Utilization of Palm Oil Fuel Ash (POFA) as an Admixture for the Synthesis of a Gold Mine Tailings-Based Geopolymer Composite

Abstract

The repurposing of gold (Au) mine tailings from artisanal and small-scale mining (ASGM) operations via alkali activation technology is a promising strategy for waste reduction in developing countries. Direct activation of mine tailings, however, is challenging because these materials contain relatively low aluminum (Al)-bearing minerals. In this study, palm oil fuel ash (POFA) was elucidated as a high Al-bearing waste derived-admixture for the synthesis of an ASGM tailings-based geopolymer composite. Semi-quantitative XRD analysis showed that the tailings contained quartz (SiO2) (~58%), pyrite (FeS2) (~20%) and calcite (CaCO3) (~15%) with minor to trace amounts of aluminosilicates (~7%). Substantial amounts of environmentally regulated pollutants such as mercury (Hg) (40 mg/kg), lead (Pb) (8430 mg/kg) and arsenic (As) (300 mg/kg) were also found in the tailings. SEM-EDS, XRD and ATR-FTIR results showed the successful formation of a hybrid geopolymer-CASH matrix, which improved the unconfined compressive strength (UCS) of geopolymer composites from ~5 MPa to ~7 MPa. Furthermore, POFA did not significantly affect the thermal resistivity of geopolymer composites based on thermal analysis. Finally, the TCLP results showed that the Pb leaching concentrations from ASGM tailings exceeded environmental standards (~15,000 µg/L), which was suppressed after alkali activation to 300–500 µg/L. This means that POFA addition to ASGM tailings-based geopolymer composite improved not only its applicability as backfill, pavements and bricks but also its ability to immobilize toxic elements.

Characterization of Bulgarian Copper Mine Tailing as a Precursor for Obtaining Geopolymers

“…Qing et al [8] produced geopolymer concrete with a compressive strength of 47.6 MPa using the alkali-hydrothermal activation of quartz powder at 300 • C. Although it meets 42.5 cement standards, high temperatures may hinder its sustainability. Orozco et al [9] developed sustainable bricks by activating gold mine tailings with NaOH or (CaOH) 2 and curing at 80 • C. Opiso et al [10] found that adding 10% palm oil fuel ash to gold mine tailings-based geopolymer bricks improved their mechanical qualities and allowed for room-temperature curing, resulting in cost and CO 2 emission savings. However, creating geopolymers with suitable mechanical characteristics using MTs as raw materials is challenging due to the large number of nonreacting phases, particularly quartz.…”

Mineralogy, Geochemistry and Environmental Hazards of Different Types of Mining Waste from a Former Mediterranean Metal Mining Area

“…Nevertheless, due to the enrichment of metal mining waste in certain chemical elements of interest, in some cases, this waste could be reused as a source of raw materials for further uses, e.g., in nanomedicine [12]. The revalorization of metal mining waste using new technologies is a promising strategy for its quantitative reduction [13], as well as for the effective recovery of some elements contained in these tailings [12]. In this sense, the goal of reusing industrial waste and moving towards waste-free production is a trend that is likely to become the norm in the medium to long term, both because of the need for mineral raw materials and the depletion of their main deposits [10,14].…”

Effect of Wet–Dry Cycling on Properties of Natural-Cellulose-Fiber-Reinforced Geopolymers: A Short Review

“…The inorganic silica-alumina cementing material has a threedimensional network structure. The commonly used active silicate raw materials include fly ash [5,6], refined blast furnace slag [7] and other wastes, such as red mud, rice husk ash, and some mine tailings [8][9][10]. All kinds of geopolymers with excellent properties have been prepared.…”