Current Status and Countermeasures of Recovery of Palladium and Platinum in China
1. Properties and uses of palladium and platinum
Palladium is located in Group VIII of the fifth cycle of the Periodic Table of Elements, atomic number 46, atomic weight 106.42, density 12.02 g/cm 3 (20 Â° C), melting point 1550 Â° C, boiling point 2900 Â° C. Platinum is also located in Group VIII of the Periodic Table of Elements, atomic number 78, atomic weight 195.09, density 21.45 g/cm 3 (20 Â° C), melting point 1768 Â° C, boiling point 3827 Â° C.
Palladium, platinum and silver are malleable metals, hydrogen has great affinity. Sponge or powdered palladium can absorb 900 times its volume of hydrogen. Palladium is the most active of the platinum group elements, soluble in concentrated nitric acid and hot sulfuric acid, but insoluble in hydrochloric acid. Platinum has good chemical stability, is insoluble in any single acid, and is soluble in aqua regia.
Palladium and platinum are mainly used as catalysts in the industry and are related to hydrogenation or dehydrogenation processes. For example, palladium on carbon catalysts and platinum on carbon catalysts are chemical, pharmaceutical and pharmaceutical intermediates, perfumes, pesticides, cosmetics and polymers. The catalyst for hydrogenation reaction in the fields of modified materials has the characteristics of good selectivity, high activity and long service life.
There are many compounds of palladium and platinum. Common compounds of palladium include palladium dichloride (PdCl 2 Â· 2H 2 O), palladium nitrate [Pd(NO 3 ) 2 Â· 2H 2 O], etc., and some are directly used as catalysts, such as palladium dichloride and dichlorination. The mixed solution of copper is a catalyst for liquid phase synthesis of products such as methyl ethyl ketone, and some are used as raw materials for further production of palladium-containing catalysts such as palladium on carbon catalysts, such as palladium dichloride and palladium nitrate; Platinum [PtCl 2 (NH 3 ) 2 ], platinum dioxide [PtO 2 ], and the like. Cisplatin is a new anticancer drug.
Palladium- or platinum-containing compounds play an important role in the production of electronic components by plating or slurry-forming a palladium-containing (platinum) complex onto the surface of the device to make the device specific. Electrical performance.
In recent years, due to the rapid growth of platinum prices, the consumption of platinum jewellery has been inhibited. Due to the relatively low price of palladium, people have turned to the development of palladium jewellery. In 2005, the amount of palladium used in the manufacture of jewellery increased by 55% to 7.15 million ounces. 222.37t), while palladium used in manufacturing jewellery in China increased by 71% in 2004 to 6 million ounces (186.6 tons), accounting for 83.91% of the total palladium used in the manufacture of jewelry worldwide. For jewellery manufacturers, palladium is low in price, high in profit, and low in investment risk.
2. Overview of secondary resources of palladium and platinum
70% of the world's palladium is distributed in Russia and 50% of platinum is distributed in South Africa. Since China's palladium and platinum mineral resources are seriously insufficient, it is very important to recover palladium and platinum from the secondary resources of palladium and platinum. In 2005, palladium recovered from automotive spent catalyst reached 3.4 million ounces (105.74 tons) and recovered platinum reached 680,000 ounces (21.15 tons). The secondary resources of palladium and platinum mainly include: automobile waste catalyst, palladium (platinum) carbon waste catalyst, waste palladium (platinum) plating solution, palladium (platinum)-containing waste electronic components (integrated circuit board, contacts, contacts), Waste electronic slurry, etc.
Third, the recycling process of palladium and platinum
Due to the wide variety of secondary resources of palladium and platinum, the grades are different, and the impurity content is different. It is necessary to formulate a reasonable recovery process according to the characteristics of different secondary resource materials.
Spent catalyst, spent catalyst, spent catalyst car for palladium on alumina (Pt) in general, two kinds of process route, first type are: selective dissolution of the insoluble carrier slag â†’ â†’ â†’ separation and purification of a noble metal is dissolved. The second type is: dissolving precious metals â†’ separation and purification.
The process route for palladium (platinum) carbon waste catalyst, waste electronic slurry and the like is: roastingâ†’baking slagâ†’dissolving precious metalâ†’separation and purification.
The process route for the waste palladium (platinum) plating solution is: displacement â†’ displacement slag â†’ dissolved precious metal â†’ separation and purification.
For the palladium (platinum) waste electronic components (integrated circuit boards, contacts, contacts), the process route is: classification and disassembly â†’ roasting â†’ roasting slag â†’ dissolving precious metals â†’ separation and purification.
It should be pointed out that no matter what kind of process is adopted, it is necessary to have perfect environmental protection facilities. For example, the roaster should be equipped with a complete dust collection facility, and the exhaust gas and waste water can be discharged after being treated to the standard.
Analysis and countermeasures on the status quo of secondary resource recovery of domestic palladium and platinum
At present, the country has not issued a unified law and regulations for the recovery of precious metals secondary resources. Therefore, the recovery of secondary resources of precious metals is difficult to be unified and centralized, and a small part is carried out in state-owned companies, most of which are carried out in private and self-employed households. Under normal circumstances, the recycling carried out by state-owned companies is more formal, the process is standardized, the equipment is in good condition, the exhaust gas and wastewater treatment facilities are perfect, the working environment is good, and the recycling in private and self-employed households is chaotic, the process equipment is backward and lacks corresponding The exhaust gas and wastewater treatment facilities have a poor working environment.
An example of the recovery of palladium (platinum) from palladium (platinum) waste electronic components in Zhejiang and Guangdong is given.
Taizhou, Zhejiang is currently the largest dismantling center for used household appliances and electrical appliances in Asia. In Ningbo, Wenling, Wenzhou, Taizhou, and Guangdong, Dongguan, Puning, and Chaoshan, due to the proximity to the high seas, a large amount of palladium (platinum) waste electronic elements were smuggled from the high seas in the early 1990s. Devices (integrated circuit boards, contacts, contacts), small workshops and small smelters that recycle palladium (platinum) from these "foreign wastes" are scattered throughout the country. In Yongxing County, Quzhou City, which has the title of â€œChina Silver Capitalâ€, the amount of associated palladium, platinum and rhodium extracted from the waste slag and waste liquid from gold mines, smelters and electroplating electronics factories in Guangdong is also considerable.
The process of recovering palladium (platinum) from small workshops and small smelters in coastal areas is very simple: waste electronic components containing palladium (platinum) â†’ roasting â†’ dissolution of nitric acid (or aqua regia) â†’ precipitation of ammonium chloride â†’ water dissolution â†’ ammonia complexation â†’ Hydrazine hydrate reductionâ†’crude palladium (platinum) (90%), the process has the following disadvantages: 1 The flue gas generated during the roasting of waste electronic components will cause certain harm to the workers and the residents nearby. 2 Nitric acid dissolves the roasting slag and generates NO, NO 2 and other gases. If it is discharged without treatment, it will pollute the air. 3 The yield of palladium (platinum) is only about 90%, which cannot meet the industrial requirements. It also needs to be sent to a specialized refinery for refining and purification.
At present, the annual output of palladium (Platinum) waste electronic components (integrated circuit boards, contacts, contacts) in Zhejiang and Guangdong has not been fully statistically recovered. The annual output of palladium has reached 100-120t, which is calculated according to the current 80,000 yuan/Kg palladium. From 8 billion to 9.6 billion yuan, the annual output of recycled platinum has reached 20 to 25 tons. According to the current 270,000 yuan / Kg platinum, it is 54 to 6.75 billion yuan, with a total value of 16 billion yuan.
Since the waste electronic components containing palladium (platinum) come in through some irregular channels, there is no formal invoice, and most of these small workshops and small smelters are incomplete, and the tax credits cannot be deducted, resulting in excessive taxation. After processing into crude palladium (platinum), part of it is returned to Hong Kong, and then sold to Japan, South Korea and Taiwan through Hong Kong, mainly used to make electronic components such as circuit boards, contacts, contacts, etc. Form sales to other domestic companies or individuals.
In view of the backwardness of some small smelters' processes and equipment, and the absence of corresponding exhaust gas and wastewater treatment facilities, they cause serious pollution to the environment, and at the same time do not invoice, do not pay taxes, do not contribute to the national GDP income, and do not comply with the relevant national taxes. policy. It is recommended that relevant state departments improve relevant laws and regulations as soon as possible, ban small factories with small scale and heavy pollution, and support a group of enterprises with advanced technology, advanced equipment, certain scale and complete three-waste treatment facilities from taxation and other policies. The development of circular economy, to help them in the introduction of talent and technical advice, so that the domestic palladium, platinum secondary resource recovery into a virtuous cycle development track.
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