Aluminum recovery from milk cartons
By hydrometallurgical method using ammonium hydroxide solution (NH4OH), the authors at the Institute of Science, Technology and Environmental Management, Industrial University of Ho Chi Minh City have separated the aluminum, plastic, and paper components from the milk carton.
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Milk cartons used for aluminum separation research. Photo: NNC
Every year, Vietnam has about 15 billion used milk cartons (equivalent to 150 thousand tons) are discarded. Meanwhile, 100% of paper milk cartons can be recycled into useful materials and products. However, milk cartons are made from many layers with components, such as paper, plastic, and aluminum, so it is more difficult to recycle than plastic. In addition, milk cartons need to be separated from these components to be able to decompose.
To separate and recover aluminum from milk cartons, widely used technologies are pyrometallurgy and hydrometallurgy. In particular, fire smelting is the process of reducing metal at high temperature, so it mainly uses an incinerator, giving off a lot of heat in an environment with strong reducing agents. Therefore, this method often causes air pollution, because it contains a lot of dust or toxic organic compounds, the metal recovery rate is not high.
Hydrometallurgy is the process of recovering metals by reduction reactions at low temperatures in a chemical solvent less than 100°C. In addition, this method easily controls chemical reactions, so there is less toxic waste generation. Hydrometallurgy is also easy to operate with low cost, can recover a certain amount of metal. Therefore, the authors have carried out research on separating aluminum and plastic from milk cartons by hydrometallurgical method using NH4OH solution.
Accordingly, milk cartons after being collected are washed with clean water to remove milk residues, dirt and dried, then cut into small pieces. Soak the minced milk shell sample in diluted NH4OH solution. Use a heated magnetic stirrer to control the temperature of the solution.
After conducting the experiment, the team found that the optimal temperature to separate aluminum, plastic and paper from milk cartons was 70oC, in 30 minutes, the concentration of NH4OH solution was 5 M, the size of the shell sample milk (1x1cm), will give the highest recovery efficiency of 97.82%.
The research was reported at the 3rd Young Science Conference of Industrial University of Ho Chi Minh City. According to the authors, this is the first study tested in Vietnam on the recovery of aluminum and plastic separation from waste milk cartons by hydrometallurgy, which helps to improve the use value of waste products.
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