Valorization of clay by-product from moroccan phosphate mines for the production of fired bricks

Abstract Large clayey sedimentary layers are extracted as waste rock material to reach the phosphate ores. Considered as mining wastes intimately mixed with other silicated and carbonated lithologies, they are stored as coarse waste rocks in large dumps nearby the phosphate mines; as it is the case of Gantour mine of OCP group (Morocco). These clay occurrences have been investigated as a raw material for the production of ceramics, especially fired clay bricks. In this paper, pressed and fired briquettes made of the isolated clayey lithology were manufactured. The clay material mineralogy include dolomite, quartz, palygorskite, and montmorillonite. The as-formed briquettes were oven dried at 105 °C then fired in the range 900–1100 °C. Both raw and sintered samples (at various temperature) were investigated by differential thermal and thermogravimetric analysis (TG-DTA), X-ray diffraction (XRD), optical and scanning electron microscope (OM-SEM) and Fourier Transform Infra-Red (FTIR). Main physical and mechanical properties were assessed and correlated to the microstructural changes. The obtained results revealed that sintering temperature increase led to dehydroxylation of clay minerals, persistence of quartz and neo-formation of diopside, anorthite, hematite and magnetite. SEM secondary electron images showed bricks vitrification together with micro-porosity formation during firing, which greatly influenced the mechanical properties. The elaborated bricks displayed acceptable water absorption capacity and firing shrinkage rate with good flexural strength, showing that they could be used in the bricks manufacturing. This clay lithology from phosphate mines should then be considered as a raw material to be valorized and reused.