Current status of precious metal extraction and refining technology

Precious metals mainly refer to eight metal elements, including gold, silver, and platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, platinum). Most of these metals have beautiful colors and are highly resistant to chemicals, making them less likely to cause chemical reactions under normal conditions. Materials containing precious metals can be divided into two categories: one is mineral resources, referred to as primary resources; Another type is renewable resources, which are precious metal products that are scrapped during use. These resources are diverse in types and forms, ranging from a few parts per ten thousand to almost pure metals, and are called secondary resources. The smelting technology of precious metals has made significant progress in recent years, and the effective extraction of precious metals can be divided into three parts: enrichment, separation, and refining. The industrial application of solvent extraction technology is commonly used for refining and extracting precious metals from solutions containing multiple metal components. In recent years, there has been continuous innovation and development in extraction and separation processes and extraction equipment. The existing precious metal extraction devices have the disadvantages of being unable to extract multiple times, slow extraction speed, and poor extraction efficiency. The extraction equipment has also developed from traditional mixed clarification tanks to modern CWL-M new liquid liquid centrifugal extraction machines. The equipment has good energy-saving effect and low power consumption. In terms of corrosion resistance, for highly corrosive systems, polymer composite materials are used instead of traditional metal materials to solve the corrosion problem of the equipment. In terms of stability performance, an upper suspension structure has been adopted, eliminating the bottom bearing and mechanical seal of the equipment, simplifying the equipment structure, and fundamentally solving the problems of traditional centrifugal extraction machines that are prone to leakage, frequent mechanical failures, and short service life. The equipment adopts various mixed structures, with good separation effect and small liquid holding capacity. Due to strong continuity of process operation, high degree of automation, greatly shortened cycle time, improved recovery rate and product purity, significant technical and economic benefits have been achieved, making it an important equipment and method for precious metal separation and refining.

The traditional process of smelting precious metal gold platinum palladium involves repeated melting crystallization and repeated reduction purification. A new extraction process is used to extract gold, platinum and palladium. The gold, platinum and palladium ores are first dissolved by aqueous solution chlorination method. After dissolution, the gold is first reduced with reduced sulfur dioxide or sodium sulfate, and the reduction potential is controlled (the potential is increased to control the mol degree) to reduce the gold to make coarse gold powder, which is used to refine gold. The remaining liquid is platinum, palladium, zinc, bismuth and other metals, which are added with ammonium chloride in the way of ammonium, By introducing palladium into the liquid phase, platinum enters the solid phase, forming a coarse separation of platinum and palladium. Afterwards, the aqueous solution is chlorinated and dissolved into a liquid, and palladium is targeted for extraction. After extraction, the organic phase is loaded and impurities are washed with hydrochloric acid, and then purified water or sodium hydroxide is used for backextraction. After adjusting the extraction residue of palladium, platinum is extracted with N235. The extraction rate of platinum is high (99.95%), and the extraction rate of copper, iron, nickel, cobalt and other base metals is very low. The process is novel, with good connection between the front and back, and a wide range of applications. Extract base metals from the platinum extraction residue using P204, and precipitate them with ammonium chloride for chemical purposes in a rhodium iridium solution extracted from gold, palladium, and platinum. Burnt platinum powder is melted and refined into platinum ingots.

The extraction of metal ions from precious metal solutions is related to their valence state configuration and solution properties. Many extraction mechanisms and extraction process research results indicate that the valence state and state of chloride anions in the solution are controlled by the central ion and solution properties, and their changes lead to significant changes in extraction behavior.