Abstract
The mining industry generates large quantities of waste as tailings. The tailings have an adverse environmental impact. This study explored the utilization and stabilization of Barberton gold mine tailings (GMTs) and basic oxygen furnace slag (BOFS) to synthesize geopolymers for other applications. The geochemical, chemical, and geotechnical properties of GMT, BOFS, GMT geopolymer, and GMT: BOFS geopolymer were also studied. Sodium hydroxide (NaOH) and potassium hydroxide (KOH) were used as alkaline activators. The highest unconfined compressive strength (UCS) recorded for GMT geopolymers cured for 5 days at the elevated temperature of 90°C was 4.31 MPa and 6.59 MPa for NaOH and KOH, respectively. GMT: BOFS geopolymer attained the UCS of 20.0 MPa and 25.7 MPa, with NaOH and KOH, respectively, at the same curing conditions. Characterization of the binders showed that BOFS was a good source of calcium, which had a positive effect on the geopolymer gels by balancing the ionic charges. The developed GMT: BOFS geopolymers satisfied the minimum requirements for nonfacing building masonry as stipulated by the ASTM C34-17a, ASTM C129-14c 0076a, and the SANS 227: 2007 for burnt clay masonry units and can be used as a mine backfill paste and for lightweight civil applications. The geopolymers passed the toxicity characteristic leaching procedure (TCLP), and the results yielded low heavy metals concentration, indicating that the geopolymers will not leach to the environment.
Highlights
Mine tailings are the major wastes generated by the mining industry. is waste is commonly landfilled as mine dumps.e major challenge with landfilling is the environment due to water and soil contamination and air pollution
In South Africa, there are more than 500 gold mine tailings (GMTs) occupying the land, with adverse effects on the environment. ree methods have been reported as solutions to reduce the environmental impacts posed by mine tailings: (1) isolation of mine, (2) chemical stabilization of mine tailings, and (3) a combination of these two methods [2, 3]. e isolation of tailings entails techniques such as tailings capping the confinement of the tailings by constructing a system with a closure similar to that of landfills [4]
In the chemical stabilization process, the heavy metals are mobilized by introducing cementitious materials or chemicals into mine tailings [1]. is process can be conducted through chemical reactions and/or physical encapsulation [1]
Summary
Mine tailings are the major wastes generated by the mining industry. is waste is commonly landfilled as mine dumps. In South Africa, the iron World Steel Association production statistics showed a generation of up to 37 million tons of blast furnace slag over a 12 year period [23] Both GMT and BOFS contaminate the environment because of the pollutants in the material. Granulated blast furnace slag was alkaline activated by NaOH and KOH to develop a building and construction material [26]. Fly ash and ground granulated blast furnace slag were used to develop a geopolymer paste, using NaOH and sodium silicate (Na2SiO3) as an activator [28]. Geopolymers were synthesized from alkaline activation of gold tailings using cement, NaOH, and Na2SiO3 [33]. E other reported studies show the addition of cement in the mix design and pretreating gold tailings at elevated temperatures, which is energy intensive. E readily available GMT used in this study had an alumina silicate ratio of 4.75; this makes geopolymerization of tailings a sustainable solution to deal with GMT waste. e developed geopolymers were evaluated for potential environmental impact. is study presents the holistic beneficiation of two materials, which contribute to environmental pollution and provide a novel solution for alternative cost-effective and environmentally friendly building materials
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