Recycling of Waste Corundum Abrasive Powder in MK-Based Geopolymers

Abstract

Recycling corundum abrasive powder in metakaolin-based geopolymer formulations is proposed to reduce the amount of waste to be treated or disposed of in landfills, allowing to decrease ecological damage as well as to reduce transport costs for removal. The addition of waste corundum, as an important source of Al2O3, has proved to increase the slightly ionic conductivity of the leachate solution obtained after immersion in water of samples at 28 d of curing at room temperature. With the same curing conditions, the geopolymerization process has not been disturbed as evidenced by the FT-IR peak shift and XRD patterns. It was recorded a decrease in resistance to compression of the consolidated geopolymers of about 5% with 10 wt% addition and of about 77% with the addition of 20 wt% of waste corundum. In any case, the waste abrasive powder does not release heavy metals when added to a geopolymeric formulation based on MK, NaOH, and Na-silicate, and does not show relevant antibacterial properties, indicating the formation of a stable and safe final product with a ceramic-like appearance.

Entrapment of Acridine Orange in Metakaolin-Based Geopolymer: A Feasibility Study

“…Indeed, as the geopolymerization occurred, the band at 1090 cm −1 assigned to the asymmetric stretching of Si-O-T (T = Si or Al) shifted at 1017 (7 days) to 1011 cm −1 (58 days, Figure 3 A) in the GP sample. This shift has been already explained in the literature by the substitution of Si by Al atoms in the 3D network [ 36 , 40 , 41 ]. The bands at 820 cm −1 and 880 cm −1 were assigned to Al(IV)-OH and Al(IV)-O- vibrations, whereas the signal at 465 cm −1 was assigned to Si-OH symmetric bending [ 42 , 43 ].…”

“…The antibacterial test was performed by the Kirby–Bauer method [ 35 ] on S. aureus (Gram-positive) and E. coli (Gram-negative) microbial strains. The whole adopted procedure can be described in five steps: (i) agar-based media preparation, (ii) sample preparation and sterilization, (iii) bacterial strain preparation, (iv) bacterial incubation, and (v) inhibition halo diameter (IHD) and bacterial viability (BV, %) measurements [ 36 ].…”

Chemical and Mechanical Properties of Metakaolin-Based Geopolymers with Waste Corundum Powder Resulting from Erosion Testing

“…Aside from automotive or naval paint sludge and other liquid waste from sand- and grit-blasting technologies, solid grit (abrasive particles) contaminated with various types of materials has been added to cement formulations since 1991 [ 9 ], with the aim of reducing the instruction of fine aggregates such as sand [ 10 , 11 , 12 , 13 ]. The valorization of abrasive waste powders in AAM formulations in the literature has also been reported for waste garnet abrasive powders generated from automated and manual blasting process [ 14 , 15 ], corundum abrasive powders [ 16 ], and corundum containing powders [ 17 ]. The observed role of these abrasive powders was, in most cases, to be that of an inert filler, even though in some cases limited reactivity was observed, specifically of the fine abrasion residues [ 16 ].…”

“…The valorization of abrasive waste powders in AAM formulations in the literature has also been reported for waste garnet abrasive powders generated from automated and manual blasting process [ 14 , 15 ], corundum abrasive powders [ 16 ], and corundum containing powders [ 17 ]. The observed role of these abrasive powders was, in most cases, to be that of an inert filler, even though in some cases limited reactivity was observed, specifically of the fine abrasion residues [ 16 ]. Moreover, there are some studies [ 18 , 19 ] that reported that reactive alumina forms when added to AAMs, exploiting the advantage of partial solutions in alkaline media.…”

“…With this investigation, we intend to valorize, as a partial reactive filler, a spent abrasive corundum powder up to 20 wt% to a metakaolin-based geopolymer binder. In a previous preliminary study [ 16 ], we selected a coarse grain grit (average grain size of about 230 µm) composed mainly of corundum, Al 2 O 3 , which was substituted to MK in the mix design, and showed advantages in terms of increased mechanical resistance. With the same objective, hereafter, we presented the results that were collected for a finer spent corundum grit (52 µm) that was either added as well as substituted to the MK source; once again, metakaolin was considered to be a reference aluminosilicate powder suitable for understanding the role of the waste and its impurities during alkali activation.…”