S NPs induced a significant change in the soil microbiome structure, at class, genera and OTU levels. For instance, a significantly higher abundance of Chitinophagia, known for its lignocellulose-degrading activity, was observed in Ag2S NPs-treated soil toward the control. Nevertheless, stronger effects were observed in AgNO3-treated soil, over time, due to its higher silver dissolution rate in porewater. Additionally, only the AgNO3-treated soil stimulates the abundance of ammonia-oxidizing (AOB; amoA gene) and nitrite-oxidizing (NOB; nxrB gene) bacteria, which are involved in the nitrification process. Distinct variants of amoA and nxrB genes emerged in silver-treated soils, suggesting a potential succession of AOB and NOB with different degree of silver-tolerance. Our study highlights the latter effects of Ag2S NPs on the soil microbiome composition, while AgNO3 exerted a stronger effect in both composition and functional parameters.

Microplasma synthesis of silver nanoparticles in PVP solutions using sacrificial silver anodes

The method of contact glow discharge with the using of “sacrificial” silver anodes have been proposed for synthesis of silver nanoparticles (AgNPs) stabilized by polyvinylpyrrolidone (PVP). Using transmission electron microscopy, it was found that the mean size of AgNPs decrease from 10 to 5 nm with increasing of PVP concentration from 2.5 to 10 g/L. At the same time, the polydispersity index of AgNPs non-monotonically depends on concentration of stabilizer and the narrowest size distribution (less than 15%) was observed at PVP concentration equal to 5 g/L. The electrochemical investigations of Ag anodic dissolution associated with the recorded UV-Vis spectra of the obtained AgNPs solutions suggest that (i) the rate of silver dissolution depend on the nature of regulating agent—NaOH or CH3COONa; (ii) silver anodes are not passivated in the presence of PVP; (iii) unlike to the process of chemical reduction of silver ions by PVP using of the contact glow discharge technique provides a pseudo-stationary process mode, i.e., the stability of rates of nucleation and growth of AgNPs via stability both of Ag+ and solvated electrons concentrations that leads to formation of nearly monodisperse nanoparticles.

Silver leaching from miargyrite (AgSbS2) sulfosalt in the system S2O32--Ca(OH)2: Kinetic analysis and experimental design approach

This investigation reports the silver dissolution kinetics from a ore-type sulfosalt identified as miargyrite, which prevails in the chemical concentration process of polymetallic concentrates, in the S2O32--Ca(OH)2 system as well as a statistical study of the design of experiments concerning the effect of temperature (T), calcium hydroxide concentration ([Ca(OH)2]), thiosulfate concentration ([S2O32-]), particle size (d0) and stirring speed (RPM). The results show that temperature is the variable with the most significant effect on the dissolution rate of silver and obtains an activation energy (Ea) of 57.19 kJ mol-1, followed by particle size and hydroxide concentration. Furthermore, it was observed that stirring speed does not affect the dissolution rates in basic medium. These results are consistent and demonstrate that the dissolution reaction is controlled by the chemical reaction. The study of the factorial design was relevant to elucidate the behavior of the variables with the greatest impact in the experimental kinetic study. Finally, kinetic and statistical models were proposed to describe the silver dissolution process in an alkaline medium. The highest silver dissolution was achieved using the following conditions V = 0.5 L, mineral = 40 g L-1, PO2 = 1 atm, t = 360 min, d0 = -105 + 74 μm, [S2O32-] = 0.5 mol L-1, [Ca(OH)2] = 0.05 mol L-1, T = 338 K and RPM = 670 min-1.

Electrophoretic Deposition and Characteristics of Chitosan–Nanosilver Composite Coatings on a Nanotubular TiO2 Layer

The surface treatment of titanium implants has been applied mainly to increase surface bioactivity and, more recently, to introduce antibacterial properties. To this end, composite coatings have been investigated, particularly those based on hydroxyapatite. The present research was aimed at the development of another coating type, chitosan–nanosilver, deposited on a Ti13Zr13Nb alloy. The research comprised characterization of the coating’s microstructure and morphology, time-dependent nanosilver dissolution in simulated body fluid, and investigation of the nanomechanical properties of surface coatings composed of chitosan and nanosilver, with or without a surface-active substance, deposited at different voltages for 1 min on a nanotubular TiO2 layer. The microstructure, morphology, topography, and phase composition were examined, and the silver dissolution rate in simulated body fluid, nanoscale mechanical properties, and water contact angle were measured. The voltage value significantly influenced surface roughness. All specimens possessed high biocompatibility. The highest and best adhesion of the coatings was observed in the absence of a surface-active substance. Silver dissolution caused the appearance of silver ions in solution at levels effective against bacteria and below the upper safe limit value.

Extraction of silver from a refractory silver ore by sono-cyanidation.

In this study, effect of ultrasound on silver extraction from a refractory silver ore containing both native silver and various silver sulphide minerals was investigated. Main effects and interaction effects of pulp density, ultrasonic frequency, cyanide concentration, air flow rate and agitation speed on the extraction rate of silver were studied by a two-level fractional factorial experimental design. A few additional cyanidation tests were also conducted to verify the findings of the designed experiments. It was found that the overall extraction yield was varied from 67% to 90% depending on the operating conditions used in the sono-cyanidation tests (48h). However, it was varied from 63% to 80% by same operating conditions used in the direct cyanidation tests at the same cyanidation time. It was observed that an increase in the ultrasonic frequency has a negligible effect on the silver recovery. More importantly, it was determined that there were insignificant differences between the 24-h sono-cyanidation results and the 48-h direct cyanidation results for each cyanidation conditions. This finding, which is very important from the cyanidation practice standpoint, indicates that the cyanidation time can be reduced up to 50%, or the capacity of an operating silver extraction plant can be increased up to 100% by the sono-cyanidation by the refractory silver ores. In order to describe the rate of silver dissolution in the cyanide solutions, the experimental data were analysed using shrinking core models. It was found that there is a good fit between the experimental data and the models, indicating the rate of silver dissolution in cyanide can be described by a two-stage, porous layer diffusion controlled, shrinking core model.

Silver dissolution in a novel leaching system: Reaction kinetics study

Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing the alkaline sodium thiosulfate-potassium ferricyanide leaching system. The reaction kinetics of silver dissolution in this system was investigated via the rotating disk electrode technology. The influences of important parameters, including the rotation speed, sodium thiosulfate concentration, potassium ferricyanide concentration, and temperature, on the silver dissolution rate were systematically investigated. The activation energy was measured to be 17.96 kJ·mol-1 when the silver dissolution was controlled by a diffusion process. When the silver dissolution was in the region of mixed control, the reaction orders of ferricyanide and thiosulfate were found to be 0.57 and 0.19, respectively, and the reaction orders of ferricyanide and thiosulfate were 0.55 and 0.22, respectively, when the silver dissolution was controlled by surface reaction. This study has great potential for the development of an environmentally friendly silver recovery process from end--of-life products.

A two-phase gradual silver release mechanism from a nanostructured TiAlV surface as a possible antibacterial modification in implants

Titanium biomaterials are widely used in the medical field due to their biocompatibility and excellent corrosion and mechanical resistance. However, these materials have no antibacterial properties. To obtain an antibacterial active surface, a nanostructure of Ti6Al4V alloy was created. This specific nanostructure contained nanotubes and micro-cavities and was used as a substrate for silver anchoring. The electrochemical approach to silver reduction was studied. It is a common approach for silver deposition and in this work, inhomogeneities in the nanostructure were used as a preferential area for silver localisation. The galvanostatic regimen of deposition allowed for a technically quantitative process and the required silver placement. The experimental conditions used enabled testing and silver dissolution rate evaluation within a reasonable time span. Based on the corrosion and analytical results (EDS, XPS and ICP-MS), a two-phase silver release mechanism was confirmed. The openings of the individual nanotubes were filled with silver nanoparticles, whose release was relatively fast. By contrast, the silver anchored inside the cavities allowed the silver to release gradually. Antibacterial efficiency against Staphylococcus aureus and Escherichia coli was successfully demonstrated. Cytotoxicity testing with murine fibroblasts showed cell metabolic activity far above the normative limit of 70%.

An environmentally friendly system for high efficient silver recovery from anode slime

Anode slime is an extremely valuable secondary resource for the recovery of silver and has attracted wide attentions. Effective metal recovery is usually constrained by either environmental hazards or high consumption of lixiviant for cyanide and non-cyanide leaching reagents. To tackle these issues in the process of silver recovery from anode slime, this research demonstrated a new leaching system with using an efficient oxidant which encapsulates cyanide into ferric complexes to ensure it not releasing into the environment while effective silver recovery was achieved. Comparing with the traditional tetra-amine copper oxidant, it was found that the dissolution rate of silver was significantly improved and leachate consumption was largely decreased. The effects of stirring speed, sodium thiosulfate concentration, oxidant concentration, solution pH and time on silver dissolution were investigated. When the novel system of iron-encapsulated cyanide was applied to extract silver from anode slime, the final conversion rates of silver was 97% after 60 minutes. This system has great potential in silver recovery from anode slime.

LOCAL PARAMETERS OF THE SURFACE ROUGHNESS OF ELECTROCHEMICALLY DEALLOYED Ag-Pd ALLOYS

Local characteristics of surface roughness of the polycrystalline Ag-Pd solid solutions (4 and 8 at. % Pd) which underwent potentiostatic electrochemical dealloying in an acidic nitrate aqueous solution were determined by scanning electron and atomic force microscopy. A qualitative analysis of the SEM and AFM micrographs demonstrated substantial morphological roughening of the surface of Ag-Pd alloys. This results from the formation of hollows and cracks caused by selective leaching of electronegative silver and recrystallization of electropositive palladium into its highly-developed phase. A quantitative analysis of the AFM-data allowed us to determine the numerical values of the main local roughness characteristics of anodically modified alloys. The negative value of the coefficient of surface asymmetry indicates the formation of deep cavities during the dealloying process. The recorded mean roughness generally depends on the AFM-scanning zone, but it stabilizes if the scan zone exceeds several tens of micrometers. The roughness of dealloyed Ag-Pd systems is of micro- and nano-size and increases with anodic potential and electric charge of the electrochemical modification of both studied Ag4Pd and Ag8Pd alloys. This effect can be accounted for by a significant rise in the anodic dissolution rate of silver from the alloys in the overcritical region of polarization, resulting in the formation of deeper surface defects. An increase in the average height of surface irregularities with modification time conforms to the square root law, confirming the non-stationary mass transfer kinetics of the selective dissolution process. Variation of the anodic potential and electric charge makes it possible to find the optimal conditions for the electrochemical synthesis of electrode Ag-Pd materials with given values of arithmetic mean and root-mean-square roughness. The assumption that harmonic sinusoidal function represents the Ag-Pd surface microprofile proved the linear dependence of the roughness factor on dealloying time.

To the Problem of Reducing the Amount of Harmful Emissions when Refining Silver

The work is devoted to the study of the possibilities of minimizing the release of nitrogen oxides during the dissolution of silver in nitric acid solutions during refining of the gold and silver alloy. Using a rotating disk, the maximum concentration of nitric acid is determined, at which the oxidation potential of the system is insufficient for the oxidation of silver. It has been established that at a temperature of 363 K and a concentration of HNO3 = 50 g/l, the dissolution rate of silver does not exceed 0.00022∙10-5 mol/(cm2∙s), and such conditions can be considered as background for an environmentally friendly process. To initiate dissolution, hydrogen peroxide was used as an alternative oxidizing agent. As a criterion for the rational use of the oxidant and the ecological purity of the process, the excess pressure over the solution was evaluated. The influence of the initial and current composition of the solution, temperature, and conditions of oxidant supply to the reactor on the kinetics of the target process was studied. It is shown that at a silver dissolution rate of 2.7∙10-6 mol/(cm2∙s), no release of nitrogen oxides was observed.

Maximization of the silver recovery with the “monoethanolamine-copper-ammonium sulfate” novel system. A step towards the development of a less toxic leaching technology

In the present research, the monoethanolamine‑copper-ammonium novel system was studied systematically to develop an alternative sustainable process for the dissolution of silver. This paper presents the effect of varying the concentration of cupric sulfate, ammonium sulfate, monoethanolamine and temperature on the silver leaching kinetics. The study was complemented with SEM-EDS, X-ray diffraction characterization techniques and thermodynamic analysis in order to understand the phenomena taking place in this novel leaching system. The results revealed that an increase in the cupric sulfate and ammonium sulfate concentration favors the silver dissolution rate and recovery. However, a massive increase in the concentration of cupric sulfate and ammonium sulfate, e.g., 0.4M and 1.06M, respectively, promotes the significant precipitation of Cu(OH)2, which hinders the silver dissolution. On the other hand, when the system is operated with a Cu2+ and NH4+ concentration lower than 0.3M and 0.8M, respectively, the silver dissolution is favored. The thermodynamic and SEM-EDS analysis along with the leaching tests revealed that Cu(NH3)42+, Cu(MEA)42+ and Cu(OH)2 (partially precipitated on the silver particles) are the oxidizing agents for silver. Oxidized silver can be complexed by the free ammonia produced in the system and monoethanoamine (MEA). Temperature is an important variable to accelerate the silver dissolution kinetics, the results showed that 83% of silver can be leached at 360min employing 0.3M Cu2+, 0.8M NH4+, 0.05M MEA at 45°C. Finally, the addition of MEA in the system is fundamental to decrease the massive precipitation of Cu(OH)2 species, promoting the silver dissolution rate at 45°C.

Highly efficient and selective leaching of silver from electronic scrap in the base-activated persulfate – ammonia system

A system composed of persulfate salt and ammonia in highly alkaline aqueous solution is developed and examined for leaching metallic silver from elements of the electronic waste materials (e-scrap). Strong base activates persulfate ions providing in situ generation of highly reactive oxygen molecules. The oxidized metal forms then well soluble complex ions with ammonia ligands. The kinetic studies of the leaching process were performed for pure metallic silver. They revealed that the efficiency of the process is affected by the type of the persulfate salt. By employing potassium persulfate one obtains significantly (more than 50% for silver plates and more than 100% for silver powder) increased efficiency of silver dissolution compared to the solution composed of either sodium or ammonium persulfates. In the range of persulfate concentrations between 0.02 and 0.23mol/L the apparent reaction order with respect to the persulfate concentration was similar for all persulfate salts and was estimated to be around 0.5. The room temperature (22±2°C) seems to be an optimal temperature for the leaching process. An increase in the temperature resulted in the significant drop in the silver dissolution rate due to the decreased solubility of oxygen. Based on these results a possible mechanism of dissolving silver is discussed and the optimal composition of the leaching solution is formulated. The obtained formulation of the leaching solution was applied for the extraction of silver coatings of Cu-based e-waste scrap and the obtained results revealed an important effect of copper in the mechanism of the leaching process. The regression analysis of the leaching curve indicated that each gram of base-activated potassium persulfate under the specified conditions may leach almost 100mg of silver coatings in a form of well soluble diamminesilver (I) complex. The silver complex can be relatively easy reduced to metallic silver. The method developed is relatively cheap, low toxic and does not produce harmful by-products.

Oxidative dissolution of silver nanoparticles: A new theoretical approach

A general model of an oxidative dissolution of silver particle suspensions was developed that rigorously considers the bulk and surface solute transport. A two-step surface reaction scheme was proposed that comprises the formation of the silver oxide phase by direct oxidation and the acidic dissolution of this phase leading to silver ion release. By considering this, a complete set of equations is formulated describing oxygen and silver ion transport to and from particles’ surfaces. These equations are solved in some limiting cases of nanoparticle dissolution in dilute suspensions. The obtained kinetic equations were used for the interpretation of experimental data pertinent to the dissolution kinetics of citrate-stabilized silver nanoparticles. In these kinetic measurements the role of pH and bulk suspension concentration was quantitatively evaluated by using the atomic absorption spectrometry (AAS). It was shown that the theoretical model adequately reflects the main features of the experimental results, especially the significant increase in the dissolution rate for lower pH. Also the presence of two kinetic regimes was quantitatively explained in terms of the decrease in the coverage of the fast dissolving oxide layer. The overall silver dissolution rate constants characterizing these two regimes were determined.

Complex electrochemical studies on silver-coated metallic implants for orthopaedic application

Silver grains were deposited by pulse current technique onto different implant materials—Ti6Al4V and CoCrMo alloys—that are commonly used in orthopaedic surgery. The electrochemical behaviour of the coatings and the silver ion release rate were investigated by polarization potentiodynamic and electrochemical impedance spectroscopy (EIS) methods over a period of several weeks in isotonic salt solution. For antimicrobial applications, it is very important to maintain a continuous and long-term release of silver ions. The corrosion properties of silver-coated different implant materials and the silver dissolution rate were compared. The open circuit potentials shifted to more positive values for both uncoated and coated substrate materials in 0.9 % sodium chloride solution. The silver modified implants possess more negative corrosion potentials than that of pure implants. The potentiodynamic curves revealed that the silver-modified implant materials have higher anodic and cathodic current densities compared to bare implant by almost one order of magnitude. The values of charge transfer resistance decreased in approximately 10 days for all silver-coated samples but after that, slightly changed due to the layer passivation. The morphology of the coatings was studied by scanning electron microscopy (SEM) micrographs and energy dispersive spectroscopy (EDX) measurements. To determine the silver ion concentration released from the silver-modified implant materials into physiological solution during different time of immersion, inductively coupled plasma mass spectroscopy (ICP-MS) method was used.

Bacterial growth on a superhydrophobic surface containing silver nanoparticles

The antibacterial effect of silver can be exploited in the food and beverage industry and medicinal applications to reduce biofouling of surfaces. Very small amount of silver ions are enough to destructively affect the metabolism of bacteria. Moreover, superhydrophobic properties could reduce bacterial adhesion to the surface. In this study we fabricated superhydrophobic surfaces that contained nanosized silver particles. The superhydrophobic surfaces were manufactured onto stainless steel as combination of ceramic nanotopography and hydrophobication by fluorosilane. Silver nanoparticles were precipitated onto the surface by a chemical method. The dissolution of silver from the surface was tested in an aqueous environment under pH values of 1, 3, 5, 7, 9, 11 and 13. The pH value was adjusted with nitric acid and ammonia. It was found that dissolution rate of silver increased as the pH of the solution altered from the pH of de-ionized water to lower and higher pH values but dissolution occurred also in de-ionized water. The antimicrobial potential of this coating was investigated using bacterial strains isolated from the brewery equipment surfaces. The results showed that the number of bacteria adhering onto steel surface was significantly reduced (88%) on the superhydrophobic silver containing coating.

Effect of Silver in Thiosulfate Leaching of Gold–Silver Alloys in the Presence of Copper and Ammonia Relative to Pure Gold and Silver

One promising alternative to cyanide for the leaching of gold is thiosulfate due to its low toxicity and efficiency in leaching gold from low-grade and carbonaceous ores and concentrates. Much of the published research focuses to optimizing the reagent concentrations to develop a suitable process for industrial applications. However, there are few studies on the effect of silver content on gold dissolution rate in the thiosulfate leaching system. In this paper, the dissolution rate of pure gold, pure silver, and gold–silver alloys of silver compositions, 4, 8, 20, and 50 wt% are reported. The effects of various parameters on the rate of gold and silver dissolution have been determined. The results show that the pure silver dissolution rate is around 6.89 times greater than pure gold. The results show that silver enhances gold dissolution in thiosulfate solutions. The dissolution rate of gold from pure gold is higher than that obtained from 4% and 8% silver alloys, but less than that obtained from 20% and 50% silver alloys.

Silver sulfide leaching with thiosulfate in the presence of additives Part I: Copper–ammonia leaching

Thiosulfate is a promising alternative for the hydrometallurgical treatment of silver sulfide ores. In this study, the copper–ammonia catalyzed thiosulfate leaching of a silver sulfide rotating disk is investigated. The leaching of silver sulfide by a copper–ammonia thiosulfate solution occurs either by the substitution of cupric or cuprous for silver. The cupric reaction is favored due to a thermodynamic barrier to the cuprous reaction. At 1mM copper, there is evidence of partial chemical control for copper–ammonia leaching with a maximum silver dissolution rate achieved when cupric is stabilized in solution with ammonia and for solutions with high thiosulfate availability. The addition of ethylenediaminetetraacetic acid decreased the leaching rate of the silver sulfide disk due to decreased cupric reactivity, although this comes with the benefit of increased cupric stability.

Efecto de la Temperatura y Concentración de Tiosulfatos sobre la Velocidad de Disolución de Plata contenida en Desechos Mineros usando Soluciones S2O3(2-)-O2-Zn2+

The effect of the temperature and thiosulfate concentration on the dissolution rate of silver contained in mining wastes, using the system S2O3 2- -O2–Zn 2+ was studied. In the State of Hidalgo in Mexico, thousands of tons of waste mining having around 71 grams of silver per ton of waste have been accumulated over the years. This is the main reason that motivates this study. It was observed that the temperature drastically affects the leaching rate of the silver showing an activation energy Ea= 55.85 kJ mol -1 , implying that the dissolution reaction is controlled by the chemical reaction. The thiosulfate concentration shows a considerable influence on the precious metal dissolution rate. The maximum silver dissolution was found to be approximately 97% at 45 °C and 40 gL -1 of [S2O3 2- ]. It is concluded that the process studied represents a good alternative