Short answers, pulled from the story.
The Hall-Heroult process is the major industrial method for smelting aluminium. It works by dissolving aluminium oxide in molten cryolite and passing an electric current through the mixture to deposit liquid aluminium at the cathode. The process produces aluminium with a purity of 99.5-99.8%.
Charles Martin Hall and Paul Heroult each discovered the process independently in 1886. Both men were 22 years old at the time. Hall opened the first large-scale aluminium production plant in Pittsburgh in 1888, which later became the Alcoa corporation.
Electrolysis of aluminium oxide demands continuous high-current operation at temperatures between 940 and 980 degrees Celsius. The theoretical minimum energy requirement is 6.23 kilowatt-hours per kilogram of aluminium, but in practice the process commonly requires 15.37 kilowatt-hours. Cells must run 24 hours a day to prevent the molten material from solidifying.
A 2012 estimate put carbon dioxide emissions at 12.7 tons per ton of aluminium produced. The process also generates hydrogen fluoride and, during the anode effect, produces tetrafluoromethane and hexafluoroethane, which are potent greenhouse gases. Modern facilities recycle almost all fluoride compounds, and particulates are captured with electrostatic or bag filters.
Before 1886, aluminium was produced by heating ore with elemental sodium or potassium in a vacuum, a complicated process using materials that were themselves expensive. Aluminium cost more than gold or platinum in the early 19th century, and still cost more than silver when it was chosen to cap the Washington Monument in 1884.
Soderberg anodes are self-baking and use a single anode per cell that is continuously replenished with coke-and-pitch briquettes as its bottom is consumed. Prebaked anodes are baked in gas-fired ovens before use; a typical cell holds 24 of them in two rows, each computer-controlled. Prebaked anodes release fewer carcinogenic pollutants and are less prone to the anode effect, but cells using them are more expensive to build and maintain.