Abstract
Red mud presents significant environmental problems, so that its incorporation in geopolymers could represent an alternative solution to produce valuable products from this residue. Novel geopolymers using red mud as source of alumina and waste glass as silica supplier were developed, using sodium hydroxide as the only ‘non-waste’ material. The formation of a homogeneous polymeric gel, confirmed by solid-state NMR and EDX analysis, promoted the stabilization of possible pollutants. Moreover, the materials exhibit a remarkable compressive strength (up to 45 MPa, for 60 wt% red mud).
Highlights
Red mud is an inorganic residue generated during the industrial production of alumina by the Bayer process
Red mud has been already proposed as raw material in geopolymer production, but always with a supplementary Al source, such as metakaolin [4] or fly ash [5], mainly to enhance the mechanical strength of the products
A high SiO2 /Al2 O3 ratio corresponded to an enhanced content of waste glass in the mixture: on one hand, the evolution of compressive strength suggested an upper limit to glass cullet incorporation; on the other hand, the relatively high compressive strength achieved (30–45 MPa) is interesting for the significant amount of red mud incorporated [2]
Summary
Red mud is an inorganic residue generated during the industrial production of alumina by the Bayer process. An annual world production of 21 million tons of aluminum corresponds to 82 million tons of red mud waste, so that new applications of this industrial residue are urgently needed. Construction materials such as cements, lightweight aggregates and geopolymers are considered interesting solutions for red mud safe disposal [2]. The present study aimed to use red mud as the only Al source and to eliminate the use of relatively expensive Na-silicate activating solu tion This was supported by the use, as silica source, of soda lime glass (SLG) from urban waste collection. The specific waste glass fraction employed, where plastic and ceramic impurities are concentrated, is currently mostly landfilled [6]
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