Questions about Metals.

1.
Iron < aluminium < copper < silver < gold < platinium
2.
In theory, all metal can be recycled.
3.
Price for ore & price of extraction compare with price of collection of recycled metal & price of purification.
4.
Recycling metals require much labour and land, but labour and land as the cost of recycling is very high in Hong Kong, so the cheap material's recycle value is low because of the high running cost in Hong Kong.
I hope this can help your understanding.

old metal can be recycled to form new metal