Abstract
The presence of heavy metals was analysed from oil samples employing the dry ashing method. The specific densities and viscosities of the spent and virgin AZ oil samples were determined and found to be 0.9230, 0.9501 and 70.27, 73.27cP respectively. Kinetic and thermodynamic studies of the adsorption of lead (Pb) and chromium (Cr) from the spent oil was also investigated. The spent oil samples were digested and mixed with methyl isobutyl ketone (MIBK), agitated with activated carbon produced from Thevetia peruviana (bush milk) shells at various contact times of 2, 4, 5, 10, 15, 20, 30, 40, 50, 60, 90 and 120 minutes. Kinetic studies revealed that for lead (Pb), the rate constants were found to be 0.044, 0.060 and 0.067 ppm/min at 27oC, 35 oC and 45 oC, respectively, while higher values or rate constants of 0.126, 0.127 and 0,168 ppm/min were observed at 27 oC, 35 oC and 45 oC, respectively, for chromium (Cr). For the thermodynamic studies the Gibb's free energy (ΔG) values were; –1.29, -1.61 and –1.82 KJmol-1at 27 oC, 35 oC and 45 oC, respectively, indicating spontaneity. However, the Gibb's free energy (ΔG) for chromium showed +0.050, -2.13 and -2.14 KJmol-1at 27 oC, 35 oC and 45 oC, indicating non-spontaneity at 27 oC. The positive values of ΔS for both metals with Pb (21 - 30 Jmol-1) and Cr (695 – 1867 Jmol-1 ) indicated that the metals were dissociatively adsorbed onto the adsorbent while for the E values, Cr (8 – 61 KJmol-1) had a higher than with Pb (6 – 35 KJmol-1) further explaining the non-spontaneity of the process for Cr at some reaction condition.
Highlights
Managing heavy metals in the environment is greatly of global concern
Wastes from industries that carry out processes like electroplating, metal finishing, metallurgy, tannery operations, chemical processing, mine drainages, battery manufacturing, leachates from land fills, contaminated ground waters from hazardous waste sites, disposal of automobile oils and domestic waste are some of the main sources of these heavy metal in the environment (Meal et al, 1990; Reed et al, 1994; Leke et al, 2011; Bhat and Khan, 2011; Leke et al, 2012; and Safarzadeh et al, 2018)
This research was aimed at studying the trends of adsorption of two heavy metals (Pb and Cr) from spent engine oils onto activated carbon prepared from Thevetia peruviana shells with respect to time and temperature
Summary
Managing heavy metals in the environment is greatly of global concern. This is because they contaminate the abiotic factors of the environment like the soil, water and air, which in turn become toxic to the biotic factors (plants and animals) of the environment. Wastes from industries that carry out processes like electroplating, metal finishing, metallurgy, tannery operations, chemical processing, mine drainages, battery manufacturing, leachates from land fills, contaminated ground waters from hazardous waste sites, disposal of automobile oils and domestic waste are some of the main sources of these heavy metal in the environment (Meal et al, 1990; Reed et al, 1994; Leke et al, 2011; Bhat and Khan, 2011; Leke et al, 2012; and Safarzadeh et al, 2018) Since these heavy metals are toxic to life, the need for their safe handling, removal or recovery from their sources before disposal to the environment has attracted the attention of the research world. Adsorbents employed for the adsorption of heavy metals include activated carbon, kaoline clay, zeolite and silica gel (Greankoplis, 1995; Mohammad and Nwaedozie, 2011; Leke et al, 2012)
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