Elaboration of geopolymers based on clays by-products from phosphate mines for construction applications. (10th July 2020)

• Record Type: Journal Article
• Authors: Mabroum, S.; Aboulayt, A.; Taha, Y.; Benzaazoua, M.; Semlal, N.; Hakkou, R.
• Is Part Of: Journal of cleaner production. Volume 261(2020)
• Publication Date: 2020-07-10
• Subjects: Phosphate mines -- Mine waste -- Clayey lithology -- Valorization -- Geopolymers -- Circular economy; Factory and trade waste -- Management -- Periodicals; Manufactures -- Environmental aspects -- Periodicals; Déchets industriels -- Gestion -- Périodiques; Usines -- Aspect de l'environnement -- Périodiques; 628.5
• DOI: 10.1016/j.jclepro.2020.121317
• Languages: English
• ISSNs: 0959-6526

Abstract

Abstract: Yellow clays from Moroccan phosphate mines are extracted with other waste rocks lithologies and stored in large dumps within the mine site. The present paper investigates the use of this by-product as a new aluminosilicate source for geopolymers elaboration at the laboratory scale. Yellow clays studied are mainly composed of montmorillonite, dolomite and quartz as major phases. The Toxicity Characteristic Leaching Procedure (TCLP) showed no existence of contaminant. In order to reach thermal activation, the raw clays were first calcined at different temperatures between 500 and 900 °C. Raw and calcined clays were characterized using thermogravimetric analysis (TGA), X-Ray Diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. For the synthesis of geopolymers, calcined powder was mixed with an alkaline solution presenting different NaOH/Na2 SiO3 ratios. The compressive strength was measured at 7, 14 and 28 days and material porosity was determined using Mercury Intrusion Porosimetry method in order to explain the mechanical behavior. XRD, 27 Al and 29 Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopy, Fourier transformed infrared and TGA have been used to investigate the gel structure. The thermal treatment at 900 °C allowed the destruction of crystalline structure of montmorillonite clays, as well as the formation of new phases such as periclase (MgO) and gehlenite (Ca2 Al2 SiO7 ). Furthermore, the 27 Al - 29 Si MAS-NMR and the XRD analysis of the elaborated materials confirmed the formation of two cementitious gels C-A-S-H (Calcium aluminum silicate hydrate) and N-A-S-H (Sodium aluminum silicate hydrate). The compressive strength was around 25 MPa at 28 days. The obtained results are promising; they have shown that elaborated materials can be adapted for construction applications. In this case, it is recommended that economic and commercial study be developed. Graphical abstract: Image 1 Highlights: Yellow clays by-products from Moroccan phosphate mines were studied as a precursor for the synthesis of geopolymers. The temperature of activation of yellow clay was 900 °C. Formation of two type of gels after alkali activation. The compressive strength reached 25 MPa after 28 days of curing at ambient temperature.