Technical Process of Extraction and Recovery of Ruthenium from Secondary Resources

Precious metal ruthenium has excellent physical properties，such as hard and brittle，high melting point，not easy to cast，and has excellent catalytic activity，good electrical conductivity and high temperature and corrosion resistance. Ruthenium has stable chemical properties and is almost insoluble in acid，it cannot be corroded in royal water at 100 ℃，and it is also difficult to dissolve in hydrofluoric acid and phosphoric acid. Ruthenium can react with fluorine，chlorine and bromine under heating. When the temperature reaches 300 ℃，RuF5 is generated with fluorine. At 450 ℃，chlorine can form RuCl3，and ruthenium powder is heated to 900 ℃ on the surface. RuO3 and RuO4 can be formed when the temperature rises to 1000 ℃. Ruthenium with these special physicochemical prop‑ erties has a wide range of applications and a large consumption. Ruthenium mineral resources are very few，so extracted from second‑ ary resources containing ruthenium，ruthenium is an important way to obtain ruthenium resources. With the extraction and recovery of ruthenium resources，the upgrading of refining process and the improvement of production capacity，the refining cycle and extraction cost of ruthenium are greatly shortened，the circulation of ruthenium is relatively fast，and the price of ruthenium is greatly reduced. Secondary resources containing ruthenium include royal water-insoluble slag in precious metal extraction，ruthenium target waste mate‑ rial，loading catalyst，electroplating ruthenium，and so on. Ruthenium accounts for 49.4% of the total secondary resource，including about 10.4%，13% and 26% of PtRu4，PtRu5 and PtRu10 alloys. The distribution of ruthenium used for making ruthenium electrode ac‑ counts for 18.2% of the total secondary resource，while ruthenium accounts for about 1.2% of the ruthenium catalyst resources. This pa‑ per briefly described the properties of ruthenium and its compounds，as well as the uses of ruthenium in catalysis，target materials，electroplating，alloys，and medicine，and details the extraction and recovery technology and value-added utilization technology of ru‑ thenium in secondary resources. For the ruthenium resources in solid waste，chlorination method，alkali melting distillation method，ozone oxidation method，pretreatment activation-dissolution method and other methods could be used，while for liquid waste，precipi‑ tation method，electrolysis method，adsorption and extraction method could be used. Chlorination method wasone of the most used sol‑ id waste treatment methods，and it was usually divided into fire method chlorination method and wet method chlorination method. The process had low economic cost，short production process，relatively simple operation，and high leaching rate of ruthenium. But there was a risk of environmental pollution caused by chlorine gas leakage. The alkali melting distillation method had good solubility to the ruthenium waste catalyst，but in treating the ruthenium-containing minerals. Alkali metal salts could cause crucible corrosion and in‑ troduce impurities into the distillation process，thus reducing the recovery rate of ruthenium. The dissolution rate of ruthenium in ozone oxidation method was 99.8%，but the disadvantage was that O3 had strong oxidation and high corrosion resistance，and O3 was difficult to preserve. Therefore，it was not suitable for bulk recovery of ruthenium-containing waste materials. The pretreatment activation-disso‑ lution method was simple，low equipment requirements，high dissolution rate of ruthenium，but the process was seriously polluted，and impurities were easy to be introduced in the operation process. The thiourea precipitation method was a commonly used method of waste liquid treatment，which could selectively extract ruthenium from the waste liquid. In the process of electrolysis，base metal impu‑ rities would not be introduced，so the product purity was high. However，ruthenium was easily oxidized and further passivated in the process of electrolysis，which led to the slow experimental speed. In addition，this process had the disadvantages of high requirements for experimental equipment and long experimental period. The adsorption and extraction method were divided into resin adsorption and resin absorption and extraction. The separation and enrichment of target ions could be effectively realized. The resin absorption and ex‑ traction method were relatively safe，with a shorter period，and the recovery rate of ruthenium was higher. Since RuO4 was an oxide of ruthenium and was volatile，this crude product could be further separated and purified by means of oxidative distillation. The oxidative distillation of ruthenium included hydrolytic distillation and concentrated distillation，which had different practical operation process characteristics. The hydrolysis distillation had a high recovery rate，but the operation process was relatively complex，the experiment had a long time，and it was difficult to filter and separate the hydrolysis products. The concentrated distillation operation was relatively simple and the operation cycle was short，but the distillation effect was not stable enough. Because the ruthenium metal itself had ex‑ cellent catalytic activity and stability，and its hydrogen precipitation performance was good，its electrocatalytic performance was sec‑ ond only to platinum or even better than platinum，as a substitute for platinum，making the ruthenium resources to further achieve val‑ ue-added utilization. Finally，the current situation of ruthenium resource recovery was summarized and discussed，whichwas of great significance to extract and recycle from ruthenium secondary resources and make more efficient and environmentally friendly recycling of precious metals to ensure the supply and sustainable development of strategic precious metals in China. © 2024 Editorial Office of Chinese Journal of Rare Metals. All rights reserved.