1. What is the difference between spoils and tailings?

The difference is where the material came from. Spoils come from overburden and is discarded as waste, whereas, tailings come from left over dredging of steam beds that are discarded as waste as well.

Tailings: The waste that remains after the minerals have been extracted from an ore by ore dressing; gangue, slimes

Spoils: Material (such as rock or earth) removed in the course of an excavation, or in mining or dredging