This work investigates how silica and lignocellulose additives affect the production of metakaolin based-geopolymer foam filters. Lignocellulosic material from wood powder sawdust (S), silica from rice husk ash (RHA), calcined (Sa) and uncalcined (Sab) sand were separately used together with high amorphous silica fume (foaming agent) and integrated into the matrix (metakaolin and solution). The different geopolymer pastes were cured at 70 °C to enhance the pore formation. Results presented the

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... eopolymer foams filter as sponge-like composites having 58-68% of porosity with 1-4 MPa of compressive strength. RHA and Sa lead to materials with more meso and macropores. Sawdust based-geopolymer (the hardest foam) containing channel pores predominated by coarse pores exhibited a flow rate of 4 mL min −1 . The absence of the bands of MB from FT-IR spectra and UV spectra (663 nm) of MB filtrate (totally blue discoloured) indicated that, geopolymers foams filters designed are suitable for dyes and wastewater filtration. Graphic abstract Keywords Meso and macro pores · Silica · Lignocellulosic · Geopolymers · Foams · Filters Various methods of producing porous geopolymers have been reported by many researchers. The usage of by-products (rice husk ashes, sawdust, cotton stalk fiber) to improve pore-related properties such as density, microstructure, and thermal conductivity is well established [13, [15] [16] [17] [18] [19] [20] . For example, Tene et al. [13] and Ngouloure et al. [14] demonstrated that lightweight metakaolinbased geopolymers reinforced by sawdust and rice husk ash exhibited good properties for thermal insulation application, respectively. Rasouli et al. [21] introduced polylactic acid fibers with different diameters to fabricate well-aligned microporous metakaolin based geopolymer by extrusion method. Their results revealed that porous bodies synthetized with smallest polylactic acid fibers diameter exhibit higher water permeability. In addition, another classes of pore-forming agent commonly used in geopolymer technology is silica fume [22] [23] [24] [25] . Silica fume is a micro silica by-product derives from the production of silicon and ferrosilicon alloys through the reduction of high pure quartz with coal in electric furnace [23] .This technique offers the advantage to allow sponge-like structure through dihydrogen generation in alkaline medium from the reaction between free silicon (in silica fume powder) with alkaline solution [22] .