Aluminum anodizing waste and its uses: An overview of potential applications and market opportunities

The aluminum anodizing process generates a large volume of waste composed mainly of amorphous aluminum hydroxide with chemical compatibility to be used in other industrial processes as an alternative starting raw material. This waste has several application possibilities such as the production of refractories, ceramic pigments, bricks, and many others. However, despite its potential features, its recycling process is far from well consolidated. This work highlights the most important contributions regarding Al-anodizing waste (AAW) features and their potential applications from the last 30 years. We provide the most complete and detailed characterization of AAW including chemical, physical, thermal, and microstructural analysis. The characterization analyzes were performed in a Brazilian waste sample and were compared with AAW worldwide. Additionally, our characterization results also considered differentiate previous processing; this, it many other possibilities are suggested that have not been explored thus far. The recycling feasibility of AAW is discussed according to the following criteria: classification, including legislation and standards; potentiality, including physical and chemical characteristics and purity; quantity, including production data; viability, including availability, costs regarding disposal and recycling process, and available technology for recycling; and applicability, including market opportunities. Moreover, alumina recovery from AAW and the related environmental aspects are discussed.