Pyrometallurgical Recovery of Indium from Dental Metal Recycling Sludge by Chlorination Treatment with Ammonium Chloride

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1 Materials Transactions, Vol. 51, No. 6 (1 pp to 11 #1 The Japan stitute of Metals Pyrometallurgical Recovery of dium from Dental Metal Recycling Sludge by Chlorination Treatment with Ammonium Chloride samu Terakado* 1, Takashi Saeki* 2, Ryoji Irizato* 3 and Masahiro Hirasawa Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya University, Nagoya , Japan the present paper we address the novel chlorination process for recovery of indium selectively from dental metal recycling sludge which contains considerably high amount of indium. The process is based on the utilization of ammonium chloride, NH 4 Cl, as chlorination reagent. It was found that indium could be successfully recovered from the sludge in the form of volatile indium chloride by heating the mixture of sludge and NH 4 Cl at the temperature of C under inert atmosphere. The influence of process parameters, such as composition of NH 4 Cl, was investigated in order to achieve high process efficiency. [doi:1.23/matertrans.m] (Received January 21, 1; Accepted March 3, 1; Published April 15, 1 Keywords: indium, recovery, chlorination, dental metal recycling sludge, ammonium chloride 1. troduction dium is a trace element in some zinc, lead, copper, and tin ores, and produced mainly as by-product of zinc refining process. 1,2 The global demand of indium metal is steadily increasing with the increase in the production of flat panel display, in which indium is used in transparent electrical conductor film as indium tin oxide, IT. Recently, indium is also utilized as an alloying element of lead-free electronic solders. The establishment of the recovery process from indium-containing waste is, therefore, of great importance. Various techniques have been proposed so far, mainly based on the hydrometallurgical processes. 3 Among the wastes containing indium, dental metal recycle sludge is one of the attractive indium resources. The sludge is a by-product of precious metal recycling from dental alloy scraps and contains :8 mass% of indium in some cases. the present paper we report the novel pyrometallurgical method of the indium recovery from the indium-rich sludge based on a selective chlorination reaction. Chlorination process plays an important role in the extractive metallurgy. Typical chlorination reagents are Cl 2 or HCl gas and metal salts such as NaCl and CaCl 2. For example, hwa et al. 4 reported the development of a commercial plant for the production of high-purity metals such as gallium, indium and bismuth by chlorination process using Cl 2 gas as chlorination reagent. Besides the good effectiveness and usefulness of the processes, chlorine and hydrogen chloride gases are very corrosive in nature, so that special attention must be paid for the leakage of the reactor. As for the metal salts, the handling of reagent is quite easy, but one needs higher treatment temperature, usually over C, than that in the case of chlorine gas in order to achieve sufficient reaction rate. Thus, exploring alternative chlorination reagents that can be used at lower temperature with convenient handling is intriguing to establish simpler and effective process. As an example, Jena et al. 5 examined * 1 Corresponding author, teramon@numse.nagoya-u.ac.jp * 2 Graduate Student, Nagoya University. Present Address: Nagoya Railroad Co., Ltd., Nagoya , Japan * 3 Graduate Student, Nagoya University. Present Address: BSCH Co., Ltd., Tokyo 15-83, Japan the chlorination of vanadium pentoxide at the temperature between 553 and 788 K by carbon tetrachloride gas, that shows, however, also corrosive property. the present study we have successfully applied ammonium chloride as chlorination reagent for the chlorination of indium in the sludge. The process is based on the thermal decomposition of NH 4 Cl into NH 3 and HCl gases, and the consequent chlorination of indium specie in the sludge. dium chloride has high vapour pressure at C, and it deposits at colder part of 2 C in the reactor. The treatment is especially profitable with respect to the relatively low treatment temperature ( C as well as simpler handling of the reagent in comparison with the cases of conventional chlorination reagents. Various process parameters including the composition of the sludge NH 4 Cl mixture, reaction atmosphere, and deposition temperature are discussed. 2. Experimental 2.1 Materials Dental metal recycling sludge rich in indium was supplied from Yamamoto Precious Metal Co., Ltd. A SEM image of the sludge is shown in Fig. 1. The morphology is quite complex: fibrous and spherical materials with different sizes are observed. For the analysis of the contents of metallic elements in the sludge, we have leached mg of the sludge with ml of aqua regia, and the obtained solution has been analyzed with ICP spectrometer (SPS 15VR, Seiko struments. The result of the quantitative analysis of some metallic elements is summarized in Table 1. bviously in the table, the sludge consists of various compounds of metal elements. Typical phases of the sludge were characterized by scanning electron microscopy with energy dispersive spectrometer, SEM-EDS, (JSM-633F&JED-21, JEL as shown in Fig. 2. The presence of Si 2, alkaline and alkaline earth oxides as well as the complex oxides of indium and tin was observed. 2.2 Chlorination treatment The chlorination reaction was carried out in a quartz tube equipped in a horizontal electric furnace. The size of the

Pyrometallurgical Recovery of dium from Dental Metal Recycling Sludge by Chlorination Treatment with Ammonium

Pd Pt Cu Ni Co Ag Au Ti 78 4 1:9 :2 :5 :2 38 2 22 1 1 1 2: :2 1:5 :3 1:4 :1 :7 :3 Si 3 µ m Fig.

quartz tube was inner diameter of 26 mm, outer diameter of 3 mm, and the length of mm.

powder (99.5%, Wako pure chemicals. The total weight of the mixture was mg.

9999% or air gas ﬂow with the ﬂow rate of ml/min.

mullite reaction boat was introduced quickly from the cold part to the reaction zone inside the reaction tube.

A water trap was set in the oﬀ-gas line connected to the reaction tube in order to collect the evolved gas.

tube. This material is hereafter denoted as reaction products.

The solution was then ﬁltered with mixed cellulose ﬁlter paper with the average pore size of.1 mm.

The amount of ammonium and chloride ions were also measured for the water-leached solution of the reaction

an ion meter (IM-, TA-DKK. 3. Results and Discussion 3.

2 Pyrometallurgical Recovery of dium from Dental Metal Recycling Sludge by Chlorination Treatment with Ammonium Chloride Table Metal content of supplied sludge (in mg metal/g sludge, dry matter. Pd Pt Cu Ni Co Ag Au Ti :9 :2 :5 : : :2 1:5 :3 1:4 :1 :7 :3 Si 3 µ m Fig. 1 Representative SEM image of the sludge employed for chlorination reaction in the present study. quartz tube was inner diameter of 26 mm, outer diameter of 3 mm, and the length of mm. Samples for the chlorination reaction were prepared by mechanical mixing of the sludge and ammonium chloride powder (99.5%, Wako pure chemicals. The total weight of the mixture was mg. The powder mixture was pelletised with the load of ca. 2:5 18 Pa. Reactions were conducted under helium ( % or air gas ﬂow with the ﬂow rate of ml/min. After the temperature of high temperature zone of the furnace was stabilised, sample mixture contained in a mullite reaction boat was introduced quickly from the cold part to the reaction zone inside the reaction tube. Typical reaction temperature was C and the reaction time was 3 min, if not speciﬁed in the present report. A water trap was set in the oﬀ-gas line connected to the reaction tube in order to collect the evolved gas. After a reaction run the condensation of yellowish material was observed at the cold part of the quartz reaction tube. This material is hereafter denoted as reaction products. The product was carefully leached by pure water or dilute hydrochloric acid aqueous solution (ca..6 M. The solution was then ﬁltered with mixed cellulose ﬁlter paper with the average pore size of.1 mm. The amount of metal ions in the ﬁltrate was analyzed by ICP spectrometer. The amount of ammonium and chloride ions were also measured for the water-leached solution of the reaction products, the water trap as well as the water-leached solution of the residue remaining in the reaction boat with an ion meter (IM-, TA-DKK. 3. Results and Discussion 3.1 Chlorination treatment with ammonium chloride Table 2 shows the typical results of the ICP analysis for the reaction products. They are presented in terms of metal Na Ca Fig. 2 Elemental mapping of representative phases of the sludge. concentration of the water-leached solution of the reaction products, whereby the sample solution is prepared to the total volume of ml precisely. The deposition of reaction products occurs obviously at reaction temperature above 2 C in the presence of ammonium chloride. The analytical

3 1138. Terakado, T. Saeki, R. Irizato and M. Hirasawa Composition (mass% (Sludge : NH 4 Cl Table 2 Representative results of the recovery of metals at different reaction conditions (in mg/l. Reaction temperature ( C Pd Pt Cu Ni Co Au Ti 2: n.d..2 n.d. 1.3 n.d..2 n.d..1 2:3 2.8 n.d..2 n.d. n.d. n.d..2 n.d.. 1: n.d. n.d..2 n.d. n.d. n.d..2 n.d.. Metal concentration in aqueous solution where reaction products from sludge sample of mg were collected with pure water and the ICP sample was prepared to the volume of ml. Table 3 Results of Cl,NH þ 4 and ph of the leached solutions of residue and reaction product as well as water trap. Cl þ NH 4 ph Residue leached with pure water 39 1 :3 : 4.4 Reaction product leached with pure water Water trap Total Results for ions are presented as (amount of ion/(total amount the corresponding ion in the initial sample., Leaching with HCl soln., Leaching with H 2, Leaching with HCl soln., Leaching with H 2 results of the amount of Cl and NH 4 þ in the water-leached solutions of reaction residue and reaction product as well as in the water trap, together with the value of ph, are summarized in Table 3. A reasonable mass balance has been observed for the ions in the present reaction. The results show that the main product in the water trap is obviously ammonia, while the reaction residue contains mainly HCl. The reaction product is considered as indium chloride together with hydrogen chloride. It is well known that ammonium chloride decomposes into HCl and NH 3 above 332 C, and the latter defuses faster than the former decomposition product. The reaction mechanism is thus summarized briefly as follows: (1 decomposition of NH 4 Cl, (2 evaporation of ammonia, (3 chlorination of indium, and the consequent evaporation (with the simultaneous HCl evaporation and the deposition at the cold part of the reaction tube. 3.2 fluence of the concentration of ammonium chloride ne of the most important process parameters for chlorination treatment is the partial pressure of chlorine as well as that of oxygen. This can also affect the concentration of impurities in the reaction product, most probably tin chloride. We have, therefore, studied the dependence of composition of the ammonium chloride in order to examine the influence of the partial pressures. Figure 3 shows the result of the recovery ratio, i.e. (Recovered amount of metal/(itial amount of metal in the sludge sample, of indium and tin as a function of concentration of ammonium chloride in the initial mixture. The experiments were performed at C for 3 min under helium atmosphere. Clearly, the recovery ratio of indium increases with increasing amount of the chlorination reagent. As for the influence of the reaction atmosphere, the recovery rate of indium decreases at higher oxygen partial pressure, as shown in Fig. 4 for the reaction under helium and air atmosphere. NH 4 Cl (mass% Fig. 3 Recovery ratio of indium and tin as a function of NH 4 Cl concentration in the mixture. The products are leached with either pure water or dilute hydrochloric acid aqueous solution. The reaction is conducted at C for 3 min., Helium, Air NH 4 Cl (mass% Fig. 4 Recovery ratio as a function of ammonium chloride composition under helium and air reaction atmosphere (Reaction temperature at C, Reaction time = 3 min. The products are collected by pure water. An interesting observation is the different leaching behaviour of tin and indium by pure water and HCl solution. While the leaching behaviour of indium does not change by different leaching solutions, tin could not be detected by ICP measurement after leaching with pure water. This is due to the formation of white colloidal precipitates during the leaching treatment; the precipitates are removed from the leached solution by filtration prior to ICP measurement. The compounds are water-insoluble tin oxide resulting from the hydrolysis of tin chloride in water solution of ph 3 (Table 3. n the other hand, the precipitation of tin compounds does not occur in the acid-leached solution. The result indicates the possibility of separation of indium

4 Pyrometallurgical Recovery of dium from Dental Metal Recycling Sludge by Chlorination Treatment with Ammonium Chloride log(p Cl Cl (l Cl 3 (s 2 3 (s 2 2 Temperature, T/ C - (l Distance from the center of the furnace, d /cm log(p 2 Fig. 6 Recovery ratio and the corresponding average temperature at deposition point (Reaction temperature = C, Reaction time = 3 min. -1 Cl 4 (g 6 4 Cl 4 Cl 2 (l 2 Cl 2 log(p Cl (l 2 (s log(p/pa -2-4 Cl log(p 2 Fig. 5 Potential stability diagram of the -Cl- and -Cl- systems at C. A circle inside the figure is the partial pressure of oxygen and chlorine in the present experimental condition calculated with FactSage software with assumption where indium and tin exists as pure solid oxides, i.e. 2 3 and 2. and tin by leaching of chlorination product with water and the consequent filtration. Thermodynamic aspects of the chlorination reaction of the sludge have been investigated with the software package FactSage Ver.6. (Thermfact and GTT-Technologies. Figure 5 shows potential stability diagrams of the -Cl- and -Cl- systems at C. We have also evaluated the oxygen and chlorine partial pressure for sample mixture with composition of 5 mass% of NH 4 Cl under inert atmosphere, assuming the coexistence of indium and tin solid oxides, namely 2 3 and 2, in the sludge. The calculation result of the partial pressure is displayed as circle in the figure. As clearly seen in the figure, both indium and tin can be chlorinated under the equilibrium condition. The increase in oxygen partial pressure is, on the other hand, unfavourable for the formation of indium and tin chloride. The thermodynamic consideration can explain the experimental observation of the influence of the reaction atmosphere reasonably. The potential phase stability diagram indicated that selective chlorination of indium was difficult, so that other possibility of the selective recovery of indium should be considered Temperature, T / C Fig. 7 Vapour pressure of some indium and tin chlorides as a function of temperature that is calculated with thermochemical data Possibility of the selective recovery of indium by control of the condensation temperature The influence of condensation temperature of the reaction product was examined. For this purpose we have collected the reaction products with HCl solution at different positions along the reaction tube; the average temperature of each position was measured prior to the reaction. Figure 6 shows the recovery ratio of indium and tin and the corresponding temperature along the reaction tube. The chlorination reaction was carried out at a temperature of C for the composition of ½sludgeŠ : ½NH 4 ClŠ ¼3:2 by weight. The separation of indium and tin inside the reaction tube is obvious in the figure. dium chloride is mainly collected at 27 C, while the tin chloride is collected at lower temperature (25 C. Figure 7 shows the vapour pressure of some indium and tin chlorides as a function of temperature, that is calculated from thermochemical data. 6 At temperatures between and 3 C, the vapour pressures of tin chlorides are higher than those of indium chloride. Thus, selective collection of indium is possible with the control of the deposition temperature. With respect to the reaction mechanism, our preliminary experiment of the chemical analysis of tin products showed that they deposited in oxidation state 4 even for the product formed in helium atmosphere. At the tin-rich deposition temperature, i.e. 25 C, tetravalent tin chloride should

5 11. Terakado, T. Saeki, R. Irizato and M. Hirasawa evaporate, as indicated by the vapour pressure data shown in Fig. 7. Further study is needed in order to clarify the reaction mechanism, since many factors are involved including the formation of ammonia, a possible reductant, that can play a complex role in the reaction. Moreover, indium forms variety of chloride compounds with complex valency and different thermal properties which can affect the process performance of the separation. The existence of tin compounds can also affect the chlorination behaviour of indium. 3.4 utlook of the process We have experimentally shown the selective chlorination of indium from the sludge by the reaction with ammonium chloride at relatively low temperature ( C. The process is quite simple: satisfactory recovery of indium is possible by heating of the simple mechanical mixture of sludge and NH 4 Cl powder. The handling of the chemicals is easy, and the process does not require severe gas-tight reaction line in contrary with the processes using Cl 2 or HCl gas. Furthermore, in comparison with other salt type chlorination reagents such as NaCl and KCl, the reaction temperature is much lower in the present system. A possible contamination of tin can be eliminated by the leaching of chlorination product with pure water as well as by a careful control of condensation temperature. Moreover, there is another advantage of the present process which results from the fact that both the decomposition products of ammonium chloride, i.e. acidic HCl and alkaline NH 3, are employed in metal recovery. The formation of (H 3 is feasible by a treatment of reaction products with ammonia aqueous solution, namely water trap in the present experimental setup. The hydroxide can be utilised by conventional metal recovery processes. A disadvantage of the current process is that high amount of the chlorination reagent is required. More than 5 mass% of ammonium chloride is needed to achieve the indium recovery ratio of 7%. The increase in the contact area between the sludge and the chlorination reagent can be a key point for the improvement of the process efficiency. It is considered that the present simple method can be applied not only for the sludge but also for the recovery of indium from other kinds of indium-containing wastes. Further studies including IT glass slide wastes are currently under investigation. 4. Summary the present study we have shown that ammonium chloride can be successfully applied as chlorination reagent for the recovery of indium from dental metal recycling sludge. Heat treatment of the mixture of sludge and chlorination reagent at C results in a sufficient indium recovery. This simple process has potential application for the recovery of indium from other waste. Further fundamental researches such as reaction kinetics are required to optimize the process parameters. Acknowledgements Part of the present work was supported by a grant-in-aid for scientific research (K213 from the Ministry of Environment, Japan. REFERENCES 1 A. M. Alfantazi and R. R. Moskalyk: Minerals Eng. 16 ( C. E. T. White and J. A. Slattery: Hydrometallurgy of Copper, Its By-products, Rarer Metallurgical Processing Dallas Symposium, ed. by L. A. Haas and D. R. Weir, (Society of Mining Engineers of the AIME, New York, 1983 pp A. P. Paiva: Sep. Sci. Technol. 36 ( H. hwa, A. Yukinobu, J. Nabeshima and M. Yasukawa: Extraction Metallurgy 89, (stitution of Mining and Metallurgy, London, 1989 pp P. K. Jena, E. A. Brocchi and J. González: Metall. Mater. Trans. B 36 ( I. Barin: Thermochemical data of pure substances, (VCH, Weinheim, 1995.

Indium Recovery from Indium Tin Oxide, ITO, Thin Film Deposited on Glass Plate by Chlorination Treatment with Ammonium Chloride

Materials Transactions, Vol. 52, No. 8 (2011) pp. 1655 to 1660 #2011 The Japan Institute of Metals Indium Recovery from Indium Tin Oxide, ITO, Thin Film Deposited on Glass Plate by Chlorination Treatment