Iridium sponge is a precious platinum group metal, which has excellent physical and chemical properties such as high melting point, high hardness, high density and high corrosion resistance, and is widely used in high-tech and military technology fields. However, the resources of iridium sponge are very scarce, and only a few countries in the world have the mining and production capacity of iridium sponge, and the reserves of iridium sponge in China are extremely limited, mainly relying on imports. Therefore, the use of iridium sponge from secondary resources can not only save resources and reduce costs, but also ensure the country's strategic security and economic development.
The secondary resources of iridium sponge mainly include waste iridium sponge complexes, waste iridium sponge catalysts, and iridium-containing sponge wastes generated in the production of iridium sponge complexes and iridium sponge catalysts, such as obsolete phosphorescent iridium sponge complexes, nano-iridium sponge catalysts, iridium sponge coatings and protective films, etc. From these secondary resources, the sponge iridium is mainly used in two processes: fire method and wet process.
The pyrometallurgical method is a special melting technology for smelting metals and alloys at high temperatures, which can make several selectable metals or alloys fused with sponge iridium slag, and then pure sponge iridium powder can be obtained by acid leaching or alkali leaching. The advantages of the pyrometry are that it can simplify the subsequent processing process, reduce the cost of hydration refining, and can produce finer and purer sponge iridium powder; The disadvantage of the fire method is that it requires high temperatures, and in the process of melting at high temperatures, iridium sponge will volatilize and cause absolute losses, and at the same time, it will also cause pollution to the environment.
The wet process is a kind of use of the difference in the solubility of substances in the immiscible two-solvent system, the use of sponge iridium and extractants to form a soluble organic solvent chelate, and the sponge iridium from the aqueous phase to the organic phase to achieve the purpose of separation or enrichment. Common sponge-iridium extractants include phosphorus-containing extractants and amine extractants. The advantages of the wet process are that high extraction rates can be achieved with a small number of extraction stages, and the extraction equipment is simple, easy to operate, selective, and easy to automate. The disadvantages of the wet process are that the concentration of the feed solution is not too high, and the reverse extraction rate of sponge iridium can only reach 90%.
At present, China has mastered the core technology of iridium sponge from secondary resources, which can achieve high efficiency and high purity of iridium sponge, which provides strong support for China's iridium sponge industry. According to statistics, China's annual iridium sponge from secondary resources accounts for about 30% of China's iridium sponge consumption, which is equivalent to saving $50 million in foreign exchange expenditure. Sponge iridium from secondary resources is not only conducive to China's resource conservation and recycling, but also conducive to China's scientific and technological innovation and the improvement of international competitiveness.