Ag Leaching Research Articles

Echinops bannaticus plant and Zinnia grandiflora extract as char biosource and reducing agent for the biosynthesis of Ag on magnetic char‐polymer: An efficient catalyst for water treatment

In attempt to expand the use of natural compounds for waste treatment, a novel catalyst with the utility for dye reductive degradation is reported. In the catalyst synthesis procedure, the plant Echinops bannaticus was applied as a biosource and hydrothermally treated to furnish a hydrochar that served as a support. The latter was magnetized, vinyl functionalized, and then polymerized with copolymer of 2‐hydroxyethyl methacrylate and methacrylate polyhedral oligomeric silsesquioxane. Subsequently, Ag nanoparticles were stabilized on the resultant composite with the aid of Zinnia grandiflora extract as a natural reducing agent. The resulting catalyst displayed high catalytic activity for the reduction of methylene orange and rhodamine B dyes in aqueous media at room temperature. The effects of the reaction variables, including the reaction time and temperature, and the catalyst loading, were examined and the kinetic and thermodynamic terms for both reactions were evaluated. Ea, ΔH#, and ΔS# values for the reduction of methyl orange were estimated as 50.0 kJ/mol, 51.50 kJ/mol, and −102.42 J mol−1 K−1, respectively. These values for rhodamine B were measured as 28.0 kJ/mol, 25.5 kJ/mol, and −187.56 J mol−1 K−1, respectively. The recyclability test also affirmed that the catalyst was recyclable for several runs with insignificant Ag leaching and decrement of its activity.

Dissolution of Silver and Gold with Sodium Hypochlorite and Hydrochloric Acid in Refractory Minerals (Mangano-Argentiferous)

The present study examined a process for precious metal recovery (silver and gold) from difficult minerals which exhibit refractory characteristics to cyanidation and ammonium thiosulfate leaching (low extraction and high consumption of leaching agent). It is well known that mangano-argentiferous minerals are mainly composed of manganese, silver, gold, and iron. In this research, a mineral sample from Monte del Favor mine, located in Hostotipaquillo, Jalisco, Mexico, was physically and chemically characterized by X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), fire assay, and atomic absorption spectroscopy (AAS). Two-stage leaching was carried out: first to eliminate manganese from the sample using sodium sulfite (Na2SO3) as a reductive reagent and sulfuric acid (H2SO4) and a second stage to dissolve silver and gold with sodium hypochlorite (NaClO) and hydrochloric acid (HCl); the results show extraction around 96% for Mn and 98.73% and 83% of Ag and Au, respectively. The usefulness of high acidity and Na2SO3 to obtain good results in Mn and Ag leaching is discussed along with the roles that HCl and NaClO play in the dissolution of Ag and Au values.

Zeolite-embedded silver extends antimicrobial activity of dental acrylics.

The insertion of prosthetic devices into the oral cavity affects the oral microflora and results in accumulation of microorganisms on the prosthetic surface. Such fouling of denture surfaces can lead to a number of oral diseases and consequently to the replacement of the denture. Here, we report the post-synthesis introduction of silver in zeolite-loaded dental acrylic (DAZ) resins that does not influence the mechanical or aesthetic properties of the DA resins, and provides them with a long-term antimicrobial activity. Na-FAU zeolite (2 wt%) was incorporated into DA resin, which was conventionally processed and cut into 10 mm × 20 mm × 3 mm coupons. The Na+ in the zeolite was then exchanged with Ag+ via immersion of the DAZ coupons in 0.01 M AgNO3 solution to obtain DAZ/Ag-treated coupons used in antimicrobial tests. Antimicrobial tests showed that the DAZ/Ag-treated coupons were active against Candida albicans (a reference and a clinically relevant strain), Streptococcus mutans and Fusobacterium nucleatum. Ag leaching tests on the Ag-charged coupons at 1, 2, 3, 4, 7, 14, 30 and 45 days of incubation in distilled water at 37 °C, indicated sustained release of silver. Antimicrobial tests using a reference Candida albicans strain showed that the leached coupons retained antimicrobial activity after 45 days immersion in distilled water, but, after 60 days incubation no antimicrobial activity was observed. Cytotoxicity assay results indicated that the DAZ/Ag-treated coupons showed no additional cytotoxicity compared to neat dental acrylic coupons.

Recovery of Gold and Silver from Secondary Sources of Electronic Waste Processing by Thiourea Leaching

Fine materials, such as flue dust, generated during processing of electronic waste (e-waste) contain valuable metal resources, such as Au and Ag. However, recovery of valuable metals from this flue dust has not been extensively studied. In this study, a leaching process was investigated for effective recovery of Au and Ag from flue dust. In particular, thiourea was used as leaching reagent to replace cyanide, which has environmental problems. The effects of various parameters on the process, such as leaching time (1–10 h), thiourea concentration (20–60 g/L), and pulp density (20–100 g/L) as well as reaction temperature (20–60°C), were systematically examined. One- and two-step leaching methods were proposed to recover Au and Ag, respectively. Au and Ag leaching efficiencies of about 90% and 100% were obtained by one-step thiourea leaching. However, metals such as Fe and Al were also dissolved together. In the two-step process, Fe and Al were dissolved using H2SO4 as a first step, then Au and Ag were recovered using thiourea leaching. Using this two-step process, Au and Ag were dissolved at higher purity than when using the one-step leaching process, achieving leaching efficiencies of about 98% and 100%, respectively. This investigation will lead to a cost-effective method for recovering precious metals from secondary waste.

Silver Recovery from Laundry Washwater: The Role of Detergent Chemistry

The use of silver nanoparticles as an antimicrobial agent on textiles is rising. Ag leaching during laundry and its subsequent discharge in the environment pose ecotoxicological risks. Removing Ag from laundry washwater is therefore an environmental necessity, but its recovery also leads to environmental sustainability. Low Ag concentration, competition from other cations (such as Ca2+, Mg2+, and Na+), and complexity of the detergent matrix make the recovery process challenging. The present study utilizes a thiol-group functionalized ion-exchange resin in a fixed-bed column to remove Ag from laundry washwater and recover it as Ag2S nanoparticles or high-purity powder. The role of each detergent component in affecting Ag speciation and the resin performance has been analyzed. Builders and bleaching agents are reported to negatively impact the resin performance. pH and cocationic species (Ca2+) concentration are reported to be critical parameters for the successful recovery scheme. The work demonstrates a c...

Kinetic Study of Ag Leaching from Arsenic Sulfosalts in the S2O32−-O2-NaOH System

In Zimapan, Mexico abundant mineral species have been identified. However, a significant number of these precious metals appear to be related to complex sulfides, as is the case of silver (Ag) in sulfosalts. In this work, a kinetic study of the formation of Ag complexes in the AgAsS2-S2O32−-O2-NaOH system from a Zn concentrate found in the Zimapan mining district was conducted. The kinetic model application on Ag leaching shows a linear adjustment in the valuation of the particle size effect. The rate of formation of Ag complexes is dependent of temperature, leaching agent concentration and OH− concentration. Furthermore, graphical verification of the kinetic models indicates that the kinetics of the formation of Ag complexes correspond to the shrinking core model with chemical controls as the controlling stage. The formation of Ag complexes was confirmed by Fourier transform infrared (FTIR) spectroscopy.

Enhanced photocatalytic degradation of bisphenol A with Ag-decorated S-doped g-C3N4 under solar irradiation: Performance and mechanistic studies

Ag-decorated S-doped g-C3N4 composites with different % w/w Ag were synthesized via chemical reduction method. The Ag/S-doped g-C3N4 composites were used as photocatalysts for aqueous bisphenol A (BPA) degradation under solar irradiation. Investigation of the photocatalysts using various characterization methods including X-ray diffractometry, scanning electron microscopy and transmission electron microscopy indicated that the Ag nanoparticles (average size = 10–20 nm) were well-crystalline and uniformly distributed on the S-doped g-C3N4 (SCN) surface. The photocatalytic performance of SCN was ∼3 times more efficient than that of the g-C3N4, while the Ag/SCN with 12% w/w Ag (Ag-SCN-12) exhibited the highest photocatalytic activity for BPA degradation followed by 8% w/w Ag/SCN, 4% w/w Ag/SCN, SCN, and Ag. The effects of pH and Ag-SCN-12 loading on photocatalytic BPA degradation were also investigated. The results showed that the Ag-SCN-12 was highly stable (<40 µg L−1 Ag leaching) and could be reused for at least 4 cycles without significant deterioration to its catalytic activity. The incorporation of Ag into the SCN enhanced the photocatalytic activity of SCN due to the improved electron-hole pair separation and decreased electron-hole pair recombination rate as evidenced by the photoluminescence emission study. The predominant reactive oxygen species (ROS) generated by the Ag-SCN-12 photocatalytic system was O2− which formed secondary ROS (OH, and 1O2) for BPA degradation. The mechanism of ROS generation during the photocatalytic process is also proposed. Based on the BPA degradation intermediates identified using the LC/MS/MS, the BPA degradation pathways in the photocatalytic system are elucidated.

Effects of Particle Morphology on the Antibiofouling Performance of Silver Embedded Polysulfone Membranes and Rate of Silver Leaching

Herein we report the effects of particle morphology on the antibiofouling performance and silver leaching of silver embedded polysulfone (PSf) membranes. Composite PSf membranes were incorporated with three silver particles with different size and shape: microparticle (mAg), nanoparticle (npAg), and nanowire (nwAg). Biofouling of a control and Ag-embedded PSf membranes were monitored in a direct observation system, and bacterial antiadhesive property was observed only with membranes incorporated with nanoscale Ag particles, i.e., npAg and nwAg. Ag leaching experiments indicate that Ag release from composite membrane during filtration did not corroborate with Ag dissolution, suggesting liberation of whole Ag particles. mAg-PSf registered the highest Ag release despite the slowest dissolution kinetics of mAg, which accounted for its lack of antiadhesion property despite similar antimicrobial activities. Overall, the study highlights the role of particle morphology in regulating Ag leaching and thus in contr...

Surface modification of a polyethylene film for anticoagulant and antimicrobial catheter

A functional anticoagulant and antibacterial coating for polyethylene (PE) films is described. The stepwise preparation of this nanocomposite surface coating involves O2 plasma etching of PE film, carbodiimide coupling of cysteamine to the etched PE film, binding of Ag to sulfhydryl groups of cysteamine, and assembly of heparin capped AgNPs on the PE film. The nanocomposite film and its components were characterized by 1H-nuclear magnetic resonance spectroscopy, attenuated total reflectance-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and field emission-scanning electron microscopy. The resulting PE films demonstrate anticoagulant activity using a hemoglobin whole blood clotting assay, and anti-bacterial activity against Bacillus cereus 3551 (Gram-positive) and Escherichia coli BL21 (Gram-negative) bacteria. The hydrophilicity of the heparin coated PE was determined by contact angle measurements; and the stability of the nanocomposite film, with respect to Ag leaching, was assessed by atomic absorption spectroscopy.

기계적-화학적 활성화와 티오요소-티오시안산염 혼합용액에 의한 Au·Ag 용출 향상

Au 정광으로부터 Au Ag의 용출율을 향상시키기 위하여 기계적-화학적 활성화와 티오요소-티오시안산염 혼합용액을 적용하였다. 기계적-화학적 활성화를 이루기 위하여 정광 시료를 건식으로 그리고 습식으로 미분쇄하였다. 입도분포 분석과 XRD 분석 결과, 평균 입도 크기와 결정크기는 정광 시료보다 건식-시료에서 그리고 건식-시료보다 습식-시료에서 더 작게 나타났다. SEM과 XRD 분석 결과 기계적-화학적 활성화에 의해서 습식-시료에서 비정질화 현상이 관찰되었다. Au Ag에 대한 용출실험을 티오요소 용액, 티오시안산염 용액 그리고 티오요소-티오시안산염 혼합 용액으로 각각 수행하였다. Au Ag 용출율은 정광 시료보다 건식-시료에서 그리고 건식-시료보다 습식-시료에서 더 높게 나타났다. Au Ag는 티오요소 용액에서 보다 티오시안산염 용액에서 그리고 티오시안산염 용액에서보다 티오요소-티오시안산염 혼합 용액에서 더 높게 용출되었다. 습식-시료와 티오요소-티오시안산염 혼합 용액을 적용할 때 Au Ag가 99% 이상으로 용출되었다. In order to enhance the Au Ag leach rate, a mechanochemical activation process and a mixed thiourea-thiocyanate solution has been applied to Au concentrate. To achieve mechanochemical activation, the Au concentrate was mechanically ground using a dry and a wet process. The results of a particle size distribution analysis and an XRD analysis, average particle size and crystallite size were much smaller in the dry-sample than in the concentrate sample. As well the size was smaller in the wet-sample than in the dry-sample. In SEM and XRD analysis, the amorphization effect was observed in the wet-sample due to mechanochemical activation. Au Ag leaching experiments were carried out with a thiourea solution, a thiocyanate solution and a mixed thiourea-thiocyanate solution. The Au Ag leach rate was much greater in the dry-ground-sample than in the concentrate sample, and the leach rate was greater in the wet-ground-sample than in the dry-sample. The Au Ag leach rate was much greater in the thiocyanate solution than in the thiourea solution, and the leaching rate was much greater in the mixed thiourea-thiocyanate solution than in the thiocyanate solution. Up to a 99% leach rate for Au Ag were only achieved in the wet-sample using the mixed thiourea-thiocyanate leaching solution.

Poly(dimethylsiloxane)-containing thermoplastic elastomer/gold-silver alloy nanocomposites for thermally/oxidatively stable and antimicrobial coating

Polymer materials with embedded silver (Ag) nanoparticle (NP) are of considerable interest owing to their enhanced antimicrobial activity and physical properties compared to host polymer. Antimicrobial and thermally/oxidatively stable coating not only enhances the durability of the coated material but also reduces the growth of bacteria/fungus and thus reduces the chance of infection. For this purpose, we have prepared polydimethylsiloxane-containing predominantly poly(meth)acrylates-based pentablock thermoplastic elastomer (TPE)/gold (Au)–Ag alloy nanocomposites (NCs) with antimicrobial activity and enhanced physical properties. In situ simultaneous reduction of appropriate amount of metal salts in the presence of block copolymer produced Au–Ag NPs of size 5–10 nm. Such embedded 5–10 nm sized particles (loading, 0.1–0.2 wt%) improved the mechanical property, thermal/oxidative stability, and antimicrobial activity of the NCs. The NC films also exhibited tunable surface wetting behavior and optical properties. The NC films showed low level of Ag leaching as confirmed by inductively coupled plasma spectrometer and UV–visible spectroscopy. Improved thermal/oxidative resistance of the TPE/Au–Ag alloy NCs enhanced antimicrobial activity, together with low level of leaching characteristic of the embedded NPs deemed suitable for further use of these NCs material for antimicrobial and oxidatively stable coating applications. POLYM. COMPOS., 36:2103–2112, 2015. © 2014 Society of Plastics Engineer

Solder Joint Failure Modes in the Conventional Crystalline Si Module

In the conventional PV module system based on crystalline Si solar cell, solder joint has been used for electrical connection in the four positions such as (1) Cu ribbon interconnection on Ag electrode of Si solar cell, (2) electrical connection of Cu ribbon, (3) by-pass diode connection in the junction box, (4) inverter connection. There are two kinds of solder joint failure modes, (1) Ag or Cu leaching into solder and (2) long-term solder joint fatigue. In both cases, crack is generated and DC arcing discharge may happen at the crack. It is well known phenomena as Ag leaching in the electronic packaging that Ag easily dissolves into solder during the soldering process. Because Ag3Sn compound formed in the solder as result of Ag leaching is rigid and brittle material, crack is generated at the interface between solder and Ag dissolved area. It induces to increase contact resistivity of Cu ribbon and Ag electrode of Si cell and to disconnect the Cu ribbon from Si cell in the worst case. It has been reported as solder joint failure that the bus line of Cu ribbon heated up is one of suspicious causes of PV fire. [4] We observed the two types of crack after 1000 thermal cycles from +85 to -40 degree C. The crack at the interface between Cu ribbon and Ag electrode may be due to Ag leaching. The crack inside solder joint composed of large grain growing by repeated thermal stress is typical long-term fatigue. Considering highly reliable PV module system, we should pay attention to protect solder joint failure.

Assessment of Pb, Cd, Cr and Ag leaching from electronics waste using four extraction methods

Heavy metals present in electronic components may leach upon disposal and therefore pose significant environmental hazards. The potential leaching of Pb, Cd, Cr and Ag from PC cathode ray tubes, printed circuit boards (PCBs), PC mice, TV remote controls, and mobile phones was assessed. After controlled crushing, each component was extracted using the Toxicity Characteristic Leaching Procedure (TCLP), EPA Method 1312 (SPLP), NEN 7371 (Dutch Environmental Agency), and DIN S4 (Germany). The TCLP consistently leached the greatest amounts of Pb from all components. The SPLP, NEN 7371 and DIN S4 extracted relatively small amounts of metals compared with the TCLP and were not considered effective as leaching tests for e-waste. The smallest size fraction (< 2 mm) of CRT glass and PCBs leached significantly (p < 0.05) highest Pb via the TCLP. A modified TCLP removed 50.9% more extractable Pb compared with the conventional procedure.

Study on the Recovery Silver and Nanoparticles Synthesis from LTCC By-products of Lowly Concentrated Silver

&lt;p&gt;In this paper, the recovery and nanoparticle synthesis of Ag from low temperature co-fired ceramic (LTCC) by-products are studied. The effect of reaction behavior on Ag leaching conditions from the LTCC by-products is confirmed. The optimum leaching conditions are determined to be: 5 M HNO&lt;sub&gt;3&lt;/sub&gt;, a reaction temperature of 75°C, and a pulp density of 50 g/L at 60 min. For the selective recovery of Ag, the [Cl]/[Ag] equivalence ratio experiment is performed using added HCl; most of the Ag (more than 99%) is recovered. The XRD and MP-AES results confirm that the powder is AgCl and that impurities are at less than 1%. Ag nanoparticles are synthesized using a chemical reduction process for recycling, NaBH4 and PVP are used as reducing agents and dispersion stabilizers. UV-vis and FE-SEM results show that AgCl powder is precipitated and that Ag nanoparticles are synthesized. Ag nanoparticles of 100% Ag are obtained under the chemical reaction conditions.&lt;/p&gt;