Electroless recovery of silver by inherently conducting polymer powders, membranes and composite materials

Selective adsorption of Ag (Ⅰ) from aqueous solutions using Chitosan/polydopamine@C@magnetic fly ash adsorbent beads

A Chitosan/polydopamine@C@magnetic fly ash (CPCMFA) adsorbent bead was prepared for adsorption of Ag (Ⅰ) in aqueous solutions and exhibited good selectivity for Ag (Ⅰ) ion. To investigate its adsorption behaviors, equilibrium, kinetic and selective studies were conducted through batch experiments. Additionally, the influence of the pH value was also evaluated. In addition, the nature, composition, morphology, and magnetic property of the prepared adsorbent beads were characterized by Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) analysis, thermogravimetric-differential scanning calorimetry (TG-DSC) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating-sample magnetometry (VSM). The freeze-dry form of CPCMFA also exhibited high adsorption capacity and selectivity for Ag (Ⅰ), with a maximum adsorption capacity of 57.02 mg/g at pH 4 and 30 °C. The experimental data were well described by the Langmuir isotherm and elovich kinetic models. The thermodynamics parameters, ΔH = 10.653 kJ/mol, ΔS = 96.63 J/mol K and ΔG < 0, demonstrate that the adsorption of Ag (Ⅰ) on the freeze-dry form adsorbent is spontaneous and endothermic. Moreover, regeneration studies showed the high recyclability of the adsorbent, which after five cycles of use it was still able to adsorb 95.7% of the amount adsorbed by the fresh adsorbent.

Preparation of Conductive Polyester Fibers Using Continuous Two-Step Plating Silver

Polyester fibers are used in various fields, due to their excellent mechanical and chemical stability. However, the lack of conductivity limits their application potential. In order to prepare conductive polyester fibers, silver is one of the most widely used materials to coat the surface of the fibers. This work aimed to prepare silver-coated polyester fibers by a continuous two-step method, which combined the operations of continuous electroless plating and electroplating. Meanwhile, we designed specialized equipment for the continuous plating of silver on the polyester fibers under a dynamic condition. The mechanical property, washability, electrical resistivity, and electrical conductivity of the resultant conductive polyester fibers obtained from different silver-plating conditions were also characterized. The results demonstrated that the conductive fibers prepared by continuous two-step silver plating equipment, had good electrical conductivity with better mechanical properties and washability.

Electroless plate of polyaniline-silver composite layer on polyester fibers

Antistatic fibers or conductive fibers can be obtained from formation of a metal conductive layer, for example silver, on the surface of polymeric fibers through a redox reaction. However, in the process of fabricating silver-polymer conductive fibers, the binding force between silver and the polymeric fiber matrix is too weak and the poor weather resistance greatly affects the performance of the conductive fibers. This work aims to synthesize composite conductive layers of polyaniline (PANi)-silver coated on polyester fibers to prepare conductive polymeric fibers, in order to improve the combining ability between the conductive layers and the fiber matrix. The morphology, thermostability, mechanical properties, washing resistance and corrosion resistance of the resultant fibers obtained from different synthesis conditions were characterized. Batch experimental results showed that the concentration of the reagent and the reaction time could affect the resistance of the PANi-silver coated conductive fibers. The results also demonstrated that the PANi-silver composite conductive fibers have better properties than those of the silver-polymer conductive fibers.

A comparison of ultrasound-augmented and conventional leaching of silver from sintering dust using acidic thiourea

In the process of steel manufacture, up to ten millions of tons of sintering dust (SD) are produced annually in China, which contain noble metals such as Ag. Therefore, recovery of silver (Ag) from SD could be a potential economic and environmental activity. The purpose of this article is to generate information about reaction kinetics of silver leaching with thiourea from SD, comparing the conventional and ultrasonic-augment leaching. The effects of various control parameters such as the ultrasound power, particle size, leaching temperature and thiourea concentration on leaching rate of silver were studied. The results showed 89% silver recovery for conventional process against 95% for ultrasound assisted leaching. The ultrasonic wave increased the leaching rate and shorten the reaction time. The rate controlling step was analyzed using shrinking core model and the rate controlling step is identified to be the diffusion through the product layer in both conventional and ultrasonic-augment leaching processes. The activation energies were estimated to be 28.01kJ/mol and 18.19kJ/mol, and the reaction order were 0.89 and 0.71, respectively.

Silver recovery aqueous techniques from diverse sources: Hydrometallurgy in recycling

The demand of silver is ever increasing with the advance of the industrialized world, whereas worldwide reserves of high grade silver ores are retreating. However, there exist large stashes of low and lean grade silver ores that are yet to be exploited. The main impression of this work was to draw attention to the most advance technologies in silver recovery and recycling from various sources. The state of the art in recovery of silver from different sources by hydrometallurgical and bio-metallurgical processing and varieties of leaching, cementing, reducing agents, peeling, electro-coagulants, adsorbents, electro-dialysis, solvent extraction, ion exchange resins and bio sorbents are highlighted in this article. It is shown that the major economic driver for recycling of depleted sources is for the recovery of silver. In order to develop an nature-friendly technique for the recovery of silver from diverse sources, a critical comparison of existing technologies is analyzed for both economic viability and environmental impact was made in this amendment and silver ion toxicity is highlighted.

Mechanistic study of silver nanoparticle formation on conducting polymer surfaces

Conducting polymer (polyaniline) sheets are shown to be active substrates to promote the growth of nanostructured silver thin films with highly tunable morphologies. Using the spontaneous electroless deposition of silver, we show that a range of nanostructured metallic features can be controllably and reproducibly formed over large surface areas. The structural morphology of the resulting metal-polymer nanocomposite is demonstrated to be sensitive to experimental parameters such as ion concentration, temperature, and polymer processing and can range from densely packed oblate nanosheets to bulk crystalline metals. The deposition mechanisms are explained using a diffusion-limited aggregation (DLA) model to describe the semi-fractal-like growth of the metal nanostructures. We find these composite films to exhibit strong surface-enhanced Raman (SERS) activity, and the nanostructured features are optimized with respect to SERS activity using a self-assembled monolayer of mercapto-benzoic acid as a model Raman reporter. SERS enhancements are estimated to be on the order of 10(7). Through micro-Raman SERS mapping, these materials are shown to exhibit uniform SERS responses over macroscopic areas. These metal-polymer nanocomposites benefit from the underlying polymer's processability to yield SERS-active materials of almost limitless shape and size and show significant promise for future SERS-based sensing and detection schemes.