title: Phosphate sludge: thermal transformation and use as lightweight aggregate material.
abstract: Phosphate sludge generated from beneficiation plants of Moroccan phosphate rocks was investigated at 900-1200 °C by X-ray diffraction, scanning electron microscopy, thermal analysis and Fourier-transform infrared spectroscopy. Mixtures of the phosphate sludge and a swelling clay (up to 30 wt.%) were investigated and their properties (shrinkage, density, water absorption and compressive strength) were measured as a function of temperature and clay addition. The results showed that gehlenite neoformed from lime of decomposed carbonates and breakdown products of clay minerals and that fluorapatite (original mineral) resisted heating until fusion. The measured properties were mainly controlled by temperature, and the effect of clay addition was less regular, except for water absorption. Considering the mixtures densities (1.44-3.02 g/cm(3)), lightweight agglomerates can be produced at 900 or 1100 °C, but their compressive strengths were relatively low (2-4.5 MPa). Based on SiO2-Al2O3-Fluxes diagram and taking account of the chemical composition of the materials used, the production of expanded aggregates requires clay additions as high as 80 wt.%.
authors.affiliation: LPCME, URAC20, Université Cadi Ayyad, Faculté des Sciences Semlalia, Bd. Prince My Abdellah, B.P. 2390, 40001 Marrakech, Morocco; LCME, Université Cadi Ayyad, Faculté des Sciences et Techniques, Av. A. Khattabi, B.P. 549, 40000 Marrakech, Morocco; IM2NP, Institut des Matériaux Microélectronique Nanosciences de Provence, Université du Sud Toulon-Var, Bât. R - B.P. 20132, 83 957 La Garde Cedex, France.
authors.forename: M
authors.initials: M
authors.lastname: Loutou
authors.forename: M
authors.initials: M
authors.lastname: Hajjaji
authors.forename: M
authors.initials: M
authors.lastname: Mansori
authors.forename: C
authors.initials: C
authors.lastname: Favotto
authors.forename: R
authors.initials: R
authors.lastname: Hakkou
mesh_terms: D008855:Microscopy, Electron, Scanning; D009018:Morocco; D010710:Phosphates / Q000032:analysis / Q000737:chemistry*; D059027:Recycling; D012722:Sewage / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D010710:Phosphates; D012722:Sewage
keywords: Clay; Lightweight aggregates; Microstructure; Phosphate sludge; Thermal transformation