Search

The phosphate mining industry produces large amounts of waste rocks during the open-pit mining operation. In the present paper, phosphate waste rocks, abundant in different regions of Morocco, are investigated as a candidate material for partial/entire replacement of conventionally used industrial minerals. Several recipes for the production of tiles are tested, based on raw materials from five representative phosphate waste rocks mine sites and a raw clay from Safi's region in Morocco. The phosphate waste rocks are shown to be mainly composed of phyllosilicates (smectite, sepiolite, and palygorskite), carbonates (dolomite and calcite), and silica frameworks (quartz, tridymite, and cristobalite) as major phases. The raw samples and calcined mixtures were characterized by using X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD), thermogravimetric analysis (TGA), and Fourier transformed infrared spectroscopy (FTIR). Properties analyses revealed that the produced ceramic tiles can be classified as porous bodies. The tiles based on 100% of phosphate waste rocks have shown excellent mechanical properties (∼55 MPa) in terms of compression and they can be used in the traditional wall tiles called "Zellige" in Morocco. [ABSTRACT FROM AUTHOR]

• Phosphate mining wastes rocks as a promising secondary resource material in civil engineering. • Depper understanding of alkali activation of Phosphate mining waste rocks from the cover layer. • Phase composition investigated through MAS NMR-based analyses. • Formation of various hydration products, including C S H, C-(A)-S H, N-(A)-S H and C-(N)-A S H gels. This study details the effect of silica modulus variation (SiO 2 /Na 2 O 1.25, 1.50 and 1.75) on the mechanical properties and the microstructure evolution of Alkali Activated Materials (AAM) based on phosphate mining waste rocks and issued from the cover layer. The mechanical behavior of samples was assessed by compression and flexural strength tests at 7 and 28 days of curing. A resulting highly compact microstructure was formed by decreasing the silica modulus (Ms), leading to an enhancement of the mechanical strength. The microstructure of hardened specimens was studied using X-ray Diffraction (XRD), Fourier Transform InfraRed (FTIR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray spectroscopy (EDX) and 29Si, 27Al, 23Na Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The results show the formation of C S H gels as main reaction products, C–(A)–S H and N–(A)–S H gels, with the possible formation of a hybrid C–(N–A)–S H gels. The structure of these formed gels appears to depend on the raw material's chemical composition, as confirmed by MAS NMR and SEM/EDX analysis. These results provide insight in alkali activation of phosphate mining waste from the cover layer, which can promote their valorization in several construction applications, and consequently, contribute to sustainable phosphate mining.. [ABSTRACT FROM AUTHOR]