Short answers, pulled from the story.
Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. The reducing agent is commonly a fossil-fuel source of carbon, such as carbon monoxide from incomplete combustion of coke.
Humans learned to smelt metals in prehistoric times more than 8000 years ago. The earliest current evidence of copper smelting dates from between 5500 BC and 5000 BC found in Pločnik and Belovode, Serbia.
The blast furnace was introduced by China in the 13th century during the High Middle Ages. China had been using it since as early as 200 BC during the Qin dynasty.
The smelter in Flin Flon, Canada was one of the largest point sources of mercury in North America in the 20th century. Even after releases were drastically reduced, landscape re-emission continued to be a major regional source of mercury.
Air pollution standards exist under the Clean Air Act published by the Environmental Protection Agency. Water pollution standards operate under the Clean Water Act with treatment technologies including recycling of wastewater and settling basins.