I am trying to use red mud (bauxite residue) as aluminosilicate source in geopolymers, but I am concerned of using this kind of toxic materials in the lab. Is there any known concerns about the toxicity of red mud usage in concrete geopolymer manufacturing and research?
Mahmoud, I did research on using red mud in geopolymers in my Ph.D. dissertation. My focus was on mechanical properties, but also I tested leaching on heavy metals according to standard DIN 38414-S4. You can find more on pages 183-186 Thesis Mogućnost primene industrijskih nusproizvoda u geopolimernim...
(but it's in Serbian language so...).
Good luck!
Dear Mahmoud,
red mud isn’t amorphous and hasn’t the reactive Alumina necessary to obtain good and stable geopolymerization.
In my experience this waste can‘t be used as precursor for Geopolymer , but due it’s alkalinity maybe can be suitable for Alkali Activation.
But you will have to find a way to stabilize the material under water immersion. AAM aren’t polymers but hydrated materials , Portland like, so aren’t at all geopolymers.
Geopolymers are mineral polymers and can be obtained in alkaline (at lower alkalinity than AAM so without using corrosive reagent) and acidic media. They aren’t a sub-class of AAM but are completely different materials, because even mix design and mixing method is different from AAM.
Other issue of AAM with red mud is the low mechanical properties with, instead, high efflorescence, due to free alkali salts migration to the surface.
Alkaline cations in GP are balanced on the precursor and when hardened they become part of the new condensed minerals (cannot be leached out from the matrix, then even in water curing the reaction can go further and after 28 days the mechanical properties are almost the same if compared with the sample cured by air, of course at room temperature).
Instead, Alkaline liquid in AAM (different molar ratio and concentration than the GP range) acts as the most important binder so it’s strongly alkaline, but unbalanced and usually over saturated. It shows high performance by air (after drying or thanks to heat curing) but very weak if put in water. Rarely AAM can stay 28 days in water maintaining enough strength to be tested. Normally they collapse after 3 to 7 days or in the best cases show a reduced strength till 80% less than the value achieved by air. This weakness is also unstable so it’s quite normal to see very different results even between samples prepared in the same moment.
Hoping to be useful
Have a good work
Best regards
Alex Reggiani
Dear Alex,
thank you so much for the great explanation!
best,
Mahmoud
The content of Na2O in red mud accounts for 5% ~ 12%, which can be used as raw material for the preparation of inorganic polymers. However, sodium in red mud mainly exists in the form of combined state such as sodalite or nepheline. When red mud is directly used to prepare polymers, only the attached alkali can be used. Because silicon components are difficult to be decomposed effectively, a large number of elements such as bound alkali and aluminum silicon cannot participate in the polymerization reaction and cannot form strength contributors. Besides, the radioactivity of red mud also needs to be detected or prevented.
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