Silver recovery from an effluent generated by plating industry using a rotating cylinder electrode (RCE)

Adsorption characteristics of Ag+ on sphalerite surface: a combined experimental and first-principle study

The rapid development of industrial society is also accompanied by the generation of a large amount of heavy metal wastewater, which has caused serious harm to the ecological environment and human society. Natural sphalerite has an important value in the environmental field due to its own semiconducting properties. In order to effectively remove Ag+ from wastewater containing silver, this study develops a natural mineral-based Ag+ adsorbent material (sphalerite) based on elemental affinity qualities and mineralization principles. The results of batch experiments showed that the initial Ag+ concentration of 50 mg/L reduced to 0.094 mg/L with a reaction duration of 15 min, a sphalerite dose of 5 g/L, an initial particle size of -400 mesh (38 μm), a reaction temperature of 25 °C, and a pH of 5. The highest adsorption capacity is 19.77 mg/g, and the adsorption behavior is consistent with the Freundlich isotherm model and pseudo-second-order adsorption kinetics. The results of solution chemical analysis indicate that the presence of Ag+ is primarily influenced by the presence of S2-. Further analysis using SEM-EDS, FTIR, and XPS techniques reveals that Ag+ is chemically adsorb onto the mineral surface, resulting in the formation of Ag2S. DFT calculations further confirm the overlap between the Ag 4d orbitals and the S 3p orbitals on the surface of sphalerite, further confirming its chemical adsorption. Mulliken populations suggest that charge transfer occurs between Ag+ and S atoms in the sphalerite surface. This research systematically reveals the Ag+ adsorption mechanism on sphalerite surface and expands research ideas for treating heavy metal wastewater.

Silver extraction using emulsion liquid membrane system containing D2EHPA-TBP as synergistic carrier: optimization through response surface methodology

The present investigation deals with silver extraction using an emulsion liquid membrane. The emulsion liquid membrane system consists of paraffin as organic phase, Span 80 as surfactant, Di-(2-ethylhexyl) phosphoric acid (D2EHPA) and Tributyl Phosphate (TBP) as carrier, and hydrochloric acid as stripping agent. Experiments were designed and modeled by response surface methodology using Design Expert 11 software, which determines the extraction rate as a function of Span 80 concentration, D2EHPA concentration, TBP concentration, HCl concentration, and treatment ratio. The ANOVA results indicate that the model is statistically significant because of the high R² (0.9828) and the low p-value of <0.0001. The results showed that the silver extraction increases by increasing all affecting parameters up to their optimal values and after that extraction rate decreases with increasing of them. The process was optimized to obtain maximum extraction rate, minimum D2EHPA concentration, and minimum treatment ratio. The optimal conditions were obtained at a surfactant concentration 3.26% (V/V), D2EHPA concentration 0.0045 mol/L, TBP concentration 5% (V/V), HCl concentration 0.56 mol/L, and treatment ratio 0.5. Under these conditions, the silver extraction rate was 99.87%.

Overview of recent developments of resource recovery from wastewater via electrochemistry-based technologies

As the rapid increase of the worldwide population, recovering valuable resources from wastewater have attracted more and more attention by governments and academia. Electrochemical technologies have been extensively investigated over the past three decades to purify wastewater. However, the application of these technologies for resource recovery from wastewater has just attracted limited attention. In this review, the recent (2010-2020) electrochemical technologies for resource recovery from wastewater are summarized and discussed for the first time. Fundamentals of typical electrochemical technologies are firstly summarized and analyzed, followed by the specific examples of electrochemical resource recovery technologies for different purposes. Based on the fundamentals of electrochemical reactions and without the addition of chemical agents, metallic ions, nutrients, sulfur, hydrogen and chemical compounds can be effectively recovered by means of electrochemical reduction, electrochemical induced precipitation, electrochemical stripping, electrochemical oxidation and membrane-based electrochemical processes, etc. Pros and cons of each electrochemical technology in practical applications are discussed and analyzed. Single-step electrochemical process seems ineffectively to recover valuable resources from the wastewater with complicated constituents. Multiple-step processes or integrated with biological and membrane-based technologies are essential to improve the performance and purity of products. Consequently, this review attempts to offer in-depth insights into the developments of next-generation of electrochemical technologies to minimize energy consumption, boost recovery efficiency and realize the commercial application.

Copper and Antimony Recovery from Electronic Waste by Hydrometallurgical and Electrochemical Techniques

A strategy for the efficient recovery of highly pure copper and antimony metals from electronic waste (e-waste) was implemented by the combination of hydrometallurgical and electrochemical processes. The focus is on copper recovery as the main component in the leached solution, whereas the antimony recovery process was established as a purification step in order to achieve a highly pure copper deposit. The strategy includes mechanical methods to reduce the size of the wasted printed circuit boards to enhance the efficiency of antimony and copper lixiviation via ferric chloride in acidic media (0.5 M HCl) followed by an electrowinning process. In order to establish the best parameters for copper electrowinning, the leached solution was characterized by cyclic voltammetry and cathodic polarization. Then, an electrochemical reactor with a rotating cylinder electrode was used to evaluate the copper concentration decay, the cathodic current efficiency, the specific energy consumption, and mass-transfer coefficient. Furthermore, antimony was recovered via precipitation by a pH modification in accordance with the Pourbaix diagram. Under this methodology, two valuable products from the e-waste were recovered: a 96 wt % pure copper deposit and 81 wt % pure antimony precipitate. The strategy for recovery of other metal ions, such as lead, present in the e-waste at high concentrations will be reported in further works.

Recent trends in removal and recovery of heavy metals from wastewater by electrochemical technologies

Heavy metal-laden water and wastewater pose a threat to biodiversity, including human health. Contaminated wastewater can be treated with several separation and purification methods. Among them, electrochemical treatment is a notable clean technology, versatile and environmentally compatible for the removal and recovery of inorganic pollutants from water and wastewater. Electrochemical technology provides solution for the recovery of metals in their most valuable state. This paper analyses the most recent electrochemical approaches for the removal and recovery of metal ions. Various current works involving cell design and electrode development were addressed in distinguished electrochemical processes, namely, electrodeposition, electrocoagulation, electroflotation, and electrosorption. Cathodic reduction of metal ions has been proven in result to metal deposit on the metal, metal oxide, stainless steel, and graphite electrode. However, little progress has been made toward electrode modification, particularly the cathode for the purpose of cathodic reduction and deposition. Meanwhile, emerging advanced materials, such as ionic liquids, have been presented to be prominent to the technological advancement of electrode modifications. It has been projected that by integrating different priorities into the design approach for electrochemical reactors and recent electrode developments, several insights can be obtained that will contribute toward the enhancement of the electrochemical process performance for the effective removal and recovery of heavy metals from water and wastewater in the near future.