Synthesis and characterization of coal fly ash and palm oil fuel ash modified artisanal and small-scale gold mine (ASGM) tailings based geopolymer using sugar mill lime sludge as Ca-based activator

Abstract

The continuous accumulation of artisanal and small-scale gold mining (ASGM) tailings in the Philippines without adequate storage and disposal facility could lead to human health and environmental disasters in the long run. In this study, ASGM tailings was simultaneously stabilized and repurposed as construction material via geopolymerization using coal fly ash, palm oil fuel ash and a powder-based alkali activator. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) identified iron sulfides in the tailings containing arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn), which could be released via weathering. The average unconfined compressive strengths (UCS) of tailings-based geopolymers at 14 days curing were 7.58 MPa and 7.7 MPa with fly ash and palm oil fuel ash, respectively. The tailings-based geopolymers with palm oil fuel ash had higher UCS most likely due to CASH reaction product formation that improved strength formation. The toxicity characteristic leaching procedure (TCLP) results showed very low leachabilities of As, Pb and Fe in the geopolymer materials suggesting ASGM tailings was effectively encapsulated within the geopolymer matrix. Overall, the geopolymerization of ASGM tailings is a viable and promising solution to simultaneously stabilize mining and industrial wastes and repurpose them into construction materials.

Arsenic(V) Immobilization in Fly Ash and Lead-Zinc Mine Tailing-based Geopolymer: Performance and Mechanism Insight

“…This observation can be explained by the fact that the specimen with the least As V content (i.e., FMA10G-02a) holds the maximum amorphous phases (Figure 4a), which are more reactive than the crystalline phases in specimens with higher As V content (i.e., FMA10G-02b, and FMA10G-02c, see Figure 4a) to react with CO2 in the air to form the surface CaCO3. Given the above results, As V is likely to be immobilized in the geopolymer gels by physical encapsulation after curing for a short period (e.g., 2 -7 days), 20,[22][23] and then to be incorporated into the crystalline minerals (e.g., calcium silicate and CSH) during the phase transition processes as a result of prolonging the curing time.…”

Arsenic(V) Immobilization in Fly Ash and Lead-Zinc Mine Tailing-based Geopolymer: Performance and Mechanism Insight

“…by alkali activation has been demonstrated to be an effective alternative to immobilize arsenic into the geopolymer matrix. [18][19][21][22][23] Geopolymer binders derived from both the alkali activation of coal fly ash 21 and the high-energy ball milling activation of granulated lead smelting slag 22 have shown excellent ability to stabilize the municipal solid waste incinerator fly ash (MSWI FA) with high arsenic content. Recently, it was reported that red mudmetakaolin (MK) based geopolymer shows a good arsenic retention capability as well as a high compressive strength (~ 15 MPa), making it an environmentally friendly backfilling material for sustainable remediation of arsenic pollution.…”

“…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.…”

“…Besides, since the geopolymer has high compressive strength (> 7.5 MPa), it can also be used as construction materials. 23 While many studies have demonstrated that geopolymer matrix plays a crucial role in the immobilization of arsenic wastes, the underlying mechanisms remain poorly understood due to the contradictory results that have often been presented. During the geopolymerization process, arsenic can react either with calciumrich components to form calcium arsenate precipitates, with Friedel's salt to yield As-Friedel's salt mineral, or with the geopolymer gels (e.g., calcium silicate hydrate (CSH), calcium aluminum hydrate (CAH)) to form surface complexes.…”

Fresh mechanical and durability properties of alkali-activated fly ash-slag concrete: a review

“…It forms a dense matrix exhibiting excellent engineering properties. The main products formed in a low calcium system are sodium-aluminosilicate-hydrate gels with pseudo-zeolite structures [11,[13][14][15].…”