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In the process of metal waste recycling, the removal of impurities is a crucial step. This not only affects the purity of the recovered metal, but also directly affects the recovery efficiency and cost. In this paper, several common methods of impurity removal in metal waste recycling will be discussed.

1. Physical methods Physical methods are the most basic impurity removal methods, mainly including the following:

1.1 Magnetic separation Magnetic separation is the process of using magnetic materials to separate metal waste. This method is suitable for removing ferromagnetic impurities such as iron and steel.

1.2 Screening Screening is the separation of metal waste of different particle sizes through the screen. This method can remove large non-metallic impurities.

1.3 Air separation Air separation uses the difference in the behavior of materials with different densities in the air flow to separate light and heavy materials.

2. Chemical methods Chemical methods remove impurities from metal waste through chemical reactions, including:

2.1 Pickling Pickling is the use of acidic solutions (such as sulfuric acid, hydrochloric acid) to dissolve oxides and other impurities on metal surfaces.

2.2 Electrolysis Electrolysis is a process in which metal ions are deposited from a solution by means of an electric current, thereby removing impurities.

3. Mechanical methods Mechanical methods remove impurities through physical forces, including:

3.1 Crushing Crushing is the breaking of large pieces of metal waste into small pieces to facilitate subsequent processing.

3.2 Shearing Shearing is the cutting of metal scrap into smaller dimensions by shear force, which helps to remove attached impurities.

4. Heat treatment method Heat treatment method removes impurities through high temperature treatment, including:

4.1 Smelting Smelting is the melting of scrap metal at high temperatures, and impurities will float to the surface or sink to the bottom during the melting process, so as to be removed.

4.2 Pyrolysis Pyrolysis is the heating of metal waste under conditions of no oxygen or low oxygen to decompose organic impurities.

5. Biological methods Biological methods are an emerging impurity removal technology that uses microbial metabolic processes to remove impurities from metal waste.

5.1 Microbial leaching Microbial leaching is the conversion of impurities in metal waste into soluble substances by specific microorganisms, which are then separated by solution.

Impurity removal in metal waste recycling is a complex process, which needs to be selected according to the type of waste and the characteristics of impurities. With the development of technology, more efficient and environmentally friendly impurity removal methods may be developed in the future.