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Synthesis and Characterization of Metakaolin–Wollastonite Geopolymer Foams for Removal of Heavy Metal Ions from Water

Year: 2025

Type: article

Abstract: Over the past few decades, researchers have focused on developing new compositions and preparation techniques for geopolymers, as multifunctional products, to optimize their characteristics for use in multiple applications. Therefore, this paper investigates metakaolin geopolymer foam and introduces new geopolymer foams based on hybrid metakaolin and wollastonite mineral precursors for water purification. The geopolymer foams were prepared using an alkaline activator, mineral-based powders (wollastonite and metakaolin), a foaming agent (aluminum powder), and a foam stabilizer (olive oil). In addition to mechanical tests and assessments of the adsorption capacity of heavy metal ions, the geopolymer foams were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The geopolymer foams exhibited unique pore structures, containing four classes of pore networks with diameters around 1000 µm, 25 µm, 3 µm, and a well-arranged mesopore network of 50 nm. The utilization of wollastonite (CaSiO3) alongside metakaolin as a hybrid precursor led to fundamental changes in the composition of the geopolymer binders: a new crystal phase, Ca5(SiO4)2(OH)2, was formed, and the Si-Al-Na crystal phase disappeared, which led to an increase in the amorphous phase from 87% to 92%. The adsorption rate of heavy metal ions, namely Cr, Co, Cu, Zn, Pd, and As, increased upon introducing wollastonite as a precursor, with absorption rates ranging from 11% to 68%. The findings also revealed that wollastonite significantly increased the geopolymers foams’ compressive strength and elastic modulus from 30 KPa to 67 KPa and from 31 MPa to 126 MPa, respectively.

Source: Materials

DOI: 10.3390/ma18030678

Authors: Mazen Alshaaer, Bader Alharbi, Obaid Alqahtani, Mohammed S. Alotaibi, Abdullah Alzayed, Juma’a Al-Kafawein

Institutions: Vrije Universiteit Brussel, Prince Sattam Bin Abdulaziz University, King Faisal University

Language: English

Topic: Concrete and Cement Materials Research

Subfield: Civil and Structural Engineering

Field: Engineering

Domain: Physical Sciences

SDG: Responsible consumption and production

Open Access status: gold

Estimated APC paid: $3,137