abstract
In this study, and for the first time, red mud (RM)-based geopolymer spheres were synthesised, with varying porosity and RM content, and then their use as pH regulators was evaluated. The aluminosilicate sources of these inorganic polymers were 100% waste-based, consisting of a mixture of RM and fly ash wastes. Geopolymer spheres containing up to 60 wt.% RM were successfully produced, while higher RM contents distorted the specimens' spherical shape. Results showed that alkalis leaching from the spheres over time can be controlled by their porosity, while the RM content induces only minor changes to leaching. The RM-based spheres leached up to 0.0237 mol/dm(3)g of OH- ions from their structure, this being among the highest values ever reported for geopolymers. This allowed a continuous and prolonged pH buffer capacity with narrow pH decay over the 28 days (2.4 pH units), suggesting the use of the RM-based spheres as pH buffering materials in wastewater treatment and anaerobic digestion systems.
keywords
CONTINUOUS ANAEROBIC-DIGESTION; ASH-BASED GEOPOLYMERS; FLY-ASH; BUFFER CAPACITY; WASTE; REMOVAL; MICROSTRUCTURE; WASTEWATERS; HYDROLYSIS; MONOLITHS
subject category
Engineering; Environmental Sciences & Ecology
authors
Novais, RM; Carvalheiras, J; Seabra, MP; Pullar, RC; Labrincha, JA
our authors
João António de Sousa Carvalheiras
PhD Student
João António Labrincha Baptista
Full professor
Maria Paula Seabra
Assistant Professor
Rob Pullar
Collaborator
Rui Miguel Novais
Assistant Professoracknowledgements
This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID /CTM /50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. R.C. Pullar thanks the FCT for funding under grant IF/00681/2015.