GEOCHEMICAL EVALUATION OF TAILINGS AND MINE DRAINS IN IFE/IJESA GOLD MINING ENVIRONMENT, OSUN STATE, NIGERIA

Abstract

Ife/Ijesa gold mining environment was evaluated for heavy metals in the tailings, acid mine drains and plants grown around the site to prevent possible health consequences. Elemental profile, geochemical oxide and mineral compositions of the tailings were determined using Atomic Absorption Spectrophotometry (AAS) Proton Induced X-ray Emission spectrophotometry (PIXE) and X-Ray Diffractometer (XRD) respectively. The result obtained for physicochemical parameters of the mine drain samples indicated the pH ranged from 3.0 to 4.8 which is acidic and below acceptable range for health risk, Positive values obtained from redox potential is an indication the drains are in oxidation state and higher levels of electric conductivity and sulphate. The physico-chemical parameters of tailings ranges obtained were pH (6.0 – 7.3), Eh (−16 - 95 Mev), EC (49 - 156 μS/cm), RH (0.20-2.60%), CEC (3.64-6.45 coml/kg), TOC (3.57-18.62%), TOM (6.15-22.93%). Heavy metals analysis of the mine drains shows that the concentration of Cd, Co, Pb, Cr and Zn exceeded permissible limit set by WHO except Cu and Mn. The metal contents (mg/Kg) range over the following interval: Na: (421-1894), Mg: (1489-8725), K: (697-18055), Cu: bld-14876), Al: (79755-163454), Si: (232714-343312), P: (225-1450), Cl: (42-554), Ti: (280-16451), Cr: (69-2020), Mn: (139-1304), Fe: (30715-144010), Cu: ( 21-580) and some other elements with low concentration. Correlation, principal component and cluster analyses of the elemental analysis suggested probable natural and anthropogenic sources of the metals in the tailings. The contamination level of heavy metals was assessed on the basis of geo-accumulation index ( Igeo ), and ecological risk. The analysis of I geo revealed moderately-heavily to heavily extremely contaminated. Contamination factor of Cr indicated considerably contaminated. Mn, Fe, Zn and Pb indicated moderate contamination while Cu shown very high contamination. The pollution load index indicated that all the sites are progressively deteriorating. The value of Er showed a low level of heavy metals except Cu which shows considerable contamination. Sequential extraction revealed that the heavy metals from tailings in the mining sites were distributed in all extractive steps based on the modified Tessier’s procedure (water soluble, exchangeable, bound to carbonates, bound to iron and manganese oxide, bound to organic matter and residual). The contents of Co, Cr, Cd, Cu, Ni, Mn, Pb, Zn in the six fractions were determined by AAS. The bulk of the metals were retained in the residual fraction for metals like Ni, Mn, Zn , Cr, and Co while only Cu were scantly extracted in carbonate and Fe-Mn fraction. Cd and Pb shows considerable percentage of the metals retained in all the fraction extracted.The geochemical oxide composition were identified using Proton Induced X ray emission and the results indicated that SiO2>Al2O3>Fe2O3>TiO2>K2O>MgO>CaO>Na2O>P2O5>MnO>Cr2O3>SrO>K2O>P2O5. The mineralogical components in the tailing samples were determined by a quantitative x-ray diffraction techniques using Rietveld method. Geostatistical relationships among the known points were determined using ArcGIS 10.2 software to interpolate minerals concentration with respect to the study area. The Rietveld method gave generally Quartz value as 73.73-92.76%, IImenite as 0.38-4.77%, Kaolinite group as 3.19-20.83%, Muscovite as 0.77-70% with trace of other minerals. The high percentage of quartz is an indication of a sandy environment with loose binding site.