Environmental polluting effects of liquid wastes and phosphate sludge generated by the Djebel Onk mining complex

Abstract

The production of phosphate concentrates is confronted with problems of treatment of wastes, of which the quantities are considerable. These wastes contain a large number of elements that are harmful to the environment. In this case, of phosphate wastes from Djebel Onk in the form of sludge that are the subject of our work, several trace elements have been recorded in limited levels. Indeed, elements such as lead and chromium have levels that exceed 60 and 300 ppm respectively. They far exceed the requirements of the mineral industry. The legislation, the severity of which varies from country to country, increasingly requires rigorous management and monitoring of these wastes in order to guarantee the protection of the environment from these toxic substances contained in the wastes. This work focuses on the management of phosphate wastes from Djebel Onk in liquid or sludge form. Current practices on their evacuation from neighbouring valleys to the operating site may harm the local environment. Moreover, the flow of this sludge which is increasingly thickened becomes more difficult. In this context, for environmental considerations and in order to define a concept linked to sustainable development, this study advocates a new approach in the recovery of phosphate wastes. It is based on the intrinsic properties of the present minerals determined by qualitative and quantitative analysis developed by different characterization techniques (XRD, XRF, IR, etc.). This makes it possible to define the chemical and mineralogical composition of liq- uid phosphate wastes which are rich in calcite (44.45 % in CaO) to those of phosphate elements (21 % in P2O5) and gangue minerals such as dolomite (7, 6 % in MgO), and quartz (5.8 % in SiO2). The microscopic observations carried out on these wastes showed the presence of the main minerals identified by XRD: fluorapatite, hydroxylapatite, carbonate, dolomite, calcite and quartz. The sought objective is to contribute to controlling these impurities to recover them from the water generated by the industrial installations for the exploitation of these materials with a view to their reuse in the laundries of the mining complex.