engleski

The influence of Fe species from red mud on the mechanical properties of geopolymer binder

Bauxite residue, often called red mud, is an aluminosilicate waste material rich in iron generated in the Bayer alumina production process. Due to the high pH, which is a consequence of residual NaOH from the Bayer process, the bauxite residue proves to be a potential candidate for use in new, alternative types of mineral binders such as geopolymers. Also, this waste material is rich in Fe species (from which red colour comes) and some research indicates that Fe species ascend into Si−O−T geopolymer structure (where T = Si or Al) and replace part of Al3+ ions, which ultimately gives new material properties. Geopolymer binders are obtained by reacting aluminosilicate with a solution of alkali oxide and/or its silicate (usually Na, K and Cs). This type of binder has a great advantage over Portland cement in terms of environmental protection and reduction of CO2 emissions because it most often uses waste aluminosilicate materials, mainly fly ash and slag, and recently, for the above reasons, bauxite residue. In order to examine the influence of Fe species from red mud (bauxite residue) on the structure and properties of geopolymer, the structural characterization of the industrial waste red mud sample and prepared red mud containing geopolymer sample (composed of 20 wt.% of bauxite residue and 80 wt.% of metakaolin) was performed using XRD, SEM/EDS and 57Fe Mössbauer spectroscopy. Mössbauer spectra of both samples showed the presence of a sextet with asymmetrically broadened lines, which can be attributed to the magnetically ordered Fe(III) in Al-containing hematite, and an asymmetric quadrupole doublet, which could be attributed to Fe(III) in octahedral and tetrahedral sites of aluminosilicate cancrinite and katoite detected in samples by XRD and/or to superparamagnetic Fe oxide nanoparticles. Also, the compressive strength of geopolymer paste, considered as a main engineering property of construction materials, was tested in this research.

Mossbauer effect ; geopolymers ; red mud ; bauxite residue

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