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

Abstract

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 < Fcritical (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 ΔS° values indicated decreased randomness at solid/liquid interface during the extraction. ΔG° 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.