Study of the Bioaccumulation of mineral components in soils backfilled with slag and sludge from scrap metal, scrap recycling foundries in Kinshasa (DRC)

Abstract

Because of their multi-element chemical composition and especially because of the presence of trace metal elements (TME) at relatively high levels, sludge and slag from foundries are classified as hazardous waste. For this reason, they must undergo all the rigorous management imposed on such types of waste. However, those in charge of the Kinshasa scrap foundries remain deaf to this.Indeed, these scraps from the scrap metal foundries of Kinshasa are spread in plots, streets and avenues of the city of Kinshasa to be used as backfill without prior treatment to the detriment of a suffering population subject to serious environmental problems (potholes, erosion heads, floods, etc.).After chemical analysis of these wastes, it turns out that they contain Na2O, CaO, Cr2O3, MnO, Fe2O3, NiO, CuO, La2O3, Eu2O3, Yb2O3, OsO4, Br, SiO2, K2O, TiO2, V2O5, ZnO, Ti2O3, Au, Sc2O3, SrO, ZrO2, Nb2O5, RuO2, BaO, Re2O7, Al2O3, MgO, Rb2O, HgO [1], while the chemical analysis of the soils backfilled by these slags and sludges of the foundries reveals that they contain all these components except Na2O, Br, Ti2O3, Nb2O5, BaO and Rb2O. Also, some typical components such as AsO3, As2O4, PbO and P2O5 which were not measured in the slag and sludge of the smelters were measured in the soils backfilled by the said slag and sludge.Furthermore, the comparison of the chemical composition of the soils backfilled by SBFs with that of the soils not affected by the backfill shows that P2O5, Al2O3, MgO, OsO4, La2O3, Yb2O3 and SO3, components of the backfilled soils, were not measured in the non-filled soils (blank sample).From a semi-quantitative point of view, it has just been demonstrated that almost all components of the soils backfilled with slag and sludge from smelters have relatively higher concentrations than their counterparts in the unfilled soils, with the exception of SiO2, V2O5 and Sc2O3.