Mining waste is a byproduct of the extraction of minerals and metals from the earth. Two common types of mining waste are SLAG and tailings. SLAG is a byproduct of smelting ore, which is a process used to separate metal from its ore. Tailings are the leftover material after ore has been processed and the desired metal has been extracted. Both SLAG and tailings can contain hazardous materials, such as heavy metals, and must be disposed of properly.