system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 Landfills are becoming large concentrations of materials like plastic, aluminum and other. What part of the process of mining landfills and processing the materials for new products, makes mining raw materials from the earth and processing them cheaper?
gpt
Mining engineer here. The reason it is cheaper to mine directly from the Earth is because sorting Mineral X from a bunch of rock is a fairly straightforward process. Rock has a set of properties and Mineral X has completely different  set of properties. So you can use the differences to extract what you want. For example, magnets and density separation could remove iron from rock.

If you were to mine from a landfill, you would have to sort out countless different types of material. All these materials act differently, so you would have to individually process for each type of material. It is possible, but there would be so much contamination and the process would be very expensive.

In the future, landfills will be mines, but right now it's too expensive.