Identification, geolocation and characterization of slag and sludge discharge sites from foundries (SBF) which recycle scrap metal in Kinshasa : DRC

The iron and steel industries generate large quantities of solid waste which is not always easy to manage because of the heavy metals it contains. In most cases, they are used in concrete or bitumen but sometimes as backfill; however, this always requires rigorous control followed by prior treatment. In general, the installation of a foundry requires the creation of a place to store solid waste (slag heap). The scrap metal foundries in Kinshasa do not have appropriate structures for the evacuation or conservation of their waste. They are satisfied with the environmental failure found in the surroundings to liquidate these dangerous wastes in full view of the competent authorities.During our investigations carried out in a sector which contains the aforementioned foundries and whose measured surface is 523272 ha, seventy-six sites on which were spread the slags and muds of the recycling foundries of the scrap were located. The calculation made on the estimates of the weight of these scraps indicates that on average a site contains 592 tons of slag and sludge of the said foundries. These are spread over an average area of 923 m2 and occupy an average volume of 355 m3. In sum, over an average period of 10 years, nearly 45,000 tons of slag and sludge from the scrap metal foundries have been spread on the streets and avenues of our study area over a total surface area of 7,0152 m2 and a relative volume of 26,971 m3.After analysis of the field data, it appears that Block 4 contains a large quantity of slag and sludge from the foundries but also the largest surface area and volume. This is related to the socio-environmental configuration of the area where not only are there several potholes but also the area has no drainage channels for rainwater (hence the recurrent and persistent flooding).In the principal component analysis (PCA), the seventy-six sites are divided into three different clusters, the first of which has only one site, the second has six sites, and the last has the majority of sites, namely sixty-nine. The sites in classes one and two are distinguished by variables (weight, area and volume) that are higher than their respective averages, while those in class three are distinguished by data that are lower than their averages.The evaluation of the daily production of slag and sludge of the said foundries indicates a relative volume of 16 tons. This gives a projected total of 60226 tons of slag and sludge since the installation of these foundries in the city of Kinshasa. The calculation of the difference proves that our study area contains at least 75% of this waste, without counting those contained in third party plots. Furthermore, our investigations attest that a part of the slag and sludge from the foundry that was not evaluated was dumped in the districts bordering our study area, which have similar topographic and environmental characteristics.