Chemical speciation,bioavailability and risk assessment of potentially toxic metals in soils around petroleum product marketing company as environmental degradation indicators

The study aims at investigating chemical speciation,bioavailability and risk assessment of some selected metals in soils around refined petroleum depot using the concentrations of the metals as variables to ascertain the impacts of the activities within the petroleum depot.Surface-soils(0e15 cm)were collected from within the premises of Pipelines and Product Marketing Company,Ibadan,Nigeria,while control samples were collected at 200 m away from the study location.Electrical conductivity and pH were measured using a calibrated dual purpose meter,while elemental analysis was done using Atomic absorption spectroscopy analytical technique.The results showed that the soils exhibited low ecological risk;minor enrichment for Mn,moderately severe enrichment for Ni and Co,severe enrichment for Cr and extremely severe enrichment for Pb,Zn and Cd.There was low contamination factor for Pb,Ni,Mn,Cr,Co,and Fe and moderate contamination by Zn and Cd.Geo-accumulation index results indicated unpolluted with Ni,Mn,Cr,Co,and Fe,unpolluted to moderately polluted with Pb and Zn and moderately to strongly polluted with Cd.Inter-element clustering results indicated chemical affinity and/or similar genetic origin among the elements.Speciation analysis suggested that Fe,Co,Cr,Cd,and Ni occurred in the residual fraction;Pb,and Zn in the carbonate fraction,while Mn have its highest percentage in the Fe eMn oxides fraction.Percentage mobility and bioavailability showed that most of the metals are immobile and non-bioavailable.Study concluded that the oil-impacted soils were contaminated with most of the metals,but with low ecological risk.

Thermodynamic study of the removal of heavy metal ions from heavy oils using tetramethyl ammonium hydroxide pentahydrate ionic liquid

This study investigated efficiency of tetramethyl ammonium hydroxide pentahydrate(TMAH)in removal of heavy metal ions from heavy oils obtained from Nigerian oil sands by Soxhlet-extraction technique.Metals were removed from the heavy oils at variable temperatures using TMAH.Elemental analysis was done using Atomic absorption spectrophotometry(AAS).Percentage recovery was≥92.85%,confirming reliability of results.Total metal concentrations followed order:Ni>Pb>Mn>Cu>Cr>Cd.Analysis of variance results showed that F<F_(critical)(0.01<3.68),indicating acceptance of null hypothesis.Cluster analysis result indicated three major inter-elemental clustering groups,indicating chemical affinity and/or similar sources,while T-test result indicated significant differences.Metal removal efficiency decreased with increased temperature,indicating exothermic process.Thermodynamic parameter values were negative,confirming exothermic reactions.Also,negative△DS°values indicated decreased randomness at solid/liquid interface during the extraction.△DG°negative values indicated feasible and spontaneous extraction.Conclusively,the distribution of metals in the analyzed heavy oils followed similar trend,due to similarity in their geological activity,source rock type,maturation and depositional environment.Thermodynamics parameters values showed the extraction process was exothermic,feasible and spontaneous thus,proving metal extraction using TMAH to be efficient.