Use of alumina phosphate waste to produce building materials
Authors: Diagne Mababa 
Published: May 2013

The generation of a fine fraction of sedimentary alumina phosphate before the manufacturing process of phosphoric acid –used as fertilizer– poses a crucial environmental issue related to the large quantities of fines stored for a long time in the wildlife without treatment or recycling in the region of Thiès in Sénégal by the Industries Chimiques du Sénégal (ICS) and the Société Sénégalaise des Phosphates de Thiès (SSPT). This work deals with the use of the fines particles of phosphate generated by the physical processing (crushing, transport and screening) of the raw material by the both mining companies. These fines particles of phosphates cover all the fauna and flora surrounding the sector with whitish dust particularly during the Harmattan, a hot and dry wind, while they can be leached during the rainy season to contaminate groundwater and then cause diseases to the populations who drink that water. Indeed, these materials, which are stored in large quantities as “waste”, and which pollute, the space and the environment, can be recycled as refractory materials useful in manufacturing such as bricks or paving blocks. The purpose of this study is to find, from these discarded fines that are not yet processed, a good and new material in terms of physical and mechanical characteristics that will meet a customary standard. This will allow not only to reduce their potential hazard by reducing the pollution for the consumption of the fines in order to generate a useful material especially in the surrounding villages of the mining sector, but also to employ young people in working age in this fines recycling process, to create jobs and therefore additional economic resources that allow a better life because the majority of the youngsters from these areas are unemployed.

The formulation of a well-known mixture containing fines of sedimentary alumina phosphate of particles size ranging between 0.063 mm to 5 mm, with chemical composition similar to that of volcanic slag, sodium silicate called water-glass as binder of mineral elements; and water, led to the manufacturing of geomaterials blocks with 20×10×6 cm3 size by baking them several hours on an oven at the constant temperature of 225°C. The sodium silicate density was 1.4.

Good mechanical and physical characteristics were achieved through systematic testing. Strength splitting rupture tests, total water content determination, size measurements of the blocks (length, width and thickness) as well as the loss on ignition on ambient atmosphere were achieved on the blocks after treatment for a complete identification. Average values of 3.03 MPa and 2.5% were obtained as results respectively for the splitting rupture strength and for the total water content. Negative variations of −2.05 mm, −0.59 mm and 1.69 mm on average values were obtained respectively on their length, their width and their thickness for a value of 5.30% of loss on ignition. The blocks are exposed on the fire on their upper surface whilst the heating effect falls of rapidly at the other side. The deduction of the compressive resistance strength from the average value of splitting rupture gave a value of 40.5 MPa. This value testifies very good mechanical resistance strength of the material which is made by the fines of phosphate. These characteristics obtained are compared here to the European Standard values EN 1338 for paving blocks. The values obtained for all the tests attest good manufacturing material. This new material can also be used as refractory materials in the ovens and in pottery materials.