吉村 彰大

Indium is a rare metal that is an essential raw material for indium tin oxide (ITO) essential for transparent electrodes for displays. However, its supply is unstable as it is a by-product of zinc. In this research, we investigated the domestic substance flow of indium used for liquid crystal applications in Japan. Accordingly, we quantitatively evaluated the amount of indium contained in the process loss and the content of indium in end-of-life products. Through this quantification, we examined the visualization of loss in the entire flow and the usability of end-of-life products as secondary production. Consequently, it was found that the amount of indium used in the production of end-use-products in Japan has increased significantly due to the growth of liquid crystal display TVs, particularly in preparation for the transition to terrestrial digital broadcasting in 2011, and has drastically decreased after 2012. Meanwhile, some manufacturing bases have been relocated from Japan to other countries, and a certain proportion of end-use-products are imported, by which we infer the domestic input amount of end-use-products in recent years is estimated to have remained at approximately 4 t. Based on the result, after having continued to increase to the maximum value of approximately 70 t in 2014, the in-use stock has exhibited a gradually decreasing trend. Moreover, the indium content in end-of-life products has continued to increase, and in 2015, it exceeded the amount of the end-use-products input into society. Furthermore, compared with the process loss at the time of processing from ITO to a display, the gap has been narrowed from 100 times or more, and the indium content in end-of-life products in 2008 to about 15 times in 2017. These results suggest that the recycling potential of end-of-life products has increased with the spread of indium-based products.

<sec> <title>Abstract</title> Artisanal and small-scale gold mining (ASGM) utilizes mercury (Hg) for the extraction of gold (Au) and is responsible for the largest anthropogenic source of emissions and releases of Hg to the environment. Previous estimates of Hg use in ASGM have varied widely. In this effort, Hg losses in ASGM were derived from the difference between estimates of total Au production and the production reported by conventional gold mining. On the basis of this result, the average ratio of Hg lost to Au produced in ASGM was estimated to be 1.96 in Africa, 4.63 in Latin America, and 1.23 in Asia. The difference among regions can be attributed to the amalgamation procedure used by the miners, in which whole-ore amalgamation is predominant in Latin America and Asia. The obtained estimated ratio of Hg_lost:Au_produced suggested the possibility to detect either Au or Hg smuggling from one country to another. On the other hand, the importance of considering cyanidation in ASGM was also suggested. </sec><sec> <title>Graphical Abstract</title> </sec>

Chalcopyrite (CuFeS2) is the most refractory copper mineral when treated in conventional sulfate media leaching systems. This is the first study to examine the use of a dimethyl sulfoxide (CH3SOCH3, DMSO) solution containing copper chloride (CuCl2) for the leaching of chalcopyrite. Leaching experiments for a copper concentrate composed mainly of chalcopyrite were conducted at ambient pressure at 313-413 K. The leaching fractions of Cu, Fe, S, Au, and As were investigated. It was found that 90% of the Cu was extracted in 2 h, and 94% was extracted in 4 h at 373 K, which is competitive with other conventional processes. A DMSO solution containing CuCl2 could selectively dissolve the valuable metals Cu and Au from chalcopyrite, but leave minerals with little economic value such as pyrite (FeS2) and As in the residue. Chalcopyrite is oxidized by cupric ion in proportion to the stoichiometric ratio of Cu in the concentrate to the initial cupric ion in the DMSO solution, which is enhanced by the presence of oxygen below 373 K.

In this research, a recycling process for palladium using "dry aqua regia," which consists of iron(III) chloride-potassium chloride, was proposed. Palladium was dissolved in "dry aqua regia," and the dissolved palladium was recovered by leaching with potassium chloride solution with added ammonium chloride and nitric acid. Palladium was almost completely dissolved in 3 h at 600 K, and the recovery ratio of dissolved palladium was up to 80%. In addition, the dissolution of palladium in coexistence with platinum and the dissolution of platinum-palladium alloy by "dry aqua regia" were also tested. The dissolved palladium and platinum were separated and recovered by solid-liquid separation technique using the difference in solubility of their compounds in potassium chloride and sodium chloride solutions. As a result, pure compounds of each element were recovered. This result suggested the possibility of using "dry aqua regia" for the separation of platinum-group metals.Graphical Abstract

We conducted experiments using unit processes to prove the feasibility of the concept of an environmentally sound Au recovery process from waste electrical and electronic equipment (WEEE) using organic aqua regia, i.e., a propylene carbonate (PC) solution containing CuBr2 and KBr. First, the WEEE samples (memory card and mobile phone board) were finely ground. The samples were then carbonized and oxidized to decompose the polymers and oxidize the base metals. The leaching of Au from the oxidized samples was then carried out in a PC solution with 0.2 M of CuBr2 and 0.2 M of KBr over 353-373 K, followed by biphasic separation with sulfuric acid. The dissolved Au in the PC phase was recovered via ascorbic acid reduction. The mass balance of Au in the leaching was investigated. The maximum recovery ratios of Au from the memory card and mobile phone board were 79% and 83%, respectively. The cost of leaching was preliminarily estimated.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland. We developed a liquid-phase synthesis method for Pd-based nanostructure, in which Pd dissolved in dimethyl sulfoxide (DMSO) solutions was precipitated using acid aqueous solution. In the development of the method, in situ monitoring using atmospheric scanning electron microscopy (ASEM) revealed that three-dimensional (3D) Pd-based nanonetworks were deformed to micrometer-size particles possibly by the surface tension of the solutions during the drying process. To avoid surface tension, critical point drying was employed to dry the Pd-based precipitates. By combining ASEM monitoring with critical point drying, the synthesis parameters were optimized, resulting in the formation of lacelike delicate nanonetworks using citric acid aqueous solutions. Precipitation using HCl acid aqueous solutions allowed formation of 500-nm diameter nanorings connected by nanowires. The 3D nanostructure formation was controllable and modifiable into various shapes using different concentrations of the Pd and Cl ions as the parameters.

© 15th International Symposium on East Asian Resources Recycling Technology, EARTH 2019. All rights reserved. Platinum group metals (PGMs) are important material for the autocatalysts. However, they are very rare metals, and the efficient recycling is required for the conservation of natural resources. In this research, the authors proposed a novel recycling process of platinum (Pt) using molten salt consists of FeCl3 and KCl as “dry aqua regia”. This dry aqua regia can dissolve Pt directly and can recover dissolved Pt by the leaching and precipitation. The dissolution rate was equivalent to that of by 50 °C of aqua regia, and the maximum recovery ratio was up to 80% by the optimization of recovery process. Through this research, the authors confirmed the availability of the Pt recovery process using dry aqua regia.

The authors have investigated a novel process of platinum recycling using "dry aqua regia". In our previous work, the recovery of platinum was successfully conducted by solvent leaching, but it yielded a mixture of K-2(PtCl6) and FeOx. In this study, a solid-liquid separation process using KCl and NaCl solutions and a precipitation process using NH4Cl were adopted to obtain pure platinum. Impurities like FeCl3, FeOx, and KCl were removed by a solid-liquid separation process, and pure (NH4)(2)(PtCl6) was obtained by NH4Cl addition. Then, the obtained (NH4)(2)(PtCl6) was calcinated to yield pure platinum by thermal decomposition. High-purity platinum was obtained with a recovery ratio of up to 79%. Therefore, the usability of the recycling process using "dry aqua regia" was significantly improved.

In this report, we present a novel method to produce micrometer-sized gold particles by dissolving and recovering gold from a dimethyl sulfoxide/hydrochloric acid (DMSO/HCl) solution containing copper (II) chloride (CuCl2) and sodium chloride (NaCl). It was reported that spherical or confeito-like particles can be formed depending on the concentrations of dissolved gold and Cl-ions in the solution. In this paper, in-situ observation of gold particle formation in the solution phase was conducted using atmospheric scanning electron microscopy (ASEM). An electron-permeable window made of a pressure-resistant silicon nitride (Si3N4) film (100 nm-thick), was set at the bottom of the open ASEM sample dish, which facilitated the projection of electron beams from underneath the sample. This structure of ASEM enabled us to observe dynamic phenomena in liquid or gas phase under atmospheric pressure in real time. It was found during the in-situ observation that all of the particles formed were confeito-like in shape, which was different from the expected particle morphology.

The recovery of copper (Cu) from secondary sources has received much attention because of its scarcity of natural resources. In this work, we estimated the input, in-use stock and discard of copper and copper alloy during 1950-2015 in global scale, and forecast them until 2050. In addition, we estimated the potential of scrap recovery for copper/copper alloys. It was estimated that the total amount of in-use stock of copper and copper alloy were 177,000 kt and 44,200 kt in 2015, respectively. The in-use stock, discard and input of copper in 2050 will reach 381,000-588,000 kt, 15,400-22,200 kt and 18,990-33,000 kt, respectively, whereas those for copper alloy will reach 77,500-134,000 kt, 3,020-4,680 kt and 3,760-7,200 kt, respectively. The copper content in recoverable scraps of copper and copper alloy will reach 15,100-27,300 kt, and this accounts for 55.1-79.0% of copper content in annual input of copper and copper alloy in 2050. The range in forecast was caused by the difference in the saturation amount of in-use stock per capita and recovering rates of scraps.

We have presented a novel method for the production of gold micrometer. sized particles by dissolving and recovering gold with DMSO/HCl containing CuCl2 and NaCl. It was reported that spherical or confeito. like particles could be formed depending on the concentrations of dissolved gold and Cl. ion in the liquid. In this paper, in. situ observation for the formations of gold particles in the liquid phase was conducted using atmospheric scanning electron microscopy (ASEM). An electron. permeable window made of pressure. resistant 100 nm. thick silicon nitride (SiN) film, set into the bottom of the open ASEM sample dish, allows an electron beam to be projected from underneath the sample. This structure of ASEM enable us to observe dynamic phenomena in liquid or gas under atmospheric pressure in real time. It was found that all of the particles formed during in. situ observation were confeito. like in shape, which was different from what had been expected.

A novel method for the production of gold micrometer-sized particles from secondary sources is presented. The method consists of the leaching of gold using dimethyl sulfoxide (DMSO, (CH3)(2)SO) solutions containing copper chloride (CuCl2) followed by the precipitation of gold with hydrochloric acid (HCl). Gold was dissolved in a DMSO solution with 0.1-0.2 M CuCl2 and 0-0.3 M sodium chloride (NaCl) at 343 K. The precipitation of dissolved gold was performed by the addition of HCl, during which the effects of the concentration of the Cl- ion was investigated. It was found that the initial gold dissolution rate in DMSO solutions with CuCl2 was up to 14.8 mg cm(-2)h(-1), which was larger than the rates obtained with other leaching methods, but smaller than the author's previous research using copper bromide (CuBr2) and potassium bromide (KBr). A gold recovery efficiency of up to 92.6% was obtained by precipitation with HCl solution. We obtained "raspberry-like" or "confeito-like" gold microspheres under the condition of less than 1.5 M of Cl- ion and over 0.013 M of dissolved gold. Our results demonstrated that a circulating system for gold leaching and recovery and production of functional material could be developed, which would offer a number of advantages, including eco-friendliness, easy operation, low costs, and minimization of chemical sludge production.

A novel method for recovering gold from secondary sources, the leaching of gold using dimethyl sulfoxide (DMSO) solutions containing copper bromide followed by the precipitation of gold with water, is presented. Gold dissolution was conducted in a DMSO solution with 0.1-02 M of CuBr2 and 0-0.2 M of KBr at 333-348 K. The mechanism of gold dissolution was investigated by electrochemical measurements. The precipitation of dissolved gold was performed by the addition of water, during which the effects of the amount of water and the pH on the recovery rate were investigated. It was found that the initial gold dissolution rate in the DMSO solutions with CuBr2 was up to 37 mg cm-2 h(-1), which is larger than those obtained with other leaching methods. The results of the electrochemical measurements indicate that the anodic dissolution of gold in DMSO containing CuBr2 occurs at relatively negative potentials and is paired with the cathodic reduction of Cu2+ to Cut A recovery rate of gold up to 87% was obtained by precipitation with water. A small amount of copper was precipitated with gold, which can be avoided by using water of lower pH, as is expected by the Eh-pH diagram. Our results demonstrate that a circulating system for gold leaching and recovery, which would offer a number of advantages, including eco-friendliness, easy operation, low costs, and minimization of chemical sludge production, can be developed. (C) 2014 Elsevier B.V. All rights reserved,

Interest in recycling of rare metals has greatly increased recently because of the rapid growth in the demand for, and uneven distribution of, natural resources. Substance flow analysis (SFA) is a useful tool for determining the flow of substances in specific geographic regions. However, few SFAs have been conducted for rare metals. In this paper, we focus on indium and conduct SFAs of indium both in Japan and globally. Indium is primarily used as indium tin oxide (ITO), whose end uses can be categorized into two groups: liquid crystal displays and plasma panel displays; these are then assembled into final products. We quantified the flow of indium during its life cycle through mining, smelting and refining, manufacturing, use and waste management. For mining, smelting and refining, data were collected on the indium content in ore and production of primary metallic indium during 1999-2008. For manufacturing, we estimated the content of indium in final products, and estimated the input of indium in production as ITO in Japan. Then, we extrapolated the result to an SFA at the global scale. In-use stock and discarded indium were estimated by dynamic SFA, in which time-series data on the input of indium into final products and their lifetime distribution were used. We considered the loss of indium in each process to be the potential recyclable amount. We found that the extraction rate of indium in the mining, smelting and refining process was 8-11%, and the loss of indium in this process was 4,826 t in 2004. The loss in manufacturing amounted to 316 t, the in-use stock of indium was 116 t and the discarded indium in end-use products amounted to 5 t globally in 2004. Therefore, it was concluded that the biggest recovery potential of indium is during mining, smelting and refining.