Mineral Waste Geopolymeric Artificial Aggregates as Alternative Materials for Wastewater-Treatment Processes: Study of Structural Stability and pH Variation in Water

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Abstract
Artificial aggregates produced from mine waste geopolymeric binders were studied as a potential substrate for fixed-film wastewater-treatment processes (biofilm reactors). Waste geopolymeric artificial aggregates (WGA) of 2–3 cm in size were produced using geopolymeric mine waste mud as a precursor and both sodium silicate and sodium hydroxide as alkaline activators. Seven mixtures were produced with different atomic ratios of sodium silicate to sodium hydroxide (S/H) and of precursor (waste mud) to sodium silicate (P/S), using curing temperatures of 20°C and 130°C, for a total of 112 samples. Structural stability and pH variation after immersion in water were observed over an 18-week period. The results showed that the initial water pH decreased with the increase of the curing time, taking between 17 and 42 days to reach pH 8. The mixture cured at 20°C for 28 days appears to be suitable for use as a substrate for biofilm reactors because the initial water pH was one of the lowest (approximately p...