Foamed phosphate by-product based geopolymers and dye adsorption efficiency

• Published in: Applied clay science Vol. 257; p. 107446
• Main Authors: Karoui, Oumaima, Andrejkovičová, Slavka, Pato, Pedro, Patinha, Carla, Řimnáčová, Daniela, Perná, Ivana, Hajjaji, Walid, Rocha, Fernando, Mlayah, Ammar
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-09-2024
• Subjects: Adsorption; Calcined phosphate sludge; Foamed geopolymer; Heavy metal; Metakaolin; Metakaolin; Calcined phosphate sludge; Foamed geopolymer; Adsorption; Heavy metal
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2024.107446

This study aimed to evaluate the efficiency of incorporating Tunisian calcined phosphate sludge into the alkali activated metakaolin geopolymers to use them not only as recycling products for building materials but also as adsorbents in water treatment. Calcined phosphate sludge based geopolymers exhibited compressive strength ranging from 24.8 to 33.8 MPa, with specific surface areas of 16.3–16.9 m2/g. On the other hand, the hydrogen peroxide foamed geopolymers showed an increase in porosity and in specific surface area (close to 25 m2/g). Improved dye adsorptive capacity of geopolymers achieved a 99.9% removal rate of methylene blue within 60 min. Following Langmuir isotherm and pseudo-second-order kinetic, the adsorption of the dye in solution occurred in a monolayer on homogenous surface with chemical interaction between the adsorbate and adsorbent. With the 40% of phosphate sludge foamed geopolymers, higher adsorption capacity was achieved (Qmax = 43 mg/g). This efficiency was attributed to its mesoporous structure (calculated porosity: 43%). On the other hand, pure metakaolin geopolymers showed the weakest adsorption capacity. The reaction between phosphate sludge, unreacted NaOH and hydrogen peroxide seemed to have enhanced porosity. The obtained results demonstrated the efficiency of these mining foamed sludge based geopolymers in dye effluents treatment and immobilization of contained heavy metals.
•Increase in pore volume and specific area of foamed phosphate sludge geopolymers.•Compressive strength of unfoamed geopolymers close to Portland cement (≈30 MPa).•Increasing porosity by H2O2 caused a lower compressive strength (6–8 MPa).•40% of calcined sludge geopolymers exhibited an optimum MB adsorption capacity of 43 mg/g.•Geopolymers effectively immobilized all sludge contained heavy metals, except arsenic.