Consider the environmental accident in Hungary involving waste (‘red mud’) from aluminum manufacture. Bauxite, the ore refined to generate aluminum, contains 30 to 54 % alumina. The rest is a combination of silica, iron oxides and titanium dioxide. In the Bayer process, bauxite is digested using a solution of NaOH at 175 oC. This converts alumina in the bauxite into soluble aluminum hydroxide ions. The liquid is taken away and dehydrated converting the hydroxide back to alumina. In the final step molten aluminum oxide (with the addition of cryolite, Na3AlF6, a ‘flux’ that decreases the melting point) is electrolyzed to yield aluminum metal. Write the reaction equations for the processes above. Explain where ‘red mud’ comes from. Why is it red and caustic?
Consider the environmental accident in Hungary involving waste (‘red mud’) from aluminum manufacture. Bauxite, the ore refined to generate aluminum, contains 30 to 54 % alumina. The rest is a combination of silica, iron oxides and titanium dioxide. In the Bayer process, bauxite is digested using a solution of NaOH at 175 oC. This converts alumina in the bauxite into soluble aluminum hydroxide ions. The liquid is taken away and dehydrated converting the hydroxide back to alumina. In the final step molten aluminum oxide (with the addition of cryolite, Na3AlF6, a ‘flux’ that decreases the melting point) is electrolyzed to yield aluminum metal. Write the reaction equations for the processes above. Explain where ‘red mud’ comes from. Why is it red and caustic?
Introduction to Chemical Engineering Thermodynamics
8th Edition
ISBN:9781259696527
Author:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Publisher:J.M. Smith Termodinamica en ingenieria quimica, Hendrick C Van Ness, Michael Abbott, Mark Swihart
Chapter1: Introduction
Section: Chapter Questions
Problem 1.1P
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Consider the environmental accident in Hungary involving waste (‘red mud’) from aluminum manufacture.
Bauxite, the ore refined to generate aluminum, contains 30 to 54 % alumina. The rest is a combination of silica,
iron oxides and titanium dioxide. In the Bayer process, bauxite is digested using a solution of NaOH at 175 oC.
This converts alumina in the bauxite into soluble aluminum hydroxide ions. The liquid is taken away and
dehydrated converting the hydroxide back to alumina. In the final step molten aluminum oxide (with the addition
of cryolite, Na3AlF6, a ‘flux’ that decreases the melting point) is electrolyzed to yield aluminum metal.
Write the reaction equations for the processes above.
Explain where ‘red mud’ comes from.
Why is it red and caustic?
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