Mineralogy and geochemistry of clay fractions in soils developed from different parent rocks in Limpopo Province, South Africa

Abstract

This study investigates the mineralogical and geochemical characteristics of clay fractions in soils developed from different parent rocks in Limpopo Province, South Africa using the X-ray diffraction (XRD), X-ray Fluorescence (XRF) Spectrometry, Laser Ablation – Inductively Coupled Plasma – Mass Spectrometry (LA-ICP-MS), Fourier Transform Infrared (FTIR) Spectrophotometry, Thermogravimetric Analysis and Differential Scanning Calorimetry (TGA-DSC) analytical techniques. Health risk associated with the presence of some trace elements was also investigated. The results revealed that the clay fractions had kaolinite as the dominant clay component occurring with other weatherable minerals. The crystallinity based on FTIR for the soil kaolinites correspond to partially - poorly ordered structures. The geochemical data showed appreciable accumulation of trace elements in the clay fractions. The absence of negative Ce anomaly in the chrondrite-normalised rare earth elements (REE) pattern in the clay fractions suggest the alteration of the primary minerals took place under suboxic conditions. The average non-carcinogenic hazard index (HI) were 1.52, 1.08, and 2.01 for children and 0.18, 0.13, and 0.24 for adults in the clay fractions from basalt, granite, and arkosic sandstone, respectively. The HI > 1 for children suggest non-carcinogenic health risk to children with ingestion pathway contributing the highest. The average carcinogenic risk index values were >10−3 for children and adults with respect to Cr, Ni, and Pb in the clay fractions. This suggests very high carcinogenic risk to children and adult population in decreasing order from clay fractions in arkosic sandsone > basalt > granite, respectively.