There are three main recovery methods for spent palladium-carbon catalysts: incineration, high-temperature chlorinated volatilisation and wet treatment with organic solvents. Among them, incineration is a commonly used recovery method. At high temperatures, the carbon in the spent palladium-carbon catalyst is burnt to produce C02 volatilisation, while the palladium remains in the burnt ash. Subsequently, the palladium in the burnt ash is transferred to a solution by dissolving it, and then the palladium is separated and purified. This method has the advantage of a high palladium recovery rate, which can typically be over 95 per cent. However, the incineration method also has some disadvantages, such as high energy consumption and environmental pollution. Therefore, it is necessary to consider its advantages and disadvantages comprehensively and choose a suitable recovery method in practical application.

High-temperature chlorinated volatilisation is another effective recovery method. At high temperature, the palladium in the spent palladium-carbon catalyst is volatilised by generating chloride by passing C2 or adding chloride. Subsequently, efficient recovery of palladium can be achieved through absorption and purification steps. This method also has a high palladium recovery rate and relatively low energy consumption and environmental pollution compared to the incineration method. However, high-temperature chlorinated volatilisation requires special equipment and operating conditions and is technically demanding.

Organic solvent wet treatment is a relatively new recovery method. It first uses organic solvents to remove the organic matter in the spent palladium-carbon catalyst by leaching, and then the palladium is dissolved and transferred to the solution. Finally, a refining step allows high purity palladium to be obtained. This method has the advantages of easy operation and low environmental pollution. However, the selection of organic solvents and the treatment process need to be strictly controlled to ensure the recovery efficiency and the purity of palladium.

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During the recovery process, attention needs to be paid to the protection of the environment. For the waste gas generated by the incineration method, effective purification measures need to be adopted to reduce the pollution to the atmosphere. For the waste gas generated by the high temperature chlorination volatilisation method, it also needs to be collected and treated to avoid adverse effects on the environment. At the same time, the waste liquid and waste residue generated during the recovery process also need to be properly treated to prevent pollution of soil and water bodies.

In addition to traditional recycling methods, some new technical means, microbial leaching and so on, have emerged in recent years. These new methods have the advantages of high efficiency and environmental protection, which provide new ideas for the recovery of spent palladium-carbon catalysts. However, these new methods need to be further studied and optimised in practical applications to improve their stability and practicality.

In conclusion, the recovery of palladium from spent palladium-carbon catalysts is a research direction of great significance. By choosing suitable recovery methods and technological means, not only can the recovery rate of palladium be improved and the production cost be reduced, but also the impact on the environment can be reduced. In the future, with the continuous progress of science and technology and the improvement of environmental protection awareness, it is believed that more efficient and environmentally friendly recovery methods will emerge, contributing to the sustainable development of the petrochemical industry.