Evaluation of Pollution Linked to Open-Air Storage of Black Shale by the Company Frontier S.A in Sakania in the South-East of the DR. Congo

Abstract

The black shale from the company “Frontier S.A” in Sakania is impregnated with sulphide minerals such as pyrite which is an iron sulphide (FeS2) and chalcopyrite which is a double sulphide of copper and iron (Cu FeS2). Due to its storage in the open air, these sulphides are particularly oxidized. In addition, this black shale presents a certain physical and chemical instability which can be the basis of the degradation of the nearby surrounding environments (watercourses, soils, groundwater, etc.). It results from our chemical characterization tests that this black shale contains 0.05% Cu, 0.007% Co, 1.3% Fe, 0.007% Ni, 0.001% As; 0.0012% Pb; 0.0021 Cd; 1.75% of S.The mineralogical analysis reveals that the sample contains the main minerals: sulphides, in the form of chalcopyrite and pyrite; oxidized, in the form of quartz; carbonates, in the form of dolomite and calcite, and graphitic material (C). For the determination of the character of acid mine drainage, the static tests for predicting the AMD on the one hand, gave values for the net neutralization potential (NNP) and the ratio between the neutralization and acidification potentials (RPN). respectively 37.5 and 41.39, that is to say values classifying the black shale of Frontier as not generating ADM. And on the other hand, during the kinetic tests using the principle of testing periodic leaching of the sample over a long period, the percolates obtained made it possible to monitor the pH (between 6.2 to 7.07), the redox potential (between -39.8 to 92mV), the electrical conductivity (between 640 to 672μS/Cm), as well as the concentration rate of metals (low mobilization). This made it possible to conclude that the AMD did not exist on the site.