| Scattered metal indium with unique and excellent physical and chemical properties has become one of the most significant support materials in the modern electronics industry. Sixty to eighty percent of global gross output of indium has been applied to the manufacture of ITO transparent conductive film, which is the best conductive film material and has no alternative to be compared or replaced at present. Therefore, tremendous support of the global production of displays with various size including flat-panel TVs, computers, cell phones, etc. with indium, and thus plays increasingly important role in the national economy.As China is rich in indium resource which ranks first in the world, indium resources mainly concentrated in the western regions including Guangxi, Yunnan, Neimenggu and Qinghai etc. The annual output of the materials with rich zinc and indium is about 30,000 tons by pyrometallurgy. It contains zinc 24,000 tons and indium 100 tons, which contribute to its high value of comprehensive utilization. Nevertheless, for a long time there has been little efficient and advanced processing techniques to treat such materials with zinc and indium. Accordingly to study and develop the new technologies of efficient extraction of indium and zinc from such materials with zinc and indium is of great significance.According to the materials with zinc and indium by pyrometallurgy in this thesis, a new process was proposed on the basis of the analyzing the phases and properties of the materials, referring to a large number of datas and comparing with a variety of treatment, which combined vacuum distillation, wet leaching, purification, enrichment, replacement, and electrolysis purification. The key technologies as indicated above were also studied in terms of theoretical research, applied basic research and experimental study. (1)The principle, mechanism and thermodynamics, kinetics of metal evaporation, condensing, impurity separation was studied in theory firstly, and the separation coefficient, evaporation rate, gas composition and gas-liquid equilibrium diagram of indium and main impurities were calculated. Then the vacuum distillation tests of the materials with indium and crude indium were carried out on the basis hereinabove, which examined the related indicators and process conditions of zinc recovery and indium enrichment from the materials with indium and zinc, and the trend and distribution of impurity elements in the distillation of crude indium. The relevant indicators and operating conditions can be applied in for the following of industrial design and application. (2)Electrode potential-pH diagram based on indium, mechanism, process thermodynamics and kinetics of leaching replacement process were studied, which includes rich indium slag leaching, related tests of the replacement process. The influences of the acidity, liquid-solid ratio and time on the rate of extraction of indium and the influences of the replacement of choice, size, temperature and time on the replacement rate were also observed, and related parameters were obtained. (3) Through the small-scale tests in the process of electrolysis in accordance with the basic principles of electrolysis, reliable technical parameters were gained. (4)On the basis of the small-scale test(100g), bench-scale test(20kg) and industrial test(200kg) of vacuum distillation of crude indium, appropriative equipments with different capacity were developed.The operating parameters of the process-were determined by theory and experimental research as follows:1) Vacuum distillation of the materials with indium and zinc:distillation temperature: 900-950℃, furnace pressure:<100Pa, smelting time:16-20h, recovery rate of indium: 97%, recovery rate of zinc:99%, multiple of indium enrichment:7 times.2) Leaching of slag with rich indium was divided into neutral leaching and acid leaching:①NNeutral leaching:ratio of liquid-solid:6-8:1, temperature:80-90℃,time:about 6 hours, before acid:H2SO4120-150 g/l; end acid:PH= 5.0～5.4.②Acid leaching:ratio of liquid-solid:8-10:1, temperature:80-90℃, time:about 12 hours, before acid:H2SO4150～200 g/l, end acid:PH≤1.5.3) Process conditions of the replacement of zinc powder:mass ratio of zinc powder and indium, replacement time:72h, replacement temperature:≥20℃, pH:1～1.5, zinc content in zinc powder:>99.9%, particle size:80～120 mesh.4) Process conditions of vacuum distillation of crude indium:temperature:750-850℃, degree of vacuum:<10Pa, removal efficiency of zinc cadmium:>98%, as replacement of chemical methods.5) Process conditions of electrolytic refining of crude indium: Current density:80 A/mCell voltage:0.25～0.35VCenter distance between two electrode with same electrode:70 mmElectrolysis cycle:anode cycle 14-21 days, cathode cycle 5-7 daysElectrolyte temperature:20-30℃Composition of electrolyte(g4) are as follows:Fine indium with indium content more than 99.99%(4N) can be obtained after the electrolysis of indium.Its key point of innovation cover 5 items:①The integrated innovative new process of the extraction of the metal zinc and indium;②The technology of vacuum distillation of the materials containing indium;③Slags with rich indium were leached by sulfuric acid in two steps including neutral and acid leaching, and sponge indium was thus prepared by the replacement of zinc powder;④The technology of refined indium production combining vacuum distillation of crude indium with electrolytic refinement;⑤Vacuum equipments matched with the new technology. In addition, industrial design and experiment of refined indium with the scale of 10 tons per year of indium fine design and industrialization has been proceeding. Practices prove that the new technology developed has many advantages including high technical integration, short flow, high recovery rate of indium and little pollution.So far product line of refined indium with annual output of 10 tons/year was built in Yunnan Province by the integrated process technologies and equipments which realized industrial application successfully in 2004. Part of the key technologies and equipments in this process was also applied in several domestic enterprises of refining indium. Up to the end of 2006, the output of the refined indium(99.993%) has achieved 62 tons while the output of zinc has reaches over 5,000 tons, and the output value has increased by 500 million yuan, which covers foreign exchange 8.1 million US dollars and profits and taxes nearly 100 million yuan. Under the cooperation with the enterprises which owns the greatest resources, Asia's largest indium-production factories (annual output of indium 60 tons/year) are prepared to be built by virtue of this technology.This innovative technology with autonomous intellectual property rights were authorized 3 state invention patents. Identified by the relevant experts, the integrated technology was agreed that it's the pioneer technology at home and abroad and has reached the international advanced level. Besides, this technology has won the first prize of China Nonferrous Metal Industry Association for scientific and technological inventions and first prize of scientific and technological inventions in Yunnan Province in 2007.In conclusion, this technology has a vast range of prospects for promotion and popularization, and can realize the comprehensive efficient reasonable utilization of the mineral resources and clean production of metal indium. Meanwhile it plays a demonstrative role for vacuum smelting of scattered metals, especially for the promotion and popularization of the purification of scattered metals and high-purity products. Furthermore, there's positive meaning for the scientific and technological progress of non-ferrous metallurgical industry. |
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