Physicochemical and mineralogical characterization of sandy sediments from urban rivers of Kinshasa, Democratic Republic of Congo

Abstract

River sediments in Kinshasa offer a promising yet largely untapped resource for construction materials, primarily due to the scarcity of comprehensive data on their physicochemical and mineralogical properties. This study investigates sediments from seven distinct locations (Makelele 1 & 2, Kalamu, Nsele, N’djili, Kinkole, and Maluku) using a suite of analytical techniques: X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM–EDS), particle size distribution, and sand equivalent (SE) evaluation. Grain size distribution revealed a progression from fine sands (N’djili, Nsele, Makelele) through medium sands (Kalamu) to coarse sands (Kinkole, Maluku). All samples demonstrated SE values exceeding 80%, indicating high sand purity and a low proportion of fines. XRF analysis showed a silica-rich chemical composition with SiO₂ accounting for 97.27% of the total oxides. Minor constituents included CaO (1.48%), Fe₂O₃ (0.64%), and Al₂O₃ (0.62%). Trace oxides were present descending order: Sb₂O₅ > SnO₂ > ZnO > NiO > CuO > Cr₂O₃. Moderate concentration of heavy metals La (619 mg.kg−1), Ce, Cs, Ba, and Pr were detected warranting consideration depending on the intended application. XRD results confirmed quartz as the predominant mineral phase (97.88–98.72%), with calcite (0.24–0.31%) and hematite (0.21–0.27%) appearing as minor phase. These findings align closely with the chemical profiles obtained via XRF. SEM–EDS analysis provided microstructural insights, revealing detrital quartz-rich nature of these sediments. Their high purity and favourable granulometric characteristics suggest strong potential for use as construction aggregates. However, geomechanical testing is recommended to validate their performance under practical conditions.