Editing Bayer process (section)

== Waste ==
[[Red mud]] is the waste product that is produced in the digestion of bauxite with sodium hydroxide. It has high calcium and sodium hydroxide content with a complex chemical composition, and accordingly is very caustic and a potential source of pollution. The amount of red mud produced is considerable, and this has led scientists and refiners to seek uses for it. It has received attention as a possible source of [[vanadium]]. Due to the low extraction yield much of the gallium ends up in the aluminium oxide as an impurity and in the red mud.

One use of red mud is in ceramic production. Red mud dries into a fine powder that contains iron, aluminium, calcium and sodium. It becomes a health risk when some plants use the waste to produce aluminium oxides.<ref>{{cite journal|title=The Surface Chemistry of Bayer Process Solids: A Review|journal=Colloids and Surfaces A: Physicochemical and Engineering Aspects|volume=146|issue=1–3|pages=359–374|doi=10.1016/S0927-7757(98)00798-5|year=1999|last1=Hind|first1=Andrew R.|last2=Bhargava|first2=Suresh K.|last3=Grocott|first3=Stephen C.}}</ref>

In the United States, the waste is disposed in large [[Reservoir|impoundments]], a sort of reservoir created by a dam. The impoundments are typically lined with clay or synthetic liners. The US does not approve of the use of the waste due to the danger it poses to the environment. The EPA identified high levels of arsenic and chromium in some red mud samples.<ref>{{cite web|title=TENORM: Bauxite and Alumina Production Wastes|url=https://www.epa.gov/radiation/tenorm-bauxite-and-alumina-production-wastes|website=www.epa.gov|publisher=United States Environmental Protection Agency|access-date=12 April 2018|date=2015-04-22}}</ref>

=== Ajka alumina plant accident ===
{{main|Ajka alumina plant accident}}

On October 4, 2010, the Ajka alumina plant in Hungary had an [[Ajka alumina plant accident|incident]] where the western dam of its red mud reservoir collapsed. The reservoir was filled with {{convert|700,000|m3|e6cuft|abbr=off}} of a mixture of red mud and water with a pH of 12. The mixture was released into the valley of Torna river and flooded parts of the city of Devecser and the villages of Kolontár and Somlóvásárhely. The incident resulted in 10 deaths, more than a hundred injuries, and contamination in lakes and rivers.<ref>{{cite journal|last1=Ruyters|first1=Stefan|last2=Mertens|first2=Jelle|last3=Vassilieva|first3=Elvira|last4=Dehandschutter|first4=Boris|last5=Poffijin|first5=Andre|last6=Smolders|first6=Erik|title=The Red Mud Accident in Ajka (Hungary): Plant Toxicity and Trace Metal Bioavailability in Red Mud Contaminated Soil|journal=Environmental Science & Technology|volume=45|issue=4|pages=1616–1622|doi=10.1021/es104000m|pmid=21204523|year=2011|bibcode=2011EnST...45.1616R|url=https://figshare.com/articles/journal_contribution/2692039/files/4367983.pdf}}</ref>