CHEMICAL ANALYSIS OF BAUXITE AND RUTILE ORES, CONTAMINATED VICINITY SOIL, SEDIMENT AND PLANTS (VIGNA UNGUICULATA) IN KANAM AND WASE, PLATEAU STATE-NIGERIA

Abstract

Contamination of agricultural soils, water and sediments and depletion of the environment through unregulated mining activities poses a great threat on the environment and human. A non-destructive analytical technique (XRF) was employed to characterize bauxite and rutile ores and their vicinity soil and sediment, plant (vigna unguiculata) roots and stems. Bauxite ore had high clay (23.5%) content, suggesting that the ore cannot be utilized directly unless it is beneficiated to meet metallurgical required grade. The elemental composition of farmland soil within bauxite mineral vicinity revealed silicon (20.9%), Fe (10.7%), Al (9.4%), K (9.0%), Mg (2.5%), Ca (1.6%) and Ti (1.0%) as major components of the soil. Toxic heavy metals residues such as V (0.06%), Cr (0.02%) and Ba (0.19%) were also recorded. Soil contamination with Cr due to bauxite ore mining considerably affects the biological activity of the soil. ED-XRF for soil sediment within this proximate mining vicinity revealed higher value for Fe (16.6%) compared to bauxite vicinity soil. Similarly, the characterization of rutile ore using this technique unveiled the interlocking of soil minerals such as Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Sn, Ba, Ta and W in various proportions with titanium oxide having a relatively high concentration (25.3%). Although lower soil contamination was observed in the rutile vicinity soil and sediment compared to the former (bauxite vicinity soil), titanium contamination was recorded (2.9) higher than the Russian general toxicology and Dutch standards for soils (<1). Soil contamination in this mineral vicinity was due to continuous interference of the soil and soil organic matter. The chemical characterization of plant (vigna unguiculata) roots from the mineral exploration vicinity also revealed the usual soil elements Mg, Al, Si, K, Ca and Fe as major elements as well as Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Zr, Nb, Mo, Ag, Sn, Ba, W and Ta as trace or minor elements respectively, and of great concern is the presence of Cr (0.03), Ni (0.004), Co (0.02), Mn (0.16) Cu (0.256) and Zn (0.06) in the roots and stems. . Low values observed for most metals in the stem XRF are due to the fact that metals (essential and non-essential) are trapped through the roots then subsequently transported to other sections of the plants. XRF analysis of the soil control samples (500 m away from bauxite and rutile ores vicinities) unveiled low values for most heavy metals, this suggests that mineral mining exploration in this location is the major source of soil heavy metals contamination. Contamination factor (Cⁱ_f<1), ecological risk (Erⁱ<40) and geo-accumulation index (I_geo.) for heavy metals Cr, Cu. Ni and Zn revealed low contamination, low ecological risk and Igeo values. However, the pollution load index (PLI) suggests that the entire mineral exploration area soil and sediment were moderately polluted with Cr (>1) and unpolluted with Cu, Ni and Zn metals. The enrichment factor (EF) ranged between depletion to mineral enrichment-very high enrichment.