Indium recovery method

Abstract

The present invention relates to the recovery of indium metal from indium tin oxide (ITO) coated glass surfaces by an electrochemical method.

Description

[0001] DESCRIPTION

[0002] INDIUM RECOVERY METHOD

[0003] Technical Field of the Invention

[0004] The present invention relates to the recovery of indium metal from indium-tin oxide (ITO) coated glass surfaces by an electrochemical method.

[0005] State of the Art of the Invention (Prior Art)

[0006] Indium is mainly used in the production of indium tin oxide (ITO). Indium ore does not exist in nature, is obtained as a by-product in the smelting of zinc and tin ores, and is present in much smaller quantities (0.0001 ~ 0.1 percent) than needed. The need for indium is steadily growing due to the significant increase in the use of devices such as tablets, smartphones, PV, LCD, OLED displays, and e-books. Apart from electronic devices, indium also plays an important role in semiconductor applications such as photovoltaic films, LEDs, and laser diodes. Given its economic importance and increasing supply risk, the development of new technologies for the recycling of indium from waste electronic products is considered an important factor for sustainability.

[0007] Several methods for recovering indium from ITO coated glasses have been reported in the literature (Zhang et al., 2015); (Yang et al., 2013); (Lee et al., 2013); (Rocchetti et al., 2015). In these studies, waste LCDs, polarizing films, liquid crystal components, and ITO glass layers are first separated from each other and ITO glass panels are subjected to cleaning (Fontana et al., 2021). This separation involves process steps such as chemical / thermal treatments and rinsing, which process removes most of the organic components, including liquid crystals and polarization coatings. Further processing is required to recover indium from the glass surface containing indium oxide and tin oxide.

[0008] Pyrochemistry, pyrometallurgy and hydrometallurgy methods for indium recovery from ITO coated glass materials are mentioned.

[0009] In the literature, hydrometallurgical treatment including leaching, concentration, separation, and electrorefining steps is considered to be the most suitable approach for the recycling of indium from waste panels (Zhang et al., 2015). The leaching step is carried out in strong acidic solutions such as sulfuric acid, nitric acid, hydrochloric acid or sodium hydroxide and sodium hypochlorite, which support the solubility of indium oxide. The leaching process involves the application of complexing agents such as cyanide and thiosulfate as well as oxidants such as ferric iron and hydrogen peroxide to increase the yield (Isildar et al., 2018). In addition, direct indium recovery efficiency is not at the desired rate due to the compounding of indium with tin oxide during the process (Li et al., 2011). Therefore, the hydrometallurgy recovery method has disadvantages such as the use of environmentally harmful, corrosive and hazardous chemicals, as well as additional costs and time due to indium reduction not occurring at the desired efficiency and purity, which reduces feasibility.

[0010] In the pyrochemical method, thermal reduction or chlorination processes are used to recover indium from ITO waste (Fan et al., 2021). In this context, chlorination reaction or chlorinated separation under vacuum are the main pyrochemical approaches (Ma and Xu, 2013) that can be used in indium extraction (Ma et al., 2012). In general, this method involves chlorination of indium with the aid of chlorine, carbon tetrachloride, hydrogen chloride, ammonium chloride, sodium chloride, calcium chloride, and other similar chemicals (Ebin and Isik, 2016). Due to the moderate evaporation temperature of the resulting metal chlorides, the metals then can be optionally separated and purified (Ebin and Isik, 2016). However, the additional processes required for the purification and separation of indium chloride into indium metal result in significant additional production costs. The indium chloride and tin chloride obtained after chlorination are evaporated and then condensed to recover the metal. This postchlorination process is preferred as it has relatively low temperature compared to pyrochemical approaches involving conventional thermal processes. Chlorination process can be carried out in air or nitrogen (vacuum) environment. The cost of indium recovery rate in air is quite low, however processing in vacuum conditions increases the production cost. In addition to these disadvantages of the method, hydrogen chloride and chlorine gases have a negative impact on the environment and human health due to their nature. Therefore, special attention needs to be paid to any reactor leakage, with special operational requirements such as vacuum conditions (Terakado et al., 2010). In this method, the recovery rate can reach high values depending on the vacuum conditions, concentration of reducing or chlorinating agent, and temperature (Ma et al., 2012). The fact that the pyrometallurgical method consists of many stages and all stages are carried out at high temperature and the reaction environment has very specific conditions causes the recovery process to result in high costs and is not considered as a sustainable method.

[0011] In pyrometallurgy technology where thermal processes are applied, ITO-containing scrap is processed at high temperature in the furnace to recycle precious metals and other unwanted materials are separated as slag (Zhang and Xu, 2016). In the first step of the prometallurgical process, the metals in the structure of ITO are reduced to indium-tin (In-Sn) alloy at a relatively low temperature in the presence of carbon monoxide gas. In the second stage, indium in the In-Sn alloy is selectively evaporated by utilizing the vapor pressure difference and increasing the temperature, and metallic indium is collected by cooling the resulting indium vapor. The removal of unwanted substances and the resulting hazardous gases in this process entails complex and costly cleaning processes. In addition, one of the most important steps of the pyrometallurgical metal recovery procedure from ITO waste is the inability to separate the indium-tin alloy formed during the process; therefore, the inability to separate indium metal from tin at the desired efficiency and purity is the biggest problem of this process (Itoh and Maruyama, 2011). Therefore, studies on the reducing and vaporizing properties of the ln-Sn-0 system are still being carried out to improve this technique (Chen et al., 2019).

[0012] Compared to hydrometallurgy, pyrometallurgical metal recovery technique is less preferred due to excessive energy use, increased metal evaporation loss and high pollutant emissions. On the other hand, the hydrometallurgical process involves the use of large quantities of caustic and volatile acids, which increase operational risks and are harmful to human health and the environment. Therefore, although significant progress has been made in the industrial indium recovery process of ITO waste material, there is still room for improvement for a sustainable and viable method.

[0013] Summary and Objects of the Invention

[0014] The object of the invention is to develop a fast and environmentally friendly alternative indium recovery method. Accordingly, the present invention relates to the recovery of indium metal from an indium tin oxide (ITO) coated glass surface by an electrochemical method.

[0015] The invention also relates to the obtaining of indium metal from the ITO coated glass surface by electrochemical reduction in a single step without any damage to the glass.

[0016] Compared to prior art methods, the invention provides an efficient and economical approach for recovering indium from ITO coated waste glass surface in a single step process using environmentally friendly solvents, which takes place in as little as 30 minutes and at a lower temperature of 70-80 °C.

[0017] In addition to fast indium recovery in a single step, the present invention also provides high efficiency and high purity indium recovery.

[0018] Descriptions of the Figures Describing the Invention

[0019] Fig. 1. XRD analysis of the sample prepared in aqueous reline containing pure reline and 1 M water (In JCPDS 05-0642: standard).

[0020] Fig. 1a. XRD analysis of samples prepared in pure reline and aqueous reline with different water contents (aqueous reline solutions containing 1 M, 3 M, 5 M and 9 M water) (Zn JCPDS 04-0831 : standard).

[0021] Fig. 2. SEM image for ITO coated glass surface before the electrochemical process of the invention.

[0022] Fig. 3. SEM image for electrically reduced ITO film in (a) pure reline solution (b) 1 :2:1 molar ratio ChCI:urea:water solution (c) 1:2:3 molar ratio ChCI: urea: water solution.

[0023] Fig. 4. XRD analysis of ITO coated glass surface (cathode) electrochemically treated for different durations (In JCPDS 05-0642: standard, ln20s JCPDS 06-0416: standard).

[0024] Fig. 5. XRD analysis of the working electrode electrochemically treated in ChCI:urea:water solution in 1 :2:3 molar ratio at different ZnCI2amounts.

[0025] Fig. 6. a) TEM images and b) histogram of particle size distribution for indium particles obtained in aqueous reline electrolyte containing 3 M water.

[0026] Detailed Description of the Invention

[0027] The present invention relates to the recovery of indium metal from indium-tin oxide (ITO) coated glass surfaces by a single-step and rapid electrochemical method. Within the scope of the invention, an environmentally friendly, economical and fast electrochemical reduction method for the recovery of indium has been developed.

[0028] The electrochemical method of the invention for the recovery of indium comprises an electrolysis process is applied in which a deposition voltage sufficient to enable indium deposition on the cathode surface is applied to an indium tin oxide (ITO)-coated glass surface selected as a cathode, to an anode, immersed in an electrolyte comprising at least one deep eutectic solvent (DES) based on choline chloride, at a constant temperature below 100 °C.

[0029] In the recovery method of the invention; it is seen that the electrochemical process taking place in the electrolyte containing at least one deep eutectic solvent (DES) based on choline chloride causes structural changes in the indium-tin oxide layer and as a result, indium metal is reduced and separated from the indium-tin oxide (ITO) layer on the ITO coated glass surface and deposited on the cathode surface.

[0030] Here, any of the ITO coated glass panels used in many electro-optical applications such as PV, LCD, OLED, smartphone, etc. can be used as ITO coated glass surface.

[0031] Indium has a melting point of 156.6 °C, which creates difficulties when depositing sticky metallic indium at temperatures approaching its melting point. Therefore, it is important to keep the temperature below 100 °C. In the invention, a constant temperature in the range of 70°C-80 °C, and particularly preferably 80 °C, is preferably provided to ensure optimum metal deposition on the ITO substrate.

[0032] In the preferred embodiment of the invention, -1,6 V deposition voltage is applied to ITO coated glass surface (cathode) and pure zinc wire (anode) electrodes immersed in electrolytes containing deep eutectic solvent or a water-containing mixture of this solvent at 80 °C, reducing indium metal and separating it from the indium-tin oxide (ITO) layer on the ITO-coated glass surface and depositing it on the cathode surface.

[0033] In the electrolysis experiments carried out in DES with different water content within the scope of the invention, the highest indium reduction potential varies in the range of - 1.2- -1.4 V. However, since DES causes ohmic losses, i.e., energy losses, it is necessary to apply a higher potential. In this context, although it depends on the DES content, it is generally recommended that the potential to be applied should be above - 1.4 V. At the same time, trials were also performed for -2.1 V value and reduction was observed, but considering that this recovery would not be feasible in terms of energy efficiency and cost, impurity and reduction efficiency studies were not performed for potential values above -1.6 V. In the light of all these studies, for the preferred embodiment of the invention, a range of - 1.5 to -1.6 V, and in particular a deposition voltage of -1.6 V, is recommended. Here, (-) is used to refer to the voltage direction, i.e. the anode potential.

[0034] In said recovery method, ITO coated glass surface is used as the working electrode, i.e. cathode, and pure zinc wire is used as the counter electrode, i.e. anode. In addition to zinc, options such as platinum, gold, and silver can also be used as anodes. The sheet resistance of the ITO coated glass surface used can vary from 6 ohm / sq to 100 ohm / sq. Likewise, the film thickness can vary between 20-200 nm. The ITO-coated glass surface used as the cathode in the invention preferably has a sheet resistance of 20 ohms / sq, preferably has a film thickness of 168 nm, and preferably has dimensions of 6 cm x 2 cm. The pure zinc wire used as anode is preferably 7 cm long and 3 mm in diameter.

[0035] In the preferred embodiment of the invention, in order to remove the impurities on the surface by manually cutting the electrodes with a diamond-tipped glass cutter before the process and keeping them in an open environment, they were washed with detergent before the electrochemical process, then kept in an ultrasonic bath containing acetone solution, ethanol solution, and distilled water for 15 minutes, respectively, and dried at 70 °C for one day, and then used in experiments. In alternative embodiments of the invention, depending on the cleanliness or impurity of the surface, the cleaning step may not be required.

[0036] In the preferred embodiment of the invention, electrochemical processes are carried out by immersing a 4 cm section of the electrodes in an electrolyte consisting of zinc chloride (ZnCh) support electrolyte, deep eutectic solvent (DES) and aqueous mixtures in a volume of 70 ml. At the same time, the electrochemical process is carried out at a constant temperature of 80 °C in a jacketed vessel with hot water circulation. Compared to the pyrometallurgical method, where the metal is heated to melting temperatures, indium recovery with the invention is carried out at temperatures as low as 80 degrees and therefore does not require large amounts of energy consumption.

[0037] In addition, the distance between electrodes was preferably set to the standard 7 mm. The electrochemical process was preferably continued for 30 minutes under the specified conditions.

[0038] With the invention, indium reduction takes place within 1-2 minutes and the highest yields are achieved in as little as 30 minutes. In fact, very rapid reduction is observed within seconds after the start of electrolysis, which was correlated with time-dependent current measurements by connecting the electrodes in parallel. The amount of indium reduced with time, i.e. the recovery efficiency increases. The correlation between the amount of indium reduced and time was also studied within the scope of the study and it was observed that 30 minutes electrolysis time was the time with the highest efficiency in the studies carried out at different time intervals between 2 minutes to 4 hours (Fig. 4). As shown in Fig. 3, XRD patterns were used to examine the crystal structures of the ITO film after undergoing various electrochemical processes and analyzes. X-ray diffraction analysis (XRD analysis) of the working electrode surface for various processing times reveals that indium undergoes a reduction reaction and forms indium metal crystal structures, as evidenced by the presence of peaks in accordance with the JCPDS 05-0642 standard. The reduction of the working electrode is clearly visible even after the first 2 minutes on the working electrode surface as crystal planes indium 101 , 002, 110 and 202 at scattering angles (20) of 32.96, 36.15, 39.38, and 69.31, respectively. All of these peaks are associated with the body-centered tetragonal phase of indium, indicating that the crystal structure formed on the electrode surface is consistent with the expected phase of indium under these conditions. The formation of this crystal structure occurs even in a relatively short time frame of only 2 minutes, indicating that the reduction reaction is fast and efficient.

[0039] The biggest disadvantage of hydrometallurgical methods is the necessity of additional measures for the disposal of acid-base solutions harmful to the environment and human health used in the leaching process during and after use. Similarly, gases such as SC>2and CO2 formed as a result of pyrometallurgical processes used in indium recovery cause environmental problems such as air pollution. Therefore, in the present invention, an environmentally friendly alternative recovery method has been provided by eliminating the damages caused by other recovery methods by using an environmentally friendly deep eutectic solvent (DES) based on choline chloride. At the same time, one of the reasons for using deep eutectic solvents is that these solvents can be used repeatedly as electrolytes without degradation.

[0040] Both solvents, commercially called reline and ethaline, are deep eutectic solvents (DES) based on choline chloride (ChCI). In the experimental studies carried out within the scope of the invention, preferably pure reline, pure ethaline, ethaline-reline mixture and aqueous mixtures thereof were tried as electrolytes. In previous studies with DES aqueous mixtures containing different amounts of water, it is known that hydrogen bonds weaken, but the effect on indium reduction has been studied for the first time with the present invention. There are studies in the literature showing that hydrogen bonds weaken / strengthen in ChCkurea-based DES mixtures containing different amounts of water depending on the amount of water. Based on the information in these studies, electrochemical experiments were carried out for the first time in this study using ITO electrode with different ChCl-based DES mixtures and aqueous solvents and discussed in line with the literature information. According to the findings of this application within the scope of the invention, the basic structure of the choline chloride based deep eutectic solvent (DES) electrolytes used provides more favorable conditions for reduction than acidic environment. In this context, the pH values of the DES used were studied and electrolysis experiments were also carried out at pH values of 8, 6 and 5 without disrupting the DES structure. In all experiments, the results show that the reduction mechanism is mainly related to the hydrogen bonds in the DES structure and the stronger the hydrogen bonds, the higher the rate of indium reduction.

[0041] Reline is obtained by mixing choline chloride and urea in a 1 :2 molar ratio. Similarly, ethaline is a mixture of choline chloride and ethylene glycol (EG) in a molar ratio of 1:2. In the preferred embodiment of the invention, these mixtures are obtained by stirring at 400 rpm and 80 °C for about 2 hours until a smooth and clear liquid is obtained. However, in alternative embodiments of the invention, commercially available pure reline and / or pure ethaline solutions having the same content can also be used.

[0042] Similarly, studies have been carried out with aqueous mixtures of these pure deep eutectic solvents within the scope of the invention, however, since these aqueous mixtures are not commercially available, they were prepared in different ratios within the scope of the invention. Aqueous mixtures of reline and ethaline are obtained by adding water at different ratios of 1 , 3, 5 and 9 molars to choline chloride and urea and ethylene glycol mixtures respectively at a molar ratio of 1 :2, and stirring at 400 rpm and 80°C until a smooth and clear liquid is obtained.

[0043] According to the results of the study of DES aqueous mixtures; the increase in the molecular interactions of ChCI:urea:water compositions at a molar ratio of 1 :2:1 resulted in an increase in the indium recovery rate. The XRD patterns presented in Fig. 1 show that indium oxide is reduced to different levels in the samples obtained using pure reline, aqueous reline containing 1M water (1 :2:1 ChCI:urea:water) and aqueous reline containing 3M water (1:2:3 ChCI:urea:water) electrolyte samples. Again, similar to the surfaces obtained in pure DES-type electrolytes for all samples, no zinc deposition was observed in hydrated reline. Again, as can be seen in Fig. 1 , the main indium metal peak (101) at 32.96° 20 on the surface of the electrically reduced samples was highest when aqueous reline containing 1M water was used as the electrolyte and decreased when the electrochemical experiment was performed in aqueous reline mixture containing 3M water. These results enrich the understanding of the effect of the hydrogen bonding strength of the electrolyte on the electro-reduction of indium metal and show that the aqueous reline mixture containing 1M water with the highest hydrogen bonding is the most suitable electrolyte for this process. Therefore, in the preferred embodiment of the invention, an aqueous solution of ChCI:urea:water in a molar ratio of 1:2:1 is used.

[0044] In addition, at a higher water ratio, i.e. above 5 M water in a 1:2 M ChCkurea DES, the hydrogen bonds between the compounds are relatively weakened and the diffusion of water in the DES is increased, resulting in first reduction of indium and then zinc deposition on the electrode surface under the same conditions with electrochemical process. Since both urea and chloride ions are hydrolyzed to a certain extent by water, the blocking effect of the large and complex ions preventing the deposition of Zn on the surface is weakened, resulting in Zn crystals, as can be seen from the graph in Fig. 1a. This suggests that the presence of water plays an important role in the behavior of the molecular interaction in the reline by reducing the hydrogen bonding strength and increasing the ionic diffusivity, which helps zinc ions to be deposited on the surface of the working electrode. From the same graph (Fig. 1a), it can be observed that the diffraction patterns related to indium crystal peaks do not disappear, but become less intense with increasing water fractions. This result proves once again that the rate of indium reduction depends on the interaction between molecules and the hydrogen bonding of the electrolyte. In other words, in 5 M and 9 M water fractions, both urea and anions show higher diffusivity, indicating a change in the electrochemical mechanism. The rate of reduction of indium is directly related to the concentration of water in the electrolyte, which in turn affects hydrogen bonding and molecular interactions in the system.

[0045] In the preferred embodiment of the invention, ZnCl2 is added as a supporting electrolyte to the prepared pure or aqueous deep eutectic solvent. Supporting electrolytes play a crucial role in determining the final outcome of surface deposits, such as their morphology, composition, and size. In the first experiments with DES, 0.1 M KCI was used as the supporting electrolyte as it is a typical supporting electrolyte in aqueous systems. However, it was observed that KCI did not dissolve in pure reline or ethaline. This led to the choice of ZnCh instead of KCI because it has similar anion groups to the ChCl-based DES used in this study. This choice helped to avoid some possible anion exchanges and at the same time ZnCl2 is completely soluble in reline and ethaline solutions. Also, Cl- ions and other anions in the DES solution tend to adsorb on the working electrode. This was mainly studied to adjust or divert the sediments. In general, Cl- ions do not form complexes with metal ions or can only form to a very small extent. This was another important motivation for the identification of ZnCh as the supporting electrolyte. Therefore, 0.1 M ZnCh was dissolved in DES stirred at 400 rpm for 20 min at 70-80 °C.

[0046] It is also important to note that the role of the supporting electrolyte was considered as it affects the electrical double layer (EDL) structure and current density throughout the electrochemical experiment when its concentration is increased. In this context, electrochemical experiments were carried out in reline with a 2-electrode configuration at different ZnCh concentrations (0.1 M, 0.2 M and 0.4 M) and without supporting electrolyte ZnCh, under the same conditions such as deposition time (30 min), current (-1.6 V) and temperature (80 °C). The XRD results in Fig. 5 show that an increase in the concentration of ZnCh in the electrolyte can lead to changes in the reduction and deposition processes. Zinc chloride added up to 0.2 molar supports indium reduction, while use above this ratio negatively affects the process as it causes zinc deposition on the surface in addition to indium reduction. These changes can be attributed to differences in bulk transport, speciation and layering mechanisms during the electrochemical process. The addition of the physical properties of the reline varies significantly with the rate of increase of ZnCl2 associated with the addition of water, which can similarly lead to a weakening of the hydrogen bond network in the reline. This disruption of the bond structure increases the average gap size between the reline components and thus promotes the bulk transport of zinc ions. Therefore, at higher concentrations of zinc chloride, such as 0.4 M, it is possible to deposit zinc on surfaces through indium reduction, similar to that observed in aqueous reline mixture with water of 9 molars added. As can be seen from these results, zinc deposition and indium reduction rate depend on the concentrations of water in the aqueous electrolyte solution and ZnCh added as supporting electrolyte.

[0047] It has been observed that the indium metal is reduced by separating from the ITO layer and deposited on the surface in the form of spherical particles with an average diameter of 140 nm and in powder form on the cathode surface. Solid particles formed on the surface of the working electrode were also analyzed by transmission electrode microscopy (TEM), high-resolution transmission electrode microscopy (HRTEM) and selected area electron diffraction (SAED) analyzes. TEM image of the particles (Fig. 6(a)) shows that the nanoparticles are mostly spherical. The particle size distribution is between 50 to 300 nm and the average particle size was measured with the help of Image J software and determined as 140nm (Fig. 6(b)). TEM image of the particles revealed their spherical shape, confirming the success of the synthesis process. These results indicate that the synthesis process was successful and indium nanoparticles were obtained.

[0048] Scanning electron microscopy (SEM) images in Fig. 3 for surfaces electrochemically treated with pure reline or aqueous reline solutions also show the formation of spherical particles. Fig. 2 shows the SEM micrograph of the ITO thin film surfaces before the application of the electrochemical method of the invention. This image shows that electrochemical treatment of surfaces with reline solutions can lead to the formation of nano-sized spherical indium particles. In addition, the images showed that the extracted indium particles on the top of the substrate after electrochemical experiments in pure reline and also in ChCI:urea:water solutions at a molar ratio of 1 :2:1 were more crystalline and significantly larger with a higher diameter, which is consistent with XRD analysis showing more intense and sharper indium peaks compared to the ChCI:urea:water correlation at a molar ratio of 1 :2:3. In addition, the SEM image of 1 :2:1 molar ratio ChCI:urea:water revealed a homogeneous and closer size distribution of nanometric indium nanoparticles, which were more uniformly distributed along the substrate surface than the sample surface obtained in 1:2:3 molar ratio ChCI:urea:water electrolyte. In accordance with the crystalline structure of these samples, morphological examinations also show that the concentration of water in the electrolyte has a significant effect on the size, distribution, and crystallinity of the extracted indium particles. All these results also explain the choice of ChCI:urea:water aqueous solution in a 1 :2:1 molar ratio as the electrolyte in the preferred embodiment of the invention.

[0049] In the prior art pyrometallurgical and hydrometallurgical methods, ITO coated glass is crushed and ground and only indium is recovered. Thanks to the method of the invention, indium metal is separated from the cathode surface from which it is recovered without any degradation of said surface material. For this reason, the glass surface or in other words the glass substrate, which is also a valuable material and used as a cathode, is obtained in a reusable form without any degradation and breakage. Crushing and grinding of scrap glass requires energy. Therefore, the fact that the method of the invention does not require a crushing-grinding process provides a significant advantage in terms of energy efficiency as well as the recovery of the glass as a whole. In addition, the glass substrates used in ITO-coated glass samples are also special, and in this context, the recycling of the substrate is an additional contribution to the circular economy.

[0050] Spherical indium particles formed by the decomposition of indium metal from the ITO coated glass surface used as a cathode can be easily separated from the cathode surface by mechanical scraping or stripping. In the preferred embodiment of the invention, indium metal is obtained by stripping the cathode surface.

[0051] Comparison of the d-range between TEM / SAED and X-ray diffraction patterns revealed that the crystalline phases on the surface belong only to indium metal and indium oxide. No impurity or formation of any other compound or alloy other than indium metal and indium tin oxide structure was observed on the surface. Therefore, the recovered indium metal can be reused without any purification process. Hydrometallurgy includes many steps such as grinding, leaching, leaching, purification, and metal recovery. The main pyrometallurgical processes are milling, drying, calcination, roasting, smelting, and refining. Both hydrometallurgical and pyrometallurgical methods require additional processes, such as many steps and purification step, which adds additional time and cost. Within the scope of the present invention, high purity indium recovery is achieved in a single chemical step by direct application without the need for an additional step such as purification or separation.

[0052] At the same time, experimental studies were carried out to analyze whether it is possible to use the indium metal, which is easily separated from the working electrode after the electrochemical process, directly as an ITO source, and it was observed in the conducted studies that the indium metal reduced on the surface was re-oxidized after calcination and returned to the ITO structure.

[0053] In this direction, within the scope of the present invention, when the samples obtained from electrolysis studies in aqueous reline electrolyte containing 0.1 M ZnCI2 were subjected to 500 °C heat for 30 minutes, ITO structure was observed on the surface again, but the shifts observed in the peak values in the XRD results were interpreted as introduction of zinc metal into the structure, albeit slightly.

[0054] In the studies conducted, the observation that indium metal reduced on the surface is re-oxidized and returned to the ITO structure after being subjected to calcination process paves the way for obtaining coatings with different surface properties by doping the ITO thin film with different metals.

[0055] For example, zinc-indium-tin oxide (ZITO) coatings with important electrical and catalytic properties are obtained by retaining zinc metal on the surface (by changing the amount of zinc chloride or water in the electrolyte) in addition to indium recovery. In pyrometallurgical and hydrometallurgical methods, this is not possible as the ITO- coated glass from which the indium is recovered is crushed and ground.

[0056] For this reason, in the alternative embodiment of the invention, when the indium metal obtained on the surface is calcined again at 500 degrees in an air environment for about 30 minutes without being separated from the glass surface, the ITO layer can be formed again on the glass surface with a reversible reaction. In particular, when the indium metal on the surface is subjected to heat treatment in an air-permeable calcination furnace at 500 °C for 30 minutes, the indium metal on the surface is completely oxidized and returns to its pre-electrochemical process state. This feature of the samples obtained in this study creates a new and important research area in terms of the formation of different structures (ZITO etc.) on the surface as explained in detail above.

Claims

CLAIMS1. An electrochemical method for the recovery of indium, characterized in that an electrolysis process is applied in which a deposition voltage sufficient to enable indium deposition on the cathode surface is applied to an indium tin oxide (ITO)-coated glass surface selected as a cathode and to an anode, immersed in an electrolyte comprising at least one deep eutectic solvent (DES) based on choline chloride, at a constant temperature below 100 °C.

2. The method according to claim 1, characterized in that the indium deposited on the cathode surface is scraped or stripped off the surface.

3. The method according to claim 1, characterized in that the electrolysis process is carried out at a constant temperature in the range of 70 °C-80 °C.

4. The method according to claim 3, characterized in that: it is applied at a constant temperature of 80 °C.

5. The method according to claim 1, characterized in that a deposition voltage in the range of -1.2--2.1 is applied.

6. The method according to claim 1, characterized in that a deposition voltage above -1.4 V is applied.

7. The method according to claim 1, characterized in that a deposition voltage in the range of -1.5-1.6 is applied.

8. The method according to claim 1 , characterized in that the indium-tin oxide(ITO) coated glass surface selected as the cathode has a sheet resistance of 20 ohm / sq and a film thickness of 168 nm.

9. The method according to claim 1, characterized in that the anode is pure zinc wire.

10. The method according to claim 1, characterized in that the electrolyte comprises a mixture of said pure solvents or an aqueous mixture of said pure solvent.

11. The method according to claim 1 or 10, characterized in that the choline chloride-based pure deep eutectic solvent is pure reline and / or pure ethaline.

12. The method according to claim 10 or 11, characterized in that the aqueous mixture of pure solvent comprises 1 M pure reline or 1 M pure ethaline and 1 M, 3 M, 5 M or 9 M water.

13. The method according to claim 12, characterized in that the electrolyte comprises 1 M pure reline and 1 M water.

14. The method according to claim 1 , characterized in that the electrolyte further comprises zinc chloride (ZnCh).

15. The method according to claim 14, characterized in that the electrolyte comprises 0.1 M-0.2 M zinc chloride.

16. The method according to claim 14, characterized in that it comprises 0.1 M zinc chloride.

17. The method according to claim 1, characterized in that the electrolysis process is applied in the range of 2 minutes to 4 hours.

18. The method according to claim 17, characterized in that the electrolysis process is applied in the range of 2-30 minutes.

19. The method according to claim 18, characterized in that the electrolysis process is applied for 30 minutes.

20. The method according to claim 1, characterized in that the electrolyte comprises at least 9 M water or at least 0.2 M zinc chloride.

21. An indium-tin oxide coating method, comprising the steps of depositing on the cathode surface by a method according to claim 1 , and calcining the deposited portion and coating it back onto said glass surface by reversible reaction.

22. A zinc-indium-tin oxide coating method, comprising the steps of calcining a portion deposited and being deposited on the surface of the cathode by a method according to claim 19, and coating it back onto said glass surface by reversible reaction.

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