Acidic industrial wastewater requires effective pH adjustment prior to discharge or reuse. The use of unground biomass ash as a geopolymer binder offers potential benefits in reducing processing energy and costs while promoting industrial waste utilisation. This study investigates geopolymer binders produced from unground palm oil fuel ash and fly ash for wastewater acidity reduction. Geopolymer mortars were synthesised using sodium hydroxide (NaOH) concentrations of 10–16 M, cured at 65°C for 24 h, and air cured. Compressive strength was evaluated at 3, 14, 28, and 56 days. Acid neutralisation performance was assessed by immersing geopolymer specimens in hydrochloric acid (HCl) with an initial pH of 3, including a single-cycle test at 28 days and repeated exposure over 15 cycles with pH measured after 24 h. Results showed that compressive strength increased with NaOH concentration up to 14 M but slightly declined at 16 M. The acidic solution pH increased above 9 within 24 h, with the 14 M mixture exhibiting the highest neutralisation efficiency. Although pH gradually decreased over cycles, geopolymer mortars consistently maintained alkaline conditions and outperformed conventional cement mortar under repeated acidic exposure. The use of unground palm oil fuel ash eliminates grinding and reduces energy consumption.
Chalee et al. (Sat,) studied this question.