Recovery of indium from end-of-life liquid-crystal display panels using aminopolycarboxylate chelants with the aid of mechanochemical treatment

Recycling and reutilization of smelting dust as a secondary resource: A review

Smelting dust is a toxic waste produced in metal-mineral pyrometallurgical processes. To eliminate or reduce the adverse environmental impacts of smelting dust, valuable components need to be selectively separated from the toxic components present in the waste. This paper reviews the chemical composition, phase composition and particle size distribution characteristics of smelting dust, and the results show that smelting dust has excellent physicochemical characteristics for recovering valuable metals. The process flow, critical factors, development status, advantages and disadvantages of traditional technologies such as pyrometallurgy, hydrometallurgy and biometallurgy were discussed in depth. Conventional treatment methods typically prioritize separating and reclaiming specific elements with high concentrations. However, these methods face challenges such as excessive chemical usage and limited selectivity, which can hinder the sustainable utilization of smelting dust. With the increasing scarcity of resources and strict environmental requirements, a single treatment process can hardly fulfil the demand, and a physical field-enhanced technology for releasing and separating valuable metals is proposed. Through analysing the effect of electric field, microwave and ultrasound on recovering valuable metals from smelting dust, the enhancement mechanism of physical field on the extraction process was clarified. This paper aimed to provide reference for the resource utilization of smelting dust.

Simultaneous preconcentration and pre-column derivatization for rapid analysis of nitrilotriacetic acid in environmental waters by high performance liquid chromatography

A simplified sample pretreatment procedure was developed for quantitative measurement of nitrilotriacetic acid (NTA) in environmental water. On the basis of coordination capacity between NTA and metal ions, aluminum-based metal organic framework (MOF, MIL-53(Al)) was adopted for the adsorption of NTA, followed by stripping with copper sulfate as the eluent. The adsorbed NTA was converted into Cu-NTA during the desorption process, which facilitated the ensuing measurement by high performance liquid chromatography (HPLC). A linear range within 0.10 - 10 mg L^-1 was achieved, along with a limit of detection (LOD, S/N=3, n=7) of 0.03 mg L^-1 and an enrichment factor of 10.4. The developed method was validated by the analysis of sea water, influent of wastewater treatment plant and industrial wastewater, with satisfactory recoveries (90.2 - 91.1%) obtained.

Indium recovery from spent liquid crystal displays by using hydrometallurgical methods and microwave pyrolysis

Indium recovery from spent liquid crystal displays (LCDs) of monitors was studied by using microwave pyrolysis as a pretreatment step prior to hydrometallurgical processes including acid leaching, solvent extraction, and stripping. After microwave pyrolysis at 150 W for a processing time of 50 min, the hydrometallurgical processes were carried out to sequentially solubilize and increase the purity of indium ions in the product solution. The leaching efficiency of indium was approximately 98% when using 0.5 M of sulfuric acid at a solid-to-liquid ratio (S/L) of 0.1 g/mL. Afterwards, the indium ions in the leachate were extracted by using 20% di(2-ethylhexyl)phosphoric acid (D2EHPA) in kerosene. The purity of indium ions in the organic phase was approximately 87% at an oil-to-aqueous ratio (O/A) of 1/10. Finally, the indium ions in the extract were stripped by using 6 M of hydrochloric acid at an O/A ratio of 10/1. The purity of indium ions in the aqueous phase was as high as 99.98%. The final recovery rate of indium from spent LCDs was approximately 75%, substantially higher than those that were obtained by using shredding or grinding pretreatment. The maximum processing capacity of microwave pyrolysis of spent LCDs could be approximately 500 g, which means that it would only need 0.5 kWh of electricity for the microwave pyrolysis of 1 kg of spent LCDs. According to the experimental results and advantages, it can be concluded that microwave pyrolysis is an effective technique for the pretreatment of spent LCDs.

Optimized indium solubilization from LCD panels using H2SO4 leaching

Spent liquid crystal displays (LCDs) are a secondary source of precious/strategic metals, including indium (In). The present study involved optimizing the solubilization of this strategic element from samples of indium tin oxide (ITO) glass prepared from LCD screens of computer monitors and laptop screens. The influence of operating conditions on In solubilization, as well as optimum conditions for sulfuric acid leaching were defined by a Box-Behnken-type experimental design methodology. Optimum operating conditions include a leaching step for 30 min at a temperature of 70 °C in the presence of 0.4 N H₂SO₄ and a pulp density of 50% (w/v). Under these conditions, the quadratic model established to predict the solubilization of In from ITO glass samples provided an In solubilization efficiency of 89.7%, which was validated experimentally (99.5%). The analysis of direct operating costs and capital costs for the implementation of such a leaching process revealed that the process is conceivable for a high-capacity plant processing ~100 t/day of ITO glass.

Adsorption of indium by waste biomass of brown alga Ascophyllum nodosum

The biosorption capacities of dried meal and a waste product from the processing for biostimulant extract of Ascophyllum nodosum were evaluated as candidates for low-cost, effective biomaterials for the recovery of indium(III). The use of indium has significantly grown in the last decade, because of its utilization in hi-tech. Two formats were evaluated as biosorbents: waste-biomass, a residue derived from the alkaline extraction of a commercial, biostimulant product, and natural-biomass which was harvested, dried and milled as a commercial, "kelp meal" product. Two systems have been evaluated: ideal system with indium only, and double metal-system with indium and iron, where two different levels of iron were investigated. For both systems, the indium biosorption by the brown algal biomass was found to be pH-dependent, with an optimum at pH3. In the ideal system, indium adsorption was higher (maximum adsorptions of 48 mg/g for the processed, waste biomass and 63 mg/g for the natural biomass), than in the double metal-system where the maximum adsorption was with iron at 0.07 g/L. Good values of indium adsorption were demonstrated in both the ideal and double systems: there was competition between the iron and indium ions for the binding sites available in the A. nodosum-derived materials. Data suggested that the processed, waste biomass of the algae, could be a good biosorbent for its indium absorption properties. This had the double advantages of both recovery of indium (high economic importance), and also definition of a virtuous circular economic innovative strategy, whereby a waste becomes a valuable resource.

Indium and tin recovery from waste LCD panels using citrate as a complexing agent

In this work, an environmentally-friendly leaching process for the recovery of indium (In) and tin (Sn) from LCD panel waste was investigated. Easily degradable citrates (C₆H₅O₇^3-), i.e., sodium citrate and citric acid, were used as complexing agents. The morphology and composition of the species present in the LCD powder before and after the leaching processes were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The concentrations of In, Sn, and iron (Fe) present in the leachate were determined by atomic absorption spectrometry (AAS). The necessary thermodynamic conditions for achieving substantial In recovery were established by using MEDUSA software. The optimal process conditions were determined experimentally by varying the initial citrate concentration as well as by using reducing or oxidizing media, respectively hydrazine (N₂H₄) or hydrogen peroxide (H₂O₂). It was found that using N₂H₄ in a citrate solution as a reducing agent enhances the leaching efficiency. However, high concentrations of Sn and Fe with respect to In were found in the LCD powder. Therefore, a pretreatment processes to first remove the excess of Sn and Fe, which compete with In for the citrate, was implemented. Leaching with 1 M citrate, 0.2 M N₂H₄, at pH = 5, using sodium hydroxide (NaOH) at solid:liquid (S:L) ratio of 20 g∙L^-1, yielded a remarkably high In recovery of 98.9% after 16.6 h.

Commercial indium recovery processes development from various e-(industry) waste through the insightful integration of valorization processes: A perspective

Recycling of the waste LCD and recovery of indium which is an important classified critical raw material rarely have been industrially valorized for the circular economy due to lack of technology. Waste specific technology development is a cost-intensive and time-consuming process for the recycling industry. Hence, integrating existing technology for the purpose can address the e-waste issue in general and waste LCD in particular. Waste LCD and LCD industry itching wastewater are two important challenges can be addressed through an insightful combination of two. Hence, here possible integration of waste LCD leaching process with ITO wastewater treatment has been focused on indium recovery purpose. From our perspective process integration can be managed in two different ways, i.e., waste-to-waste mix stream process and integration of two different valorization processes for complete recovery of indium. With reference to indium recovery and context of e-waste recovery the process integration can be managed in two different ways, i.e., (i) waste LCD leaching with ITO etching industry wastewater then valorized (Waste-to-waste mix stream), (ii) Integration of waste LCD leaching process with ITO wastewater treatment process (integration of two valorization processes).Through proposed process semiconductor manufacturing industry and ITO recycling industry can address various issues like; (i) waste disposal, as well as indium recovery, (ii) brings back the material to production stream and address the circular economy, (ii) can be closed-loop process with industry and (iii) can be part of cradle-to-cradle technology management and lower the futuristic carbon economy, simultaneously.

Chelator-induced recovery of rare earths from end-of-life fluorescent lamps with the aid of mechano-chemical energy

Rare-earths (REs) are key components for the transition to a greener energy profile and low carbon society. The elements turn out to be of limited availability in the market, due to the supply-demand issues, exponential price rises, or geopolitics, which has led to a focus on the exploration of secondary sources for RE reclamation. End-of-life (EoL) nickel-metal hydride batteries, permanent magnets, and fluorescent lamps (FL) have been the primary sources for recyclable REs, while the recovery of REs in EoL FL (Ce, Eu, La, Tb, or Y) includes comparatively fewer processing steps than the other potential sources. In the current work, we proposed a simple, energy-efficient protocol for EoL FL processing, using chelators in combination with ball milling. The parameters for optimum chelator-assisted recovery (chelator concentration, solid-to-liquid ratio, solution pH), and milling variables (ball size, ball weight, milling speed, milling duration), were evaluated at room temperature (RT, 25 ± 2 °C). The dissolution of REs with ethylenediaminetetraacetic acid (EDTA), ethylenediaminedisuccinic acid, methylglycinediacetic Acid, or 3-hydroxy-2,2'-iminodisuccinic acid, was compared at RT, while EDTA was used as the reference chelator throughout. Increasing the system temperature from 25 to 135 °C achieved at least double Eu and Y recovery, relative to that at RT, whereas the recovery rate improvement for Ce, La or Tb was insignificant. Mechano-chemical treatment at RT, via wet milling of EoL FL, with chelators, yielded a five order of magnitude increase in Ce, La and Tb recovery, however, plus a two-order increase for Eu or Y, compared with non-abetted operating conditions. It was also found that higher impact energy achieved improved recovery over a reduced milling duration with this technique having the added advantage of minimal acid consumption and reduced effluent production.

An environmentally friendly ball milling process for recovery of valuable metals from e-waste scraps

The present study reports a mechanochemical (MC) process for effective recovery of copper (Cu) and precious metals (i.e. Pd and Ag) from e-waste scraps. Results indicated that the mixture of K₂S₂O₈ and NaCl (abbreviated as K₂S₂O₈/NaCl hereafter) was the most effective co-milling reagents in terms of high recovery rate. After co-milling with K₂S₂O₈/NaCl, soluble metallic compounds were produced and consequently benefit the subsequent leaching process. 99.9% of Cu and 95.5% of Pd in the e-waste particles could be recovered in 0.5mol/L diluted HCl in 15min. Ag was concentrated in the leaching residue as AgCl and then recovered in 1mol/L NH₃ solution. XRD and XPS analysis indicated that elemental metals in the raw materials were transformed into their corresponding oxidation state during ball milling process at low temperature, implying that solid-solid phase reactions is the reaction mechanism. Based on the results and thermodynamic parameters of the probable reactions, possible reaction pathways during ball milling were proposed. Suggestion on category of e-waste for ball milling process was put forward according to the experiment results. The designed metal recovery process of this study has the advantages of highly recovery rate and quick leaching speed. Thus, this study offers a promising and environmentally friendly method for recovering valuable metals from e-waste.

An investigation of trends in precious metal and copper content of RAM modules in WEEE: Implications for long term recycling potential

Precious metal (PM) and copper content of dynamic-RAM modules placed on the market during 1991-2008 has been analysed by AAS following comminution and acid digestion. Linear regression analysis of compositional data ordered according to sample chronology was used to identify historic temporal trends in module composition resulting from changes in manufacturing practices, and to project future trends for use in more accurate assessment of future recycling potential. DRAM was found to be 'high grade' waste with: stable levels of gold and silver over time; 80% reduction in palladium content during 1991-2008; and 0.23g/module/year increase in copper content with a 75% projected increase from 2008 by 2020. The accuracy of future recycling potential projections for WEEE using current methods based on static compositional data from current devices is questionable due to likely changes in future device composition. The impact on recycling potential projections of waste laptops, smart phones, cell phones and tablets arising in Europe in 2020 resulting from a 75% increase in copper content is considered against existing projections using static compositional data. The results highlight that failing to consider temporal variations in PM content may result in significant discrepancies between projections and future recycling potential.

Separation and recovery of glass, plastic and indium from spent LCD panels

The present paper deals with physico-mechanical pre-treatments for dismantling of spent liquid crystal displays (LCDs) and further recovery of valuable fractions like plastic, glass and indium. After a wide experimental campaign, two processes were designed, tested and optimized. In the wet process, 20%, 15% and 40% by weight of the feeding panels are recovered as plastic, glass and indium concentrate, respectively. Instead, in the dry process, only two fractions were separated: around 11% and 85% by weight are recovered as plastic and glass/indium mixture. Indium, that concentrated in the -212μm fraction, was completely dissolved by sulphuric acid leaching (0.75molL^-1 H₂SO₄ solution, 80°C, 10%vol H₂O₂, pulp density 10%wt/vol, leaching time 3h). 100% of indium can be extracted from the pregnant solution with 5%wt/vol Amberlite™ resin, at room temperature and pH 3 in 24h. Indium was thus re-extracted from the resin by means of a 2molL^-1 H₂SO₄ solution, at room temperature and S/L of 40%wt/vol.

The geochemically-analogous process of metal recovery from second-hand resources via mechanochemistry: An atom-economic case study and its implications

In the context of recycling metal to embrace the sustainability challenge, this work proposes a geochemically-analogous process of metal recovery through mechanochemistry for the first time, to avoid the limitations of on-going methods and to establish an innovative technology philosophy. This work systematically investigates this geochemically-analogous process, to keep it green and to generalize it further. Copper recovery from waste printed circuit boards (WPCBs), a typical copper-rich waste, is chosen as a case study in this work. Nearly 98% of the copper in the WPCBs can be recycled in the optimized conditions and 82.3% of the sulfur can be reused, by means of the process. Based on the experimental result, this paper purports a closed-loop route of copper recovery which follows the green chemistry principles (high yield, high atom economy and no secondary pollution). This route can be generalized into other second-hand resources that are rich in copper. Some other metals (e.g. lead) that are commonly present as corresponding sulfides in nature can be taken into consideration in this geochemically-analogous process as well.

Pyrolysis characteristics and pyrolysis products separation for recycling organic materials from waste liquid crystal display panels

Waste liquid crystal display (LCD) panels mainly contain inorganic materials (glass substrate with indium-tin oxide film), and organic materials (polarizing film and liquid crystal). The organic materials should be removed beforehand since the organic matters would hinder the indium recycling process. In the present study, pyrolysis process is used to remove the organic materials and recycle acetic as well as and triphenyl phosphate (TPP) from waste LCD panels in an environmental friendly way. Several highlights of this study are summarized as follows: (i) Pyrolysis characteristics and pyrolysis kinetics analysis are conducted which is significant to get a better understanding of the pyrolysis process. (ii) Optimum design is developed by applying Box-Behnken Design (BBD) under response surface methodology (RSM) for engineering application which is significant to guide the further industrial recycling process. The oil yield could reach 70.53 wt% and the residue rate could reach 14.05 wt% when the pyrolysis temperature is 570 °C, nitrogen flow rate is 6 L min(-1) and the particle size is 0.5 mm. (iii) Furthermore, acetic acid and TPP are recycled, and then separated by rotary evaporation, which could reduce the consumption of fossil energy for producing acetic acid, and be reused in electronics manufacturing industry.

Ultrasonically treated liquid interfaces for progress in cleaning and separation processes

Cleaning and separation processes of liquids can be advanced by acoustic cavitation through bubbles with unique physico-chemical properties.

Resource recovery from waste LCD panel by hydrothermal transformation of polarizer into organic acids

Based on the significant advantages of hydrothermal technology, it was applied to treat polarizer from the waste LCD panel with the aim of transforming it into organic acids (mainly acetic acid and lactic acid). Investigation was done to evaluate the effects of different factors on yields of organic acids, including the reaction temperature, reaction time and H2O2 supply, and the degradation process of polarizer was analyzed. Liquid samples were analyzed by GC/MS and HPLC, and solid-phase products were characterized by SEM and FTIR. Results showed that at the condition of temperature 300 °C and reaction time 5 min, the organic materials reached its highest conversion rate of 71.47% by adding 0.2 mL H2O2 and acetic acid was dominant in the products of organic acids with the yield of 6.78%. When not adding H2O2 to the system, the yields of lactic and acetic acid were respectively 4.24% and 3.80% at a nearly equal degree, they are suitable for esterification to form ethyl lactate instead of separating them for this case. In the hydrothermal process, polarizer was first decomposed to monosaccharides, alkane, etc., and then furfural and acids are produced with further decomposition.

Application of mechanochemistry to metal recovery from second-hand resources: a technical overview

In the context of huge imbalance between increasing demand for metals and the finiteness of metal resources in nature, recycling metal from second-hand resources, especially e-waste, is of great importance, to embrace the sustainability challenge. Inspired by its hundreds of uses in extractive metallurgy, mechanochemistry has been introduced to recover metals from waste since the 1990s. The mechanochemical recycling process is technically feasible to recover metals from waste in a high yield, such as Pb recovery from cathode ray tube (CRT) funnel glass, Li and Co recovery from lithium-ion batteries, rare earth recovery from fluorescent lamps. In recovery from LCD screens, Cu recovery from waste printed circuit boards and Au, Mo and Ni recovery from waste. Particle size reduction, specific surface area increase, crystalline structure decomposition and bond breakage have been identified as the main changes induced by the mechanochemical processes in the studies. Also, the activation energy required decreases and reaction activity increases, subsequently. This paper presents a technical overview of the applications of mechanochemistry to metal recycling from waste. The current application pattern, reaction mechanisms, equipment used, method procedures, and the future research direction are discussed in detail. This work presents the limitation of current mechanochemical application in metal recovery and gives a perspective of the future development of mechanochemistry as well.

Cross-current leaching of indium from end-of-life LCD panels

Indium is a critical element mainly produced as a by-product of zinc mining, and it is largely used in the production process of liquid crystal display (LCD) panels. End-of-life LCDs represent a possible source of indium in the field of urban mining. In the present paper, we apply, for the first time, cross-current leaching to mobilize indium from end-of-life LCD panels. We carried out a series of treatments to leach indium. The best leaching conditions for indium were 2M sulfuric acid at 80°C for 10min, which allowed us to completely mobilize indium. Taking into account the low content of indium in end-of-life LCDs, of about 100ppm, a single step of leaching is not cost-effective. We tested 6 steps of cross-current leaching: in the first step indium leaching was complete, whereas in the second step it was in the range of 85-90%, and with 6 steps it was about 50-55%. Indium concentration in the leachate was about 35mg/L after the first step of leaching, almost 2-fold at the second step and about 3-fold at the fifth step. Then, we hypothesized to scale up the process of cross-current leaching up to 10 steps, followed by cementation with zinc to recover indium. In this simulation, the process of indium recovery was advantageous from an economic and environmental point of view. Indeed, cross-current leaching allowed to concentrate indium, save reagents, and reduce the emission of CO2 (with 10 steps we assessed that the emission of about 90kg CO2-Eq. could be avoided) thanks to the recovery of indium. This new strategy represents a useful approach for secondary production of indium from waste LCD panels.

Recycling metals from wastes: a novel application of mechanochemistry

Recycling metals from wastes is essential to a resource-efficient economy, and increasing attention from researchers has been devoted to this process in recent years, with emphasis on mechanochemistry technology. The mechanochemical method can make technically feasible the recycling of metals from some specific wastes, such as cathode ray tube (CRT) funnel glass and tungsten carbide waste, while significantly improving recycling efficiency. Particle size reduction, specific surface area increase, crystalline structure decomposition and bond breakage have been identified as the main processes occurring during the mechanochemical operations in the studies. The activation energy required decreases and reaction activity increases, after these changes with activation progress. This study presents an overall review of the applications of mechanochemistry to metal recycling from wastes. The reaction mechanisms, equipment used, method procedures, and optimized operating parameters of each case, as well as methods enhancing the activation process are discussed in detail. The issues to be addressed and perspectives on the future development of mechanochemistry applied for metal recycling are also presented.

Recycling acetic acid from polarizing film of waste liquid crystal display panels by sub/supercritical water treatments

Waste liquid crystal display (LCD) panels mainly contain inorganic materials (glass substrate) and organic materials (polarizing film and liquid crystal). The organic materials should be removed first since containing polarizing film and liquid crystal is to the disadvantage of the indium recycling process. In the present study, an efficient and environmentally friendly process to obtain acetic acid from waste LCD panels by sub/supercritical water treatments is investigated. Furthermore, a well-founded reaction mechanism is proposed. Several highlights of this study are summarized as follows: (i) 99.77% of organic matters are removed, which means the present technology is quite efficient to recycle the organic matters; (ii) a yield of 78.23% acetic acid, a quite important fossil energy based chemical product is obtained, which can reduce the consumption of fossil energy for producing acetic acid; (iii) supercritical water acts as an ideal solvent, a requisite reactant as well as an efficient acid-base catalyst, and this is quite significant in accordance with the "Principles of Green Chemistry". In a word, the organic matters of waste LCD panels are recycled without environmental pollution. Meanwhile, this study provides new opportunities for alternating fossil-based chemical products for sustainable development, converting "waste" into "fossil-based chemicals".

Biodegradable chelating agents for industrial, domestic, and agricultural applications--a review

Aminopolycarboxylates, like ethylenediaminetetraacetic acid (EDTA) and diethylenetriaminepentaacetic acid (DTPA), are chelating agents widely used in several industrial, agricultural, and domestic applications. However, the fact that they are not biodegradable leads to the presence of considerable amounts in aquatic systems, with serious environmental consequences. The replacement of these compounds by biodegradable alternatives has been the object of study in the last three decades. This paper reviews the most relevant studies towards the use of environmentally friendly chelating agents in a large number of applications: oxidative bleaching, detergents and cleaning compositions, scale prevention and reduction, remediation of soils, agriculture, electroplating, waste treatment, and biocides. Nitrilotriacetic acid (NTA), ethylenediaminedisuccinic acid (EDDS), and iminodisuccinic acid (IDS) are the most commonly suggested to replace the nonbiodegradable chelating agents. Depending on the application, the requirements for metal complexation might differ. Metal chelation ability of the most promising compounds [NTA, EDDS, IDS, methylglycinediacetic acid (MGDA), L-glutamic acid N,N-diacetic acid (GLDA), ethylenediamine-N,N'-diglutaric acid (EDDG), ethylenediamine-N,N'-dimalonic acid (EDDM), 3-hydroxy-2,2-iminodisuccinic acid (HIDS), 2-hydroxyethyliminodiacetic acid (HEIDA), pyridine-2,6-dicarboxylic acid (PDA)] with Fe, Mn, Cu, Pb, Cd, Zn, Ca, and Mg was simulated by computer calculations. The advantages or disadvantages of each compound for the most important applications were discussed.

Synergism of mechanical activation and sulfurization to recover copper from waste printed circuit boards

This work proposed a synergistic route of mechanic activation and sulfurization to recover copper from waste printed circuit boards for the first time and take successful use of free radical theory in assessing the synergism mechanism.

Chelant-induced reclamation of indium from the spent liquid crystal display panels with the aid of microwave irradiation

Indium is a rare metal that is mostly consumed as indium tin oxide (ITO) in the fabrication process of liquid crystal display (LCD) panels. The spent LCD panels, termed as LCD-waste hereafter, is an increasing contributor of electronic waste burden worldwide and can be an impending secondary source of indium. The present work reports a new technique for the reclamation of indium from the unground LCD-waste using aminopolycarboxylate chelants (APCs) as the solvent in a hyperbaric environment and at a high-temperature. Microwave irradiation was used to create the desired system conditions, and a substantial abstraction of indium (≥80%) from the LCD-waste with the APCs (EDTA or NTA) was attained in the acidic pH region (up to pH 5) at the temperature of ≥120 °C and the pressure of ~50 bar. The unique point of the reported process is the almost quantitative recovery of indium from the LCD-waste that ensured via the combination of the reaction facilitatory effect of microwave exposure and the metal extraction capability of APCs. A method for the selective isolation of indium from the extractant solution and recycle of the chelant in solution is also described.