Development of Sustainable Composite Construction Materials from Platinum Group Metals Furnace Slag

Abstract

Waste from mining activities is considered to contribute mostly to the total global waste streams with an annual estimate of over one hundred billion tonnes. Platinum Group Metals mining companies in Zimbabwe generate a significant amount of waste annually, and a continuous increase in waste generation is anticipated due to the expansion of mining activities. This work focuses on mining waste management, targeting PGM furnace slag to make sustainable composite construction materials, particularly bricks. Earth-based clays namely Zvishavane clay (ZC) and Chinhoyi clay (CC) were employed as binders for the slag. Several characterization techniques including, x-ray fluorescence, sieve analysis, specific gravity, and atterberg limits were conducted on the raw materials. The elemental analysis of PGM slag revealed no traces of harmful heavy metals making it safe for use in brick manufacturing. The following PGM slag weight percent combinations were prepared: 0wt.%, 20wt.%, 40wt.%, 50wt.%, and 60wt.%. A manual method was adopted to produce laboratory-scale bricks from a mold of dimensions 230 mm × 115 mm × 75 mm. The bricks were naturally dried and fired at 950 ℃, 1000 ℃, 1050 ℃, and 1100 ℃ in an electric kiln for each defined combination. The physical and mechanical properties of the fired bricks were assessed for their appropriateness in construction through the following tests: compressive strength, water absorption, soundness, hardness, and efflorescence. The compressive strength test results for the defined combinations and firing temperatures ranged from 5.6 MPa to 11.2 MPa for ZC as the binder and 5.4 MPa to 10.1 MPa for CC as the binder. The water absorption test results for the specified xii combinations and firing temperatures ranged from 7.1% to 11.5% for ZC as the binder and 10.1% to 11.8% for CC as the binder. The optimum brick properties were achieved with 50wt.% slag combination, 10.7% forming water, and 950 ℃ firing temperature with ZC employed as the binder. The optimum compressive strength and water absorption percentage reported from this study were 11.2 MPa and 7.1%, respectively. The bricks revealed positive efflorescence results owing to the existence of Fe and CaO in the raw materials. The compressive strengths and water absorption test results complied with the standard guidelines by ASTM and IS, suggesting that PGM slag can be recycled to make bricks acceptable in the construction industry. Recycling PGM slag in developing sustainable composite construction materials can be the most feasible solution to the disposal challenges.