Research Progress in the Recovery and High-Value Utilization of Spent Vanadium-Titanium Based Catalysts

In the field of industrial denitration, Selective Catalytic Reduction (SCR) technology is highly favored for its efficiency. However, SCR catalysts inevitably lose activity over time and are difficult to regenerate through conventional means, resulting in a significant amount of spent catalysts. These spent catalysts contain valuable components such as vanadium (V), tungsten (W), and titanium (Ti), and their effective recovery can enable resource recycling.

This article focuses on the deactivation mechanisms and recycling pathways of commercial vanadium-titanium-based catalysts currently in use. It provides a detailed summary and comparison of the two main recycling methods: hydrometallurgical and pyrometallurgical processes, and discusses the reaction mechanisms involved and the advantages and disadvantages of each. Faced with the challenges of full element recovery in typical methods, this article collates cooperative treatment recycling processes, finding that current work needs to focus on reducing process costs and simplifying procedures while further improving recovery rates. Additionally, the high-value utilization of valuable components is also worthy of in-depth research. This article aims to provide a reference for the future recycling and utilization of spent catalysts, which is crucial for resource recovery and green low-carbon development.

Selective Catalytic Reduction (SCR) technology, due to its high efficiency and applicability, has become a core technology for NO_x emission reduction in industries such as steel, cement, and glass. As these industries increasingly rely on SCR technology, the recycling and high-value utilization of spent catalysts have become an urgent issue that needs to be addressed. When spent catalysts are difficult to regenerate, the recovery of valuable components becomes the preferred option.

Thermal treatment methods dominate the recycling process due to their high extraction rates but also bring about issues of high energy consumption and environmental pollution. In contrast, hydrometallurgical processes are favored for their simplicity, low cost, and high single-metal extraction rates, yet their development is limited by the low extraction rates of leaching agents for multiple valuable elements and the leaching of many impurities. Therefore, the integration of multiple processes and the development of high-value-added products represent the future direction for SCR catalyst recycling.

In the recycling process of SCR catalysts, the key lies in the efficient extraction of vanadium (V), tungsten (W), and titanium (Ti) while reducing energy consumption and environmental harm. Both acid and alkali methods can effectively recover over 90% of V, but given the toxicity of V, the use of a reducing acid leaching method is recommended to prioritize vanadium extraction, facilitating the preparation of high-purity V₂O₅. The recovery of W and Ti is more challenging, especially for W, whose leaching rate is limited by the choice and concentration of solvents, with low-concentration alkali leaching rates typically around 70%. Ti is only soluble in concentrated alkali solutions, and due to the high proportion of titanium in spent catalysts, its extraction would consume a large amount of reagents, leading to high costs. Thus, the most reasonable method is to use alkali to leach W while controlling the alkali concentration to retain as much Ti as possible in the residue. The alkaline leachate contains high levels of silicon and aluminum impurities, which need to be purified before the recovery of products. Additionally, the presence of heavy metals in spent catalysts requires targeted adjustments to the recycling process to enhance recovery rates and purity.

Currently, research on the recycling and utilization of spent vanadium-titanium catalysts focuses on the impact of operating conditions and reaction mechanisms on recovery rates, with insufficient evaluation of energy consumption and environmental impacts during the recycling process. Future studies could employ life cycle assessment and material flow analysis to evaluate the environmental impacts and resource efficiency of spent catalyst recycling. Moreover, the development of new and efficient leaching agents, optimization of thermal and hydrometallurgical process conditions, and exploration of high-value utilization pathways for spent catalysts, such as the preparation of new materials or as raw materials for other industrial processes, will be key to advancing SCR catalyst recycling technology.