in simplified term: Shredding, separation of ferrous and non ferrous followed by melting and purification

You can read more in this book by

Waste Production and Utilization in the Metal Extraction Industry by Ndlovu et al

It's similar to regular smelting of ores- roasting, reduction, and flux additives. https://en.wikipedia.org/wiki/Smelting

At the front, there must be a separation out of undesirable materials, and at the end, there should be a determination of purity and major contaminants.