Facile indium recovery from waste liquid crystal displays: Chloride-facilitated indium electroreduction and stepwise Cu/MoO2 and indium electrodeposition

Bibliometric analysis and systematic review of electrochemical methods for environmental remediation

Electrochemical methods are increasingly favored for remediating polluted environments due to their environmental compatibility and reagent-saving features. However, a comprehensive understanding of recent progress, mechanisms, and trends in these methods is currently lacking. Web of Science (WoS) databases were utilized for searching the primary data to understand the knowledge structure and research trends of publications on electrochemical methods and to unveil certain hotspots and future trends of electrochemical methods research. The original data were sampled from 9080 publications in those databases with the search deadline of June 1st, 2022. CiteSpace and VOSviewer software facilitated data visualization and analysis of document quantities, source journals, institutions, authors, and keywords. We discussed principles, influencing factors, and progress related to seven major electrochemical methods. Notably, publications on this subject have experienced significant growth since 2007. The most frequently-investigated areas in electrochemical methods included novel materials development, heavy metal remediation, organic pollutant degradation, and removal mechanism identification. "Advanced oxidation process" and "Nanocomposite" are currently trending topics. The major remediation mechanisms are adsorption, oxidation, and reduction. The efficiency of electrochemical systems is influenced by material properties, system configuration, electron transfer efficiency, and power density. Electro-Fenton exhibits significant advantages in achieving synergistic effects of anodic oxidation and electro-adsorption among the seven techniques. Future research should prioritize the improvement of electron transfer efficiency, the optimization of electrode materials, the exploration of emerging technology coupling, and the reduction in system operation and maintenance costs.

Physicochemical reactions in e-waste recycling

Electronic waste (e-waste) recycling is becoming a global concern owing to its immense quantity, hazardous character and the potential loss of valuable metals. The many processes involved in e-waste recycling stem from a mixture of physicochemical reactions, and understanding the principles of these reactions can lead to more efficient recycling methods. In this Review, we discuss the principles behind photochemistry, thermochemistry, mechanochemistry, electrochemistry and sonochemistry for metal recovery, polymer decomposition and pollutant elimination from e-waste. We also discuss how these processes induce or improve reaction rates, selectivity and controllability of e-waste recycling based on thermodynamics and kinetics, free radicals, chemical bond energy, electrical potential regulation and more. Lastly, key factors, limitations and suggestions for improvements of these physicochemical reactions for e-waste recycling are highlighted, wherein we also indicate possible research directions for the future.

Catalysis of Indium Ion Electroreduction in the Presence of Acetazolamide in Chlorates(VII) Solutions with Varied Water Activity

The influence of acetazolamide (ACT) on the kinetics and the mechanism of electroreduction of In(III) ions as a function of changes of the water activity was investigated using electrochemical methods (DC, SWV, CV and EIS, CV). The multi-step mechanism of the electroreduction process should take into account the dehydration step of indium ions and the presence of In-ACT (,,cap-pair" effect) active complexes, mediating electron transfer, located in the adsorption layer. Differences in the electrode mechanism in the presence of ACT were observed for higher chlorates(VII) concentrations (above 4 mol ⋅ dm-3 chlorates(VII)) reflected by a lack of step wise nature of the electrode process. The highest catalytic activity was observed in 4 mol ⋅ dm-3 chlorates(VII).

Highly selective recovery of gold and silver from E-waste via stepwise electrodeposition directly from the pregnant leaching solution enabled by the MoS2 cathode

The recycling of electronic waste, i.e., waste Printed Circuit Boards (WPCBs), provides substantial environmental and economic advantages. In fact, the concentration of valuable precious and base metals in WPCBs is even higher compared to those found in mined ores. Nevertheless, it is still challenging to selectively extract precious metals with low concentrations from the pregnant leaching solution, due to the co-deposition of base metals, like Cu, which have higher concentrations. In this research, stepwise recovery of precious metals and copper directly from WPCBs thiosulfate leaching solution was facilitated by the Ti cathode coated with MoS2 (MoS2/Ti). The in-situ enrichment of Au(S2O3)23- and Ag(S2O3)23- at the surface of MoS2 enables the high efficiency and selectivity of electrodeposition, which has been confirmed through COMSOL Multiphysics simulations and visualization. As a result, the first-step electrodeposition at 0.6 V recovered 92.44 % Au and 98.18 % Ag without any co-deposition of Cu. Subsequently, the second-step recovery employed a constant current of 0.03 A, achieving 100 % recovery of copper within 12 h. Furthermore, this study optimized the reduction potential, NH3·H2O concentration, and S2O32- concentration for the stepwise electrodeposition process. These findings provide valuable insights for establishing a closed loop circular economy in the electronics industry.

Solid-phase extraction and separation of indium with P2O4-UiO-66-MOFs (di-2-ethylhexyl phosphoric acid-UiO-66-metal-organic frameworks)

Compared with the traditional liquid-liquid extraction method, solid-phase extraction agents are of great significance for the recovery of indium metal due to their convenience, free of organic solvents, and fully exposed activity. In this study, P₂O₄ (di-2-ethylhexyl phosphoric acid) was chemically modified by using UiO-66 to form the solid-phase extraction agent P₂O₄-UiO-66-MOFs (di-2-ethylhexyl phosphoric acid-UiO-66-metal-organic frameworks) to adsorb In(III). The results show that the Zr of UiO-66 bonds with the P-OH of P₂O₄ to form a composite P₂O₄-UiO-66-MOF, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). The adsorption process of indium on P₂O₄-UiO-66-MOFs followed pseudo first-order kinetics, and the adsorption isotherms fit the Langmuir adsorption isotherm model. The adsorption capabilities can reach 192.8 mg/g. After five consecutive cycles of adsorption-desorption-regeneration, the indium adsorption capacity by P₂O₄-UiO-66-MOFs remained above 99%. The adsorption mechanism analysis showed that the P=O and P-OH of P₂O₄ molecules coated on the surface of P₂O₄-UiO-66-MOFs participated in the adsorption reaction of indium. In this paper, the extractant P₂O₄ was modified into solid P₂O₄-UiO-66-MOFs for the first time. This work provides a new idea for the development of solid-phase extractants for the recovery of indium.

A method for using the residual energy in waste Li-ion batteries by regulating potential with the aid of overvoltage response

The value of considerable residual energy in waste Li-ion batteries (WLIBs) is always neglected. At present, "this energy" is always wasted during the discharge process of WLIBs. However, if this energy could be reused, it would not only save a lot of energy but also avoid the discharge step of recycling of WLIBs. Unfortunately, the instability of WLIBs potential is a challenge to efficient utilization of this residual energy. Here, we propose a method that could regulate the cathode potential and current of the battery by simply adjusting the solution pH to utilize 35.08%, 88.4%, and 84.7% of the residual energy for removing heavy metal ions from wastewater, removing Cr (VI) from wastewater, and recovering copper from the solution, respectively. By taking advantage of the high internal resistance R of WLIBs and the sudden change of battery current I caused by iron passivation on the positive electrode of the battery, this method could induce the response of overvoltage η (η = IR) inside the battery at different pH levels to regulate the cathode potential µ of the battery to the three intervals. The potential ranges of the battery cathode corresponding to pH < 3.4, pH ≈ 3.4, and pH > 4 were µ > -0.47V, -0.47V < µ < -0.82V, and µ < -0.82V, respectively. This study provides a promising way and theoretical basis for the development of technologies for reusing residual energy in WLIBs.

Electrorefining and electrodeposition for metal separation and purification from polymetallic concentrates after waste printed circuit board smelting

Multi metal recycling from waste printed circuit boards (WPCBs) is attractive for resource conservation and sustainability. While smelting is commonly adopted to produce polymetallic concentrates from WPCBs, current processes cost oxidation smelting and fire refining followed by electrorefining to deport co-existing base metals and recover copper, which can cause substantial metal losses, long steps, and lack of effective methods for subsequent base metal recycling. Here, direct electrorefining of polymetallic concentrates (Cu-Ni-Fe-Pb-sn-Au-Ag) combined with electrodeposition was investigated to realize multi metal separation and purification. It was found that direct electrorefining of concentrates in H₂SO₄/CuSO₄ electrolyte at 0.4 V realized >98% base metal dissolution and copper production (∼99% purity), serving as a combined metal leaching and copper electrowinning procedure. PbSO₄-SnO₂-Cu₅FeS₄ precipitate was formed in anode slime, with Ag-Au enriched by 8.5-61 times. Analysis on subsequent selective metal electrodeposition revealed the blocking effect of Zn²⁺ and overlapped potential region of Fe²⁺-Ni²⁺, emphasizing the importance of Zn and Fe pre-separation during smelting and chemical precipitation. Electrodeposition experiments demonstrated high selectivity for Cu and Ni at 0.05 and -0.7 V, where Ni²⁺ shows complex electroreduction behaviors. The proposed process can serve as an alternative feasible route for multi metal recycling from WPCBs.

Indium Recovery by Adsorption on MgFe2O4 Adsorbents

Indium and its compounds have many industrial applications and are widely used in the manufacture of liquid crystal displays, semiconductors, low temperature soldering, and infrared photodetectors. Indium does not have its own minerals in the Earth's crust, and most commonly, indium is associated with the ores of zinc, lead, copper and tin. Therefore, it must be recovered as a by-product from other metallurgical processes or from secondary raw materials. The aim of this study is to investigate the adsorption properties for recovering indium from aqueous solutions using iron-magnesium composite (MgFe₂O₄). In addition, the results show that the material offers very efficient desorption in 15% HCl solution, being used for 10 adsorption-desorption cycle test. These results provide a simple and effective process for recovering indium. Present study was focuses on the synthesis and characterization of the material by physico-chemical methods such as: X-ray diffraction, FT-IR spectroscopy, followed by the adsorption tests. The XRD indicates that the MgFe₂O₄ phase was obtained, and the crystallite size was about 8 nm. New prepared adsorbent materials have a point of zero charge of 9.2. Studies have been performed to determine the influence of pH, initial indium solution concentration, material/solution contact time and temperature on the adsorption capacity of the material. Adsorption mechanism was established by kinetic, thermodynamic and equilibrium studies. At equilibrium a maximum adsorption capacity of 46.4 mg/g has been obtained. From kinetic and thermodynamic studies was proved that the studied adsorption process is homogeneous, spontaneous, endothermic and temperature dependent. Based on Weber and Morris model, we can conclude that the In (III) ions takes place at the MgFe₂O₄/In (III) solution-material interface.

Novel Electrodeposition Method for Cu-In-Cd-Ga Sequential Separation from Waste Solar Cell: Mechanism, Application, and Environmental Impact Assessment

While CIGS solar cell has been experiencing an expanded photovoltaic market and increasing research interest in cell design, its treatment after obsoletion remains an upcoming issue. The heavy metals involved, such as Cd, can threat the environment, while strategic resources, such as rare metals In and Ga, offer a great recycling oppotunity. However, due to its multimetal feature, traditional recycling methodology shows poor separation-extraction efficiency and additional environmental burdens with intense reagent consumption and waste generation. Here, we report a sequential electrodeposition method for pure metal recycling from this Cu-In-Cd-Ga quaternary system in a more environmentally friendly and efficient manner. Stability constant-corrected redox potential supplemented with metal electroreduction tests predicts well the potential window for sequential electrodeposition. Cu and In electrodeposition shows 100% separation with high Coulombic efficiency (>80%), whereas Ga electrodeposition presents slower kinetics and performs better at a pH of 2.5. Environmental impact assessment indicates that the proposed recycling route allows remarkable reduction of global warming and toxicity impacts compared with metal production from virgin mining and reference processes. We further unveiled the applicability of the electrodeposition technique in the context of anthropogenic mineral recycling, emphasizing resource sustainability and cleaner production.