Solidification of (Pb–Zn) mine tailings by fly ash-based geopolymer I: influence of alkali reagents ratio and curing condition on compressive strength

Abstract

Fly ash-based geopolymer is a crucial application for tackling climate change, limiting the production of greenhouse emissions. The main aim of this study was to determine the effect of the fundamental parameters on compressive strength to ensure a feasible and effective solidification of mine tailings. Three sodium hydroxide (NaOH) molarities (5, 8, and 10 M) and sodium silicate (Na 2 SiO 3 ) were combined to form the alkaline solution. Four fly ash (FA) proportions (28%, 44%, 54, and 61%) of the dry mix and mine tailings (MT) were utilized as raw materials. This study demonstrated that both 25 °C and 65 °C have a considerable effect on the mechanical properties of geopolymers. The UCS value increased with an increase in NaOH molarity. In addition, the highest Unconfined Compressive Strength (UCS) value was achieved (36.04 MPa) at 10 M. Furthermore, the results also showed that UCS values kept decreasing with the increase of SiO 2 /Al 2 O 3 and Na 2 O/ SiO 2 ratios. The optimal UCS values found were in the range of 0.28-0.38 liquid/solid ratio. It has been concluded that the previously mentioned parameters have a strong influence on the mechanical strength of fly ash-based geopolymer with the new proposed FA proportion.

Arsenic(V) immobilization in fly ash and mine tailing-based geopolymers: Performance and mechanism insight

“…31 These will in turn lead to faster geopolymer formation, and thereby increase the geopolymer compressive strength. The UCS improvement with NaOH concentration has also been observed previously, 27,[31][32][33][34] especially in mixtures with a large number of amorphous aluminosilicate phases. 32,35 This observation is also validated in the present study that the activation of the FA/MT mixtures with 10 M NaOH resulted in the highest UCS (i.e., 35.52 and 37.07 MPa for 7-day and 28-day UCS, respectively) when the mixture with FA content as high as 54 wt.% was used (Figures 1a and S2b).…”

“…This is because FA particles contain more amorphous phases than the MT powder and are thereby more reactive to the NaOH solution. 27 It is of interest to note, however, that the UCS value of geopolymer specimen activated with 10 M NaOH is lower than that activated with 8 M NaOH in the case of geopolymers with 28 wt.% of FA (Figures 1a and S2). This can be explained by the negative effect of excess NaOH on geopolymer formation which has also been observed previously.…”

“…The physicochemical characteristics of both the FA and the MT can be found elsewhere. 27 The GY consists of kidney bean-shaped gypsum (CaSO4‧2H2O, JCPDS #33-0311) powders of size ranging from ~ 10 to ~ 55 μm (see Figure S1 in the Supporting Information).…”

“…41 Our previous work has also confirmed that curing at 65 °C can improve the overall strength of the geopolymer specimens as compared to those cured at 25 °C. 27 Therefore, the effect of curing time on UCS in this study was investigated by evaluating the compressive strength of specimens cured at 65 °C for different curing times. Geopolymer specimens prepared with varying FA and As V contents, NaOH concentrations, and cured for 7, 14, and 28 days were evaluated and the results are presented in Figure 2b−d.…”

“…24 Compared to metakaolinbased geopolymers, mine tailing-based geopolymers have a lower carbon footprint, making them more desirable for use as building materials and as a matrix for immobilizing toxic wastes. 23,[25][26][27] For instance, when using sugar mill lime sludge as a Ca-based activator, it was suggested that coal fly ash and mine tailing-based geopolymer can effectively stabilize the mine tailings with high levels of arsenic and heavy metals. Besides, since the geopolymer has high compressive strength (> 7.5 MPa), it can also be used as construction materials.…”