Formulation and Characterization of Light Aggregates from Phosphate Ore Processing Waste from the Hahotoe and Kpogame Mines, Potential Use for Agricultural Applications

This study relates to the development of light aggregates from phosphate sludge, rejects to sieves and clays. Three types of aggregates denoted S9, S10 and S11 have been developed. Samples S9 are composed of clay, screenings and phosphate sludge, samples S10 of clay and screenings and samples S11 of clay and phosphate sludge. The influence of temperature and cooking time on the properties (water absorption, density, porosity, etc.) of the aggregates produced was studied, as well as their mineralogical composition. For this purpose, three different cooking temperatures 900°C, 950°C and 1000°C, and two cooking times 30 and 60 min were considered. This study showed that the water absorption of aggregates cooked for 30 min varies between 12.71% and 14.93% while that of aggregates cooked for 60 min varies between 12.78% and 15.16%. The lowest water absorption is observed at the S10 aggregates sintered at 900°C for 30 min while the highest water absorption is observed at the S9 aggregates sintered at 900°C for 60 min. The dry density of aggregates cooked for 30 min varies between 1.27 and 1.68 g/cm3 while that of aggregates cooked for 60 min varies between 1.75 and 2.13 g/cm3. With the exception of S11 aggregates baked at 950 and 1000°C for 60 min, which have their density greater than 2 g/cm3, all the others can be considered light aggregates. It should also be noted that the aggregates cooked for 30 min have a lower density than the aggregates cooked for 60 min. The porosity of the aggregates cooked for 30 min varies between 16.30 and 20%, on the other hand the aggregates cooked for 60 min varies between 19.06 and 23.64%. X-ray diffraction analysis of the aggregates shows that they are mainly composed of fluoroapatite, quartz, hematite and plagioclases (albite, labradorite, and anorthite). The study also showed that the amount of quartz and fluoroapatite decrease with temperature. On the basis of the physical and mineralogical analysis carried out on the light aggregates, we could find them suitable for agricultural applications, especially their uses as substrates in hydroponics, in greenhouse cultivation in general, and in gardening.