Evaluation of Flue Gas Desulfurization (FGD) Waste Potentiality from Coal-Fired Power Plants to Obtain Alkali-Activated Materials

The sulfur dioxide removal in thermoelectric plants occurs through flue gas desulfurization (FGD), which produces waste that needs to be correctly disposed of. This exploratory research aims to characterize waste obtained from an FGD plant in Candiota, Rio Grande do Sul, Brazil, and evaluate its potential as alternative mineral source in obtaining alkali-activated materials (AAM). The dried and processed waste was called FGD-D, and AAM was produced by mixing FGD-D with sodium-based alkaline activating solutions. The amounts of FGD at formulations ranged from 31.6 (F1) to 38.9 wt.% (F4), and the use of metakaolin was not necessary. The results show that the chemical composition of FGD-D is composed mainly of calcium oxides (38 wt.%), sulfur (22 wt.%), and silica (19 wt.%). Crystalline phases and a high amorphous fraction were identified in the residual samples. The use of FGD-D in AAM proved to be an alternative mineral source, showing an exothermic reaction with subsequent rapid hardening and increased compressive strength values ranged from 7.7 ± 1.3 Mpa for F1 to 14.4 ± 1.8 Mpa for F4 at seven days. The results demonstrate the potential of using FGD-D in AAM formulations, opening positive perspectives for a more sustainable destination for these residual materials.