Effect of NaOH-treated sawdust incorporated in geopolymer matrix on compressive strength and adsorption property

Abstract

Sawdust is a multifunctional renewable biomaterial that can be incorporated into several materials to improve their properties. In the present work, the effect of sawdust incorporation in a geopolymer matrix on the compressive strength and porosity of the synthesized composite was investigated. A prior chemical treatment of sawdust with sodium hydroxide was performed to improve its compatibility with the geopolymer matrix obtained from reaction between metakaolin and sodium waterglass. Characterizations revealed an effective geopolymerization regardless the amount of sawdust added (from 0% to 10%). Compared to untreated sawdust which causes a decrease of the compressive strength, an increase of the compressive strength of the geopolymer was observed in the presence of the treated lignocellulosic material (63.04 MPa at 0% to a maximum of 75.22 MPa at 2%) followed by a decrease for higher sawdust percentage (48.48 MPa at 10%). This result confirmed the beneficial effect of the alkaline treatment of sawdust. Methylene blue (MB) was used as model cation in order to evaluate geopolymer composite porosity for cationic pollutants adsorption. Adsorption rate was found to increase with sawdust percentage in the composite, highlighting the positive effect of sawdust particles in pollutant diffusion within the network of composite materials. The diffusion coefficients increased with the percentage of sawdust in the composite materials. Preliminary work on cobalt(II) adsorption revealed good performances marked by higher and comparable adsorption capacities (in the range 0.82 to 0.90 mmol g⁻¹) regardless the amount of sawdust used in the composite.